On Tue, 21 Mar 2017, Jakub Jelinek wrote:
> Hi!
>
> For non-gimple reg types var = x ? y : z; is gimplified as
> x ? (var = y) : (var = z);. The problem is that if var is TREE_READONLY,
> we can gimplify one of those assignments by promoting them to TREE_STATIC
> (if not addressable) and making the initializer into their DECL_INITIAL.
> That doesn't work well, because then we conditionally store into that and
> during optimizations, as it is a TREE_READONLY var with DECL_INITIAL, just
> use that initializer for optimizations.
>
> The following patch fixes that by clearing TREE_READONLY flag if we are
> going to store it more than once.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2017-03-21 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/80129
> * gimplify.c (gimplify_modify_expr_rhs) <case COND_EXPR>: Clear
> TREE_READONLY on result if writing it more than once.
>
> * g++.dg/torture/pr80129.C: New test.
>
> --- gcc/gimplify.c.jj 2017-03-21 07:56:55.000000000 +0100
> +++ gcc/gimplify.c 2017-03-21 13:37:45.555612652 +0100
> @@ -5098,6 +5098,13 @@ gimplify_modify_expr_rhs (tree *expr_p,
> if (ret != GS_ERROR)
> ret = GS_OK;
>
> + /* If we are going to write RESULT more than once, clear
> + TREE_READONLY flag, otherwise we might gimplify it
> + incorrectly. */
> + if (DECL_P (result)
Can it ever be that result is sth like decl.component? At least I
don't see GENERIC restricted in a way that it cannot. (and generally
assigning to sth TREE_READONLY is fishy at best...)
I see how this fixes the problem at hand (and in a safe way), so the
patch is probably ok, just looking how to avoid this situation in
a more general (and better) way.
> + && TREE_TYPE (TREE_OPERAND (cond, 1)) != void_type_node
> + && TREE_TYPE (TREE_OPERAND (cond, 2)) != void_type_node)
> + TREE_READONLY (result) = 0;
> if (TREE_TYPE (TREE_OPERAND (cond, 1)) != void_type_node)
> TREE_OPERAND (cond, 1)
> = build2 (code, void_type_node, result,
> --- gcc/testsuite/g++.dg/torture/pr80129.C.jj 2017-03-21 13:40:04.179852313
> +0100
> +++ gcc/testsuite/g++.dg/torture/pr80129.C 2017-03-21 13:41:32.121735570
> +0100
> @@ -0,0 +1,14 @@
> +// PR c++/80129
> +// { dg-do run }
> +// { dg-options "-std=c++11" }
> +
> +struct A { bool a; int b; };
> +
> +int
> +main ()
> +{
> + bool c = false;
> + const A x = c ? A {true, 1} : A {false, 0};
> + if (x.a)
> + __builtin_abort ();
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
