Re: [PATCH 5/6] PHIOPT: Ignore predicates for match-and-simplify phi-opt

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

On Sun, Apr 23, 2023 at 12:11 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This fixes a missed optimization where early phi-opt would
> not work when there was predicates. The easiest fix is
> to change empty_bb_or_one_feeding_into_p to ignore those
> statements while checking for only feeding statement.
>
> Note phi-opt-23.c and phi-opt-24.c still fail as we don't handle
> diamond form in match_and_simplify phiopt yet.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

> gcc/ChangeLog:
>
>         * tree-ssa-phiopt.cc (empty_bb_or_one_feeding_into_p):
>         Instead of calling last_and_only_stmt, look for the last statement
>         manually.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/ssa-ifcombine-13.c: Add -fno-ssa-phiopt.
> ---
>  .../gcc.dg/tree-ssa/ssa-ifcombine-13.c        |  4 +++-
>  gcc/tree-ssa-phiopt.cc                        | 22 +++++++++++++++++--
>  2 files changed, 23 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c
> index 425eb3d6481..7976544c79b 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c
> @@ -1,5 +1,7 @@
>  /* { dg-do compile } */
> -/* { dg-options "-O1 -fdump-tree-optimized-details-blocks --param logical-op-non-short-circuit=1" } */
> +/* Disable phi-opt as it is no longer confused by predicate which had allowed ifcombine to work in the past.
> +   Note this testcase is about ifcombine rather than phi-opt. */
> +/* { dg-options "-O1 -fdump-tree-optimized-details-blocks --param logical-op-non-short-circuit=1 -fno-ssa-phiopt" } */
>
>  _Bool f1(_Bool a, _Bool b)
>  {
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index cb4d8788b56..ffd6a4e6f35 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -962,9 +962,27 @@ empty_bb_or_one_feeding_into_p (basic_block bb,
>    if (!gimple_seq_empty_p (phi_nodes (bb)))
>      return false;
>
> -  stmt_to_move = last_and_only_stmt (bb);
> +  gimple_stmt_iterator gsi;
> +
> +  gsi = gsi_start_nondebug_after_labels_bb (bb);
> +  while (!gsi_end_p (gsi))
> +    {
> +      gimple *s = gsi_stmt (gsi);
> +      gsi_next_nondebug (&gsi);
> +      /* Skip over Predict and nop statements. */
> +      if (gimple_code (s) == GIMPLE_PREDICT
> +         || gimple_code (s) == GIMPLE_NOP)
> +       continue;
> +      /* If there is more one statement return false. */
> +      if (stmt_to_move)
> +       return false;
> +      stmt_to_move = s;
> +    }
> +
> +  /* The only statement here was a Predict or a nop statement
> +     so return true. */
>    if (!stmt_to_move)
> -    return false;
> +    return true;
>
>    if (gimple_vuse (stmt_to_move))
>      return false;
> --
> 2.39.1
>