Re: [PATCH] Fix tree-opt/PR106087: ICE with inline-asm with multiple output and assigned only static vars

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

On Fri, Jul 8, 2022 at 6:33 AM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> The problem here is that when we mark the ssa name that was referenced in the now removed
> dead store (to a write only static variable), the inline-asm would also be removed
> even though it was defining another ssa name. This fixes the problem by checking
> to make sure that the statement was only defining one ssa name.
>
> OK? Bootstrapped and tested on x86_64 with no regressions.
>
>         PR tree-optimization/106087
>
> gcc/ChangeLog:
>
>         * tree-ssa-dce.cc (simple_dce_from_worklist): Check
>         to make sure the statement is only defining one operand.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.c-torture/compile/inline-asm-1.c: New test.
> ---
>  gcc/testsuite/gcc.c-torture/compile/inline-asm-1.c | 14 ++++++++++++++
>  gcc/tree-ssa-dce.cc                                |  5 +++++
>  2 files changed, 19 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.c-torture/compile/inline-asm-1.c
>
> diff --git a/gcc/testsuite/gcc.c-torture/compile/inline-asm-1.c b/gcc/testsuite/gcc.c-torture/compile/inline-asm-1.c
> new file mode 100644
> index 00000000000..0044cb761b6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/inline-asm-1.c
> @@ -0,0 +1,14 @@
> +/* PR tree-opt/106087,
> +   simple_dce_from_worklist would delete the
> +   inline-asm when it was still being referenced
> +   by the other ssa name. */
> +
> +static int t;
> +
> +int f(void)
> +{
> +  int tt, tt1;
> +  asm("":"=r"(tt), "=r"(tt1));
> +  t = tt1;
> +  return tt;
> +}
> diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
> index bc533582673..602cdb30ceb 100644
> --- a/gcc/tree-ssa-dce.cc
> +++ b/gcc/tree-ssa-dce.cc
> @@ -2061,6 +2061,11 @@ simple_dce_from_worklist (bitmap worklist)
>        if (gimple_has_side_effects (t))
>         continue;
>
> +      /* The defining statement needs to be defining one this name. */

only this name?

> +      if (!is_a<gphi *>(t)

I suppose we could turn this into is_a<gasm *>(t) since that's
the only stmt kind with multiple (non-virtual) definitions?

OK with those changes.

> +         && !single_ssa_def_operand (t, SSA_OP_DEF))
> +       continue;
> +
>        /* Don't remove statements that are needed for non-call
>          eh to work.  */
>        if (stmt_unremovable_because_of_non_call_eh_p (cfun, t))
> --
> 2.17.1
>