Re: [PATCH] gimplify: Clear TREE_READONLY on automatic vars being stored into [PR104529]

[Richard Biener via Gcc-patches]

> Am 04.03.2022 um 10:04 schrieb Jakub Jelinek via Gcc-patches 
> <gcc-patches@gcc.gnu.org>:
> 
> Hi!
> 
> The following testcase regressed when SRA started punting on stores to
> TREE_READONLY vars.  We document that:
> "In a VAR_DECL, PARM_DECL or FIELD_DECL, or any kind of ..._REF node,
> nonzero means it may not be the lhs of an assignment."
> so the SRA change looks desirable.  On the other side, at least in this
> testcase the TREE_READONLY is set there intentionally from the
> PR85873 fix, because gimplify_init_constructor itself uses TREE_READONLY
> on the object to determine if it can perform promotion to static const
> or not.
> 
> So, similarly to other spots in the gimplifier where we also clear
> TREE_READONLY when we emit IL that stores into the object, this
> does the same in gimplify_init_constructor, but in the way so that
> the TREE_READONLY test for the promotion to static const keeps working
> and doesn't change anything for notify_temp_creation mode, which doesn't
> emit any IL, just tests if it would need a temporary or not.
> 
> This keeps PR85873 testcase working as before and fixes this regression.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok.

Thanks,
Richard 

> 2022-03-04  Jakub Jelinek  <ja...@redhat.com>
> 
>    PR middle-end/104529
>    * gimplify.cc (gimplify_init_constructor): Clear TREE_READONLY
>    on automatic objects which will be runtime initialized.
> 
>    * g++.dg/tree-ssa/pr104529.C: New test.
> 
> --- gcc/gimplify.cc.jj    2022-03-03 09:13:16.000000000 +0100
> +++ gcc/gimplify.cc    2022-03-03 15:21:02.270198275 +0100
> @@ -5120,6 +5120,12 @@ gimplify_init_constructor (tree *expr_p,
>      {
>        if (notify_temp_creation)
>          return GS_OK;
> +
> +        /* The var will be initialized and so appear on lhs of
> +           assignment, it can't be TREE_READONLY anymore.  */
> +        if (VAR_P (object))
> +          TREE_READONLY (object) = 0;
> +
>        is_empty_ctor = true;
>        break;
>      }
> @@ -5171,6 +5177,11 @@ gimplify_init_constructor (tree *expr_p,
>        break;
>      }
> 
> +    /* The var will be initialized and so appear on lhs of
> +       assignment, it can't be TREE_READONLY anymore.  */
> +    if (VAR_P (object) && !notify_temp_creation)
> +      TREE_READONLY (object) = 0;
> +
>    /* If there are "lots" of initialized elements, even discounting
>       those that are not address constants (and thus *must* be
>       computed at runtime), then partition the constructor into
> --- gcc/testsuite/g++.dg/tree-ssa/pr104529.C.jj    2022-03-03 
> 14:57:30.216939375 +0100
> +++ gcc/testsuite/g++.dg/tree-ssa/pr104529.C    2022-03-03 14:57:23.002040380 
> +0100
> @@ -0,0 +1,20 @@
> +// PR middle-end/104529
> +// { dg-do compile { target c++11 } }
> +// { dg-options "-O2 -fdump-tree-optimized" }
> +// { dg-final { scan-tree-dump-not "MEM\[^\n\r]*MEM" "optimized" } }
> +
> +#include <cstddef>
> +#include <vector>
> +
> +struct S {
> +  unsigned int a;
> +  std::vector<unsigned char> b;
> +  std::vector<unsigned char> c;
> +};
> +
> +std::size_t
> +foo ()
> +{
> +  S test[] = { { 48, { 255, 0, 0, 0, 0, 0 } } };
> +  return sizeof (test);
> +}
> 
>    Jakub
>