Implement goto restrictions.

[pf3gnuchains/gcc-fork.git] / gcc / go / gofrontend / gogo.cc

// gogo.cc -- Go frontend parsed representation.

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

#include "go-system.h"

#include "go-c.h"
#include "go-dump.h"
#include "lex.h"
#include "types.h"
#include "statements.h"
#include "expressions.h"
#include "dataflow.h"
#include "runtime.h"
#include "import.h"
#include "export.h"
#include "backend.h"
#include "gogo.h"

// Class Gogo.

Gogo::Gogo(Backend* backend, int int_type_size, int pointer_size)
  : backend_(backend),
    package_(NULL),
    functions_(),
    globals_(new Bindings(NULL)),
    imports_(),
    imported_unsafe_(false),
    packages_(),
    init_functions_(),
    need_init_fn_(false),
    init_fn_name_(),
    imported_init_fns_(),
    unique_prefix_(),
    unique_prefix_specified_(false),
    interface_types_(),
    named_types_are_converted_(false)
{
  const source_location loc = BUILTINS_LOCATION;

  Named_type* uint8_type = Type::make_integer_type("uint8", true, 8,
                                                   RUNTIME_TYPE_KIND_UINT8);
  this->add_named_type(uint8_type);
  this->add_named_type(Type::make_integer_type("uint16", true,  16,
                                               RUNTIME_TYPE_KIND_UINT16));
  this->add_named_type(Type::make_integer_type("uint32", true,  32,
                                               RUNTIME_TYPE_KIND_UINT32));
  this->add_named_type(Type::make_integer_type("uint64", true,  64,
                                               RUNTIME_TYPE_KIND_UINT64));

  this->add_named_type(Type::make_integer_type("int8",  false,   8,
                                               RUNTIME_TYPE_KIND_INT8));
  this->add_named_type(Type::make_integer_type("int16", false,  16,
                                               RUNTIME_TYPE_KIND_INT16));
  this->add_named_type(Type::make_integer_type("int32", false,  32,
                                               RUNTIME_TYPE_KIND_INT32));
  this->add_named_type(Type::make_integer_type("int64", false,  64,
                                               RUNTIME_TYPE_KIND_INT64));

  this->add_named_type(Type::make_float_type("float32", 32,
                                             RUNTIME_TYPE_KIND_FLOAT32));
  this->add_named_type(Type::make_float_type("float64", 64,
                                             RUNTIME_TYPE_KIND_FLOAT64));

  this->add_named_type(Type::make_complex_type("complex64", 64,
                                               RUNTIME_TYPE_KIND_COMPLEX64));
  this->add_named_type(Type::make_complex_type("complex128", 128,
                                               RUNTIME_TYPE_KIND_COMPLEX128));

  if (int_type_size < 32)
    int_type_size = 32;
  this->add_named_type(Type::make_integer_type("uint", true,
                                               int_type_size,
                                               RUNTIME_TYPE_KIND_UINT));
  Named_type* int_type = Type::make_integer_type("int", false, int_type_size,
                                                 RUNTIME_TYPE_KIND_INT);
  this->add_named_type(int_type);

  // "byte" is an alias for "uint8".  Construct a Named_object which
  // points to UINT8_TYPE.  Note that this breaks the normal pairing
  // in which a Named_object points to a Named_type which points back
  // to the same Named_object.
  Named_object* byte_type = this->declare_type("byte", loc);
  byte_type->set_type_value(uint8_type);

  this->add_named_type(Type::make_integer_type("uintptr", true,
                                               pointer_size,
                                               RUNTIME_TYPE_KIND_UINTPTR));

  this->add_named_type(Type::make_named_bool_type());

  this->add_named_type(Type::make_named_string_type());

  this->globals_->add_constant(Typed_identifier("true",
                                                Type::make_boolean_type(),
                                                loc),
                               NULL,
                               Expression::make_boolean(true, loc),
                               0);
  this->globals_->add_constant(Typed_identifier("false",
                                                Type::make_boolean_type(),
                                                loc),
                               NULL,
                               Expression::make_boolean(false, loc),
                               0);

  this->globals_->add_constant(Typed_identifier("nil", Type::make_nil_type(),
                                                loc),
                               NULL,
                               Expression::make_nil(loc),
                               0);

  Type* abstract_int_type = Type::make_abstract_integer_type();
  this->globals_->add_constant(Typed_identifier("iota", abstract_int_type,
                                                loc),
                               NULL,
                               Expression::make_iota(),
                               0);

  Function_type* new_type = Type::make_function_type(NULL, NULL, NULL, loc);
  new_type->set_is_varargs();
  new_type->set_is_builtin();
  this->globals_->add_function_declaration("new", NULL, new_type, loc);

  Function_type* make_type = Type::make_function_type(NULL, NULL, NULL, loc);
  make_type->set_is_varargs();
  make_type->set_is_builtin();
  this->globals_->add_function_declaration("make", NULL, make_type, loc);

  Typed_identifier_list* len_result = new Typed_identifier_list();
  len_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* len_type = Type::make_function_type(NULL, NULL, len_result,
                                                     loc);
  len_type->set_is_builtin();
  this->globals_->add_function_declaration("len", NULL, len_type, loc);

  Typed_identifier_list* cap_result = new Typed_identifier_list();
  cap_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* cap_type = Type::make_function_type(NULL, NULL, len_result,
                                                     loc);
  cap_type->set_is_builtin();
  this->globals_->add_function_declaration("cap", NULL, cap_type, loc);

  Function_type* print_type = Type::make_function_type(NULL, NULL, NULL, loc);
  print_type->set_is_varargs();
  print_type->set_is_builtin();
  this->globals_->add_function_declaration("print", NULL, print_type, loc);

  print_type = Type::make_function_type(NULL, NULL, NULL, loc);
  print_type->set_is_varargs();
  print_type->set_is_builtin();
  this->globals_->add_function_declaration("println", NULL, print_type, loc);

  Type *empty = Type::make_interface_type(NULL, loc);
  Typed_identifier_list* panic_parms = new Typed_identifier_list();
  panic_parms->push_back(Typed_identifier("e", empty, loc));
  Function_type *panic_type = Type::make_function_type(NULL, panic_parms,
                                                       NULL, loc);
  panic_type->set_is_builtin();
  this->globals_->add_function_declaration("panic", NULL, panic_type, loc);

  Typed_identifier_list* recover_result = new Typed_identifier_list();
  recover_result->push_back(Typed_identifier("", empty, loc));
  Function_type* recover_type = Type::make_function_type(NULL, NULL,
                                                         recover_result,
                                                         loc);
  recover_type->set_is_builtin();
  this->globals_->add_function_declaration("recover", NULL, recover_type, loc);

  Function_type* close_type = Type::make_function_type(NULL, NULL, NULL, loc);
  close_type->set_is_varargs();
  close_type->set_is_builtin();
  this->globals_->add_function_declaration("close", NULL, close_type, loc);

  Typed_identifier_list* copy_result = new Typed_identifier_list();
  copy_result->push_back(Typed_identifier("", int_type, loc));
  Function_type* copy_type = Type::make_function_type(NULL, NULL,
                                                      copy_result, loc);
  copy_type->set_is_varargs();
  copy_type->set_is_builtin();
  this->globals_->add_function_declaration("copy", NULL, copy_type, loc);

  Function_type* append_type = Type::make_function_type(NULL, NULL, NULL, loc);
  append_type->set_is_varargs();
  append_type->set_is_builtin();
  this->globals_->add_function_declaration("append", NULL, append_type, loc);

  Function_type* complex_type = Type::make_function_type(NULL, NULL, NULL, loc);
  complex_type->set_is_varargs();
  complex_type->set_is_builtin();
  this->globals_->add_function_declaration("complex", NULL, complex_type, loc);

  Function_type* real_type = Type::make_function_type(NULL, NULL, NULL, loc);
  real_type->set_is_varargs();
  real_type->set_is_builtin();
  this->globals_->add_function_declaration("real", NULL, real_type, loc);

  Function_type* imag_type = Type::make_function_type(NULL, NULL, NULL, loc);
  imag_type->set_is_varargs();
  imag_type->set_is_builtin();
  this->globals_->add_function_declaration("imag", NULL, imag_type, loc);
}

// Munge name for use in an error message.

std::string
Gogo::message_name(const std::string& name)
{
  return go_localize_identifier(Gogo::unpack_hidden_name(name).c_str());
}

// Get the package name.

const std::string&
Gogo::package_name() const
{
  go_assert(this->package_ != NULL);
  return this->package_->name();
}

// Set the package name.

void
Gogo::set_package_name(const std::string& package_name,
                       source_location location)
{
  if (this->package_ != NULL && this->package_->name() != package_name)
    {
      error_at(location, "expected package %<%s%>",
               Gogo::message_name(this->package_->name()).c_str());
      return;
    }

  // If the user did not specify a unique prefix, we always use "go".
  // This in effect requires that the package name be unique.
  if (this->unique_prefix_.empty())
    this->unique_prefix_ = "go";

  this->package_ = this->register_package(package_name, this->unique_prefix_,
                                          location);

  // We used to permit people to qualify symbols with the current
  // package name (e.g., P.x), but we no longer do.
  // this->globals_->add_package(package_name, this->package_);

  if (this->is_main_package())
    {
      // Declare "main" as a function which takes no parameters and
      // returns no value.
      this->declare_function("main",
                             Type::make_function_type(NULL, NULL, NULL,
                                                      BUILTINS_LOCATION),
                             BUILTINS_LOCATION);
    }
}

// Return whether this is the "main" package.  This is not true if
// -fgo-prefix was used.

bool
Gogo::is_main_package() const
{
  return this->package_name() == "main" && !this->unique_prefix_specified_;
}

// Import a package.

void
Gogo::import_package(const std::string& filename,
                     const std::string& local_name,
                     bool is_local_name_exported,
                     source_location location)
{
  if (filename == "unsafe")
    {
      this->import_unsafe(local_name, is_local_name_exported, location);
      return;
    }

  Imports::const_iterator p = this->imports_.find(filename);
  if (p != this->imports_.end())
    {
      Package* package = p->second;
      package->set_location(location);
      package->set_is_imported();
      std::string ln = local_name;
      bool is_ln_exported = is_local_name_exported;
      if (ln.empty())
        {
          ln = package->name();
          is_ln_exported = Lex::is_exported_name(ln);
        }
      if (ln == ".")
        {
          Bindings* bindings = package->bindings();
          for (Bindings::const_declarations_iterator p =
                 bindings->begin_declarations();
               p != bindings->end_declarations();
               ++p)
            this->add_named_object(p->second);
        }
      else if (ln == "_")
        package->set_uses_sink_alias();
      else
        {
          ln = this->pack_hidden_name(ln, is_ln_exported);
          this->package_->bindings()->add_package(ln, package);
        }
      return;
    }

  Import::Stream* stream = Import::open_package(filename, location);
  if (stream == NULL)
    {
      error_at(location, "import file %qs not found", filename.c_str());
      return;
    }

  Import imp(stream, location);
  imp.register_builtin_types(this);
  Package* package = imp.import(this, local_name, is_local_name_exported);
  if (package != NULL)
    {
      if (package->name() == this->package_name()
          && package->unique_prefix() == this->unique_prefix())
        error_at(location,
                 ("imported package uses same package name and prefix "
                  "as package being compiled (see -fgo-prefix option)"));

      this->imports_.insert(std::make_pair(filename, package));
      package->set_is_imported();
    }

  delete stream;
}

// Add an import control function for an imported package to the list.

void
Gogo::add_import_init_fn(const std::string& package_name,
                         const std::string& init_name, int prio)
{
  for (std::set<Import_init>::const_iterator p =
         this->imported_init_fns_.begin();
       p != this->imported_init_fns_.end();
       ++p)
    {
      if (p->init_name() == init_name
          && (p->package_name() != package_name || p->priority() != prio))
        {
          error("duplicate package initialization name %qs",
                Gogo::message_name(init_name).c_str());
          inform(UNKNOWN_LOCATION, "used by package %qs at priority %d",
                 Gogo::message_name(p->package_name()).c_str(),
                 p->priority());
          inform(UNKNOWN_LOCATION, " and by package %qs at priority %d",
                 Gogo::message_name(package_name).c_str(), prio);
          return;
        }
    }

  this->imported_init_fns_.insert(Import_init(package_name, init_name,
                                              prio));
}

// Return whether we are at the global binding level.

bool
Gogo::in_global_scope() const
{
  return this->functions_.empty();
}

// Return the current binding contour.

Bindings*
Gogo::current_bindings()
{
  if (!this->functions_.empty())
    return this->functions_.back().blocks.back()->bindings();
  else if (this->package_ != NULL)
    return this->package_->bindings();
  else
    return this->globals_;
}

const Bindings*
Gogo::current_bindings() const
{
  if (!this->functions_.empty())
    return this->functions_.back().blocks.back()->bindings();
  else if (this->package_ != NULL)
    return this->package_->bindings();
  else
    return this->globals_;
}

// Return the current block.

Block*
Gogo::current_block()
{
  if (this->functions_.empty())
    return NULL;
  else
    return this->functions_.back().blocks.back();
}

// Look up a name in the current binding contour.  If PFUNCTION is not
// NULL, set it to the function in which the name is defined, or NULL
// if the name is defined in global scope.

Named_object*
Gogo::lookup(const std::string& name, Named_object** pfunction) const
{
  if (pfunction != NULL)
    *pfunction = NULL;

  if (Gogo::is_sink_name(name))
    return Named_object::make_sink();

  for (Open_functions::const_reverse_iterator p = this->functions_.rbegin();
       p != this->functions_.rend();
       ++p)
    {
      Named_object* ret = p->blocks.back()->bindings()->lookup(name);
      if (ret != NULL)
        {
          if (pfunction != NULL)
            *pfunction = p->function;
          return ret;
        }
    }

  if (this->package_ != NULL)
    {
      Named_object* ret = this->package_->bindings()->lookup(name);
      if (ret != NULL)
        {
          if (ret->package() != NULL)
            ret->package()->set_used();
          return ret;
        }
    }

  // We do not look in the global namespace.  If we did, the global
  // namespace would effectively hide names which were defined in
  // package scope which we have not yet seen.  Instead,
  // define_global_names is called after parsing is over to connect
  // undefined names at package scope with names defined at global
  // scope.

  return NULL;
}

// Look up a name in the current block, without searching enclosing
// blocks.

Named_object*
Gogo::lookup_in_block(const std::string& name) const
{
  go_assert(!this->functions_.empty());
  go_assert(!this->functions_.back().blocks.empty());
  return this->functions_.back().blocks.back()->bindings()->lookup_local(name);
}

// Look up a name in the global namespace.

Named_object*
Gogo::lookup_global(const char* name) const
{
  return this->globals_->lookup(name);
}

// Add an imported package.

Package*
Gogo::add_imported_package(const std::string& real_name,
                           const std::string& alias_arg,
                           bool is_alias_exported,
                           const std::string& unique_prefix,
                           source_location location,
                           bool* padd_to_globals)
{
  // FIXME: Now that we compile packages as a whole, should we permit
  // importing the current package?
  if (this->package_name() == real_name
      && this->unique_prefix() == unique_prefix)
    {
      *padd_to_globals = false;
      if (!alias_arg.empty() && alias_arg != ".")
        {
          std::string alias = this->pack_hidden_name(alias_arg,
                                                     is_alias_exported);
          this->package_->bindings()->add_package(alias, this->package_);
        }
      return this->package_;
    }
  else if (alias_arg == ".")
    {
      *padd_to_globals = true;
      return this->register_package(real_name, unique_prefix, location);
    }
  else if (alias_arg == "_")
    {
      Package* ret = this->register_package(real_name, unique_prefix, location);
      ret->set_uses_sink_alias();
      return ret;
    }
  else
    {
      *padd_to_globals = false;
      std::string alias = alias_arg;
      if (alias.empty())
        {
          alias = real_name;
          is_alias_exported = Lex::is_exported_name(alias);
        }
      alias = this->pack_hidden_name(alias, is_alias_exported);
      Named_object* no = this->add_package(real_name, alias, unique_prefix,
                                           location);
      if (!no->is_package())
        return NULL;
      return no->package_value();
    }
}

// Add a package.

Named_object*
Gogo::add_package(const std::string& real_name, const std::string& alias,
                  const std::string& unique_prefix, source_location location)
{
  go_assert(this->in_global_scope());

  // Register the package.  Note that we might have already seen it in
  // an earlier import.
  Package* package = this->register_package(real_name, unique_prefix, location);

  return this->package_->bindings()->add_package(alias, package);
}

// Register a package.  This package may or may not be imported.  This
// returns the Package structure for the package, creating if it
// necessary.

Package*
Gogo::register_package(const std::string& package_name,
                       const std::string& unique_prefix,
                       source_location location)
{
  go_assert(!unique_prefix.empty() && !package_name.empty());
  std::string name = unique_prefix + '.' + package_name;
  Package* package = NULL;
  std::pair<Packages::iterator, bool> ins =
    this->packages_.insert(std::make_pair(name, package));
  if (!ins.second)
    {
      // We have seen this package name before.
      package = ins.first->second;
      go_assert(package != NULL);
      go_assert(package->name() == package_name
                 && package->unique_prefix() == unique_prefix);
      if (package->location() == UNKNOWN_LOCATION)
        package->set_location(location);
    }
  else
    {
      // First time we have seen this package name.
      package = new Package(package_name, unique_prefix, location);
      go_assert(ins.first->second == NULL);
      ins.first->second = package;
    }

  return package;
}

// Start compiling a function.

Named_object*
Gogo::start_function(const std::string& name, Function_type* type,
                     bool add_method_to_type, source_location location)
{
  bool at_top_level = this->functions_.empty();

  Block* block = new Block(NULL, location);

  Function* enclosing = (at_top_level
                         ? NULL
                         : this->functions_.back().function->func_value());

  Function* function = new Function(type, enclosing, block, location);

  if (type->is_method())
    {
      const Typed_identifier* receiver = type->receiver();
      Variable* this_param = new Variable(receiver->type(), NULL, false,
                                          true, true, location);
      std::string name = receiver->name();
      if (name.empty())
        {
          // We need to give receivers a name since they wind up in
          // DECL_ARGUMENTS.  FIXME.
          static unsigned int count;
          char buf[50];
          snprintf(buf, sizeof buf, "r.%u", count);
          ++count;
          name = buf;
        }
      block->bindings()->add_variable(name, NULL, this_param);
    }

  const Typed_identifier_list* parameters = type->parameters();
  bool is_varargs = type->is_varargs();
  if (parameters != NULL)
    {
      for (Typed_identifier_list::const_iterator p = parameters->begin();
           p != parameters->end();
           ++p)
        {
          Variable* param = new Variable(p->type(), NULL, false, true, false,
                                         location);
          if (is_varargs && p + 1 == parameters->end())
            param->set_is_varargs_parameter();

          std::string name = p->name();
          if (name.empty() || Gogo::is_sink_name(name))
            {
              // We need to give parameters a name since they wind up
              // in DECL_ARGUMENTS.  FIXME.
              static unsigned int count;
              char buf[50];
              snprintf(buf, sizeof buf, "p.%u", count);
              ++count;
              name = buf;
            }
          block->bindings()->add_variable(name, NULL, param);
        }
    }

  function->create_result_variables(this);

  const std::string* pname;
  std::string nested_name;
  bool is_init = false;
  if (Gogo::unpack_hidden_name(name) == "init" && !type->is_method())
    {
      if ((type->parameters() != NULL && !type->parameters()->empty())
          || (type->results() != NULL && !type->results()->empty()))
        error_at(location,
                 "func init must have no arguments and no return values");
      // There can be multiple "init" functions, so give them each a
      // different name.
      static int init_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$init%d", init_count);
      ++init_count;
      nested_name = buf;
      pname = &nested_name;
      is_init = true;
    }
  else if (!name.empty())
    pname = &name;
  else
    {
      // Invent a name for a nested function.
      static int nested_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$nested%d", nested_count);
      ++nested_count;
      nested_name = buf;
      pname = &nested_name;
    }

  Named_object* ret;
  if (Gogo::is_sink_name(*pname))
    {
      static int sink_count;
      char buf[30];
      snprintf(buf, sizeof buf, ".$sink%d", sink_count);
      ++sink_count;
      ret = Named_object::make_function(buf, NULL, function);
    }
  else if (!type->is_method())
    {
      ret = this->package_->bindings()->add_function(*pname, NULL, function);
      if (!ret->is_function() || ret->func_value() != function)
        {
          // Redefinition error.  Invent a name to avoid knockon
          // errors.
          static int redefinition_count;
          char buf[30];
          snprintf(buf, sizeof buf, ".$redefined%d", redefinition_count);
          ++redefinition_count;
          ret = this->package_->bindings()->add_function(buf, NULL, function);
        }
    }
  else
    {
      if (!add_method_to_type)
        ret = Named_object::make_function(name, NULL, function);
      else
        {
          go_assert(at_top_level);
          Type* rtype = type->receiver()->type();

          // We want to look through the pointer created by the
          // parser, without getting an error if the type is not yet
          // defined.
          if (rtype->classification() == Type::TYPE_POINTER)
            rtype = rtype->points_to();

          if (rtype->is_error_type())
            ret = Named_object::make_function(name, NULL, function);
          else if (rtype->named_type() != NULL)
            {
              ret = rtype->named_type()->add_method(name, function);
              if (!ret->is_function())
                {
                  // Redefinition error.
                  ret = Named_object::make_function(name, NULL, function);
                }
            }
          else if (rtype->forward_declaration_type() != NULL)
            {
              Named_object* type_no =
                rtype->forward_declaration_type()->named_object();
              if (type_no->is_unknown())
                {
                  // If we are seeing methods it really must be a
                  // type.  Declare it as such.  An alternative would
                  // be to support lists of methods for unknown
                  // expressions.  Either way the error messages if
                  // this is not a type are going to get confusing.
                  Named_object* declared =
                    this->declare_package_type(type_no->name(),
                                               type_no->location());
                  go_assert(declared
                             == type_no->unknown_value()->real_named_object());
                }
              ret = rtype->forward_declaration_type()->add_method(name,
                                                                  function);
            }
          else
            go_unreachable();
        }
      this->package_->bindings()->add_method(ret);
    }

  this->functions_.resize(this->functions_.size() + 1);
  Open_function& of(this->functions_.back());
  of.function = ret;
  of.blocks.push_back(block);

  if (is_init)
    {
      this->init_functions_.push_back(ret);
      this->need_init_fn_ = true;
    }

  return ret;
}

// Finish compiling a function.

void
Gogo::finish_function(source_location location)
{
  this->finish_block(location);
  go_assert(this->functions_.back().blocks.empty());
  this->functions_.pop_back();
}

// Return the current function.

Named_object*
Gogo::current_function() const
{
  go_assert(!this->functions_.empty());
  return this->functions_.back().function;
}

// Start a new block.

void
Gogo::start_block(source_location location)
{
  go_assert(!this->functions_.empty());
  Block* block = new Block(this->current_block(), location);
  this->functions_.back().blocks.push_back(block);
}

// Finish a block.

Block*
Gogo::finish_block(source_location location)
{
  go_assert(!this->functions_.empty());
  go_assert(!this->functions_.back().blocks.empty());
  Block* block = this->functions_.back().blocks.back();
  this->functions_.back().blocks.pop_back();
  block->set_end_location(location);
  return block;
}

// Add an unknown name.

Named_object*
Gogo::add_unknown_name(const std::string& name, source_location location)
{
  return this->package_->bindings()->add_unknown_name(name, location);
}

// Declare a function.

Named_object*
Gogo::declare_function(const std::string& name, Function_type* type,
                       source_location location)
{
  if (!type->is_method())
    return this->current_bindings()->add_function_declaration(name, NULL, type,
                                                              location);
  else
    {
      // We don't bother to add this to the list of global
      // declarations.
      Type* rtype = type->receiver()->type();

      // We want to look through the pointer created by the
      // parser, without getting an error if the type is not yet
      // defined.
      if (rtype->classification() == Type::TYPE_POINTER)
        rtype = rtype->points_to();

      if (rtype->is_error_type())
        return NULL;
      else if (rtype->named_type() != NULL)
        return rtype->named_type()->add_method_declaration(name, NULL, type,
                                                           location);
      else if (rtype->forward_declaration_type() != NULL)
        {
          Forward_declaration_type* ftype = rtype->forward_declaration_type();
          return ftype->add_method_declaration(name, type, location);
        }
      else
        go_unreachable();
    }
}

// Add a label definition.

Label*
Gogo::add_label_definition(const std::string& label_name,
                           source_location location)
{
  go_assert(!this->functions_.empty());
  Function* func = this->functions_.back().function->func_value();
  Label* label = func->add_label_definition(this, label_name, location);
  this->add_statement(Statement::make_label_statement(label, location));
  return label;
}

// Add a label reference.

Label*
Gogo::add_label_reference(const std::string& label_name,
                          source_location location, bool issue_goto_errors)
{
  go_assert(!this->functions_.empty());
  Function* func = this->functions_.back().function->func_value();
  return func->add_label_reference(this, label_name, location,
                                   issue_goto_errors);
}

// Return the current binding state.

Bindings_snapshot*
Gogo::bindings_snapshot(source_location location)
{
  return new Bindings_snapshot(this->current_block(), location);
}

// Add a statement.

void
Gogo::add_statement(Statement* statement)
{
  go_assert(!this->functions_.empty()
             && !this->functions_.back().blocks.empty());
  this->functions_.back().blocks.back()->add_statement(statement);
}

// Add a block.

void
Gogo::add_block(Block* block, source_location location)
{
  go_assert(!this->functions_.empty()
             && !this->functions_.back().blocks.empty());
  Statement* statement = Statement::make_block_statement(block, location);
  this->functions_.back().blocks.back()->add_statement(statement);
}

// Add a constant.

Named_object*
Gogo::add_constant(const Typed_identifier& tid, Expression* expr,
                   int iota_value)
{
  return this->current_bindings()->add_constant(tid, NULL, expr, iota_value);
}

// Add a type.

void
Gogo::add_type(const std::string& name, Type* type, source_location location)
{
  Named_object* no = this->current_bindings()->add_type(name, NULL, type,
                                                        location);
  if (!this->in_global_scope() && no->is_type())
    no->type_value()->set_in_function(this->functions_.back().function);
}

// Add a named type.

void
Gogo::add_named_type(Named_type* type)
{
  go_assert(this->in_global_scope());
  this->current_bindings()->add_named_type(type);
}

// Declare a type.

Named_object*
Gogo::declare_type(const std::string& name, source_location location)
{
  Bindings* bindings = this->current_bindings();
  Named_object* no = bindings->add_type_declaration(name, NULL, location);
  if (!this->in_global_scope() && no->is_type_declaration())
    {
      Named_object* f = this->functions_.back().function;
      no->type_declaration_value()->set_in_function(f);
    }
  return no;
}

// Declare a type at the package level.

Named_object*
Gogo::declare_package_type(const std::string& name, source_location location)
{
  return this->package_->bindings()->add_type_declaration(name, NULL, location);
}

// Define a type which was already declared.

void
Gogo::define_type(Named_object* no, Named_type* type)
{
  this->current_bindings()->define_type(no, type);
}

// Add a variable.

Named_object*
Gogo::add_variable(const std::string& name, Variable* variable)
{
  Named_object* no = this->current_bindings()->add_variable(name, NULL,
                                                            variable);

  // In a function the middle-end wants to see a DECL_EXPR node.
  if (no != NULL
      && no->is_variable()
      && !no->var_value()->is_parameter()
      && !this->functions_.empty())
    this->add_statement(Statement::make_variable_declaration(no));

  return no;
}

// Add a sink--a reference to the blank identifier _.

Named_object*
Gogo::add_sink()
{
  return Named_object::make_sink();
}

// Add a named object.

void
Gogo::add_named_object(Named_object* no)
{
  this->current_bindings()->add_named_object(no);
}

// Record that we've seen an interface type.

void
Gogo::record_interface_type(Interface_type* itype)
{
  this->interface_types_.push_back(itype);
}

// Return a name for a thunk object.

std::string
Gogo::thunk_name()
{
  static int thunk_count;
  char thunk_name[50];
  snprintf(thunk_name, sizeof thunk_name, "$thunk%d", thunk_count);
  ++thunk_count;
  return thunk_name;
}

// Return whether a function is a thunk.

bool
Gogo::is_thunk(const Named_object* no)
{
  return no->name().compare(0, 6, "$thunk") == 0;
}

// Define the global names.  We do this only after parsing all the
// input files, because the program might define the global names
// itself.

void
Gogo::define_global_names()
{
  for (Bindings::const_declarations_iterator p =
         this->globals_->begin_declarations();
       p != this->globals_->end_declarations();
       ++p)
    {
      Named_object* global_no = p->second;
      std::string name(Gogo::pack_hidden_name(global_no->name(), false));
      Named_object* no = this->package_->bindings()->lookup(name);
      if (no == NULL)
        continue;
      no = no->resolve();
      if (no->is_type_declaration())
        {
          if (global_no->is_type())
            {
              if (no->type_declaration_value()->has_methods())
                error_at(no->location(),
                         "may not define methods for global type");
              no->set_type_value(global_no->type_value());
            }
          else
            {
              error_at(no->location(), "expected type");
              Type* errtype = Type::make_error_type();
              Named_object* err = Named_object::make_type("error", NULL,
                                                          errtype,
                                                          BUILTINS_LOCATION);
              no->set_type_value(err->type_value());
            }
        }
      else if (no->is_unknown())
        no->unknown_value()->set_real_named_object(global_no);
    }
}

// Clear out names in file scope.

void
Gogo::clear_file_scope()
{
  this->package_->bindings()->clear_file_scope();

  // Warn about packages which were imported but not used.
  for (Packages::iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      Package* package = p->second;
      if (package != this->package_
          && package->is_imported()
          && !package->used()
          && !package->uses_sink_alias()
          && !saw_errors())
        error_at(package->location(), "imported and not used: %s",
                 Gogo::message_name(package->name()).c_str());
      package->clear_is_imported();
      package->clear_uses_sink_alias();
      package->clear_used();
    }
}

// Traverse the tree.

void
Gogo::traverse(Traverse* traverse)
{
  // Traverse the current package first for consistency.  The other
  // packages will only contain imported types, constants, and
  // declarations.
  if (this->package_->bindings()->traverse(traverse, true) == TRAVERSE_EXIT)
    return;
  for (Packages::const_iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      if (p->second != this->package_)
        {
          if (p->second->bindings()->traverse(traverse, true) == TRAVERSE_EXIT)
            break;
        }
    }
}

// Traversal class used to verify types.

class Verify_types : public Traverse
{
 public:
  Verify_types()
    : Traverse(traverse_types)
  { }

  int
  type(Type*);
};

// Verify that a type is correct.

int
Verify_types::type(Type* t)
{
  if (!t->verify())
    return TRAVERSE_SKIP_COMPONENTS;
  return TRAVERSE_CONTINUE;
}

// Verify that all types are correct.

void
Gogo::verify_types()
{
  Verify_types traverse;
  this->traverse(&traverse);
}

// Traversal class used to lower parse tree.

class Lower_parse_tree : public Traverse
{
 public:
  Lower_parse_tree(Gogo* gogo, Named_object* function)
    : Traverse(traverse_variables
               | traverse_constants
               | traverse_functions
               | traverse_statements
               | traverse_expressions),
      gogo_(gogo), function_(function), iota_value_(-1), inserter_()
  { }

  void
  set_inserter(const Statement_inserter* inserter)
  { this->inserter_ = *inserter; }

  int
  variable(Named_object*);

  int
  constant(Named_object*, bool);

  int
  function(Named_object*);

  int
  statement(Block*, size_t* pindex, Statement*);

  int
  expression(Expression**);

 private:
  // General IR.
  Gogo* gogo_;
  // The function we are traversing.
  Named_object* function_;
  // Value to use for the predeclared constant iota.
  int iota_value_;
  // Current statement inserter for use by expressions.
  Statement_inserter inserter_;
};

// Lower variables.

int
Lower_parse_tree::variable(Named_object* no)
{
  if (!no->is_variable())
    return TRAVERSE_CONTINUE;

  if (no->is_variable() && no->var_value()->is_global())
    {
      // Global variables can have loops in their initialization
      // expressions.  This is handled in lower_init_expression.
      no->var_value()->lower_init_expression(this->gogo_, this->function_,
                                             &this->inserter_);
      return TRAVERSE_CONTINUE;
    }

  // This is a local variable.  We are going to return
  // TRAVERSE_SKIP_COMPONENTS here because we want to traverse the
  // initialization expression when we reach the variable declaration
  // statement.  However, that means that we need to traverse the type
  // ourselves.
  if (no->var_value()->has_type())
    {
      Type* type = no->var_value()->type();
      if (type != NULL)
        {
          if (Type::traverse(type, this) == TRAVERSE_EXIT)
            return TRAVERSE_EXIT;
        }
    }
  go_assert(!no->var_value()->has_pre_init());

  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower constants.  We handle constants specially so that we can set
// the right value for the predeclared constant iota.  This works in
// conjunction with the way we lower Const_expression objects.

int
Lower_parse_tree::constant(Named_object* no, bool)
{
  Named_constant* nc = no->const_value();

  // Don't get into trouble if the constant's initializer expression
  // refers to the constant itself.
  if (nc->lowering())
    return TRAVERSE_CONTINUE;
  nc->set_lowering();

  go_assert(this->iota_value_ == -1);
  this->iota_value_ = nc->iota_value();
  nc->traverse_expression(this);
  this->iota_value_ = -1;

  nc->clear_lowering();

  // We will traverse the expression a second time, but that will be
  // fast.

  return TRAVERSE_CONTINUE;
}

// Lower function closure types.  Record the function while lowering
// it, so that we can pass it down when lowering an expression.

int
Lower_parse_tree::function(Named_object* no)
{
  no->func_value()->set_closure_type();

  go_assert(this->function_ == NULL);
  this->function_ = no;
  int t = no->func_value()->traverse(this);
  this->function_ = NULL;

  if (t == TRAVERSE_EXIT)
    return t;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower statement parse trees.

int
Lower_parse_tree::statement(Block* block, size_t* pindex, Statement* sorig)
{
  // Because we explicitly traverse the statement's contents
  // ourselves, we want to skip block statements here.  There is
  // nothing to lower in a block statement.
  if (sorig->is_block_statement())
    return TRAVERSE_CONTINUE;

  Statement_inserter hold_inserter(this->inserter_);
  this->inserter_ = Statement_inserter(block, pindex);

  // Lower the expressions first.
  int t = sorig->traverse_contents(this);
  if (t == TRAVERSE_EXIT)
    {
      this->inserter_ = hold_inserter;
      return t;
    }

  // Keep lowering until nothing changes.
  Statement* s = sorig;
  while (true)
    {
      Statement* snew = s->lower(this->gogo_, this->function_, block,
                                 &this->inserter_);
      if (snew == s)
        break;
      s = snew;
      t = s->traverse_contents(this);
      if (t == TRAVERSE_EXIT)
        {
          this->inserter_ = hold_inserter;
          return t;
        }
    }

  if (s != sorig)
    block->replace_statement(*pindex, s);

  this->inserter_ = hold_inserter;
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower expression parse trees.

int
Lower_parse_tree::expression(Expression** pexpr)
{
  // We have to lower all subexpressions first, so that we can get
  // their type if necessary.  This is awkward, because we don't have
  // a postorder traversal pass.
  if ((*pexpr)->traverse_subexpressions(this) == TRAVERSE_EXIT)
    return TRAVERSE_EXIT;
  // Keep lowering until nothing changes.
  while (true)
    {
      Expression* e = *pexpr;
      Expression* enew = e->lower(this->gogo_, this->function_,
                                  &this->inserter_, this->iota_value_);
      if (enew == e)
        break;
      *pexpr = enew;
    }
  return TRAVERSE_SKIP_COMPONENTS;
}

// Lower the parse tree.  This is called after the parse is complete,
// when all names should be resolved.

void
Gogo::lower_parse_tree()
{
  Lower_parse_tree lower_parse_tree(this, NULL);
  this->traverse(&lower_parse_tree);
}

// Lower a block.

void
Gogo::lower_block(Named_object* function, Block* block)
{
  Lower_parse_tree lower_parse_tree(this, function);
  block->traverse(&lower_parse_tree);
}

// Lower an expression.  INSERTER may be NULL, in which case the
// expression had better not need to create any temporaries.

void
Gogo::lower_expression(Named_object* function, Statement_inserter* inserter,
                       Expression** pexpr)
{
  Lower_parse_tree lower_parse_tree(this, function);
  if (inserter != NULL)
    lower_parse_tree.set_inserter(inserter);
  lower_parse_tree.expression(pexpr);
}

// Lower a constant.  This is called when lowering a reference to a
// constant.  We have to make sure that the constant has already been
// lowered.

void
Gogo::lower_constant(Named_object* no)
{
  go_assert(no->is_const());
  Lower_parse_tree lower(this, NULL);
  lower.constant(no, false);
}

// Look for interface types to finalize methods of inherited
// interfaces.

class Finalize_methods : public Traverse
{
 public:
  Finalize_methods(Gogo* gogo)
    : Traverse(traverse_types),
      gogo_(gogo)
  { }

  int
  type(Type*);

 private:
  Gogo* gogo_;
};

// Finalize the methods of an interface type.

int
Finalize_methods::type(Type* t)
{
  // Check the classification so that we don't finalize the methods
  // twice for a named interface type.
  switch (t->classification())
    {
    case Type::TYPE_INTERFACE:
      t->interface_type()->finalize_methods();
      break;

    case Type::TYPE_NAMED:
      {
        // We have to finalize the methods of the real type first.
        // But if the real type is a struct type, then we only want to
        // finalize the methods of the field types, not of the struct
        // type itself.  We don't want to add methods to the struct,
        // since it has a name.
        Type* rt = t->named_type()->real_type();
        if (rt->classification() != Type::TYPE_STRUCT)
          {
            if (Type::traverse(rt, this) == TRAVERSE_EXIT)
              return TRAVERSE_EXIT;
          }
        else
          {
            if (rt->struct_type()->traverse_field_types(this) == TRAVERSE_EXIT)
              return TRAVERSE_EXIT;
          }

        t->named_type()->finalize_methods(this->gogo_);

        return TRAVERSE_SKIP_COMPONENTS;
      }

    case Type::TYPE_STRUCT:
      t->struct_type()->finalize_methods(this->gogo_);
      break;

    default:
      break;
    }

  return TRAVERSE_CONTINUE;
}

// Finalize method lists and build stub methods for types.

void
Gogo::finalize_methods()
{
  Finalize_methods finalize(this);
  this->traverse(&finalize);
}

// Set types for unspecified variables and constants.

void
Gogo::determine_types()
{
  Bindings* bindings = this->current_bindings();
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_function())
        (*p)->func_value()->determine_types();
      else if ((*p)->is_variable())
        (*p)->var_value()->determine_type();
      else if ((*p)->is_const())
        (*p)->const_value()->determine_type();

      // See if a variable requires us to build an initialization
      // function.  We know that we will see all global variables
      // here.
      if (!this->need_init_fn_ && (*p)->is_variable())
        {
          Variable* variable = (*p)->var_value();

          // If this is a global variable which requires runtime
          // initialization, we need an initialization function.
          if (!variable->is_global())
            ;
          else if (variable->init() == NULL)
            ;
          else if (variable->type()->interface_type() != NULL)
            this->need_init_fn_ = true;
          else if (variable->init()->is_constant())
            ;
          else if (!variable->init()->is_composite_literal())
            this->need_init_fn_ = true;
          else if (variable->init()->is_nonconstant_composite_literal())
            this->need_init_fn_ = true;

          // If this is a global variable which holds a pointer value,
          // then we need an initialization function to register it as a
          // GC root.
          if (variable->is_global() && variable->type()->has_pointer())
            this->need_init_fn_ = true;
        }
    }

  // Determine the types of constants in packages.
  for (Packages::const_iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    p->second->determine_types();
}

// Traversal class used for type checking.

class Check_types_traverse : public Traverse
{
 public:
  Check_types_traverse(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_constants
               | traverse_functions
               | traverse_statements
               | traverse_expressions),
      gogo_(gogo)
  { }

  int
  variable(Named_object*);

  int
  constant(Named_object*, bool);

  int
  function(Named_object*);

  int
  statement(Block*, size_t* pindex, Statement*);

  int
  expression(Expression**);

 private:
  // General IR.
  Gogo* gogo_;
};

// Check that a variable initializer has the right type.

int
Check_types_traverse::variable(Named_object* named_object)
{
  if (named_object->is_variable())
    {
      Variable* var = named_object->var_value();

      // Give error if variable type is not defined.
      var->type()->base();

      Expression* init = var->init();
      std::string reason;
      if (init != NULL
          && !Type::are_assignable(var->type(), init->type(), &reason))
        {
          if (reason.empty())
            error_at(var->location(), "incompatible type in initialization");
          else
            error_at(var->location(),
                     "incompatible type in initialization (%s)",
                     reason.c_str());
          var->clear_init();
        }
    }
  return TRAVERSE_CONTINUE;
}

// Check that a constant initializer has the right type.

int
Check_types_traverse::constant(Named_object* named_object, bool)
{
  Named_constant* constant = named_object->const_value();
  Type* ctype = constant->type();
  if (ctype->integer_type() == NULL
      && ctype->float_type() == NULL
      && ctype->complex_type() == NULL
      && !ctype->is_boolean_type()
      && !ctype->is_string_type())
    {
      if (ctype->is_nil_type())
        error_at(constant->location(), "const initializer cannot be nil");
      else if (!ctype->is_error())
        error_at(constant->location(), "invalid constant type");
      constant->set_error();
    }
  else if (!constant->expr()->is_constant())
    {
      error_at(constant->expr()->location(), "expression is not constant");
      constant->set_error();
    }
  else if (!Type::are_assignable(constant->type(), constant->expr()->type(),
                                 NULL))
    {
      error_at(constant->location(),
               "initialization expression has wrong type");
      constant->set_error();
    }
  return TRAVERSE_CONTINUE;
}

// There are no types to check in a function, but this is where we
// issue warnings about labels which are defined but not referenced.

int
Check_types_traverse::function(Named_object* no)
{
  no->func_value()->check_labels();
  return TRAVERSE_CONTINUE;
}

// Check that types are valid in a statement.

int
Check_types_traverse::statement(Block*, size_t*, Statement* s)
{
  s->check_types(this->gogo_);
  return TRAVERSE_CONTINUE;
}

// Check that types are valid in an expression.

int
Check_types_traverse::expression(Expression** expr)
{
  (*expr)->check_types(this->gogo_);
  return TRAVERSE_CONTINUE;
}

// Check that types are valid.

void
Gogo::check_types()
{
  Check_types_traverse traverse(this);
  this->traverse(&traverse);
}

// Check the types in a single block.

void
Gogo::check_types_in_block(Block* block)
{
  Check_types_traverse traverse(this);
  block->traverse(&traverse);
}

// A traversal class used to find a single shortcut operator within an
// expression.

class Find_shortcut : public Traverse
{
 public:
  Find_shortcut()
    : Traverse(traverse_blocks
               | traverse_statements
               | traverse_expressions),
      found_(NULL)
  { }

  // A pointer to the expression which was found, or NULL if none was
  // found.
  Expression**
  found() const
  { return this->found_; }

 protected:
  int
  block(Block*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  statement(Block*, size_t*, Statement*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  expression(Expression**);

 private:
  Expression** found_;
};

// Find a shortcut expression.

int
Find_shortcut::expression(Expression** pexpr)
{
  Expression* expr = *pexpr;
  Binary_expression* be = expr->binary_expression();
  if (be == NULL)
    return TRAVERSE_CONTINUE;
  Operator op = be->op();
  if (op != OPERATOR_OROR && op != OPERATOR_ANDAND)
    return TRAVERSE_CONTINUE;
  go_assert(this->found_ == NULL);
  this->found_ = pexpr;
  return TRAVERSE_EXIT;
}

// A traversal class used to turn shortcut operators into explicit if
// statements.

class Shortcuts : public Traverse
{
 public:
  Shortcuts(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_statements),
      gogo_(gogo)
  { }

 protected:
  int
  variable(Named_object*);

  int
  statement(Block*, size_t*, Statement*);

 private:
  // Convert a shortcut operator.
  Statement*
  convert_shortcut(Block* enclosing, Expression** pshortcut);

  // The IR.
  Gogo* gogo_;
};

// Remove shortcut operators in a single statement.

int
Shortcuts::statement(Block* block, size_t* pindex, Statement* s)
{
  // FIXME: This approach doesn't work for switch statements, because
  // we add the new statements before the whole switch when we need to
  // instead add them just before the switch expression.  The right
  // fix is probably to lower switch statements with nonconstant cases
  // to a series of conditionals.
  if (s->switch_statement() != NULL)
    return TRAVERSE_CONTINUE;

  while (true)
    {
      Find_shortcut find_shortcut;

      // If S is a variable declaration, then ordinary traversal won't
      // do anything.  We want to explicitly traverse the
      // initialization expression if there is one.
      Variable_declaration_statement* vds = s->variable_declaration_statement();
      Expression* init = NULL;
      if (vds == NULL)
        s->traverse_contents(&find_shortcut);
      else
        {
          init = vds->var()->var_value()->init();
          if (init == NULL)
            return TRAVERSE_CONTINUE;
          init->traverse(&init, &find_shortcut);
        }
      Expression** pshortcut = find_shortcut.found();
      if (pshortcut == NULL)
        return TRAVERSE_CONTINUE;

      Statement* snew = this->convert_shortcut(block, pshortcut);
      block->insert_statement_before(*pindex, snew);
      ++*pindex;

      if (pshortcut == &init)
        vds->var()->var_value()->set_init(init);
    }
}

// Remove shortcut operators in the initializer of a global variable.

int
Shortcuts::variable(Named_object* no)
{
  if (no->is_result_variable())
    return TRAVERSE_CONTINUE;
  Variable* var = no->var_value();
  Expression* init = var->init();
  if (!var->is_global() || init == NULL)
    return TRAVERSE_CONTINUE;

  while (true)
    {
      Find_shortcut find_shortcut;
      init->traverse(&init, &find_shortcut);
      Expression** pshortcut = find_shortcut.found();
      if (pshortcut == NULL)
        return TRAVERSE_CONTINUE;

      Statement* snew = this->convert_shortcut(NULL, pshortcut);
      var->add_preinit_statement(this->gogo_, snew);
      if (pshortcut == &init)
        var->set_init(init);
    }
}

// Given an expression which uses a shortcut operator, return a
// statement which implements it, and update *PSHORTCUT accordingly.

Statement*
Shortcuts::convert_shortcut(Block* enclosing, Expression** pshortcut)
{
  Binary_expression* shortcut = (*pshortcut)->binary_expression();
  Expression* left = shortcut->left();
  Expression* right = shortcut->right();
  source_location loc = shortcut->location();

  Block* retblock = new Block(enclosing, loc);
  retblock->set_end_location(loc);

  Temporary_statement* ts = Statement::make_temporary(Type::lookup_bool_type(),
                                                      left, loc);
  retblock->add_statement(ts);

  Block* block = new Block(retblock, loc);
  block->set_end_location(loc);
  Expression* tmpref = Expression::make_temporary_reference(ts, loc);
  Statement* assign = Statement::make_assignment(tmpref, right, loc);
  block->add_statement(assign);

  Expression* cond = Expression::make_temporary_reference(ts, loc);
  if (shortcut->binary_expression()->op() == OPERATOR_OROR)
    cond = Expression::make_unary(OPERATOR_NOT, cond, loc);

  Statement* if_statement = Statement::make_if_statement(cond, block, NULL,
                                                         loc);
  retblock->add_statement(if_statement);

  *pshortcut = Expression::make_temporary_reference(ts, loc);

  delete shortcut;

  // Now convert any shortcut operators in LEFT and RIGHT.
  Shortcuts shortcuts(this->gogo_);
  retblock->traverse(&shortcuts);

  return Statement::make_block_statement(retblock, loc);
}

// Turn shortcut operators into explicit if statements.  Doing this
// considerably simplifies the order of evaluation rules.

void
Gogo::remove_shortcuts()
{
  Shortcuts shortcuts(this);
  this->traverse(&shortcuts);
}

// A traversal class which finds all the expressions which must be
// evaluated in order within a statement or larger expression.  This
// is used to implement the rules about order of evaluation.

class Find_eval_ordering : public Traverse
{
 private:
  typedef std::vector<Expression**> Expression_pointers;

 public:
  Find_eval_ordering()
    : Traverse(traverse_blocks
               | traverse_statements
               | traverse_expressions),
      exprs_()
  { }

  size_t
  size() const
  { return this->exprs_.size(); }

  typedef Expression_pointers::const_iterator const_iterator;

  const_iterator
  begin() const
  { return this->exprs_.begin(); }

  const_iterator
  end() const
  { return this->exprs_.end(); }

 protected:
  int
  block(Block*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  statement(Block*, size_t*, Statement*)
  { return TRAVERSE_SKIP_COMPONENTS; }

  int
  expression(Expression**);

 private:
  // A list of pointers to expressions with side-effects.
  Expression_pointers exprs_;
};

// If an expression must be evaluated in order, put it on the list.

int
Find_eval_ordering::expression(Expression** expression_pointer)
{
  // We have to look at subexpressions before this one.
  if ((*expression_pointer)->traverse_subexpressions(this) == TRAVERSE_EXIT)
    return TRAVERSE_EXIT;
  if ((*expression_pointer)->must_eval_in_order())
    this->exprs_.push_back(expression_pointer);
  return TRAVERSE_SKIP_COMPONENTS;
}

// A traversal class for ordering evaluations.

class Order_eval : public Traverse
{
 public:
  Order_eval(Gogo* gogo)
    : Traverse(traverse_variables
               | traverse_statements),
      gogo_(gogo)
  { }

  int
  variable(Named_object*);

  int
  statement(Block*, size_t*, Statement*);

 private:
  // The IR.
  Gogo* gogo_;
};

// Implement the order of evaluation rules for a statement.

int
Order_eval::statement(Block* block, size_t* pindex, Statement* s)
{
  // FIXME: This approach doesn't work for switch statements, because
  // we add the new statements before the whole switch when we need to
  // instead add them just before the switch expression.  The right
  // fix is probably to lower switch statements with nonconstant cases
  // to a series of conditionals.
  if (s->switch_statement() != NULL)
    return TRAVERSE_CONTINUE;

  Find_eval_ordering find_eval_ordering;

  // If S is a variable declaration, then ordinary traversal won't do
  // anything.  We want to explicitly traverse the initialization
  // expression if there is one.
  Variable_declaration_statement* vds = s->variable_declaration_statement();
  Expression* init = NULL;
  Expression* orig_init = NULL;
  if (vds == NULL)
    s->traverse_contents(&find_eval_ordering);
  else
    {
      init = vds->var()->var_value()->init();
      if (init == NULL)
        return TRAVERSE_CONTINUE;
      orig_init = init;

      // It might seem that this could be
      // init->traverse_subexpressions.  Unfortunately that can fail
      // in a case like
      //   var err os.Error
      //   newvar, err := call(arg())
      // Here newvar will have an init of call result 0 of
      // call(arg()).  If we only traverse subexpressions, we will
      // only find arg(), and we won't bother to move anything out.
      // Then we get to the assignment to err, we will traverse the
      // whole statement, and this time we will find both call() and
      // arg(), and so we will move them out.  This will cause them to
      // be put into temporary variables before the assignment to err
      // but after the declaration of newvar.  To avoid that problem,
      // we traverse the entire expression here.
      Expression::traverse(&init, &find_eval_ordering);
    }

  if (find_eval_ordering.size() <= 1)
    {
      // If there is only one expression with a side-effect, we can
      // leave it in place.
      return TRAVERSE_CONTINUE;
    }

  bool is_thunk = s->thunk_statement() != NULL;
  for (Find_eval_ordering::const_iterator p = find_eval_ordering.begin();
       p != find_eval_ordering.end();
       ++p)
    {
      Expression** pexpr = *p;

      // The last expression in a thunk will be the call passed to go
      // or defer, which we must not evaluate early.
      if (is_thunk && p + 1 == find_eval_ordering.end())
        break;

      source_location loc = (*pexpr)->location();
      Statement* s;
      if ((*pexpr)->call_expression() == NULL
          || (*pexpr)->call_expression()->result_count() < 2)
        {
          Temporary_statement* ts = Statement::make_temporary(NULL, *pexpr,
                                                              loc);
          s = ts;
          *pexpr = Expression::make_temporary_reference(ts, loc);
        }
      else
        {
          // A call expression which returns multiple results needs to
          // be handled specially.  We can't create a temporary
          // because there is no type to give it.  Any actual uses of
          // the values will be done via Call_result_expressions.
          s = Statement::make_statement(*pexpr, true);
        }

      block->insert_statement_before(*pindex, s);
      ++*pindex;
    }

  if (init != orig_init)
    vds->var()->var_value()->set_init(init);

  return TRAVERSE_CONTINUE;
}

// Implement the order of evaluation rules for the initializer of a
// global variable.

int
Order_eval::variable(Named_object* no)
{
  if (no->is_result_variable())
    return TRAVERSE_CONTINUE;
  Variable* var = no->var_value();
  Expression* init = var->init();
  if (!var->is_global() || init == NULL)
    return TRAVERSE_CONTINUE;

  Find_eval_ordering find_eval_ordering;
  Expression::traverse(&init, &find_eval_ordering);

  if (find_eval_ordering.size() <= 1)
    {
      // If there is only one expression with a side-effect, we can
      // leave it in place.
      return TRAVERSE_SKIP_COMPONENTS;
    }

  for (Find_eval_ordering::const_iterator p = find_eval_ordering.begin();
       p != find_eval_ordering.end();
       ++p)
    {
      Expression** pexpr = *p;
      source_location loc = (*pexpr)->location();
      Statement* s;
      if ((*pexpr)->call_expression() == NULL
          || (*pexpr)->call_expression()->result_count() < 2)
        {
          Temporary_statement* ts = Statement::make_temporary(NULL, *pexpr,
                                                              loc);
          s = ts;
          *pexpr = Expression::make_temporary_reference(ts, loc);
        }
      else
        {
          // A call expression which returns multiple results needs to
          // be handled specially.
          s = Statement::make_statement(*pexpr, true);
        }
      var->add_preinit_statement(this->gogo_, s);
    }

  return TRAVERSE_SKIP_COMPONENTS;
}

// Use temporary variables to implement the order of evaluation rules.

void
Gogo::order_evaluations()
{
  Order_eval order_eval(this);
  this->traverse(&order_eval);
}

// Traversal to convert calls to the predeclared recover function to
// pass in an argument indicating whether it can recover from a panic
// or not.

class Convert_recover : public Traverse
{
 public:
  Convert_recover(Named_object* arg)
    : Traverse(traverse_expressions),
      arg_(arg)
  { }

 protected:
  int
  expression(Expression**);

 private:
  // The argument to pass to the function.
  Named_object* arg_;
};

// Convert calls to recover.

int
Convert_recover::expression(Expression** pp)
{
  Call_expression* ce = (*pp)->call_expression();
  if (ce != NULL && ce->is_recover_call())
    ce->set_recover_arg(Expression::make_var_reference(this->arg_,
                                                       ce->location()));
  return TRAVERSE_CONTINUE;
}

// Traversal for build_recover_thunks.

class Build_recover_thunks : public Traverse
{
 public:
  Build_recover_thunks(Gogo* gogo)
    : Traverse(traverse_functions),
      gogo_(gogo)
  { }

  int
  function(Named_object*);

 private:
  Expression*
  can_recover_arg(source_location);

  // General IR.
  Gogo* gogo_;
};

// If this function calls recover, turn it into a thunk.

int
Build_recover_thunks::function(Named_object* orig_no)
{
  Function* orig_func = orig_no->func_value();
  if (!orig_func->calls_recover()
      || orig_func->is_recover_thunk()
      || orig_func->has_recover_thunk())
    return TRAVERSE_CONTINUE;

  Gogo* gogo = this->gogo_;
  source_location location = orig_func->location();

  static int count;
  char buf[50];

  Function_type* orig_fntype = orig_func->type();
  Typed_identifier_list* new_params = new Typed_identifier_list();
  std::string receiver_name;
  if (orig_fntype->is_method())
    {
      const Typed_identifier* receiver = orig_fntype->receiver();
      snprintf(buf, sizeof buf, "rt.%u", count);
      ++count;
      receiver_name = buf;
      new_params->push_back(Typed_identifier(receiver_name, receiver->type(),
                                             receiver->location()));
    }
  const Typed_identifier_list* orig_params = orig_fntype->parameters();
  if (orig_params != NULL && !orig_params->empty())
    {
      for (Typed_identifier_list::const_iterator p = orig_params->begin();
           p != orig_params->end();
           ++p)
        {
          snprintf(buf, sizeof buf, "pt.%u", count);
          ++count;
          new_params->push_back(Typed_identifier(buf, p->type(),
                                                 p->location()));
        }
    }
  snprintf(buf, sizeof buf, "pr.%u", count);
  ++count;
  std::string can_recover_name = buf;
  new_params->push_back(Typed_identifier(can_recover_name,
                                         Type::lookup_bool_type(),
                                         orig_fntype->location()));

  const Typed_identifier_list* orig_results = orig_fntype->results();
  Typed_identifier_list* new_results;
  if (orig_results == NULL || orig_results->empty())
    new_results = NULL;
  else
    {
      new_results = new Typed_identifier_list();
      for (Typed_identifier_list::const_iterator p = orig_results->begin();
           p != orig_results->end();
           ++p)
        new_results->push_back(Typed_identifier("", p->type(), p->location()));
    }

  Function_type *new_fntype = Type::make_function_type(NULL, new_params,
                                                       new_results,
                                                       orig_fntype->location());
  if (orig_fntype->is_varargs())
    new_fntype->set_is_varargs();

  std::string name = orig_no->name() + "$recover";
  Named_object *new_no = gogo->start_function(name, new_fntype, false,
                                              location);
  Function *new_func = new_no->func_value();
  if (orig_func->enclosing() != NULL)
    new_func->set_enclosing(orig_func->enclosing());

  // We build the code for the original function attached to the new
  // function, and then swap the original and new function bodies.
  // This means that existing references to the original function will
  // then refer to the new function.  That makes this code a little
  // confusing, in that the reference to NEW_NO really refers to the
  // other function, not the one we are building.

  Expression* closure = NULL;
  if (orig_func->needs_closure())
    {
      Named_object* orig_closure_no = orig_func->closure_var();
      Variable* orig_closure_var = orig_closure_no->var_value();
      Variable* new_var = new Variable(orig_closure_var->type(), NULL, false,
                                       true, false, location);
      snprintf(buf, sizeof buf, "closure.%u", count);
      ++count;
      Named_object* new_closure_no = Named_object::make_variable(buf, NULL,
                                                                 new_var);
      new_func->set_closure_var(new_closure_no);
      closure = Expression::make_var_reference(new_closure_no, location);
    }

  Expression* fn = Expression::make_func_reference(new_no, closure, location);

  Expression_list* args = new Expression_list();
  if (new_params != NULL)
    {
      // Note that we skip the last parameter, which is the boolean
      // indicating whether recover can succed.
      for (Typed_identifier_list::const_iterator p = new_params->begin();
           p + 1 != new_params->end();
           ++p)
        {
          Named_object* p_no = gogo->lookup(p->name(), NULL);
          go_assert(p_no != NULL
                     && p_no->is_variable()
                     && p_no->var_value()->is_parameter());
          args->push_back(Expression::make_var_reference(p_no, location));
        }
    }
  args->push_back(this->can_recover_arg(location));

  gogo->start_block(location);

  Call_expression* call = Expression::make_call(fn, args, false, location);

  Statement* s;
  if (orig_fntype->results() == NULL || orig_fntype->results()->empty())
    s = Statement::make_statement(call, true);
  else
    {
      Expression_list* vals = new Expression_list();
      size_t rc = orig_fntype->results()->size();
      if (rc == 1)
        vals->push_back(call);
      else
        {
          for (size_t i = 0; i < rc; ++i)
            vals->push_back(Expression::make_call_result(call, i));
        }
      s = Statement::make_return_statement(vals, location);
    }
  s->determine_types();
  gogo->add_statement(s);

  Block* b = gogo->finish_block(location);

  gogo->add_block(b, location);

  // Lower the call in case it returns multiple results.
  gogo->lower_block(new_no, b);

  gogo->finish_function(location);

  // Swap the function bodies and types.
  new_func->swap_for_recover(orig_func);
  orig_func->set_is_recover_thunk();
  new_func->set_calls_recover();
  new_func->set_has_recover_thunk();

  Bindings* orig_bindings = orig_func->block()->bindings();
  Bindings* new_bindings = new_func->block()->bindings();
  if (orig_fntype->is_method())
    {
      // We changed the receiver to be a regular parameter.  We have
      // to update the binding accordingly in both functions.
      Named_object* orig_rec_no = orig_bindings->lookup_local(receiver_name);
      go_assert(orig_rec_no != NULL
                 && orig_rec_no->is_variable()
                 && !orig_rec_no->var_value()->is_receiver());
      orig_rec_no->var_value()->set_is_receiver();

      const std::string& new_receiver_name(orig_fntype->receiver()->name());
      Named_object* new_rec_no = new_bindings->lookup_local(new_receiver_name);
      if (new_rec_no == NULL)
        go_assert(saw_errors());
      else
        {
          go_assert(new_rec_no->is_variable()
                     && new_rec_no->var_value()->is_receiver());
          new_rec_no->var_value()->set_is_not_receiver();
        }
    }

  // Because we flipped blocks but not types, the can_recover
  // parameter appears in the (now) old bindings as a parameter.
  // Change it to a local variable, whereupon it will be discarded.
  Named_object* can_recover_no = orig_bindings->lookup_local(can_recover_name);
  go_assert(can_recover_no != NULL
             && can_recover_no->is_variable()
             && can_recover_no->var_value()->is_parameter());
  orig_bindings->remove_binding(can_recover_no);

  // Add the can_recover argument to the (now) new bindings, and
  // attach it to any recover statements.
  Variable* can_recover_var = new Variable(Type::lookup_bool_type(), NULL,
                                           false, true, false, location);
  can_recover_no = new_bindings->add_variable(can_recover_name, NULL,
                                              can_recover_var);
  Convert_recover convert_recover(can_recover_no);
  new_func->traverse(&convert_recover);

  // Update the function pointers in any named results.
  new_func->update_result_variables();
  orig_func->update_result_variables();

  return TRAVERSE_CONTINUE;
}

// Return the expression to pass for the .can_recover parameter to the
// new function.  This indicates whether a call to recover may return
// non-nil.  The expression is
// __go_can_recover(__builtin_return_address()).

Expression*
Build_recover_thunks::can_recover_arg(source_location location)
{
  static Named_object* builtin_return_address;
  if (builtin_return_address == NULL)
    {
      const source_location bloc = BUILTINS_LOCATION;

      Typed_identifier_list* param_types = new Typed_identifier_list();
      Type* uint_type = Type::lookup_integer_type("uint");
      param_types->push_back(Typed_identifier("l", uint_type, bloc));

      Typed_identifier_list* return_types = new Typed_identifier_list();
      Type* voidptr_type = Type::make_pointer_type(Type::make_void_type());
      return_types->push_back(Typed_identifier("", voidptr_type, bloc));

      Function_type* fntype = Type::make_function_type(NULL, param_types,
                                                       return_types, bloc);
      builtin_return_address =
        Named_object::make_function_declaration("__builtin_return_address",
                                                NULL, fntype, bloc);
      const char* n = "__builtin_return_address";
      builtin_return_address->func_declaration_value()->set_asm_name(n);
    }

  static Named_object* can_recover;
  if (can_recover == NULL)
    {
      const source_location bloc = BUILTINS_LOCATION;
      Typed_identifier_list* param_types = new Typed_identifier_list();
      Type* voidptr_type = Type::make_pointer_type(Type::make_void_type());
      param_types->push_back(Typed_identifier("a", voidptr_type, bloc));
      Type* boolean_type = Type::lookup_bool_type();
      Typed_identifier_list* results = new Typed_identifier_list();
      results->push_back(Typed_identifier("", boolean_type, bloc));
      Function_type* fntype = Type::make_function_type(NULL, param_types,
                                                       results, bloc);
      can_recover = Named_object::make_function_declaration("__go_can_recover",
                                                            NULL, fntype,
                                                            bloc);
      can_recover->func_declaration_value()->set_asm_name("__go_can_recover");
    }

  Expression* fn = Expression::make_func_reference(builtin_return_address,
                                                   NULL, location);

  mpz_t zval;
  mpz_init_set_ui(zval, 0UL);
  Expression* zexpr = Expression::make_integer(&zval, NULL, location);
  mpz_clear(zval);
  Expression_list *args = new Expression_list();
  args->push_back(zexpr);

  Expression* call = Expression::make_call(fn, args, false, location);

  args = new Expression_list();
  args->push_back(call);

  fn = Expression::make_func_reference(can_recover, NULL, location);
  return Expression::make_call(fn, args, false, location);
}

// Build thunks for functions which call recover.  We build a new
// function with an extra parameter, which is whether a call to
// recover can succeed.  We then move the body of this function to
// that one.  We then turn this function into a thunk which calls the
// new one, passing the value of
// __go_can_recover(__builtin_return_address()).  The function will be
// marked as not splitting the stack.  This will cooperate with the
// implementation of defer to make recover do the right thing.

void
Gogo::build_recover_thunks()
{
  Build_recover_thunks build_recover_thunks(this);
  this->traverse(&build_recover_thunks);
}

// Look for named types to see whether we need to create an interface
// method table.

class Build_method_tables : public Traverse
{
 public:
  Build_method_tables(Gogo* gogo,
                      const std::vector<Interface_type*>& interfaces)
    : Traverse(traverse_types),
      gogo_(gogo), interfaces_(interfaces)
  { }

  int
  type(Type*);

 private:
  // The IR.
  Gogo* gogo_;
  // A list of locally defined interfaces which have hidden methods.
  const std::vector<Interface_type*>& interfaces_;
};

// Build all required interface method tables for types.  We need to
// ensure that we have an interface method table for every interface
// which has a hidden method, for every named type which implements
// that interface.  Normally we can just build interface method tables
// as we need them.  However, in some cases we can require an
// interface method table for an interface defined in a different
// package for a type defined in that package.  If that interface and
// type both use a hidden method, that is OK.  However, we will not be
// able to build that interface method table when we need it, because
// the type's hidden method will be static.  So we have to build it
// here, and just refer it from other packages as needed.

void
Gogo::build_interface_method_tables()
{
  std::vector<Interface_type*> hidden_interfaces;
  hidden_interfaces.reserve(this->interface_types_.size());
  for (std::vector<Interface_type*>::const_iterator pi =
         this->interface_types_.begin();
       pi != this->interface_types_.end();
       ++pi)
    {
      const Typed_identifier_list* methods = (*pi)->methods();
      if (methods == NULL)
        continue;
      for (Typed_identifier_list::const_iterator pm = methods->begin();
           pm != methods->end();
           ++pm)
        {
          if (Gogo::is_hidden_name(pm->name()))
            {
              hidden_interfaces.push_back(*pi);
              break;
            }
        }
    }

  if (!hidden_interfaces.empty())
    {
      // Now traverse the tree looking for all named types.
      Build_method_tables bmt(this, hidden_interfaces);
      this->traverse(&bmt);
    }

  // We no longer need the list of interfaces.

  this->interface_types_.clear();
}

// This is called for each type.  For a named type, for each of the
// interfaces with hidden methods that it implements, create the
// method table.

int
Build_method_tables::type(Type* type)
{
  Named_type* nt = type->named_type();
  if (nt != NULL)
    {
      for (std::vector<Interface_type*>::const_iterator p =
             this->interfaces_.begin();
           p != this->interfaces_.end();
           ++p)
        {
          // We ask whether a pointer to the named type implements the
          // interface, because a pointer can implement more methods
          // than a value.
          if ((*p)->implements_interface(Type::make_pointer_type(nt), NULL))
            {
              nt->interface_method_table(this->gogo_, *p, false);
              nt->interface_method_table(this->gogo_, *p, true);
            }
        }
    }
  return TRAVERSE_CONTINUE;
}

// Traversal class used to check for return statements.

class Check_return_statements_traverse : public Traverse
{
 public:
  Check_return_statements_traverse()
    : Traverse(traverse_functions)
  { }

  int
  function(Named_object*);
};

// Check that a function has a return statement if it needs one.

int
Check_return_statements_traverse::function(Named_object* no)
{
  Function* func = no->func_value();
  const Function_type* fntype = func->type();
  const Typed_identifier_list* results = fntype->results();

  // We only need a return statement if there is a return value.
  if (results == NULL || results->empty())
    return TRAVERSE_CONTINUE;

  if (func->block()->may_fall_through())
    error_at(func->location(), "control reaches end of non-void function");

  return TRAVERSE_CONTINUE;
}

// Check return statements.

void
Gogo::check_return_statements()
{
  Check_return_statements_traverse traverse;
  this->traverse(&traverse);
}

// Get the unique prefix to use before all exported symbols.  This
// must be unique across the entire link.

const std::string&
Gogo::unique_prefix() const
{
  go_assert(!this->unique_prefix_.empty());
  return this->unique_prefix_;
}

// Set the unique prefix to use before all exported symbols.  This
// comes from the command line option -fgo-prefix=XXX.

void
Gogo::set_unique_prefix(const std::string& arg)
{
  go_assert(this->unique_prefix_.empty());
  this->unique_prefix_ = arg;
  this->unique_prefix_specified_ = true;
}

// Work out the package priority.  It is one more than the maximum
// priority of an imported package.

int
Gogo::package_priority() const
{
  int priority = 0;
  for (Packages::const_iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    if (p->second->priority() > priority)
      priority = p->second->priority();
  return priority + 1;
}

// Export identifiers as requested.

void
Gogo::do_exports()
{
  // For now we always stream to a section.  Later we may want to
  // support streaming to a separate file.
  Stream_to_section stream;

  Export exp(&stream);
  exp.register_builtin_types(this);
  exp.export_globals(this->package_name(),
                     this->unique_prefix(),
                     this->package_priority(),
                     (this->need_init_fn_ && !this->is_main_package()
                      ? this->get_init_fn_name()
                      : ""),
                     this->imported_init_fns_,
                     this->package_->bindings());
}

// Find the blocks in order to convert named types defined in blocks.

class Convert_named_types : public Traverse
{
 public:
  Convert_named_types(Gogo* gogo)
    : Traverse(traverse_blocks),
      gogo_(gogo)
  { }

 protected:
  int
  block(Block* block);

 private:
  Gogo* gogo_;
};

int
Convert_named_types::block(Block* block)
{
  this->gogo_->convert_named_types_in_bindings(block->bindings());
  return TRAVERSE_CONTINUE;
}

// Convert all named types to the backend representation.  Since named
// types can refer to other types, this needs to be done in the right
// sequence, which is handled by Named_type::convert.  Here we arrange
// to call that for each named type.

void
Gogo::convert_named_types()
{
  this->convert_named_types_in_bindings(this->globals_);
  for (Packages::iterator p = this->packages_.begin();
       p != this->packages_.end();
       ++p)
    {
      Package* package = p->second;
      this->convert_named_types_in_bindings(package->bindings());
    }

  Convert_named_types cnt(this);
  this->traverse(&cnt);

  // Make all the builtin named types used for type descriptors, and
  // then convert them.  They will only be written out if they are
  // needed.
  Type::make_type_descriptor_type();
  Type::make_type_descriptor_ptr_type();
  Function_type::make_function_type_descriptor_type();
  Pointer_type::make_pointer_type_descriptor_type();
  Struct_type::make_struct_type_descriptor_type();
  Array_type::make_array_type_descriptor_type();
  Array_type::make_slice_type_descriptor_type();
  Map_type::make_map_type_descriptor_type();
  Map_type::make_map_descriptor_type();
  Channel_type::make_chan_type_descriptor_type();
  Interface_type::make_interface_type_descriptor_type();
  Type::convert_builtin_named_types(this);

  Runtime::convert_types(this);

  Function_type::convert_types(this);

  this->named_types_are_converted_ = true;
}

// Convert all names types in a set of bindings.

void
Gogo::convert_named_types_in_bindings(Bindings* bindings)
{
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_type())
        (*p)->type_value()->convert(this);
    }
}

// Class Function.

Function::Function(Function_type* type, Function* enclosing, Block* block,
                   source_location location)
  : type_(type), enclosing_(enclosing), results_(NULL),
    closure_var_(NULL), block_(block), location_(location), fndecl_(NULL),
    defer_stack_(NULL), results_are_named_(false), calls_recover_(false),
    is_recover_thunk_(false), has_recover_thunk_(false)
{
}

// Create the named result variables.

void
Function::create_result_variables(Gogo* gogo)
{
  const Typed_identifier_list* results = this->type_->results();
  if (results == NULL || results->empty())
    return;

  if (!results->front().name().empty())
    this->results_are_named_ = true;

  this->results_ = new Results();
  this->results_->reserve(results->size());

  Block* block = this->block_;
  int index = 0;
  for (Typed_identifier_list::const_iterator p = results->begin();
       p != results->end();
       ++p, ++index)
    {
      std::string name = p->name();
      if (name.empty() || Gogo::is_sink_name(name))
        {
          static int result_counter;
          char buf[100];
          snprintf(buf, sizeof buf, "$ret%d", result_counter);
          ++result_counter;
          name = gogo->pack_hidden_name(buf, false);
        }
      Result_variable* result = new Result_variable(p->type(), this, index,
                                                    p->location());
      Named_object* no = block->bindings()->add_result_variable(name, result);
      if (no->is_result_variable())
        this->results_->push_back(no);
      else
        {
          static int dummy_result_count;
          char buf[100];
          snprintf(buf, sizeof buf, "$dret%d", dummy_result_count);
          ++dummy_result_count;
          name = gogo->pack_hidden_name(buf, false);
          no = block->bindings()->add_result_variable(name, result);
          go_assert(no->is_result_variable());
          this->results_->push_back(no);
        }
    }
}

// Update the named result variables when cloning a function which
// calls recover.

void
Function::update_result_variables()
{
  if (this->results_ == NULL)
    return;

  for (Results::iterator p = this->results_->begin();
       p != this->results_->end();
       ++p)
    (*p)->result_var_value()->set_function(this);
}

// Return the closure variable, creating it if necessary.

Named_object*
Function::closure_var()
{
  if (this->closure_var_ == NULL)
    {
      // We don't know the type of the variable yet.  We add fields as
      // we find them.
      source_location loc = this->type_->location();
      Struct_field_list* sfl = new Struct_field_list;
      Type* struct_type = Type::make_struct_type(sfl, loc);
      Variable* var = new Variable(Type::make_pointer_type(struct_type),
                                   NULL, false, true, false, loc);
      this->closure_var_ = Named_object::make_variable("closure", NULL, var);
      // Note that the new variable is not in any binding contour.
    }
  return this->closure_var_;
}

// Set the type of the closure variable.

void
Function::set_closure_type()
{
  if (this->closure_var_ == NULL)
    return;
  Named_object* closure = this->closure_var_;
  Struct_type* st = closure->var_value()->type()->deref()->struct_type();
  unsigned int index = 0;
  for (Closure_fields::const_iterator p = this->closure_fields_.begin();
       p != this->closure_fields_.end();
       ++p, ++index)
    {
      Named_object* no = p->first;
      char buf[20];
      snprintf(buf, sizeof buf, "%u", index);
      std::string n = no->name() + buf;
      Type* var_type;
      if (no->is_variable())
        var_type = no->var_value()->type();
      else
        var_type = no->result_var_value()->type();
      Type* field_type = Type::make_pointer_type(var_type);
      st->push_field(Struct_field(Typed_identifier(n, field_type, p->second)));
    }
}

// Return whether this function is a method.

bool
Function::is_method() const
{
  return this->type_->is_method();
}

// Add a label definition.

Label*
Function::add_label_definition(Gogo* gogo, const std::string& label_name,
                               source_location location)
{
  Label* lnull = NULL;
  std::pair<Labels::iterator, bool> ins =
    this->labels_.insert(std::make_pair(label_name, lnull));
  Label* label;
  if (ins.second)
    {
      // This is a new label.
      label = new Label(label_name);
      ins.first->second = label;
    }
  else
    {
      // The label was already in the hash table.
      label = ins.first->second;
      if (label->is_defined())
        {
          error_at(location, "label %qs already defined",
                   Gogo::message_name(label_name).c_str());
          inform(label->location(), "previous definition of %qs was here",
                 Gogo::message_name(label_name).c_str());
          return new Label(label_name);
        }
    }

  label->define(location, gogo->bindings_snapshot(location));

  // Issue any errors appropriate for any previous goto's to this
  // label.
  const std::vector<Bindings_snapshot*>& refs(label->refs());
  for (std::vector<Bindings_snapshot*>::const_iterator p = refs.begin();
       p != refs.end();
       ++p)
    (*p)->check_goto_to(gogo->current_block());
  label->clear_refs();

  return label;
}

// Add a reference to a label.

Label*
Function::add_label_reference(Gogo* gogo, const std::string& label_name,
                              source_location location, bool issue_goto_errors)
{
  Label* lnull = NULL;
  std::pair<Labels::iterator, bool> ins =
    this->labels_.insert(std::make_pair(label_name, lnull));
  Label* label;
  if (!ins.second)
    {
      // The label was already in the hash table.
      label = ins.first->second;
    }
  else
    {
      go_assert(ins.first->second == NULL);
      label = new Label(label_name);
      ins.first->second = label;
    }

  label->set_is_used();

  if (issue_goto_errors)
    {
      Bindings_snapshot* snapshot = label->snapshot();
      if (snapshot != NULL)
        snapshot->check_goto_from(gogo->current_block(), location);
      else
        label->add_snapshot_ref(gogo->bindings_snapshot(location));
    }

  return label;
}

// Warn about labels that are defined but not used.

void
Function::check_labels() const
{
  for (Labels::const_iterator p = this->labels_.begin();
       p != this->labels_.end();
       p++)
    {
      Label* label = p->second;
      if (!label->is_used())
        error_at(label->location(), "label %qs defined and not used",
                 Gogo::message_name(label->name()).c_str());
    }
}

// Swap one function with another.  This is used when building the
// thunk we use to call a function which calls recover.  It may not
// work for any other case.

void
Function::swap_for_recover(Function *x)
{
  go_assert(this->enclosing_ == x->enclosing_);
  std::swap(this->results_, x->results_);
  std::swap(this->closure_var_, x->closure_var_);
  std::swap(this->block_, x->block_);
  go_assert(this->location_ == x->location_);
  go_assert(this->fndecl_ == NULL && x->fndecl_ == NULL);
  go_assert(this->defer_stack_ == NULL && x->defer_stack_ == NULL);
}

// Traverse the tree.

int
Function::traverse(Traverse* traverse)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  if ((traverse_mask
       & (Traverse::traverse_types | Traverse::traverse_expressions))
      != 0)
    {
      if (Type::traverse(this->type_, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  // FIXME: We should check traverse_functions here if nested
  // functions are stored in block bindings.
  if (this->block_ != NULL
      && (traverse_mask
          & (Traverse::traverse_variables
             | Traverse::traverse_constants
             | Traverse::traverse_blocks
             | Traverse::traverse_statements
             | Traverse::traverse_expressions
             | Traverse::traverse_types)) != 0)
    {
      if (this->block_->traverse(traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  return TRAVERSE_CONTINUE;
}

// Work out types for unspecified variables and constants.

void
Function::determine_types()
{
  if (this->block_ != NULL)
    this->block_->determine_types();
}

// Get a pointer to the variable representing the defer stack for this
// function, making it if necessary.  The value of the variable is set
// by the runtime routines to true if the function is returning,
// rather than panicing through.  A pointer to this variable is used
// as a marker for the functions on the defer stack associated with
// this function.  A function-specific variable permits inlining a
// function which uses defer.

Expression*
Function::defer_stack(source_location location)
{
  if (this->defer_stack_ == NULL)
    {
      Type* t = Type::lookup_bool_type();
      Expression* n = Expression::make_boolean(false, location);
      this->defer_stack_ = Statement::make_temporary(t, n, location);
      this->defer_stack_->set_is_address_taken();
    }
  Expression* ref = Expression::make_temporary_reference(this->defer_stack_,
                                                         location);
  return Expression::make_unary(OPERATOR_AND, ref, location);
}

// Export the function.

void
Function::export_func(Export* exp, const std::string& name) const
{
  Function::export_func_with_type(exp, name, this->type_);
}

// Export a function with a type.

void
Function::export_func_with_type(Export* exp, const std::string& name,
                                const Function_type* fntype)
{
  exp->write_c_string("func ");

  if (fntype->is_method())
    {
      exp->write_c_string("(");
      exp->write_type(fntype->receiver()->type());
      exp->write_c_string(") ");
    }

  exp->write_string(name);

  exp->write_c_string(" (");
  const Typed_identifier_list* parameters = fntype->parameters();
  if (parameters != NULL)
    {
      bool is_varargs = fntype->is_varargs();
      bool first = true;
      for (Typed_identifier_list::const_iterator p = parameters->begin();
           p != parameters->end();
           ++p)
        {
          if (first)
            first = false;
          else
            exp->write_c_string(", ");
          if (!is_varargs || p + 1 != parameters->end())
            exp->write_type(p->type());
          else
            {
              exp->write_c_string("...");
              exp->write_type(p->type()->array_type()->element_type());
            }
        }
    }
  exp->write_c_string(")");

  const Typed_identifier_list* results = fntype->results();
  if (results != NULL)
    {
      if (results->size() == 1)
        {
          exp->write_c_string(" ");
          exp->write_type(results->begin()->type());
        }
      else
        {
          exp->write_c_string(" (");
          bool first = true;
          for (Typed_identifier_list::const_iterator p = results->begin();
               p != results->end();
               ++p)
            {
              if (first)
                first = false;
              else
                exp->write_c_string(", ");
              exp->write_type(p->type());
            }
          exp->write_c_string(")");
        }
    }
  exp->write_c_string(";\n");
}

// Import a function.

void
Function::import_func(Import* imp, std::string* pname,
                      Typed_identifier** preceiver,
                      Typed_identifier_list** pparameters,
                      Typed_identifier_list** presults,
                      bool* is_varargs)
{
  imp->require_c_string("func ");

  *preceiver = NULL;
  if (imp->peek_char() == '(')
    {
      imp->require_c_string("(");
      Type* rtype = imp->read_type();
      *preceiver = new Typed_identifier(Import::import_marker, rtype,
                                        imp->location());
      imp->require_c_string(") ");
    }

  *pname = imp->read_identifier();

  Typed_identifier_list* parameters;
  *is_varargs = false;
  imp->require_c_string(" (");
  if (imp->peek_char() == ')')
    parameters = NULL;
  else
    {
      parameters = new Typed_identifier_list();
      while (true)
        {
          if (imp->match_c_string("..."))
            {
              imp->advance(3);
              *is_varargs = true;
            }

          Type* ptype = imp->read_type();
          if (*is_varargs)
            ptype = Type::make_array_type(ptype, NULL);
          parameters->push_back(Typed_identifier(Import::import_marker,
                                                 ptype, imp->location()));
          if (imp->peek_char() != ',')
            break;
          go_assert(!*is_varargs);
          imp->require_c_string(", ");
        }
    }
  imp->require_c_string(")");
  *pparameters = parameters;

  Typed_identifier_list* results;
  if (imp->peek_char() != ' ')
    results = NULL;
  else
    {
      results = new Typed_identifier_list();
      imp->require_c_string(" ");
      if (imp->peek_char() != '(')
        {
          Type* rtype = imp->read_type();
          results->push_back(Typed_identifier(Import::import_marker, rtype,
                                              imp->location()));
        }
      else
        {
          imp->require_c_string("(");
          while (true)
            {
              Type* rtype = imp->read_type();
              results->push_back(Typed_identifier(Import::import_marker,
                                                  rtype, imp->location()));
              if (imp->peek_char() != ',')
                break;
              imp->require_c_string(", ");
            }
          imp->require_c_string(")");
        }
    }
  imp->require_c_string(";\n");
  *presults = results;
}

// Class Block.

Block::Block(Block* enclosing, source_location location)
  : enclosing_(enclosing), statements_(),
    bindings_(new Bindings(enclosing == NULL
                           ? NULL
                           : enclosing->bindings())),
    start_location_(location),
    end_location_(UNKNOWN_LOCATION)
{
}

// Add a statement to a block.

void
Block::add_statement(Statement* statement)
{
  this->statements_.push_back(statement);
}

// Add a statement to the front of a block.  This is slow but is only
// used for reference counts of parameters.

void
Block::add_statement_at_front(Statement* statement)
{
  this->statements_.insert(this->statements_.begin(), statement);
}

// Replace a statement in a block.

void
Block::replace_statement(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_[index] = s;
}

// Add a statement before another statement.

void
Block::insert_statement_before(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_.insert(this->statements_.begin() + index, s);
}

// Add a statement after another statement.

void
Block::insert_statement_after(size_t index, Statement* s)
{
  go_assert(index < this->statements_.size());
  this->statements_.insert(this->statements_.begin() + index + 1, s);
}

// Traverse the tree.

int
Block::traverse(Traverse* traverse)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  if ((traverse_mask & Traverse::traverse_blocks) != 0)
    {
      int t = traverse->block(this);
      if (t == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
      else if (t == TRAVERSE_SKIP_COMPONENTS)
        return TRAVERSE_CONTINUE;
    }

  if ((traverse_mask
       & (Traverse::traverse_variables
          | Traverse::traverse_constants
          | Traverse::traverse_expressions
          | Traverse::traverse_types)) != 0)
    {
      const unsigned int e_or_t = (Traverse::traverse_expressions
                                   | Traverse::traverse_types);
      const unsigned int e_or_t_or_s = (e_or_t
                                        | Traverse::traverse_statements);
      for (Bindings::const_definitions_iterator pb =
             this->bindings_->begin_definitions();
           pb != this->bindings_->end_definitions();
           ++pb)
        {
          int t = TRAVERSE_CONTINUE;
          switch ((*pb)->classification())
            {
            case Named_object::NAMED_OBJECT_CONST:
              if ((traverse_mask & Traverse::traverse_constants) != 0)
                t = traverse->constant(*pb, false);
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t) != 0)
                {
                  Type* tc = (*pb)->const_value()->type();
                  if (tc != NULL
                      && Type::traverse(tc, traverse) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                  t = (*pb)->const_value()->traverse_expression(traverse);
                }
              break;

            case Named_object::NAMED_OBJECT_VAR:
            case Named_object::NAMED_OBJECT_RESULT_VAR:
              if ((traverse_mask & Traverse::traverse_variables) != 0)
                t = traverse->variable(*pb);
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t) != 0)
                {
                  if ((*pb)->is_result_variable()
                      || (*pb)->var_value()->has_type())
                    {
                      Type* tv = ((*pb)->is_variable()
                                  ? (*pb)->var_value()->type()
                                  : (*pb)->result_var_value()->type());
                      if (tv != NULL
                          && Type::traverse(tv, traverse) == TRAVERSE_EXIT)
                        return TRAVERSE_EXIT;
                    }
                }
              if (t == TRAVERSE_CONTINUE
                  && (traverse_mask & e_or_t_or_s) != 0
                  && (*pb)->is_variable())
                t = (*pb)->var_value()->traverse_expression(traverse,
                                                            traverse_mask);
              break;

            case Named_object::NAMED_OBJECT_FUNC:
            case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
              go_unreachable();

            case Named_object::NAMED_OBJECT_TYPE:
              if ((traverse_mask & e_or_t) != 0)
                t = Type::traverse((*pb)->type_value(), traverse);
              break;

            case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
            case Named_object::NAMED_OBJECT_UNKNOWN:
              break;

            case Named_object::NAMED_OBJECT_PACKAGE:
            case Named_object::NAMED_OBJECT_SINK:
              go_unreachable();

            default:
              go_unreachable();
            }

          if (t == TRAVERSE_EXIT)
            return TRAVERSE_EXIT;
        }
    }

  // No point in checking traverse_mask here--if we got here we always
  // want to walk the statements.  The traversal can insert new
  // statements before or after the current statement.  Inserting
  // statements before the current statement requires updating I via
  // the pointer; those statements will not be traversed.  Any new
  // statements inserted after the current statement will be traversed
  // in their turn.
  for (size_t i = 0; i < this->statements_.size(); ++i)
    {
      if (this->statements_[i]->traverse(this, &i, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  return TRAVERSE_CONTINUE;
}

// Work out types for unspecified variables and constants.

void
Block::determine_types()
{
  for (Bindings::const_definitions_iterator pb =
         this->bindings_->begin_definitions();
       pb != this->bindings_->end_definitions();
       ++pb)
    {
      if ((*pb)->is_variable())
        (*pb)->var_value()->determine_type();
      else if ((*pb)->is_const())
        (*pb)->const_value()->determine_type();
    }

  for (std::vector<Statement*>::const_iterator ps = this->statements_.begin();
       ps != this->statements_.end();
       ++ps)
    (*ps)->determine_types();
}

// Return true if the statements in this block may fall through.

bool
Block::may_fall_through() const
{
  if (this->statements_.empty())
    return true;
  return this->statements_.back()->may_fall_through();
}

// Convert a block to the backend representation.

Bblock*
Block::get_backend(Translate_context* context)
{
  Gogo* gogo = context->gogo();
  Named_object* function = context->function();
  std::vector<Bvariable*> vars;
  vars.reserve(this->bindings_->size_definitions());
  for (Bindings::const_definitions_iterator pv =
         this->bindings_->begin_definitions();
       pv != this->bindings_->end_definitions();
       ++pv)
    {
      if ((*pv)->is_variable() && !(*pv)->var_value()->is_parameter())
        vars.push_back((*pv)->get_backend_variable(gogo, function));
    }

  // FIXME: Permitting FUNCTION to be NULL here is a temporary measure
  // until we have a proper representation of the init function.
  Bfunction* bfunction;
  if (function == NULL)
    bfunction = NULL;
  else
    bfunction = tree_to_function(function->func_value()->get_decl());
  Bblock* ret = context->backend()->block(bfunction, context->bblock(),
                                          vars, this->start_location_,
                                          this->end_location_);

  Translate_context subcontext(gogo, function, this, ret);
  std::vector<Bstatement*> bstatements;
  bstatements.reserve(this->statements_.size());
  for (std::vector<Statement*>::const_iterator p = this->statements_.begin();
       p != this->statements_.end();
       ++p)
    bstatements.push_back((*p)->get_backend(&subcontext));

  context->backend()->block_add_statements(ret, bstatements);

  return ret;
}

// Class Bindings_snapshot.

Bindings_snapshot::Bindings_snapshot(const Block* b, source_location location)
  : block_(b), counts_(), location_(location)
{
  while (b != NULL)
    {
      this->counts_.push_back(b->bindings()->size_definitions());
      b = b->enclosing();
    }
}

// Report errors appropriate for a goto from B to this.

void
Bindings_snapshot::check_goto_from(const Block* b, source_location loc)
{
  size_t dummy;
  if (!this->check_goto_block(loc, b, this->block_, &dummy))
    return;
  this->check_goto_defs(loc, this->block_,
                        this->block_->bindings()->size_definitions(),
                        this->counts_[0]);
}

// Report errors appropriate for a goto from this to B.

void
Bindings_snapshot::check_goto_to(const Block* b)
{
  size_t index;
  if (!this->check_goto_block(this->location_, this->block_, b, &index))
    return;
  this->check_goto_defs(this->location_, b, this->counts_[index],
                        b->bindings()->size_definitions());
}

// Report errors appropriate for a goto at LOC from BFROM to BTO.
// Return true if all is well, false if we reported an error.  If this
// returns true, it sets *PINDEX to the number of blocks BTO is above
// BFROM.

bool
Bindings_snapshot::check_goto_block(source_location loc, const Block* bfrom,
                                    const Block* bto, size_t* pindex)
{
  // It is an error if BTO is not either BFROM or above BFROM.
  size_t index = 0;
  for (const Block* pb = bfrom; pb != bto; pb = pb->enclosing(), ++index)
    {
      if (pb == NULL)
        {
          error_at(loc, "goto jumps into block");
          inform(bto->start_location(), "goto target block starts here");
          return false;
        }
    }
  *pindex = index;
  return true;
}

// Report errors appropriate for a goto at LOC ending at BLOCK, where
// CFROM is the number of names defined at the point of the goto and
// CTO is the number of names defined at the point of the label.

void
Bindings_snapshot::check_goto_defs(source_location loc, const Block* block,
                                   size_t cfrom, size_t cto)
{
  if (cfrom < cto)
    {
      Bindings::const_definitions_iterator p =
        block->bindings()->begin_definitions();
      for (size_t i = 0; i < cfrom; ++i)
        {
          go_assert(p != block->bindings()->end_definitions());
          ++p;
        }
      go_assert(p != block->bindings()->end_definitions());

      std::string n = (*p)->message_name();
      error_at(loc, "goto jumps over declaration of %qs", n.c_str());
      inform((*p)->location(), "%qs defined here", n.c_str());
    }
}

// Class Variable.

Variable::Variable(Type* type, Expression* init, bool is_global,
                   bool is_parameter, bool is_receiver,
                   source_location location)
  : type_(type), init_(init), preinit_(NULL), location_(location),
    backend_(NULL), is_global_(is_global), is_parameter_(is_parameter),
    is_receiver_(is_receiver), is_varargs_parameter_(false),
    is_address_taken_(false), is_non_escaping_address_taken_(false),
    seen_(false), init_is_lowered_(false), type_from_init_tuple_(false),
    type_from_range_index_(false), type_from_range_value_(false),
    type_from_chan_element_(false), is_type_switch_var_(false),
    determined_type_(false)
{
  go_assert(type != NULL || init != NULL);
  go_assert(!is_parameter || init == NULL);
}

// Traverse the initializer expression.

int
Variable::traverse_expression(Traverse* traverse, unsigned int traverse_mask)
{
  if (this->preinit_ != NULL)
    {
      if (this->preinit_->traverse(traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }
  if (this->init_ != NULL
      && ((traverse_mask
           & (Traverse::traverse_expressions | Traverse::traverse_types))
          != 0))
    {
      if (Expression::traverse(&this->init_, traverse) == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }
  return TRAVERSE_CONTINUE;
}

// Lower the initialization expression after parsing is complete.

void
Variable::lower_init_expression(Gogo* gogo, Named_object* function,
                                Statement_inserter* inserter)
{
  if (this->init_ != NULL && !this->init_is_lowered_)
    {
      if (this->seen_)
        {
          // We will give an error elsewhere, this is just to prevent
          // an infinite loop.
          return;
        }
      this->seen_ = true;

      Statement_inserter global_inserter;
      if (this->is_global_)
        {
          global_inserter = Statement_inserter(gogo, this);
          inserter = &global_inserter;
        }

      gogo->lower_expression(function, inserter, &this->init_);

      this->seen_ = false;

      this->init_is_lowered_ = true;
    }
}

// Get the preinit block.

Block*
Variable::preinit_block(Gogo* gogo)
{
  go_assert(this->is_global_);
  if (this->preinit_ == NULL)
    this->preinit_ = new Block(NULL, this->location());

  // If a global variable has a preinitialization statement, then we
  // need to have an initialization function.
  gogo->set_need_init_fn();

  return this->preinit_;
}

// Add a statement to be run before the initialization expression.

void
Variable::add_preinit_statement(Gogo* gogo, Statement* s)
{
  Block* b = this->preinit_block(gogo);
  b->add_statement(s);
  b->set_end_location(s->location());
}

// In an assignment which sets a variable to a tuple of EXPR, return
// the type of the first element of the tuple.

Type*
Variable::type_from_tuple(Expression* expr, bool report_error) const
{
  if (expr->map_index_expression() != NULL)
    {
      Map_type* mt = expr->map_index_expression()->get_map_type();
      if (mt == NULL)
        return Type::make_error_type();
      return mt->val_type();
    }
  else if (expr->receive_expression() != NULL)
    {
      Expression* channel = expr->receive_expression()->channel();
      Type* channel_type = channel->type();
      if (channel_type->channel_type() == NULL)
        return Type::make_error_type();
      return channel_type->channel_type()->element_type();
    }
  else
    {
      if (report_error)
        error_at(this->location(), "invalid tuple definition");
      return Type::make_error_type();
    }
}

// Given EXPR used in a range clause, return either the index type or
// the value type of the range, depending upon GET_INDEX_TYPE.

Type*
Variable::type_from_range(Expression* expr, bool get_index_type,
                          bool report_error) const
{
  Type* t = expr->type();
  if (t->array_type() != NULL
      || (t->points_to() != NULL
          && t->points_to()->array_type() != NULL
          && !t->points_to()->is_open_array_type()))
    {
      if (get_index_type)
        return Type::lookup_integer_type("int");
      else
        return t->deref()->array_type()->element_type();
    }
  else if (t->is_string_type())
    return Type::lookup_integer_type("int");
  else if (t->map_type() != NULL)
    {
      if (get_index_type)
        return t->map_type()->key_type();
      else
        return t->map_type()->val_type();
    }
  else if (t->channel_type() != NULL)
    {
      if (get_index_type)
        return t->channel_type()->element_type();
      else
        {
          if (report_error)
            error_at(this->location(),
                     "invalid definition of value variable for channel range");
          return Type::make_error_type();
        }
    }
  else
    {
      if (report_error)
        error_at(this->location(), "invalid type for range clause");
      return Type::make_error_type();
    }
}

// EXPR should be a channel.  Return the channel's element type.

Type*
Variable::type_from_chan_element(Expression* expr, bool report_error) const
{
  Type* t = expr->type();
  if (t->channel_type() != NULL)
    return t->channel_type()->element_type();
  else
    {
      if (report_error)
        error_at(this->location(), "expected channel");
      return Type::make_error_type();
    }
}

// Return the type of the Variable.  This may be called before
// Variable::determine_type is called, which means that we may need to
// get the type from the initializer.  FIXME: If we combine lowering
// with type determination, then this should be unnecessary.

Type*
Variable::type()
{
  // A variable in a type switch with a nil case will have the wrong
  // type here.  This gets fixed up in determine_type, below.
  Type* type = this->type_;
  Expression* init = this->init_;
  if (this->is_type_switch_var_
      && this->type_->is_nil_constant_as_type())
    {
      Type_guard_expression* tge = this->init_->type_guard_expression();
      go_assert(tge != NULL);
      init = tge->expr();
      type = NULL;
    }

  if (this->seen_)
    {
      if (this->type_ == NULL || !this->type_->is_error_type())
        {
          error_at(this->location_, "variable initializer refers to itself");
          this->type_ = Type::make_error_type();
        }
      return this->type_;
    }

  this->seen_ = true;

  if (type != NULL)
    ;
  else if (this->type_from_init_tuple_)
    type = this->type_from_tuple(init, false);
  else if (this->type_from_range_index_ || this->type_from_range_value_)
    type = this->type_from_range(init, this->type_from_range_index_, false);
  else if (this->type_from_chan_element_)
    type = this->type_from_chan_element(init, false);
  else
    {
      go_assert(init != NULL);
      type = init->type();
      go_assert(type != NULL);

      // Variables should not have abstract types.
      if (type->is_abstract())
        type = type->make_non_abstract_type();

      if (type->is_void_type())
        type = Type::make_error_type();
    }

  this->seen_ = false;

  return type;
}

// Fetch the type from a const pointer, in which case it should have
// been set already.

Type*
Variable::type() const
{
  go_assert(this->type_ != NULL);
  return this->type_;
}

// Set the type if necessary.

void
Variable::determine_type()
{
  if (this->determined_type_)
    return;
  this->determined_type_ = true;

  if (this->preinit_ != NULL)
    this->preinit_->determine_types();

  // A variable in a type switch with a nil case will have the wrong
  // type here.  It will have an initializer which is a type guard.
  // We want to initialize it to the value without the type guard, and
  // use the type of that value as well.
  if (this->is_type_switch_var_ && this->type_->is_nil_constant_as_type())
    {
      Type_guard_expression* tge = this->init_->type_guard_expression();
      go_assert(tge != NULL);
      this->type_ = NULL;
      this->init_ = tge->expr();
    }

  if (this->init_ == NULL)
    go_assert(this->type_ != NULL && !this->type_->is_abstract());
  else if (this->type_from_init_tuple_)
    {
      Expression *init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_tuple(init, true);
      this->init_ = NULL;
    }
  else if (this->type_from_range_index_ || this->type_from_range_value_)
    {
      Expression* init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_range(init, this->type_from_range_index_,
                                          true);
      this->init_ = NULL;
    }
  else if (this->type_from_chan_element_)
    {
      Expression* init = this->init_;
      init->determine_type_no_context();
      this->type_ = this->type_from_chan_element(init, true);
      this->init_ = NULL;
    }
  else
    {
      Type_context context(this->type_, false);
      this->init_->determine_type(&context);
      if (this->type_ == NULL)
        {
          Type* type = this->init_->type();
          go_assert(type != NULL);
          if (type->is_abstract())
            type = type->make_non_abstract_type();

          if (type->is_void_type())
            {
              error_at(this->location_, "variable has no type");
              type = Type::make_error_type();
            }
          else if (type->is_nil_type())
            {
              error_at(this->location_, "variable defined to nil type");
              type = Type::make_error_type();
            }
          else if (type->is_call_multiple_result_type())
            {
              error_at(this->location_,
                       "single variable set to multiple value function call");
              type = Type::make_error_type();
            }

          this->type_ = type;
        }
    }
}

// Export the variable

void
Variable::export_var(Export* exp, const std::string& name) const
{
  go_assert(this->is_global_);
  exp->write_c_string("var ");
  exp->write_string(name);
  exp->write_c_string(" ");
  exp->write_type(this->type());
  exp->write_c_string(";\n");
}

// Import a variable.

void
Variable::import_var(Import* imp, std::string* pname, Type** ptype)
{
  imp->require_c_string("var ");
  *pname = imp->read_identifier();
  imp->require_c_string(" ");
  *ptype = imp->read_type();
  imp->require_c_string(";\n");
}

// Convert a variable to the backend representation.

Bvariable*
Variable::get_backend_variable(Gogo* gogo, Named_object* function,
                               const Package* package, const std::string& name)
{
  if (this->backend_ == NULL)
    {
      Backend* backend = gogo->backend();
      Type* type = this->type_;
      if (type->is_error_type()
          || (type->is_undefined()
              && (!this->is_global_ || package == NULL)))
        this->backend_ = backend->error_variable();
      else
        {
          bool is_parameter = this->is_parameter_;
          if (this->is_receiver_ && type->points_to() == NULL)
            is_parameter = false;
          if (this->is_in_heap())
            {
              is_parameter = false;
              type = Type::make_pointer_type(type);
            }

          std::string n = Gogo::unpack_hidden_name(name);
          Btype* btype = type->get_backend(gogo);

          Bvariable* bvar;
          if (this->is_global_)
            bvar = backend->global_variable((package == NULL
                                             ? gogo->package_name()
                                             : package->name()),
                                            (package == NULL
                                             ? gogo->unique_prefix()
                                             : package->unique_prefix()),
                                            n,
                                            btype,
                                            package != NULL,
                                            Gogo::is_hidden_name(name),
                                            this->location_);
          else
            {
              tree fndecl = function->func_value()->get_decl();
              Bfunction* bfunction = tree_to_function(fndecl);
              bool is_address_taken = (this->is_non_escaping_address_taken_
                                       && !this->is_in_heap());
              if (is_parameter)
                bvar = backend->parameter_variable(bfunction, n, btype,
                                                   is_address_taken,
                                                   this->location_);
              else
                bvar = backend->local_variable(bfunction, n, btype,
                                               is_address_taken,
                                               this->location_);
            }
          this->backend_ = bvar;
        }
    }
  return this->backend_;
}

// Class Result_variable.

// Convert a result variable to the backend representation.

Bvariable*
Result_variable::get_backend_variable(Gogo* gogo, Named_object* function,
                                      const std::string& name)
{
  if (this->backend_ == NULL)
    {
      Backend* backend = gogo->backend();
      Type* type = this->type_;
      if (type->is_error())
        this->backend_ = backend->error_variable();
      else
        {
          if (this->is_in_heap())
            type = Type::make_pointer_type(type);
          Btype* btype = type->get_backend(gogo);
          tree fndecl = function->func_value()->get_decl();
          Bfunction* bfunction = tree_to_function(fndecl);
          std::string n = Gogo::unpack_hidden_name(name);
          bool is_address_taken = (this->is_non_escaping_address_taken_
                                   && !this->is_in_heap());
          this->backend_ = backend->local_variable(bfunction, n, btype,
                                                   is_address_taken,
                                                   this->location_);
        }
    }
  return this->backend_;
}

// Class Named_constant.

// Traverse the initializer expression.

int
Named_constant::traverse_expression(Traverse* traverse)
{
  return Expression::traverse(&this->expr_, traverse);
}

// Determine the type of the constant.

void
Named_constant::determine_type()
{
  if (this->type_ != NULL)
    {
      Type_context context(this->type_, false);
      this->expr_->determine_type(&context);
    }
  else
    {
      // A constant may have an abstract type.
      Type_context context(NULL, true);
      this->expr_->determine_type(&context);
      this->type_ = this->expr_->type();
      go_assert(this->type_ != NULL);
    }
}

// Indicate that we found and reported an error for this constant.

void
Named_constant::set_error()
{
  this->type_ = Type::make_error_type();
  this->expr_ = Expression::make_error(this->location_);
}

// Export a constant.

void
Named_constant::export_const(Export* exp, const std::string& name) const
{
  exp->write_c_string("const ");
  exp->write_string(name);
  exp->write_c_string(" ");
  if (!this->type_->is_abstract())
    {
      exp->write_type(this->type_);
      exp->write_c_string(" ");
    }
  exp->write_c_string("= ");
  this->expr()->export_expression(exp);
  exp->write_c_string(";\n");
}

// Import a constant.

void
Named_constant::import_const(Import* imp, std::string* pname, Type** ptype,
                             Expression** pexpr)
{
  imp->require_c_string("const ");
  *pname = imp->read_identifier();
  imp->require_c_string(" ");
  if (imp->peek_char() == '=')
    *ptype = NULL;
  else
    {
      *ptype = imp->read_type();
      imp->require_c_string(" ");
    }
  imp->require_c_string("= ");
  *pexpr = Expression::import_expression(imp);
  imp->require_c_string(";\n");
}

// Add a method.

Named_object*
Type_declaration::add_method(const std::string& name, Function* function)
{
  Named_object* ret = Named_object::make_function(name, NULL, function);
  this->methods_.push_back(ret);
  return ret;
}

// Add a method declaration.

Named_object*
Type_declaration::add_method_declaration(const std::string&  name,
                                         Function_type* type,
                                         source_location location)
{
  Named_object* ret = Named_object::make_function_declaration(name, NULL, type,
                                                              location);
  this->methods_.push_back(ret);
  return ret;
}

// Return whether any methods ere defined.

bool
Type_declaration::has_methods() const
{
  return !this->methods_.empty();
}

// Define methods for the real type.

void
Type_declaration::define_methods(Named_type* nt)
{
  for (Methods::const_iterator p = this->methods_.begin();
       p != this->methods_.end();
       ++p)
    nt->add_existing_method(*p);
}

// We are using the type.  Return true if we should issue a warning.

bool
Type_declaration::using_type()
{
  bool ret = !this->issued_warning_;
  this->issued_warning_ = true;
  return ret;
}

// Class Unknown_name.

// Set the real named object.

void
Unknown_name::set_real_named_object(Named_object* no)
{
  go_assert(this->real_named_object_ == NULL);
  go_assert(!no->is_unknown());
  this->real_named_object_ = no;
}

// Class Named_object.

Named_object::Named_object(const std::string& name,
                           const Package* package,
                           Classification classification)
  : name_(name), package_(package), classification_(classification),
    tree_(NULL)
{
  if (Gogo::is_sink_name(name))
    go_assert(classification == NAMED_OBJECT_SINK);
}

// Make an unknown name.  This is used by the parser.  The name must
// be resolved later.  Unknown names are only added in the current
// package.

Named_object*
Named_object::make_unknown_name(const std::string& name,
                                source_location location)
{
  Named_object* named_object = new Named_object(name, NULL,
                                                NAMED_OBJECT_UNKNOWN);
  Unknown_name* value = new Unknown_name(location);
  named_object->u_.unknown_value = value;
  return named_object;
}

// Make a constant.

Named_object*
Named_object::make_constant(const Typed_identifier& tid,
                            const Package* package, Expression* expr,
                            int iota_value)
{
  Named_object* named_object = new Named_object(tid.name(), package,
                                                NAMED_OBJECT_CONST);
  Named_constant* named_constant = new Named_constant(tid.type(), expr,
                                                      iota_value,
                                                      tid.location());
  named_object->u_.const_value = named_constant;
  return named_object;
}

// Make a named type.

Named_object*
Named_object::make_type(const std::string& name, const Package* package,
                        Type* type, source_location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_TYPE);
  Named_type* named_type = Type::make_named_type(named_object, type, location);
  named_object->u_.type_value = named_type;
  return named_object;
}

// Make a type declaration.

Named_object*
Named_object::make_type_declaration(const std::string& name,
                                    const Package* package,
                                    source_location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_TYPE_DECLARATION);
  Type_declaration* type_declaration = new Type_declaration(location);
  named_object->u_.type_declaration = type_declaration;
  return named_object;
}

// Make a variable.

Named_object*
Named_object::make_variable(const std::string& name, const Package* package,
                            Variable* variable)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_VAR);
  named_object->u_.var_value = variable;
  return named_object;
}

// Make a result variable.

Named_object*
Named_object::make_result_variable(const std::string& name,
                                   Result_variable* result)
{
  Named_object* named_object = new Named_object(name, NULL,
                                                NAMED_OBJECT_RESULT_VAR);
  named_object->u_.result_var_value = result;
  return named_object;
}

// Make a sink.  This is used for the special blank identifier _.

Named_object*
Named_object::make_sink()
{
  return new Named_object("_", NULL, NAMED_OBJECT_SINK);
}

// Make a named function.

Named_object*
Named_object::make_function(const std::string& name, const Package* package,
                            Function* function)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_FUNC);
  named_object->u_.func_value = function;
  return named_object;
}

// Make a function declaration.

Named_object*
Named_object::make_function_declaration(const std::string& name,
                                        const Package* package,
                                        Function_type* fntype,
                                        source_location location)
{
  Named_object* named_object = new Named_object(name, package,
                                                NAMED_OBJECT_FUNC_DECLARATION);
  Function_declaration *func_decl = new Function_declaration(fntype, location);
  named_object->u_.func_declaration_value = func_decl;
  return named_object;
}

// Make a package.

Named_object*
Named_object::make_package(const std::string& alias, Package* package)
{
  Named_object* named_object = new Named_object(alias, NULL,
                                                NAMED_OBJECT_PACKAGE);
  named_object->u_.package_value = package;
  return named_object;
}

// Return the name to use in an error message.

std::string
Named_object::message_name() const
{
  if (this->package_ == NULL)
    return Gogo::message_name(this->name_);
  std::string ret = Gogo::message_name(this->package_->name());
  ret += '.';
  ret += Gogo::message_name(this->name_);
  return ret;
}

// Set the type when a declaration is defined.

void
Named_object::set_type_value(Named_type* named_type)
{
  go_assert(this->classification_ == NAMED_OBJECT_TYPE_DECLARATION);
  Type_declaration* td = this->u_.type_declaration;
  td->define_methods(named_type);
  Named_object* in_function = td->in_function();
  if (in_function != NULL)
    named_type->set_in_function(in_function);
  delete td;
  this->classification_ = NAMED_OBJECT_TYPE;
  this->u_.type_value = named_type;
}

// Define a function which was previously declared.

void
Named_object::set_function_value(Function* function)
{
  go_assert(this->classification_ == NAMED_OBJECT_FUNC_DECLARATION);
  this->classification_ = NAMED_OBJECT_FUNC;
  // FIXME: We should free the old value.
  this->u_.func_value = function;
}

// Declare an unknown object as a type declaration.

void
Named_object::declare_as_type()
{
  go_assert(this->classification_ == NAMED_OBJECT_UNKNOWN);
  Unknown_name* unk = this->u_.unknown_value;
  this->classification_ = NAMED_OBJECT_TYPE_DECLARATION;
  this->u_.type_declaration = new Type_declaration(unk->location());
  delete unk;
}

// Return the location of a named object.

source_location
Named_object::location() const
{
  switch (this->classification_)
    {
    default:
    case NAMED_OBJECT_UNINITIALIZED:
      go_unreachable();

    case NAMED_OBJECT_UNKNOWN:
      return this->unknown_value()->location();

    case NAMED_OBJECT_CONST:
      return this->const_value()->location();

    case NAMED_OBJECT_TYPE:
      return this->type_value()->location();

    case NAMED_OBJECT_TYPE_DECLARATION:
      return this->type_declaration_value()->location();

    case NAMED_OBJECT_VAR:
      return this->var_value()->location();

    case NAMED_OBJECT_RESULT_VAR:
      return this->result_var_value()->location();

    case NAMED_OBJECT_SINK:
      go_unreachable();

    case NAMED_OBJECT_FUNC:
      return this->func_value()->location();

    case NAMED_OBJECT_FUNC_DECLARATION:
      return this->func_declaration_value()->location();

    case NAMED_OBJECT_PACKAGE:
      return this->package_value()->location();
    }
}

// Export a named object.

void
Named_object::export_named_object(Export* exp) const
{
  switch (this->classification_)
    {
    default:
    case NAMED_OBJECT_UNINITIALIZED:
    case NAMED_OBJECT_UNKNOWN:
      go_unreachable();

    case NAMED_OBJECT_CONST:
      this->const_value()->export_const(exp, this->name_);
      break;

    case NAMED_OBJECT_TYPE:
      this->type_value()->export_named_type(exp, this->name_);
      break;

    case NAMED_OBJECT_TYPE_DECLARATION:
      error_at(this->type_declaration_value()->location(),
               "attempt to export %<%s%> which was declared but not defined",
               this->message_name().c_str());
      break;

    case NAMED_OBJECT_FUNC_DECLARATION:
      this->func_declaration_value()->export_func(exp, this->name_);
      break;

    case NAMED_OBJECT_VAR:
      this->var_value()->export_var(exp, this->name_);
      break;

    case NAMED_OBJECT_RESULT_VAR:
    case NAMED_OBJECT_SINK:
      go_unreachable();

    case NAMED_OBJECT_FUNC:
      this->func_value()->export_func(exp, this->name_);
      break;
    }
}

// Convert a variable to the backend representation.

Bvariable*
Named_object::get_backend_variable(Gogo* gogo, Named_object* function)
{
  if (this->classification_ == NAMED_OBJECT_VAR)
    return this->var_value()->get_backend_variable(gogo, function,
                                                   this->package_, this->name_);
  else if (this->classification_ == NAMED_OBJECT_RESULT_VAR)
    return this->result_var_value()->get_backend_variable(gogo, function,
                                                          this->name_);
  else
    go_unreachable();
}

// Class Bindings.

Bindings::Bindings(Bindings* enclosing)
  : enclosing_(enclosing), named_objects_(), bindings_()
{
}

// Clear imports.

void
Bindings::clear_file_scope()
{
  Contour::iterator p = this->bindings_.begin();
  while (p != this->bindings_.end())
    {
      bool keep;
      if (p->second->package() != NULL)
        keep = false;
      else if (p->second->is_package())
        keep = false;
      else if (p->second->is_function()
               && !p->second->func_value()->type()->is_method()
               && Gogo::unpack_hidden_name(p->second->name()) == "init")
        keep = false;
      else
        keep = true;

      if (keep)
        ++p;
      else
        p = this->bindings_.erase(p);
    }
}

// Look up a symbol.

Named_object*
Bindings::lookup(const std::string& name) const
{
  Contour::const_iterator p = this->bindings_.find(name);
  if (p != this->bindings_.end())
    return p->second->resolve();
  else if (this->enclosing_ != NULL)
    return this->enclosing_->lookup(name);
  else
    return NULL;
}

// Look up a symbol locally.

Named_object*
Bindings::lookup_local(const std::string& name) const
{
  Contour::const_iterator p = this->bindings_.find(name);
  if (p == this->bindings_.end())
    return NULL;
  return p->second;
}

// Remove an object from a set of bindings.  This is used for a
// special case in thunks for functions which call recover.

void
Bindings::remove_binding(Named_object* no)
{
  Contour::iterator pb = this->bindings_.find(no->name());
  go_assert(pb != this->bindings_.end());
  this->bindings_.erase(pb);
  for (std::vector<Named_object*>::iterator pn = this->named_objects_.begin();
       pn != this->named_objects_.end();
       ++pn)
    {
      if (*pn == no)
        {
          this->named_objects_.erase(pn);
          return;
        }
    }
  go_unreachable();
}

// Add a method to the list of objects.  This is not added to the
// lookup table.  This is so that we have a single list of objects
// declared at the top level, which we walk through when it's time to
// convert to trees.

void
Bindings::add_method(Named_object* method)
{
  this->named_objects_.push_back(method);
}

// Add a generic Named_object to a Contour.

Named_object*
Bindings::add_named_object_to_contour(Contour* contour,
                                      Named_object* named_object)
{
  go_assert(named_object == named_object->resolve());
  const std::string& name(named_object->name());
  go_assert(!Gogo::is_sink_name(name));

  std::pair<Contour::iterator, bool> ins =
    contour->insert(std::make_pair(name, named_object));
  if (!ins.second)
    {
      // The name was already there.
      if (named_object->package() != NULL
          && ins.first->second->package() == named_object->package()
          && (ins.first->second->classification()
              == named_object->classification()))
        {
          // This is a second import of the same object.
          return ins.first->second;
        }
      ins.first->second = this->new_definition(ins.first->second,
                                               named_object);
      return ins.first->second;
    }
  else
    {
      // Don't push declarations on the list.  We push them on when
      // and if we find the definitions.  That way we genericize the
      // functions in order.
      if (!named_object->is_type_declaration()
          && !named_object->is_function_declaration()
          && !named_object->is_unknown())
        this->named_objects_.push_back(named_object);
      return named_object;
    }
}

// We had an existing named object OLD_OBJECT, and we've seen a new
// one NEW_OBJECT with the same name.  FIXME: This does not free the
// new object when we don't need it.

Named_object*
Bindings::new_definition(Named_object* old_object, Named_object* new_object)
{
  std::string reason;
  switch (old_object->classification())
    {
    default:
    case Named_object::NAMED_OBJECT_UNINITIALIZED:
      go_unreachable();

    case Named_object::NAMED_OBJECT_UNKNOWN:
      {
        Named_object* real = old_object->unknown_value()->real_named_object();
        if (real != NULL)
          return this->new_definition(real, new_object);
        go_assert(!new_object->is_unknown());
        old_object->unknown_value()->set_real_named_object(new_object);
        if (!new_object->is_type_declaration()
            && !new_object->is_function_declaration())
          this->named_objects_.push_back(new_object);
        return new_object;
      }

    case Named_object::NAMED_OBJECT_CONST:
      break;

    case Named_object::NAMED_OBJECT_TYPE:
      if (new_object->is_type_declaration())
        return old_object;
      break;

    case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
      if (new_object->is_type_declaration())
        return old_object;
      if (new_object->is_type())
        {
          old_object->set_type_value(new_object->type_value());
          new_object->type_value()->set_named_object(old_object);
          this->named_objects_.push_back(old_object);
          return old_object;
        }
      break;

    case Named_object::NAMED_OBJECT_VAR:
    case Named_object::NAMED_OBJECT_RESULT_VAR:
      // We have already given an error in the parser for cases where
      // one parameter or result variable redeclares another one.
      if ((new_object->is_variable()
           && new_object->var_value()->is_parameter())
          || new_object->is_result_variable())
        return old_object;
      break;

    case Named_object::NAMED_OBJECT_SINK:
      go_unreachable();

    case Named_object::NAMED_OBJECT_FUNC:
      if (new_object->is_function_declaration())
        {
          if (!new_object->func_declaration_value()->asm_name().empty())
            sorry("__asm__ for function definitions");
          Function_type* old_type = old_object->func_value()->type();
          Function_type* new_type =
            new_object->func_declaration_value()->type();
          if (old_type->is_valid_redeclaration(new_type, &reason))
            return old_object;
        }
      break;

    case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
      {
        Function_type* old_type = old_object->func_declaration_value()->type();
        if (new_object->is_function_declaration())
          {
            Function_type* new_type =
              new_object->func_declaration_value()->type();
            if (old_type->is_valid_redeclaration(new_type, &reason))
              return old_object;
          }
        if (new_object->is_function())
          {
            Function_type* new_type = new_object->func_value()->type();
            if (old_type->is_valid_redeclaration(new_type, &reason))
              {
                if (!old_object->func_declaration_value()->asm_name().empty())
                  sorry("__asm__ for function definitions");
                old_object->set_function_value(new_object->func_value());
                this->named_objects_.push_back(old_object);
                return old_object;
              }
          }
      }
      break;

    case Named_object::NAMED_OBJECT_PACKAGE:
      if (new_object->is_package()
          && (old_object->package_value()->name()
              == new_object->package_value()->name()))
        return old_object;

      break;
    }

  std::string n = old_object->message_name();
  if (reason.empty())
    error_at(new_object->location(), "redefinition of %qs", n.c_str());
  else
    error_at(new_object->location(), "redefinition of %qs: %s", n.c_str(),
             reason.c_str());

  inform(old_object->location(), "previous definition of %qs was here",
         n.c_str());

  return old_object;
}

// Add a named type.

Named_object*
Bindings::add_named_type(Named_type* named_type)
{
  return this->add_named_object(named_type->named_object());
}

// Add a function.

Named_object*
Bindings::add_function(const std::string& name, const Package* package,
                       Function* function)
{
  return this->add_named_object(Named_object::make_function(name, package,
                                                            function));
}

// Add a function declaration.

Named_object*
Bindings::add_function_declaration(const std::string& name,
                                   const Package* package,
                                   Function_type* type,
                                   source_location location)
{
  Named_object* no = Named_object::make_function_declaration(name, package,
                                                             type, location);
  return this->add_named_object(no);
}

// Define a type which was previously declared.

void
Bindings::define_type(Named_object* no, Named_type* type)
{
  no->set_type_value(type);
  this->named_objects_.push_back(no);
}

// Traverse bindings.

int
Bindings::traverse(Traverse* traverse, bool is_global)
{
  unsigned int traverse_mask = traverse->traverse_mask();

  // We don't use an iterator because we permit the traversal to add
  // new global objects.
  const unsigned int e_or_t = (Traverse::traverse_expressions
                               | Traverse::traverse_types);
  const unsigned int e_or_t_or_s = (e_or_t
                                    | Traverse::traverse_statements);
  for (size_t i = 0; i < this->named_objects_.size(); ++i)
    {
      Named_object* p = this->named_objects_[i];
      int t = TRAVERSE_CONTINUE;
      switch (p->classification())
        {
        case Named_object::NAMED_OBJECT_CONST:
          if ((traverse_mask & Traverse::traverse_constants) != 0)
            t = traverse->constant(p, is_global);
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t) != 0)
            {
              Type* tc = p->const_value()->type();
              if (tc != NULL
                  && Type::traverse(tc, traverse) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
              t = p->const_value()->traverse_expression(traverse);
            }
          break;

        case Named_object::NAMED_OBJECT_VAR:
        case Named_object::NAMED_OBJECT_RESULT_VAR:
          if ((traverse_mask & Traverse::traverse_variables) != 0)
            t = traverse->variable(p);
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t) != 0)
            {
              if (p->is_result_variable()
                  || p->var_value()->has_type())
                {
                  Type* tv = (p->is_variable()
                              ? p->var_value()->type()
                              : p->result_var_value()->type());
                  if (tv != NULL
                      && Type::traverse(tv, traverse) == TRAVERSE_EXIT)
                    return TRAVERSE_EXIT;
                }
            }
          if (t == TRAVERSE_CONTINUE
              && (traverse_mask & e_or_t_or_s) != 0
              && p->is_variable())
            t = p->var_value()->traverse_expression(traverse, traverse_mask);
          break;

        case Named_object::NAMED_OBJECT_FUNC:
          if ((traverse_mask & Traverse::traverse_functions) != 0)
            t = traverse->function(p);

          if (t == TRAVERSE_CONTINUE
              && (traverse_mask
                  & (Traverse::traverse_variables
                     | Traverse::traverse_constants
                     | Traverse::traverse_functions
                     | Traverse::traverse_blocks
                     | Traverse::traverse_statements
                     | Traverse::traverse_expressions
                     | Traverse::traverse_types)) != 0)
            {
              if (p->func_value()->traverse(traverse) == TRAVERSE_EXIT)
                return TRAVERSE_EXIT;
            }
          break;

        case Named_object::NAMED_OBJECT_PACKAGE:
          // These are traversed in Gogo::traverse.
          go_assert(is_global);
          break;

        case Named_object::NAMED_OBJECT_TYPE:
          if ((traverse_mask & e_or_t) != 0)
            t = Type::traverse(p->type_value(), traverse);
          break;

        case Named_object::NAMED_OBJECT_TYPE_DECLARATION:
        case Named_object::NAMED_OBJECT_FUNC_DECLARATION:
        case Named_object::NAMED_OBJECT_UNKNOWN:
          break;

        case Named_object::NAMED_OBJECT_SINK:
        default:
          go_unreachable();
        }

      if (t == TRAVERSE_EXIT)
        return TRAVERSE_EXIT;
    }

  return TRAVERSE_CONTINUE;
}

// Class Label.

// Clear any references to this label.

void
Label::clear_refs()
{
  for (std::vector<Bindings_snapshot*>::iterator p = this->refs_.begin();
       p != this->refs_.end();
       ++p)
    delete *p;
  this->refs_.clear();
}

// Get the backend representation for a label.

Blabel*
Label::get_backend_label(Translate_context* context)
{
  if (this->blabel_ == NULL)
    {
      Function* function = context->function()->func_value();
      tree fndecl = function->get_decl();
      Bfunction* bfunction = tree_to_function(fndecl);
      this->blabel_ = context->backend()->label(bfunction, this->name_,
                                                this->location_);
    }
  return this->blabel_;
}

// Return an expression for the address of this label.

Bexpression*
Label::get_addr(Translate_context* context, source_location location)
{
  Blabel* label = this->get_backend_label(context);
  return context->backend()->label_address(label, location);
}

// Class Unnamed_label.

// Get the backend representation for an unnamed label.

Blabel*
Unnamed_label::get_blabel(Translate_context* context)
{
  if (this->blabel_ == NULL)
    {
      Function* function = context->function()->func_value();
      tree fndecl = function->get_decl();
      Bfunction* bfunction = tree_to_function(fndecl);
      this->blabel_ = context->backend()->label(bfunction, "",
                                                this->location_);
    }
  return this->blabel_;
}

// Return a statement which defines this unnamed label.

Bstatement*
Unnamed_label::get_definition(Translate_context* context)
{
  Blabel* blabel = this->get_blabel(context);
  return context->backend()->label_definition_statement(blabel);
}

// Return a goto statement to this unnamed label.

Bstatement*
Unnamed_label::get_goto(Translate_context* context, source_location location)
{
  Blabel* blabel = this->get_blabel(context);
  return context->backend()->goto_statement(blabel, location);
}

// Class Package.

Package::Package(const std::string& name, const std::string& unique_prefix,
                 source_location location)
  : name_(name), unique_prefix_(unique_prefix), bindings_(new Bindings(NULL)),
    priority_(0), location_(location), used_(false), is_imported_(false),
    uses_sink_alias_(false)
{
  go_assert(!name.empty() && !unique_prefix.empty());
}

// Set the priority.  We may see multiple priorities for an imported
// package; we want to use the largest one.

void
Package::set_priority(int priority)
{
  if (priority > this->priority_)
    this->priority_ = priority;
}

// Determine types of constants.  Everything else in a package
// (variables, function declarations) should already have a fixed
// type.  Constants may have abstract types.

void
Package::determine_types()
{
  Bindings* bindings = this->bindings_;
  for (Bindings::const_definitions_iterator p = bindings->begin_definitions();
       p != bindings->end_definitions();
       ++p)
    {
      if ((*p)->is_const())
        (*p)->const_value()->determine_type();
    }
}

// Class Traverse.

// Destructor.

Traverse::~Traverse()
{
  if (this->types_seen_ != NULL)
    delete this->types_seen_;
  if (this->expressions_seen_ != NULL)
    delete this->expressions_seen_;
}

// Record that we are looking at a type, and return true if we have
// already seen it.

bool
Traverse::remember_type(const Type* type)
{
  if (type->is_error_type())
    return true;
  go_assert((this->traverse_mask() & traverse_types) != 0
             || (this->traverse_mask() & traverse_expressions) != 0);
  // We only have to remember named types, as they are the only ones
  // we can see multiple times in a traversal.
  if (type->classification() != Type::TYPE_NAMED)
    return false;
  if (this->types_seen_ == NULL)
    this->types_seen_ = new Types_seen();
  std::pair<Types_seen::iterator, bool> ins = this->types_seen_->insert(type);
  return !ins.second;
}

// Record that we are looking at an expression, and return true if we
// have already seen it.

bool
Traverse::remember_expression(const Expression* expression)
{
  go_assert((this->traverse_mask() & traverse_types) != 0
             || (this->traverse_mask() & traverse_expressions) != 0);
  if (this->expressions_seen_ == NULL)
    this->expressions_seen_ = new Expressions_seen();
  std::pair<Expressions_seen::iterator, bool> ins =
    this->expressions_seen_->insert(expression);
  return !ins.second;
}

// The default versions of these functions should never be called: the
// traversal mask indicates which functions may be called.

int
Traverse::variable(Named_object*)
{
  go_unreachable();
}

int
Traverse::constant(Named_object*, bool)
{
  go_unreachable();
}

int
Traverse::function(Named_object*)
{
  go_unreachable();
}

int
Traverse::block(Block*)
{
  go_unreachable();
}

int
Traverse::statement(Block*, size_t*, Statement*)
{
  go_unreachable();
}

int
Traverse::expression(Expression**)
{
  go_unreachable();
}

int
Traverse::type(Type*)
{
  go_unreachable();
}

// Class Statement_inserter.

void
Statement_inserter::insert(Statement* s)
{
  if (this->block_ != NULL)
    {
      go_assert(this->pindex_ != NULL);
      this->block_->insert_statement_before(*this->pindex_, s);
      ++*this->pindex_;
    }
  else if (this->var_ != NULL)
    this->var_->add_preinit_statement(this->gogo_, s);
  else
    go_unreachable();
}