+2005-06-23 Jason Merrill <jason@redhat.com>
+
+ PR c++/19317
+ Leave the return slot target in the MODIFY_EXPR rather than making
+ it an argument, but only use it if the CALL_EXPR has a flag set.
+ * tree.h (CALL_EXPR_HAS_RETURN_SLOT_ADDR): Rename to
+ CALL_EXPR_RETURN_SLOT_OPT.
+ * calls.c (expand_call): Adjust.
+ * tree-inline.c (expand_call_inline): Adjust.
+ * tree-pretty-print.c (dump_generic_node): Adjust.
+
+ And set the flag as appropriate.
+ * gimplify.c (gimplify_modify_expr_rhs): Set
+ CALL_EXPR_HAS_RETURN_SLOT_ADDR where the LHS is obviously safe.
+ * tree-nrv.c (execute_return_slot_opt): Set
+ CALL_EXPR_HAS_RETURN_SLOT_ADDR based on escape analysis.
+ * tree-pass.h: Declare pass_return_slot.
+ * tree-optimize.c (init_tree_optimization_passes): Add it.
+
2005-06-23 David Edelsohn <edelsohn@gnu.org>
PR target/21760
{
struct_value_size = int_size_in_bytes (TREE_TYPE (exp));
- if (CALL_EXPR_HAS_RETURN_SLOT_ADDR (exp))
- {
- /* The structure value address arg is already in actparms.
- Pull it out. It might be nice to just leave it there, but
- we need to set structure_value_addr. */
- tree return_arg = TREE_VALUE (actparms);
- actparms = TREE_CHAIN (actparms);
- structure_value_addr = expand_expr (return_arg, NULL_RTX,
- VOIDmode, EXPAND_NORMAL);
- }
- else if (target && MEM_P (target))
+ if (target && MEM_P (target) && CALL_EXPR_RETURN_SLOT_OPT (exp))
structure_value_addr = XEXP (target, 0);
else
{
+2005-06-23 Jason Merrill <jason@redhat.com>
+
+ PR c++/19317
+ * semantics.c (simplify_aggr_init_expr): Use
+ CALL_EXPR_RETURN_SLOT_OPT, not CALL_EXPR_HAS_RETURN_SLOT_ADDR.
+
2005-06-23 Volker Reichelt <reichelt@igpm.rwth-aachen.de>
* pt.c (register_specialization): Remove superfluous assertion.
style = arg;
}
- if (style == ctor || style == arg)
+ if (style == ctor)
{
- /* Pass the address of the slot. If this is a constructor, we
- replace the first argument; otherwise, we tack on a new one. */
+ /* Replace the first argument to the ctor with the address of the
+ slot. */
tree addr;
- if (style == ctor)
- args = TREE_CHAIN (args);
-
+ args = TREE_CHAIN (args);
cxx_mark_addressable (slot);
addr = build1 (ADDR_EXPR, build_pointer_type (type), slot);
- if (style == arg)
- {
- /* The return type might have different cv-quals from the slot. */
- tree fntype = TREE_TYPE (TREE_TYPE (fn));
-
- gcc_assert (TREE_CODE (fntype) == FUNCTION_TYPE
- || TREE_CODE (fntype) == METHOD_TYPE);
- addr = convert (build_pointer_type (TREE_TYPE (fntype)), addr);
- }
-
args = tree_cons (NULL_TREE, addr, args);
}
fn, args, NULL_TREE);
if (style == arg)
- /* Tell the backend that we've added our return slot to the argument
- list. */
- CALL_EXPR_HAS_RETURN_SLOT_ADDR (call_expr) = 1;
+ {
+ /* Just mark it addressable here, and leave the rest to
+ expand_call{,_inline}. */
+ cxx_mark_addressable (slot);
+ CALL_EXPR_RETURN_SLOT_OPT (call_expr) = true;
+ call_expr = build2 (MODIFY_EXPR, TREE_TYPE (call_expr), slot, call_expr);
+ }
else if (style == pcc)
{
/* If we're using the non-reentrant PCC calling convention, then we
call_expr = build_aggr_init (slot, call_expr,
DIRECT_BIND | LOOKUP_ONLYCONVERTING);
pop_deferring_access_checks ();
+ call_expr = build (COMPOUND_EXPR, TREE_TYPE (slot), call_expr, slot);
}
*tp = call_expr;
ret = GS_UNHANDLED;
break;
+ case CALL_EXPR:
+ /* For calls that return in memory, give *to_p as the CALL_EXPR's
+ return slot so that we don't generate a temporary. */
+ if (!CALL_EXPR_RETURN_SLOT_OPT (*from_p)
+ && aggregate_value_p (*from_p, *from_p))
+ {
+ bool use_target;
+
+ if (TREE_CODE (*to_p) == RESULT_DECL
+ && needs_to_live_in_memory (*to_p))
+ /* It's always OK to use the return slot directly. */
+ use_target = true;
+ else if (!is_gimple_non_addressable (*to_p))
+ /* Don't use the original target if it's already addressable;
+ if its address escapes, and the called function uses the
+ NRV optimization, a conforming program could see *to_p
+ change before the called function returns; see c++/19317.
+ When optimizing, the return_slot pass marks more functions
+ as safe after we have escape info. */
+ use_target = false;
+ else if (DECL_GIMPLE_FORMAL_TEMP_P (*to_p))
+ /* Don't use the original target if it's a formal temp; we
+ don't want to take their addresses. */
+ use_target = false;
+ else if (is_gimple_reg_type (TREE_TYPE (*to_p)))
+ /* Also don't force regs into memory. */
+ use_target = false;
+ else
+ use_target = true;
+
+ if (use_target)
+ {
+ CALL_EXPR_RETURN_SLOT_OPT (*from_p) = 1;
+ lang_hooks.mark_addressable (*to_p);
+ }
+ }
+
+ ret = GS_UNHANDLED;
+ break;
+
default:
ret = GS_UNHANDLED;
break;
--- /dev/null
+// PR c++/19317
+// If we do both NRV and caller-side return slot opt for ma = ma.f,
+// constructing fa incorrectly sets ma.i to 0.
+
+extern "C" void abort();
+
+struct A
+{
+ int i;
+ int pad[32]; // force return in memory
+ A(): i(0) {}
+ A(int ia): i(ia) {}
+};
+
+A ga(42);
+
+A f()
+{
+ A la;
+ if (ga.i != 42)
+ abort();
+ return la;
+}
+
+int main()
+{
+ ga = f ();
+}
/* Initialize the parameters. */
args = TREE_OPERAND (t, 1);
- if (CALL_EXPR_HAS_RETURN_SLOT_ADDR (t))
- {
- return_slot_addr = TREE_VALUE (args);
- args = TREE_CHAIN (args);
- }
- else
- return_slot_addr = NULL_TREE;
initialize_inlined_parameters (id, args, TREE_OPERAND (t, 2), fn, bb);
gcc_assert (TREE_CODE (DECL_INITIAL (fn)) == BLOCK);
/* Find the lhs to which the result of this call is assigned. */
- modify_dest = stmt;
- if (TREE_CODE (modify_dest) == MODIFY_EXPR)
+ return_slot_addr = NULL;
+ if (TREE_CODE (stmt) == MODIFY_EXPR)
{
- modify_dest = TREE_OPERAND (modify_dest, 0);
+ modify_dest = TREE_OPERAND (stmt, 0);
/* The function which we are inlining might not return a value,
in which case we should issue a warning that the function
uninitialized variable. */
if (DECL_P (modify_dest))
TREE_NO_WARNING (modify_dest) = 1;
+ if (CALL_EXPR_RETURN_SLOT_OPT (t))
+ {
+ return_slot_addr = build_fold_addr_expr (modify_dest);
+ modify_dest = NULL;
+ }
}
else
modify_dest = NULL;
TODO_dump_func | TODO_ggc_collect, /* todo_flags_finish */
0 /* letter */
};
+
+/* Walk through the function looking for MODIFY_EXPRs with calls that
+ return in memory on the RHS. For each of these, determine whether it is
+ safe to pass the address of the LHS as the return slot, and mark the
+ call appropriately if so.
+
+ The NRV shares the return slot with a local variable in the callee; this
+ optimization shares the return slot with the target of the call within
+ the caller. If the NRV is performed (which we can't know in general),
+ this optimization is safe if the address of the target has not
+ escaped prior to the call. If it has, modifications to the local
+ variable will produce visible changes elsewhere, as in PR c++/19317. */
+
+static void
+execute_return_slot_opt (void)
+{
+ basic_block bb;
+
+ FOR_EACH_BB (bb)
+ {
+ block_stmt_iterator i;
+ for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
+ {
+ tree stmt = bsi_stmt (i);
+ tree call;
+
+ if (TREE_CODE (stmt) == MODIFY_EXPR
+ && (call = TREE_OPERAND (stmt, 1),
+ TREE_CODE (call) == CALL_EXPR)
+ && !CALL_EXPR_RETURN_SLOT_OPT (call)
+ && aggregate_value_p (call, call))
+ {
+ def_operand_p def_p;
+ ssa_op_iter op_iter;
+
+ /* We determine whether or not the LHS address escapes by
+ asking whether it is call clobbered. When the LHS isn't a
+ simple decl, we need to check the VDEFs, so it's simplest
+ to just loop through all the DEFs. */
+ FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, op_iter, SSA_OP_ALL_DEFS)
+ {
+ tree def = DEF_FROM_PTR (def_p);
+ if (TREE_CODE (def) == SSA_NAME)
+ def = SSA_NAME_VAR (def);
+ if (is_call_clobbered (def))
+ goto unsafe;
+ }
+
+ /* No defs are call clobbered, so the optimization is safe. */
+ CALL_EXPR_RETURN_SLOT_OPT (call) = 1;
+ /* This is too late to mark the target addressable like we do
+ in gimplify_modify_expr_rhs, but that's OK; anything that
+ wasn't already addressable was handled there. */
+
+ unsafe:;
+ }
+ }
+ }
+}
+
+struct tree_opt_pass pass_return_slot =
+{
+ "retslot", /* name */
+ NULL, /* gate */
+ execute_return_slot_opt, /* execute */
+ NULL, /* sub */
+ NULL, /* next */
+ 0, /* static_pass_number */
+ 0, /* tv_id */
+ PROP_ssa | PROP_alias, /* properties_required */
+ 0, /* properties_provided */
+ 0, /* properties_destroyed */
+ 0, /* todo_flags_start */
+ 0, /* todo_flags_finish */
+ 0 /* letter */
+};
NEXT_PASS (pass_build_ssa);
NEXT_PASS (pass_build_pta);
NEXT_PASS (pass_may_alias);
+ NEXT_PASS (pass_return_slot);
NEXT_PASS (pass_del_pta);
NEXT_PASS (pass_rename_ssa_copies);
NEXT_PASS (pass_early_warn_uninitialized);
extern struct tree_opt_pass pass_build_pta;
extern struct tree_opt_pass pass_del_pta;
extern struct tree_opt_pass pass_uncprop;
+extern struct tree_opt_pass pass_return_slot;
extern struct tree_opt_pass pass_reassoc;
/* IPA Passes */
pp_character (buffer, ']');
}
- if (CALL_EXPR_HAS_RETURN_SLOT_ADDR (node))
- pp_string (buffer, " [return slot addr]");
+ if (CALL_EXPR_RETURN_SLOT_OPT (node))
+ pp_string (buffer, " [return slot optimization]");
if (CALL_EXPR_TAILCALL (node))
pp_string (buffer, " [tail call]");
break;
TREE_PRIVATE in
..._DECL
- CALL_EXPR_HAS_RETURN_SLOT_ADDR in
+ CALL_EXPR_RETURN_SLOT_OPT in
CALL_EXPR
DECL_BY_REFERENCE in
PARM_DECL, RESULT_DECL
an exception. In a CALL_EXPR, nonzero means the call cannot throw. */
#define TREE_NOTHROW(NODE) ((NODE)->common.nothrow_flag)
-/* In a CALL_EXPR, means that the address of the return slot is part of the
- argument list. */
-#define CALL_EXPR_HAS_RETURN_SLOT_ADDR(NODE) ((NODE)->common.private_flag)
+/* In a CALL_EXPR, means that it's safe to use the target of the call
+ expansion as the return slot for a call that returns in memory. */
+#define CALL_EXPR_RETURN_SLOT_OPT(NODE) ((NODE)->common.private_flag)
/* In a RESULT_DECL or PARM_DECL, means that it is passed by invisible
reference (and the TREE_TYPE is a pointer to the true type). */
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