On Tue, 26 Jan 2021, Jakub Jelinek wrote:
> Hi!
>
> In 4.8 and earlier we used to fold the following to 0 during GENERIC folding,
> but we don't do that anymore because ctor_for_folding etc. has been turned
> into a
> GIMPLE centric API, but as the testcase shows, it is invoked even during
> GENERIC folding and there the automatic vars still should have meaningful
> initializers. I've verified that the C++ FE drops TREE_READONLY on
> automatic vars with const qualified types if they require non-constant
> (runtime) initialization.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2021-01-26 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/97260
> * varpool.c (ctor_for_folding): In GENERIC return DECL_INITIAL for
> TREE_READONLY non-TREE_SIDE_EFFECTS automatic variables.
>
> * gcc.dg/tree-ssa/pr97260.c: New test.
>
> --- gcc/varpool.c.jj 2021-01-26 08:57:36.184290279 +0100
> +++ gcc/varpool.c 2021-01-26 09:46:16.453619140 +0100
> @@ -412,6 +412,12 @@ ctor_for_folding (tree decl)
> if (!TREE_STATIC (decl) && !DECL_EXTERNAL (decl))
> {
> gcc_assert (!TREE_PUBLIC (decl));
> + /* Unless this is called during FE folding. */
> + if (!in_gimple_form
Wouldn't it be better to use symtab->state == PARSING? Why isn't
it safe to always return DECL_INITIAL (but demote NULL to
error_mark_node and/or change the gimplifier to set it to
error_mark_node for autos) for TREE_READONLY && !TREE_SIDE_EFFECTS
decls (including autos)? Thus, why key on is_gimple_form at all?
> + && TREE_READONLY (decl)
> + && !TREE_SIDE_EFFECTS (decl)
> + && DECL_INITIAL (decl))
> + return DECL_INITIAL (decl);
> return error_mark_node;
> }
>
> --- gcc/testsuite/gcc.dg/tree-ssa/pr97260.c.jj 2021-01-26
> 09:45:42.933003954 +0100
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr97260.c 2021-01-26 09:45:17.277298476
> +0100
> @@ -0,0 +1,11 @@
> +/* PR tree-optimization/97260 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump "return 0;" "optimized" } } */
> +
> +int
> +foo (void)
> +{
> + const char a[] = "1234";
> + return __builtin_memcmp (a, "1234", 4);
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
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