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c++: Quash bogus -Wunused-value with new [PR107797]

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We shouldn't emit "right operand of comma operator has no effect"
when that comma operator was created by the compiler for "new int{}".
convert_to_void/COMPOUND_EXPR already checks warning_suppressed_p so
we can just suppress -Wunused-value.

	PR c++/107797

gcc/cp/ChangeLog:

	* cvt.cc (ocp_convert): copy_warning when creating a new
	COMPOUND_EXPR.
	* init.cc (build_new_1): Suppress -Wunused-value on
	compiler-generated COMPOUND_EXPRs.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wunused-value-1.C: New test.
This commit is contained in:
Marek Polacek 2023-01-19 17:12:34 -05:00
parent 72e46b3c7a
commit e3585e6acd
3 changed files with 18 additions and 2 deletions
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6
gcc/cp/cvt.cc
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@ -711,8 +711,10 @@ ocp_convert (tree type, tree expr, int convtype, int flags,
return error_mark_node;
if (e == TREE_OPERAND (expr, 1))
return expr;
return build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
TREE_OPERAND (expr, 0), e);
e = build2_loc (EXPR_LOCATION (expr), COMPOUND_EXPR, TREE_TYPE (e),
TREE_OPERAND (expr, 0), e);
copy_warning (e, expr);
return e;
}
complete_type (type);

2
gcc/cp/init.cc
View file

@ -3800,6 +3800,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
if (cookie_expr)
rval = build2 (COMPOUND_EXPR, TREE_TYPE (rval), cookie_expr, rval);
suppress_warning (rval, OPT_Wunused_value);
if (rval == data_addr && TREE_CODE (alloc_expr) == TARGET_EXPR)
/* If we don't have an initializer or a cookie, strip the TARGET_EXPR
and return the call (which doesn't need to be adjusted). */

12
gcc/testsuite/g++.dg/warn/Wunused-value-1.C Normal file
View file

@ -0,0 +1,12 @@
// PR c++/107797
// { dg-do compile { target c++11 } }
// { dg-options "-Wunused" }
void
g ()
{
(long) new int{};
long(new int{});
(long) new int();
long(new int());
}