Re: [COMMITTED] tree-optimization: [PR108684] ICE in verify_ssa due to simple_dce_from_worklist

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

On Fri, Feb 10, 2023 at 2:47 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> In simple_dce_from_worklist, we were removing an inline-asm which had a vdef.
> We should not be removing inline-asm which have a vdef as this code
> does not check to the store.
> This fixes that oversight. This was a latent bug exposed recently
> by both VRP and removal of stores to static starting to use
> simple_dce_from_worklist.
>
> Committed as approved.
> Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
>         PR tree-optimization/108684
>
> gcc/ChangeLog:
>
>         * tree-ssa-dce.cc (simple_dce_from_worklist):
>         Check all ssa names and not just non-vdef ones
>         before accepting the inline-asm.
>         Call unlink_stmt_vdef on the statement before
>         removing it.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.c-torture/compile/dce-inline-asm-1.c: New test.
>         * gcc.c-torture/compile/dce-inline-asm-2.c: New test.
>         * gcc.dg/tree-ssa/pr108684-1.c: New test.
>
> co-authored-by: Andrew Macleod  <amacleod@redhat.com>
> ---
>  .../gcc.c-torture/compile/dce-inline-asm-1.c   | 15 +++++++++++++++
>  .../gcc.c-torture/compile/dce-inline-asm-2.c   | 16 ++++++++++++++++
>  gcc/testsuite/gcc.dg/tree-ssa/pr108684-1.c     | 18 ++++++++++++++++++
>  gcc/tree-ssa-dce.cc                            |  5 +++--
>  4 files changed, 52 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
>  create mode 100644 gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr108684-1.c
>
> diff --git a/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> new file mode 100644
> index 00000000000..a9f02e44bd7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> @@ -0,0 +1,15 @@
> +/* PR tree-optimization/108684 */
> +/* This used to ICE as when we remove the store to
> +   `t`, we also would remove the inline-asm which
> +   had a VDEF on it but we didn't update the
> +   VUSE that was later on.  */
> +static int t;
> +
> +int f (int *a)
> +{
> +  int t1;
> +  asm (" " : "=X" (t1) : : "memory");
> +  t = t1;
> +  return *a;
> +}
> +
> diff --git a/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> new file mode 100644
> index 00000000000..a41b16e4bd0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> @@ -0,0 +1,16 @@
> +/* PR tree-optimization/108684 */
> +/* This used to ICE as when we removed the
> +   __builtin_unreachable in VRP, as we
> +   would also remove the branch and the
> +   inline-asm. The inline-asm had a VDEF on it,
> +   which we didn't update further along and
> +   not have the VDEF on the return statement
> +   updated.  */
> +
> +int f (int a)
> +{
> +  asm (" " : "=X" (a) : : "memory");
> +  if (a)
> +    return 0;
> +  __builtin_unreachable();
> +}
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr108684-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr108684-1.c
> new file mode 100644
> index 00000000000..3ba206f765e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr108684-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +
> +static int t;
> +
> +int f (int *a)
> +{
> +  int t1, t2 = 0;
> +  asm ("shouldshowupstill %1" : "=r" (t1), "=m"(t2) : : );
> +  t = t1;
> +  return t2;
> +}
> +
> +/* Check to make sure DCE does not remove the inline-asm as it writes to t2. */
> +/* We used to DCE this inline-asm when removing the store to t. */
> +/* { dg-final { scan-assembler "shouldshowupstill" } } */
> +/* { dg-final { scan-tree-dump-times "shouldshowupstill" 1 "optimized" } } */
> diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
> index b2fe9f4f55e..1f1ec2c8710 100644
> --- a/gcc/tree-ssa-dce.cc
> +++ b/gcc/tree-ssa-dce.cc
> @@ -2108,9 +2108,9 @@ simple_dce_from_worklist (bitmap worklist)
>
>        /* The defining statement needs to be defining only this name.
>          ASM is the only statement that can define more than one
> -        (non-virtual) name. */
> +        name. */
>        if (is_a<gasm *>(t)
> -         && !single_ssa_def_operand (t, SSA_OP_DEF))
> +         && !single_ssa_def_operand (t, SSA_OP_ALL_DEFS))
>         continue;
>
>        /* Don't remove statements that are needed for non-call
> @@ -2140,6 +2140,7 @@ simple_dce_from_worklist (bitmap worklist)
>         remove_phi_node (&gsi, true);
>        else
>         {
> +         unlink_stmt_vdef (t);

note this should never do anything

>           gsi_remove (&gsi, true);
>           release_defs (t);
>         }
> --
> 2.27.0
>