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c++: Fix -Weffc++ in templates [PR98841]

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We emit a bogus warning on the following testcase, suggesting that the
operator should return *this even when it does that already.
The problem is that normally cp_build_indirect_ref_1 ensures that *this
is folded as current_class_ref, but in templates (if return type is
non-dependent, otherwise check_return_expr doesn't check it) it didn't
go through cp_build_indirect_ref_1, but just built another INDIRECT_REF.
Which means it then doesn't compare pointer-equal to current_class_ref.

The following patch fixes it by doing in build_x_indirect_ref for
*this what cp_build_indirect_ref_1 would do.

2021-01-28  Jakub Jelinek  <jakub@redhat.com>

	PR c++/98841
	* typeck.c (build_x_indirect_ref): For *this, return current_class_ref.

	* g++.dg/warn/effc5.C: New test.
This commit is contained in:
Jakub Jelinek 2021-01-29 00:39:00 +01:00
parent 513ee7d2cd
commit 850a8ec54c
2 changed files with 26 additions and 1 deletions
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10
gcc/cp/typeck.c
View file

@ -3326,7 +3326,15 @@ build_x_indirect_ref (location_t loc, tree expr, ref_operator errorstring,
{
/* Retain the type if we know the operand is a pointer. */
if (TREE_TYPE (expr) && INDIRECT_TYPE_P (TREE_TYPE (expr)))
return build_min (INDIRECT_REF, TREE_TYPE (TREE_TYPE (expr)), expr);
{
if (expr == current_class_ptr
|| (TREE_CODE (expr) == NOP_EXPR
&& TREE_OPERAND (expr, 0) == current_class_ptr
&& (same_type_ignoring_top_level_qualifiers_p
(TREE_TYPE (expr), TREE_TYPE (current_class_ptr)))))
return current_class_ref;
return build_min (INDIRECT_REF, TREE_TYPE (TREE_TYPE (expr)), expr);
}
if (type_dependent_expression_p (expr))
return build_min_nt_loc (loc, INDIRECT_REF, expr);
expr = build_non_dependent_expr (expr);

17
gcc/testsuite/g++.dg/warn/effc5.C Normal file
View file

@ -0,0 +1,17 @@
// PR c++/98841
// { dg-do compile }
// { dg-options "-Weffc++" }
struct S {
template <typename T>
S& operator=(const T&) { return *this; } // { dg-bogus "should return a reference to" }
S& operator=(const S&) { return *this; }
};
void
foo ()
{
S s, t;
s = 1;
s = t;
}