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PR c++/20408 - unnecessary code for empty struct.

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Here initializing the argument from a TARGET_EXPR isn't an empty class
copy even though the type is !TREE_ADDRESSABLE, so we should check
simple_empty_class_p.

	* call.c (build_call_a): Use simple_empty_class_p.

From-SVN: r271523
This commit is contained in:
Jason Merrill 2019-05-22 17:39:08 -04:00 committed by Jason Merrill
parent 52ea1caf28
commit c652ff8312
5 changed files with 22 additions and 2 deletions
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3
gcc/cp/ChangeLog
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@ -1,5 +1,8 @@
2019-05-22 Jason Merrill <jason@redhat.com>
PR c++/20408 - unnecessary code for empty struct.
* call.c (build_call_a): Use simple_empty_class_p.
PR c++/86485 - -Wmaybe-unused with empty class ?:
* cp-gimplify.c (simple_empty_class_p): Also true for MODIFY_EXPR.

2
gcc/cp/call.c
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@ -393,7 +393,7 @@ build_call_a (tree function, int n, tree *argarray)
{
tree arg = CALL_EXPR_ARG (function, i);
if (is_empty_class (TREE_TYPE (arg))
&& ! TREE_ADDRESSABLE (TREE_TYPE (arg)))
&& simple_empty_class_p (TREE_TYPE (arg), arg, INIT_EXPR))
{
tree t = build0 (EMPTY_CLASS_EXPR, TREE_TYPE (arg));
arg = build2 (COMPOUND_EXPR, TREE_TYPE (t), arg, t);

2
gcc/cp/cp-gimplify.c
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@ -593,7 +593,7 @@ gimplify_must_not_throw_expr (tree *expr_p, gimple_seq *pre_p)
non-empty CONSTRUCTORs get reduced properly, and we leave the
return slot optimization alone because it isn't a copy. */
static bool
bool
simple_empty_class_p (tree type, tree op, tree_code code)
{
if (TREE_CODE (op) == COMPOUND_EXPR)

1
gcc/cp/cp-tree.h
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@ -7581,6 +7581,7 @@ extern tree cp_fully_fold_init (tree);
extern void clear_fold_cache (void);
extern tree lookup_hotness_attribute (tree);
extern tree process_stmt_hotness_attribute (tree, location_t);
extern bool simple_empty_class_p (tree, tree, tree_code);
/* in name-lookup.c */
extern tree strip_using_decl (tree);

16
gcc/testsuite/g++.dg/tree-ssa/empty-3.C Normal file
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@ -0,0 +1,16 @@
// PR c++/20408
// { dg-additional-options -fdump-tree-gimple }
// { dg-final { scan-tree-dump-times "struct Foo" 2 "gimple" } }
struct Foo {};
void foo(const Foo&);
void bar(Foo);
void fooc(void)
{
foo(Foo());
}
void barc(void)
{
bar(Foo());
}