OK.
On Tue, Mar 21, 2017 at 11:38 AM, Marek Polacek <pola...@redhat.com> wrote:
> This patch fixes a bogus maybe-uninitialized warning reported in the PR.
> The issue is that we're not able to fold away useless CLEANUP_POINT_EXPRs,
> as e.g. in
> if (<<cleanup_point 0>>)
> // bogus warning
> Here, the cleanup_point was built as <<cleanup_point 0 && (i = 4) != 0>>,
> which cp_fold_r reduces to <<cleanup_point 0>>, but leaves it as that and
> passes it to the gimplifier.
>
> Jakub suggested handling this in cp_fold. fold_build_cleanup_point_expr says
> that "if the expression does not have side effects then we don't have to wrap
> it with a cleanup point expression", so I think the following should be safe.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2017-03-21 Marek Polacek <pola...@redhat.com>
>
> PR c++/80119
> * cp-gimplify.c (cp_fold): Strip CLEANUP_POINT_EXPR if the expression
> doesn't have side effects.
>
> * g++.dg/warn/Wuninitialized-9.C: New test.
>
> diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> index ebb5da9..b4319ca 100644
> --- gcc/cp/cp-gimplify.c
> +++ gcc/cp/cp-gimplify.c
> @@ -2056,6 +2056,14 @@ cp_fold (tree x)
> code = TREE_CODE (x);
> switch (code)
> {
> + case CLEANUP_POINT_EXPR:
> + /* Strip CLEANUP_POINT_EXPR if the expression doesn't have side
> + effects. */
> + r = cp_fold (TREE_OPERAND (x, 0));
> + if (!TREE_SIDE_EFFECTS (r))
> + x = r;
> + break;
> +
> case SIZEOF_EXPR:
> x = fold_sizeof_expr (x);
> break;
> diff --git gcc/testsuite/g++.dg/warn/Wuninitialized-9.C
> gcc/testsuite/g++.dg/warn/Wuninitialized-9.C
> index e69de29..3432b4f 100644
> --- gcc/testsuite/g++.dg/warn/Wuninitialized-9.C
> +++ gcc/testsuite/g++.dg/warn/Wuninitialized-9.C
> @@ -0,0 +1,19 @@
> +// PR c++/80119
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-Wuninitialized" }
> +
> +#include <type_traits>
> +
> +template <bool b>
> +void failing_function(std::integral_constant<bool, b>)
> +{
> + int i;
> + if (b && (i = 4)) {
> + ++i; // { dg-bogus "may be used uninitialized" }
> + }
> +}
> +
> +int main (void)
> +{
> + failing_function(std::false_type());
> +}
>
> Marek
