[C++ PATCH] Fix -Wunused-but-set-* false positive with ~ of vector type (PR c++/78949)

[Jason Merrill]

OK.

On Thu, Dec 29, 2016 at 10:19 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> For integral arg, mark_exp_read is called during
> cp_perform_integral_promotions, for complex type it is called during
> cp_default_conversion, but for vector types nothing actually calls it.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk?
>
> 2016-12-29  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/78949
>         * typeck.c (cp_build_unary_op): Call mark_rvalue_use on arg if it has
>         vector type.
>
>         * c-c++-common/Wunused-var-16.c: New test.
>
> --- gcc/cp/typeck.c.jj  2016-12-21 23:12:01.000000000 +0100
> +++ gcc/cp/typeck.c     2016-12-29 13:48:58.363469890 +0100
> @@ -5907,6 +5907,8 @@ cp_build_unary_op (enum tree_code code,
>             inform (location, "did you mean to use logical not (%<!%>)?");
>           arg = cp_perform_integral_promotions (arg, complain);
>         }
> +      else if (!noconvert && VECTOR_TYPE_P (TREE_TYPE (arg)))
> +       arg = mark_rvalue_use (arg);
>        break;
>
>      case ABS_EXPR:
> --- gcc/testsuite/c-c++-common/Wunused-var-16.c.jj      2016-12-29 13:51:07.143825569 +0100
> +++ gcc/testsuite/c-c++-common/Wunused-var-16.c 2016-12-29 13:50:42.000000000 +0100
> @@ -0,0 +1,15 @@
> +/* PR c++/78949 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wunused" } */
> +
> +typedef unsigned char V __attribute__((vector_size(16)));
> +V v;
> +
> +void
> +foo ()
> +{
> +  V y = {};
> +  V x = {};    // { dg-bogus "set but not used" }
> +  y &= ~x;
> +  v = y;
> +}
>
>         Jakub