-/* Const/copy propagation and SSA_NAME replacement support routines.
+/* Copy propagation and SSA_NAME replacement support routines.
Copyright (C) 2004, 2005 Free Software Foundation, Inc.
This file is part of GCC.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING. If not, write to
-the Free Software Foundation, 59 Temple Place - Suite 330,
-Boston, MA 02111-1307, USA. */
+the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA. */
#include "config.h"
#include "system.h"
#include "ggc.h"
#include "basic-block.h"
#include "output.h"
-#include "errors.h"
#include "expr.h"
#include "function.h"
#include "diagnostic.h"
#include "tree-dump.h"
#include "tree-flow.h"
#include "tree-pass.h"
+#include "tree-ssa-propagate.h"
#include "langhooks.h"
-/* This file provides a handful of interfaces for performing const/copy
- propagation and simple expression replacement which keep variable
- annotations up-to-date.
+/* This file implements the copy propagation pass and provides a
+ handful of interfaces for performing const/copy propagation and
+ simple expression replacement which keep variable annotations
+ up-to-date.
We require that for any copy operation where the RHS and LHS have
a non-null memory tag the memory tag be the same. It is OK
replacements of one SSA_NAME with a different SSA_NAME to use the
APIs defined in this file. */
-
/* Return true if we may propagate ORIG into DEST, false otherwise. */
bool
I think that GIMPLE should emit the appropriate type-casts. For the
time being, blocking copy-propagation in these cases is the safe thing
to do. */
- if (TREE_CODE (dest) == SSA_NAME && TREE_CODE (orig) == SSA_NAME
- && POINTER_TYPE_P (type_d) && POINTER_TYPE_P (type_o))
+ if (TREE_CODE (dest) == SSA_NAME
+ && TREE_CODE (orig) == SSA_NAME
+ && POINTER_TYPE_P (type_d)
+ && POINTER_TYPE_P (type_o))
{
- tree mt_dest = var_ann (SSA_NAME_VAR (dest))->type_mem_tag;
- tree mt_orig = var_ann (SSA_NAME_VAR (orig))->type_mem_tag;
+ tree mt_dest = var_ann (SSA_NAME_VAR (dest))->symbol_mem_tag;
+ tree mt_orig = var_ann (SSA_NAME_VAR (orig))->symbol_mem_tag;
if (mt_dest && mt_orig && mt_dest != mt_orig)
return false;
else if (!lang_hooks.types_compatible_p (type_d, type_o))
{
/* If both operands are SSA_NAMEs referring to virtual operands, then
we can always propagate. */
- if (TREE_CODE (orig) == SSA_NAME)
- {
- if (!is_gimple_reg (orig))
- return true;
-
-#ifdef ENABLE_CHECKING
- /* If we have one real and one virtual operand, then something has
- gone terribly wrong. */
- gcc_assert (!is_gimple_reg (orig));
-#endif
- }
+ if (TREE_CODE (orig) == SSA_NAME
+ && !is_gimple_reg (orig))
+ return true;
/* We have a "copy" from something like a constant into a virtual
operand. Reject these. */
propagating NEW into ORIG, consolidate aliasing information so that
they both share the same memory tags. */
-static void
+void
merge_alias_info (tree orig, tree new)
{
tree new_sym = SSA_NAME_VAR (new);
== get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym))));
#endif
- /* Synchronize the type tags. If both pointers had a tag and they
- are different, then something has gone wrong. */
- if (new_ann->type_mem_tag == NULL_TREE)
- new_ann->type_mem_tag = orig_ann->type_mem_tag;
- else if (orig_ann->type_mem_tag == NULL_TREE)
- orig_ann->type_mem_tag = new_ann->type_mem_tag;
+ /* Synchronize the symbol tags. If both pointers had a tag and they
+ are different, then something has gone wrong. Symbol tags can
+ always be merged because they are flow insensitive, all the SSA
+ names of the same base DECL share the same symbol tag. */
+ if (new_ann->symbol_mem_tag == NULL_TREE)
+ new_ann->symbol_mem_tag = orig_ann->symbol_mem_tag;
+ else if (orig_ann->symbol_mem_tag == NULL_TREE)
+ orig_ann->symbol_mem_tag = new_ann->symbol_mem_tag;
else
- gcc_assert (new_ann->type_mem_tag == orig_ann->type_mem_tag);
+ gcc_assert (new_ann->symbol_mem_tag == orig_ann->symbol_mem_tag);
-#if defined ENABLE_CHECKING
- {
- struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig);
- struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new);
-
- if (orig_ptr_info
- && new_ptr_info
- && orig_ptr_info->name_mem_tag
- && new_ptr_info->name_mem_tag
- && orig_ptr_info->pt_vars
- && new_ptr_info->pt_vars)
+ /* Check that flow-sensitive information is compatible. Notice that
+ we may not merge flow-sensitive information here. This function
+ is called when propagating equivalences dictated by the IL, like
+ a copy operation P_i = Q_j, and from equivalences dictated by
+ control-flow, like if (P_i == Q_j).
+
+ In the former case, P_i and Q_j are equivalent in every block
+ dominated by the assignment, so their flow-sensitive information
+ is always the same. However, in the latter case, the pointers
+ P_i and Q_j are only equivalent in one of the sub-graphs out of
+ the predicate, so their flow-sensitive information is not the
+ same in every block dominated by the predicate.
+
+ Since we cannot distinguish one case from another in this
+ function, we can only make sure that if P_i and Q_j have
+ flow-sensitive information, they should be compatible. */
+ if (SSA_NAME_PTR_INFO (orig) && SSA_NAME_PTR_INFO (new))
{
- /* Note that pointer NEW may actually have a different set of
- pointed-to variables. However, since NEW is being
- copy-propagated into ORIG, it must always be true that the
- pointed-to set for pointer NEW is the same, or a subset, of
- the pointed-to set for pointer ORIG. If this isn't the case,
- we shouldn't have been able to do the propagation of NEW into
- ORIG. */
- gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars,
- orig_ptr_info->pt_vars));
+ struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig);
+ struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new);
+
+ /* Note that pointer NEW and ORIG may actually have different
+ pointed-to variables (e.g., PR 18291 represented in
+ testsuite/gcc.c-torture/compile/pr18291.c). However, since
+ NEW is being copy-propagated into ORIG, it must always be
+ true that the pointed-to set for pointer NEW is the same, or
+ a subset, of the pointed-to set for pointer ORIG. If this
+ isn't the case, we shouldn't have been able to do the
+ propagation of NEW into ORIG. */
+ if (orig_ptr_info->name_mem_tag
+ && new_ptr_info->name_mem_tag
+ && orig_ptr_info->pt_vars
+ && new_ptr_info->pt_vars)
+ gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars,
+ orig_ptr_info->pt_vars));
}
- }
-#endif
}
/* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
- into the operand pointed by OP_P.
+ into the operand pointed to by OP_P.
Use this version for const/copy propagation as it will perform additional
checks to ensure validity of the const/copy propagation. */
/* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
- into the tree pointed by OP_P.
+ into the tree pointed to by OP_P.
Use this version for const/copy propagation when SSA operands are not
available. It will perform the additional checks to ensure validity of
{
replace_exp_1 (op_p, val, false);
}
+
+
+/*---------------------------------------------------------------------------
+ Copy propagation
+---------------------------------------------------------------------------*/
+/* During propagation, we keep chains of variables that are copies of
+ one another. If variable X_i is a copy of X_j and X_j is a copy of
+ X_k, COPY_OF will contain:
+
+ COPY_OF[i].VALUE = X_j
+ COPY_OF[j].VALUE = X_k
+ COPY_OF[k].VALUE = X_k
+
+ After propagation, the copy-of value for each variable X_i is
+ converted into the final value by walking the copy-of chains and
+ updating COPY_OF[i].VALUE to be the last element of the chain. */
+static prop_value_t *copy_of;
+
+/* Used in set_copy_of_val to determine if the last link of a copy-of
+ chain has changed. */
+static tree *cached_last_copy_of;
+
+/* True if we are doing copy propagation on loads and stores. */
+static bool do_store_copy_prop;
+
+
+/* Return true if this statement may generate a useful copy. */
+
+static bool
+stmt_may_generate_copy (tree stmt)
+{
+ tree lhs, rhs;
+ stmt_ann_t ann;
+
+ if (TREE_CODE (stmt) == PHI_NODE)
+ return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (stmt));
+
+ if (TREE_CODE (stmt) != MODIFY_EXPR)
+ return false;
+
+ lhs = TREE_OPERAND (stmt, 0);
+ rhs = TREE_OPERAND (stmt, 1);
+ ann = stmt_ann (stmt);
+
+ /* If the statement has volatile operands, it won't generate a
+ useful copy. */
+ if (ann->has_volatile_ops)
+ return false;
+
+ /* If we are not doing store copy-prop, statements with loads and/or
+ stores will never generate a useful copy. */
+ if (!do_store_copy_prop
+ && !ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS))
+ return false;
+
+ /* Otherwise, the only statements that generate useful copies are
+ assignments whose RHS is just an SSA name that doesn't flow
+ through abnormal edges. */
+ return TREE_CODE (rhs) == SSA_NAME && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs);
+}
+
+
+/* Return the copy-of value for VAR. */
+
+static inline prop_value_t *
+get_copy_of_val (tree var)
+{
+ prop_value_t *val = ©_of[SSA_NAME_VERSION (var)];
+
+ if (val->value == NULL_TREE
+ && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var)))
+ {
+ /* If the variable will never generate a useful copy relation,
+ make it its own copy. */
+ val->value = var;
+ val->mem_ref = NULL_TREE;
+ }
+
+ return val;
+}
+
+
+/* Return last link in the copy-of chain for VAR. */
+
+static tree
+get_last_copy_of (tree var)
+{
+ tree last;
+ int i;
+
+ /* Traverse COPY_OF starting at VAR until we get to the last
+ link in the chain. Since it is possible to have cycles in PHI
+ nodes, the copy-of chain may also contain cycles.
+
+ To avoid infinite loops and to avoid traversing lengthy copy-of
+ chains, we artificially limit the maximum number of chains we are
+ willing to traverse.
+
+ The value 5 was taken from a compiler and runtime library
+ bootstrap and a mixture of C and C++ code from various sources.
+ More than 82% of all copy-of chains were shorter than 5 links. */
+#define LIMIT 5
+
+ last = var;
+ for (i = 0; i < LIMIT; i++)
+ {
+ tree copy = copy_of[SSA_NAME_VERSION (last)].value;
+ if (copy == NULL_TREE || copy == last)
+ break;
+ last = copy;
+ }
+
+ /* If we have reached the limit, then we are either in a copy-of
+ cycle or the copy-of chain is too long. In this case, just
+ return VAR so that it is not considered a copy of anything. */
+ return (i < LIMIT ? last : var);
+}
+
+
+/* Set FIRST to be the first variable in the copy-of chain for DEST.
+ If DEST's copy-of value or its copy-of chain has changed, return
+ true.
+
+ MEM_REF is the memory reference where FIRST is stored. This is
+ used when DEST is a non-register and we are copy propagating loads
+ and stores. */
+
+static inline bool
+set_copy_of_val (tree dest, tree first, tree mem_ref)
+{
+ unsigned int dest_ver = SSA_NAME_VERSION (dest);
+ tree old_first, old_last, new_last;
+
+ /* Set FIRST to be the first link in COPY_OF[DEST]. If that
+ changed, return true. */
+ old_first = copy_of[dest_ver].value;
+ copy_of[dest_ver].value = first;
+ copy_of[dest_ver].mem_ref = mem_ref;
+
+ if (old_first != first)
+ return true;
+
+ /* If FIRST and OLD_FIRST are the same, we need to check whether the
+ copy-of chain starting at FIRST ends in a different variable. If
+ the copy-of chain starting at FIRST ends up in a different
+ variable than the last cached value we had for DEST, then return
+ true because DEST is now a copy of a different variable.
+
+ This test is necessary because even though the first link in the
+ copy-of chain may not have changed, if any of the variables in
+ the copy-of chain changed its final value, DEST will now be the
+ copy of a different variable, so we have to do another round of
+ propagation for everything that depends on DEST. */
+ old_last = cached_last_copy_of[dest_ver];
+ new_last = get_last_copy_of (dest);
+ cached_last_copy_of[dest_ver] = new_last;
+
+ return (old_last != new_last);
+}
+
+
+/* Dump the copy-of value for variable VAR to FILE. */
+
+static void
+dump_copy_of (FILE *file, tree var)
+{
+ tree val;
+ sbitmap visited;
+
+ print_generic_expr (file, var, dump_flags);
+
+ if (TREE_CODE (var) != SSA_NAME)
+ return;
+
+ visited = sbitmap_alloc (num_ssa_names);
+ sbitmap_zero (visited);
+ SET_BIT (visited, SSA_NAME_VERSION (var));
+
+ fprintf (file, " copy-of chain: ");
+
+ val = var;
+ print_generic_expr (file, val, 0);
+ fprintf (file, " ");
+ while (copy_of[SSA_NAME_VERSION (val)].value)
+ {
+ fprintf (file, "-> ");
+ val = copy_of[SSA_NAME_VERSION (val)].value;
+ print_generic_expr (file, val, 0);
+ fprintf (file, " ");
+ if (TEST_BIT (visited, SSA_NAME_VERSION (val)))
+ break;
+ SET_BIT (visited, SSA_NAME_VERSION (val));
+ }
+
+ val = get_copy_of_val (var)->value;
+ if (val == NULL_TREE)
+ fprintf (file, "[UNDEFINED]");
+ else if (val != var)
+ fprintf (file, "[COPY]");
+ else
+ fprintf (file, "[NOT A COPY]");
+
+ sbitmap_free (visited);
+}
+
+
+/* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS
+ value and store the LHS into *RESULT_P. If STMT generates more
+ than one name (i.e., STMT is an aliased store), it is enough to
+ store the first name in the V_MAY_DEF list into *RESULT_P. After
+ all, the names generated will be VUSEd in the same statements. */
+
+static enum ssa_prop_result
+copy_prop_visit_assignment (tree stmt, tree *result_p)
+{
+ tree lhs, rhs;
+ prop_value_t *rhs_val;
+
+ lhs = TREE_OPERAND (stmt, 0);
+ rhs = TREE_OPERAND (stmt, 1);
+
+ gcc_assert (TREE_CODE (rhs) == SSA_NAME);
+
+ rhs_val = get_copy_of_val (rhs);
+
+ if (TREE_CODE (lhs) == SSA_NAME)
+ {
+ /* Straight copy between two SSA names. First, make sure that
+ we can propagate the RHS into uses of LHS. */
+ if (!may_propagate_copy (lhs, rhs))
+ return SSA_PROP_VARYING;
+
+ /* Notice that in the case of assignments, we make the LHS be a
+ copy of RHS's value, not of RHS itself. This avoids keeping
+ unnecessary copy-of chains (assignments cannot be in a cycle
+ like PHI nodes), speeding up the propagation process.
+ This is different from what we do in copy_prop_visit_phi_node.
+ In those cases, we are interested in the copy-of chains. */
+ *result_p = lhs;
+ if (set_copy_of_val (*result_p, rhs_val->value, rhs_val->mem_ref))
+ return SSA_PROP_INTERESTING;
+ else
+ return SSA_PROP_NOT_INTERESTING;
+ }
+ else if (stmt_makes_single_store (stmt))
+ {
+ /* Otherwise, set the names in V_MAY_DEF/V_MUST_DEF operands
+ to be a copy of RHS. */
+ ssa_op_iter i;
+ tree vdef;
+ bool changed;
+
+ /* This should only be executed when doing store copy-prop. */
+ gcc_assert (do_store_copy_prop);
+
+ /* Set the value of every VDEF to RHS_VAL. */
+ changed = false;
+ FOR_EACH_SSA_TREE_OPERAND (vdef, stmt, i, SSA_OP_VIRTUAL_DEFS)
+ changed |= set_copy_of_val (vdef, rhs_val->value, lhs);
+
+ /* Note that for propagation purposes, we are only interested in
+ visiting statements that load the exact same memory reference
+ stored here. Those statements will have the exact same list
+ of virtual uses, so it is enough to set the output of this
+ statement to be its first virtual definition. */
+ *result_p = first_vdef (stmt);
+
+ if (changed)
+ return SSA_PROP_INTERESTING;
+ else
+ return SSA_PROP_NOT_INTERESTING;
+ }
+
+
+ return SSA_PROP_VARYING;
+}
+
+
+/* Visit the COND_EXPR STMT. Return SSA_PROP_INTERESTING
+ if it can determine which edge will be taken. Otherwise, return
+ SSA_PROP_VARYING. */
+
+static enum ssa_prop_result
+copy_prop_visit_cond_stmt (tree stmt, edge *taken_edge_p)
+{
+ enum ssa_prop_result retval;
+ tree cond;
+
+ cond = COND_EXPR_COND (stmt);
+ retval = SSA_PROP_VARYING;
+
+ /* The only conditionals that we may be able to compute statically
+ are predicates involving two SSA_NAMEs. */
+ if (COMPARISON_CLASS_P (cond)
+ && TREE_CODE (TREE_OPERAND (cond, 0)) == SSA_NAME
+ && TREE_CODE (TREE_OPERAND (cond, 1)) == SSA_NAME)
+ {
+ tree op0 = get_last_copy_of (TREE_OPERAND (cond, 0));
+ tree op1 = get_last_copy_of (TREE_OPERAND (cond, 1));
+
+ /* See if we can determine the predicate's value. */
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Trying to determine truth value of ");
+ fprintf (dump_file, "predicate ");
+ print_generic_stmt (dump_file, cond, 0);
+ }
+
+ /* We can fold COND and get a useful result only when we have
+ the same SSA_NAME on both sides of a comparison operator. */
+ if (op0 == op1)
+ {
+ tree folded_cond = fold_binary (TREE_CODE (cond), boolean_type_node,
+ op0, op1);
+ if (folded_cond)
+ {
+ basic_block bb = bb_for_stmt (stmt);
+ *taken_edge_p = find_taken_edge (bb, folded_cond);
+ if (*taken_edge_p)
+ retval = SSA_PROP_INTERESTING;
+ }
+ }
+ }
+
+ if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p)
+ fprintf (dump_file, "\nConditional will always take edge %d->%d\n",
+ (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index);
+
+ return retval;
+}
+
+
+/* Evaluate statement STMT. If the statement produces a new output
+ value, return SSA_PROP_INTERESTING and store the SSA_NAME holding
+ the new value in *RESULT_P.
+
+ If STMT is a conditional branch and we can determine its truth
+ value, set *TAKEN_EDGE_P accordingly.
+
+ If the new value produced by STMT is varying, return
+ SSA_PROP_VARYING. */
+
+static enum ssa_prop_result
+copy_prop_visit_stmt (tree stmt, edge *taken_edge_p, tree *result_p)
+{
+ enum ssa_prop_result retval;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "\nVisiting statement:\n");
+ print_generic_stmt (dump_file, stmt, dump_flags);
+ fprintf (dump_file, "\n");
+ }
+
+ if (TREE_CODE (stmt) == MODIFY_EXPR
+ && TREE_CODE (TREE_OPERAND (stmt, 1)) == SSA_NAME
+ && (do_store_copy_prop
+ || TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME))
+ {
+ /* If the statement is a copy assignment, evaluate its RHS to
+ see if the lattice value of its output has changed. */
+ retval = copy_prop_visit_assignment (stmt, result_p);
+ }
+ else if (TREE_CODE (stmt) == COND_EXPR)
+ {
+ /* See if we can determine which edge goes out of a conditional
+ jump. */
+ retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p);
+ }
+ else
+ retval = SSA_PROP_VARYING;
+
+ if (retval == SSA_PROP_VARYING)
+ {
+ tree def;
+ ssa_op_iter i;
+
+ /* Any other kind of statement is not interesting for constant
+ propagation and, therefore, not worth simulating. */
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, "No interesting values produced.\n");
+
+ /* The assignment is not a copy operation. Don't visit this
+ statement again and mark all the definitions in the statement
+ to be copies of nothing. */
+ FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS)
+ set_copy_of_val (def, def, NULL_TREE);
+ }
+
+ return retval;
+}
+
+
+/* Visit PHI node PHI. If all the arguments produce the same value,
+ set it to be the value of the LHS of PHI. */
+
+static enum ssa_prop_result
+copy_prop_visit_phi_node (tree phi)
+{
+ enum ssa_prop_result retval;
+ int i;
+ tree lhs;
+ prop_value_t phi_val = { 0, NULL_TREE, NULL_TREE };
+
+ lhs = PHI_RESULT (phi);
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "\nVisiting PHI node: ");
+ print_generic_expr (dump_file, phi, dump_flags);
+ fprintf (dump_file, "\n\n");
+ }
+
+ for (i = 0; i < PHI_NUM_ARGS (phi); i++)
+ {
+ prop_value_t *arg_val;
+ tree arg = PHI_ARG_DEF (phi, i);
+ edge e = PHI_ARG_EDGE (phi, i);
+
+ /* We don't care about values flowing through non-executable
+ edges. */
+ if (!(e->flags & EDGE_EXECUTABLE))
+ continue;
+
+ /* Constants in the argument list never generate a useful copy.
+ Similarly, names that flow through abnormal edges cannot be
+ used to derive copies. */
+ if (TREE_CODE (arg) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg))
+ {
+ phi_val.value = lhs;
+ break;
+ }
+
+ /* Avoid copy propagation from an inner into an outer loop.
+ Otherwise, this may move loop variant variables outside of
+ their loops and prevent coalescing opportunities. If the
+ value was loop invariant, it will be hoisted by LICM and
+ exposed for copy propagation. */
+ if (loop_depth_of_name (arg) > loop_depth_of_name (lhs))
+ {
+ phi_val.value = lhs;
+ break;
+ }
+
+ /* If the LHS appears in the argument list, ignore it. It is
+ irrelevant as a copy. */
+ if (arg == lhs || get_last_copy_of (arg) == lhs)
+ continue;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "\tArgument #%d: ", i);
+ dump_copy_of (dump_file, arg);
+ fprintf (dump_file, "\n");
+ }
+
+ arg_val = get_copy_of_val (arg);
+
+ /* If the LHS didn't have a value yet, make it a copy of the
+ first argument we find. Notice that while we make the LHS be
+ a copy of the argument itself, we take the memory reference
+ from the argument's value so that we can compare it to the
+ memory reference of all the other arguments. */
+ if (phi_val.value == NULL_TREE)
+ {
+ phi_val.value = arg;
+ phi_val.mem_ref = arg_val->mem_ref;
+ continue;
+ }
+
+ /* If PHI_VAL and ARG don't have a common copy-of chain, then
+ this PHI node cannot be a copy operation. Also, if we are
+ copy propagating stores and these two arguments came from
+ different memory references, they cannot be considered
+ copies. */
+ if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg)
+ || (do_store_copy_prop
+ && phi_val.mem_ref
+ && arg_val->mem_ref
+ && simple_cst_equal (phi_val.mem_ref, arg_val->mem_ref) != 1))
+ {
+ phi_val.value = lhs;
+ break;
+ }
+ }
+
+ if (phi_val.value && set_copy_of_val (lhs, phi_val.value, phi_val.mem_ref))
+ retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;
+ else
+ retval = SSA_PROP_NOT_INTERESTING;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "\nPHI node ");
+ dump_copy_of (dump_file, lhs);
+ fprintf (dump_file, "\nTelling the propagator to ");
+ if (retval == SSA_PROP_INTERESTING)
+ fprintf (dump_file, "add SSA edges out of this PHI and continue.");
+ else if (retval == SSA_PROP_VARYING)
+ fprintf (dump_file, "add SSA edges out of this PHI and never visit again.");
+ else
+ fprintf (dump_file, "do nothing with SSA edges and keep iterating.");
+ fprintf (dump_file, "\n\n");
+ }
+
+ return retval;
+}
+
+
+/* Initialize structures used for copy propagation. PHIS_ONLY is true
+ if we should only consider PHI nodes as generating copy propagation
+ opportunities. */
+
+static void
+init_copy_prop (void)
+{
+ basic_block bb;
+
+ copy_of = XNEWVEC (prop_value_t, num_ssa_names);
+ memset (copy_of, 0, num_ssa_names * sizeof (*copy_of));
+
+ cached_last_copy_of = XNEWVEC (tree, num_ssa_names);
+ memset (cached_last_copy_of, 0, num_ssa_names * sizeof (*cached_last_copy_of));
+
+ FOR_EACH_BB (bb)
+ {
+ block_stmt_iterator si;
+ tree phi, def;
+ int depth = bb->loop_depth;
+
+ for (si = bsi_start (bb); !bsi_end_p (si); bsi_next (&si))
+ {
+ tree stmt = bsi_stmt (si);
+ ssa_op_iter iter;
+
+ /* The only statements that we care about are those that may
+ generate useful copies. We also need to mark conditional
+ jumps so that their outgoing edges are added to the work
+ lists of the propagator.
+
+ Avoid copy propagation from an inner into an outer loop.
+ Otherwise, this may move loop variant variables outside of
+ their loops and prevent coalescing opportunities. If the
+ value was loop invariant, it will be hoisted by LICM and
+ exposed for copy propagation. */
+ if (stmt_ends_bb_p (stmt))
+ DONT_SIMULATE_AGAIN (stmt) = false;
+ else if (stmt_may_generate_copy (stmt)
+ && loop_depth_of_name (TREE_OPERAND (stmt, 1)) <= depth)
+ DONT_SIMULATE_AGAIN (stmt) = false;
+ else
+ DONT_SIMULATE_AGAIN (stmt) = true;
+
+ /* Mark all the outputs of this statement as not being
+ the copy of anything. */
+ FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
+ if (DONT_SIMULATE_AGAIN (stmt))
+ set_copy_of_val (def, def, NULL_TREE);
+ else
+ cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
+ }
+
+ for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+ {
+ def = PHI_RESULT (phi);
+ if (!do_store_copy_prop && !is_gimple_reg (def))
+ DONT_SIMULATE_AGAIN (phi) = true;
+ else
+ DONT_SIMULATE_AGAIN (phi) = false;
+
+ if (DONT_SIMULATE_AGAIN (phi))
+ set_copy_of_val (def, def, NULL_TREE);
+ else
+ cached_last_copy_of[SSA_NAME_VERSION (def)] = def;
+ }
+ }
+}
+
+
+/* Deallocate memory used in copy propagation and do final
+ substitution. */
+
+static void
+fini_copy_prop (void)
+{
+ size_t i;
+ prop_value_t *tmp;
+
+ /* Set the final copy-of value for each variable by traversing the
+ copy-of chains. */
+ tmp = XNEWVEC (prop_value_t, num_ssa_names);
+ memset (tmp, 0, num_ssa_names * sizeof (*tmp));
+ for (i = 1; i < num_ssa_names; i++)
+ {
+ tree var = ssa_name (i);
+ if (var && copy_of[i].value && copy_of[i].value != var)
+ tmp[i].value = get_last_copy_of (var);
+ }
+
+ substitute_and_fold (tmp, false);
+
+ free (cached_last_copy_of);
+ free (copy_of);
+ free (tmp);
+}
+
+
+/* Main entry point to the copy propagator.
+
+ PHIS_ONLY is true if we should only consider PHI nodes as generating
+ copy propagation opportunities.
+
+ The algorithm propagates the value COPY-OF using ssa_propagate. For
+ every variable X_i, COPY-OF(X_i) indicates which variable is X_i created
+ from. The following example shows how the algorithm proceeds at a
+ high level:
+
+ 1 a_24 = x_1
+ 2 a_2 = PHI <a_24, x_1>
+ 3 a_5 = PHI <a_2>
+ 4 x_1 = PHI <x_298, a_5, a_2>
+
+ The end result should be that a_2, a_5, a_24 and x_1 are a copy of
+ x_298. Propagation proceeds as follows.
+
+ Visit #1: a_24 is copy-of x_1. Value changed.
+ Visit #2: a_2 is copy-of x_1. Value changed.
+ Visit #3: a_5 is copy-of x_1. Value changed.
+ Visit #4: x_1 is copy-of x_298. Value changed.
+ Visit #1: a_24 is copy-of x_298. Value changed.
+ Visit #2: a_2 is copy-of x_298. Value changed.
+ Visit #3: a_5 is copy-of x_298. Value changed.
+ Visit #4: x_1 is copy-of x_298. Stable state reached.
+
+ When visiting PHI nodes, we only consider arguments that flow
+ through edges marked executable by the propagation engine. So,
+ when visiting statement #2 for the first time, we will only look at
+ the first argument (a_24) and optimistically assume that its value
+ is the copy of a_24 (x_1).
+
+ The problem with this approach is that it may fail to discover copy
+ relations in PHI cycles. Instead of propagating copy-of
+ values, we actually propagate copy-of chains. For instance:
+
+ A_3 = B_1;
+ C_9 = A_3;
+ D_4 = C_9;
+ X_i = D_4;
+
+ In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }.
+ Obviously, we are only really interested in the last value of the
+ chain, however the propagator needs to access the copy-of chain
+ when visiting PHI nodes.
+
+ To represent the copy-of chain, we use the array COPY_CHAINS, which
+ holds the first link in the copy-of chain for every variable.
+ If variable X_i is a copy of X_j, which in turn is a copy of X_k,
+ the array will contain:
+
+ COPY_CHAINS[i] = X_j
+ COPY_CHAINS[j] = X_k
+ COPY_CHAINS[k] = X_k
+
+ Keeping copy-of chains instead of copy-of values directly becomes
+ important when visiting PHI nodes. Suppose that we had the
+ following PHI cycle, such that x_52 is already considered a copy of
+ x_53:
+
+ 1 x_54 = PHI <x_53, x_52>
+ 2 x_53 = PHI <x_898, x_54>
+
+ Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53)
+ Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53,
+ so it is considered irrelevant
+ as a copy).
+ Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and
+ x_52 is a copy of x_53, so
+ they don't match)
+ Visit #2: x_53 is copy-of nothing
+
+ This problem is avoided by keeping a chain of copies, instead of
+ the final copy-of value. Propagation will now only keep the first
+ element of a variable's copy-of chain. When visiting PHI nodes,
+ arguments are considered equal if their copy-of chains end in the
+ same variable. So, as long as their copy-of chains overlap, we
+ know that they will be a copy of the same variable, regardless of
+ which variable that may be).
+
+ Propagation would then proceed as follows (the notation a -> b
+ means that a is a copy-of b):
+
+ Visit #1: x_54 = PHI <x_53, x_52>
+ x_53 -> x_53
+ x_52 -> x_53
+ Result: x_54 -> x_53. Value changed. Add SSA edges.
+
+ Visit #1: x_53 = PHI <x_898, x_54>
+ x_898 -> x_898
+ x_54 -> x_53
+ Result: x_53 -> x_898. Value changed. Add SSA edges.
+
+ Visit #2: x_54 = PHI <x_53, x_52>
+ x_53 -> x_898
+ x_52 -> x_53 -> x_898
+ Result: x_54 -> x_898. Value changed. Add SSA edges.
+
+ Visit #2: x_53 = PHI <x_898, x_54>
+ x_898 -> x_898
+ x_54 -> x_898
+ Result: x_53 -> x_898. Value didn't change. Stable state
+
+ Once the propagator stabilizes, we end up with the desired result
+ x_53 and x_54 are both copies of x_898. */
+
+static void
+execute_copy_prop (bool store_copy_prop)
+{
+ do_store_copy_prop = store_copy_prop;
+ init_copy_prop ();
+ ssa_propagate (copy_prop_visit_stmt, copy_prop_visit_phi_node);
+ fini_copy_prop ();
+}
+
+
+static bool
+gate_copy_prop (void)
+{
+ return flag_tree_copy_prop != 0;
+}
+
+static unsigned int
+do_copy_prop (void)
+{
+ execute_copy_prop (false);
+ return 0;
+}
+
+struct tree_opt_pass pass_copy_prop =
+{
+ "copyprop", /* name */
+ gate_copy_prop, /* gate */
+ do_copy_prop, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ TV_TREE_COPY_PROP, /* tv_id */
+ PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ TODO_cleanup_cfg
+ | TODO_dump_func
+ | TODO_ggc_collect
+ | TODO_verify_ssa
+ | TODO_update_ssa, /* todo_flags_finish */
+ 0 /* letter */
+};
+
+static bool
+gate_store_copy_prop (void)
+{
+ /* STORE-COPY-PROP is enabled only with -ftree-store-copy-prop, but
+ when -fno-tree-store-copy-prop is specified, we should run
+ regular COPY-PROP. That's why the pass is enabled with either
+ flag. */
+ return flag_tree_store_copy_prop != 0 || flag_tree_copy_prop != 0;
+}
+
+static unsigned int
+store_copy_prop (void)
+{
+ /* If STORE-COPY-PROP is not enabled, we just run regular COPY-PROP. */
+ execute_copy_prop (flag_tree_store_copy_prop != 0);
+ return 0;
+}
+
+struct tree_opt_pass pass_store_copy_prop =
+{
+ "store_copyprop", /* name */
+ gate_store_copy_prop, /* gate */
+ store_copy_prop, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ TV_TREE_STORE_COPY_PROP, /* tv_id */
+ PROP_ssa | PROP_alias | PROP_cfg, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ TODO_dump_func
+ | TODO_cleanup_cfg
+ | TODO_ggc_collect
+ | TODO_verify_ssa
+ | TODO_update_ssa, /* todo_flags_finish */
+ 0 /* letter */
+};
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