Re: [PATCH] Fix middle-end/103645: empty struct store not removed when using compound literal

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Aug 8, 2022 at 5:38 AM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> For compound literals empty struct stores are not removed as they go down a
> different path of the gimplifier; trying to optimize the init constructor.
> This fixes the problem by not adding the gimple assignment at the end
> of gimplify_init_constructor if it was an empty type.
>
> Note this updates gcc.dg/pr87052.c where we had:
> const char d[0] = { };
> And was expecting a store to d but after this, there is no store
> as the decl's type is zero in size.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

> gcc/ChangeLog:
>
>         PR middle-end/103645
>         * gimplify.c (gimplify_init_constructor): Don't build/add
>         gimple assignment of an empty type.
>
> testsuite/ChangeLog:
>         * gcc.dg/pr87052.c: Update d var to expect nothing.
> ---
>  gcc/gimplify.cc                | 7 +++++--
>  gcc/testsuite/gcc.dg/pr87052.c | 6 +++---
>  2 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
> index 2ac7ca0855e..f0fbdb48012 100644
> --- a/gcc/gimplify.cc
> +++ b/gcc/gimplify.cc
> @@ -5488,8 +5488,11 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
>    if (ret == GS_ERROR)
>      return GS_ERROR;
>    /* If we have gimplified both sides of the initializer but have
> -     not emitted an assignment, do so now.  */
> -  if (*expr_p)
> +     not emitted an assignment, do so now.   */
> +  if (*expr_p
> +      /* If the type is an empty type, we don't need to emit the
> +        assignment. */
> +      && !is_empty_type (TREE_TYPE (TREE_OPERAND (*expr_p, 0))))
>      {
>        tree lhs = TREE_OPERAND (*expr_p, 0);
>        tree rhs = TREE_OPERAND (*expr_p, 1);
> diff --git a/gcc/testsuite/gcc.dg/pr87052.c b/gcc/testsuite/gcc.dg/pr87052.c
> index 18e092c4674..796fe6440c1 100644
> --- a/gcc/testsuite/gcc.dg/pr87052.c
> +++ b/gcc/testsuite/gcc.dg/pr87052.c
> @@ -23,8 +23,7 @@ void test (void)
>
>    const char d[0] = { };
>
> -  /* Expect the following:
> -     d = ""; */
> +  /* Expect nothing.  */
>
>    const char e[0] = "";
>
> @@ -36,6 +35,7 @@ void test (void)
>  /* { dg-final { scan-tree-dump-times "a = \"\\\\x00ab\";" 1 "gimple" } }
>     { dg-final { scan-tree-dump-times "b = \"a\\\\x00bc\";"  1 "gimple" } }
>     { dg-final { scan-tree-dump-times "c = \"\";"  1 "gimple" } }
> -   { dg-final { scan-tree-dump-times "d = { *};"  1 "gimple" } }
> +   { dg-final { scan-tree-dump-times "d = "  1 "gimple" } }
> +   { dg-final { scan-tree-dump-times "d = {CLOBBER\\(eol\\)}"  1 "gimple" } }
>     { dg-final { scan-tree-dump-times "e = "  1 "gimple" } }
>     { dg-final { scan-tree-dump-times "e = {CLOBBER\\(eol\\)}"  1 "gimple" } }  */
> --
> 2.27.0
>