Re: [C++ PATCH] Avoid appending a useless __builtin_unreachable in functions which do return (PR c++/83897)

[Jason Merrill <jason at redhat dot com>]

OK.

On Wed, Jan 17, 2018 at 3:10 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> I've noticed several testcases recently that have a dead
> __builtin_unreachable call in functions right after return stmt.
> They are optimized away after a while (typically in the cfg pass), but we
> don't really need to generate them when there is the return.
> The reason we don't find it is because it is wrapped in some cases in
> CLEANUP_POINT_EXPR.  That doesn't change anything on the function actually
> ending with a return.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2018-01-17  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/83897
>         * cp-gimplify.c (cp_maybe_instrument_return): Handle
>         CLEANUP_POINT_EXPR.
>
>         * g++.dg/cpp0x/pr83897.C: New test.
>
> --- gcc/cp/cp-gimplify.c.jj     2018-01-11 18:58:48.348391787 +0100
> +++ gcc/cp/cp-gimplify.c        2018-01-16 17:24:41.087336680 +0100
> @@ -1581,6 +1581,7 @@ cp_maybe_instrument_return (tree fndecl)
>           t = BIND_EXPR_BODY (t);
>           continue;
>         case TRY_FINALLY_EXPR:
> +       case CLEANUP_POINT_EXPR:
>           t = TREE_OPERAND (t, 0);
>           continue;
>         case STATEMENT_LIST:
> --- gcc/testsuite/g++.dg/cpp0x/pr83897.C.jj     2018-01-16 17:41:54.723256147 +0100
> +++ gcc/testsuite/g++.dg/cpp0x/pr83897.C        2018-01-16 17:41:34.274257947 +0100
> @@ -0,0 +1,13 @@
> +// PR c++/83897
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-O2 -fdump-tree-gimple" }
> +// { dg-final { scan-tree-dump-not "__builtin_unreachable" "gimple" } }
> +
> +struct A {};
> +struct B { int a; int b = 5; };
> +
> +A
> +bar (B)
> +{
> +  return {};
> +}
>
>         Jakub