Re: [PATCHv2 2/2] PHIOPT: Improve replace_phi_edge_with_variable for diamond shapped bb

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

On Thu, May 4, 2023 at 1:13 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> While looking at differences between what minmax_replacement
> and match_simplify_replacement does. I noticed that they sometimes
> chose different edges to remove. I decided we should be able to do
> better and be able to remove both empty basic blocks in the
> case of match_simplify_replacement as that moves the statements.
>
> This also updates the testcases as now match_simplify_replacement
> will remove the unused MIN/MAX_EXPR and they were checking for
> those.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

> gcc/ChangeLog:
>
>         * tree-ssa-phiopt.cc (replace_phi_edge_with_variable): Handle
>         diamond form bb with forwarder only empty blocks better.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/minmax-15.c: Update test.
>         * gcc.dg/tree-ssa/minmax-16.c: Update test.
>         * gcc.dg/tree-ssa/minmax-3.c: Update test.
>         * gcc.dg/tree-ssa/minmax-4.c: Update test.
>         * gcc.dg/tree-ssa/minmax-5.c: Update test.
>         * gcc.dg/tree-ssa/minmax-8.c: Update test.
> ---
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-15.c |  3 +-
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-16.c |  9 ++----
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c  |  2 +-
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c  |  2 +-
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c  |  2 +-
>  gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c  |  2 +-
>  gcc/tree-ssa-phiopt.cc                    | 35 ++++++++++++++++++++++-
>  7 files changed, 43 insertions(+), 12 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-15.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-15.c
> index 8a39871c938..6731f91e6c3 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-15.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-15.c
> @@ -30,5 +30,6 @@ main (void)
>    return 0;
>  }
>
> -/* { dg-final { scan-tree-dump-times "MIN_EXPR" 3 "phiopt1" } } */
> +/* There should only be two MIN_EXPR left, the 3rd one was removed. */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
>  /* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-16.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-16.c
> index 623b12b3f74..094364e6424 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-16.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-16.c
> @@ -25,11 +25,8 @@ main (void)
>    return 0;
>  }
>
> -/* After phiopt1, there really should be only 3 MIN_EXPR in the IR (including debug statements).
> -   But the way phiopt does not cleanup the CFG all the time, the PHI might still reference the
> -   alternative bb's moved statement.
> -   Note in the end, we do dce the statement and other debug statements to end up with only 2 MIN_EXPR.
> -   So check that too. */
> -/* { dg-final { scan-tree-dump-times "MIN_EXPR" 4 "phiopt1" } } */
> +/* After phiopt1, will be only 2 MIN_EXPR in the IR (including debug statements). */
> +/* xk will only have the final result so the extra debug info does not change anything. */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
>  /* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "optimized" } } */
>  /* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> index 2af10776346..521afe3e4d9 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-3.c
> @@ -25,5 +25,5 @@ main (void)
>    return 0;
>  }
>
> -/* { dg-final { scan-tree-dump-times "MIN_EXPR" 3 "phiopt1" } } */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
>  /* { dg-final { scan-tree-dump-times "MAX_EXPR" 0 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> index 973f39bfed3..49e27185b5e 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-4.c
> @@ -26,4 +26,4 @@ main (void)
>  }
>
>  /* { dg-final { scan-tree-dump-times "MIN_EXPR" 0 "phiopt1" } } */
> -/* { dg-final { scan-tree-dump-times "MAX_EXPR" 3 "phiopt1" } } */
> +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 2 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> index 34e4e720511..194c881cc98 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-5.c
> @@ -25,5 +25,5 @@ main (void)
>    return 0;
>  }
>
> -/* { dg-final { scan-tree-dump-times "MIN_EXPR" 2 "phiopt1" } } */
> +/* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
>  /* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> index 0160e573fef..d5cb53145ea 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/minmax-8.c
> @@ -26,4 +26,4 @@ main (void)
>  }
>
>  /* { dg-final { scan-tree-dump-times "MIN_EXPR" 1 "phiopt1" } } */
> -/* { dg-final { scan-tree-dump-times "MAX_EXPR" 2 "phiopt1" } } */
> +/* { dg-final { scan-tree-dump-times "MAX_EXPR" 1 "phiopt1" } } */
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index fbc1fd66607..7ba24211025 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -94,6 +94,7 @@ replace_phi_edge_with_variable (basic_block cond_block,
>    basic_block bb = gimple_bb (phi);
>    gimple_stmt_iterator gsi;
>    tree phi_result = PHI_RESULT (phi);
> +  bool deleteboth = false;
>
>    /* Duplicate range info if they are the only things setting the target PHI.
>       This is needed as later on, the new_tree will be replacing
> @@ -137,7 +138,14 @@ replace_phi_edge_with_variable (basic_block cond_block,
>        keep_edge = EDGE_SUCC (cond_block, 1);
>      }
>    else if ((keep_edge = find_edge (cond_block, e->src)))
> -    ;
> +    {
> +      basic_block bb1 = EDGE_SUCC (cond_block, 0)->dest;
> +      basic_block bb2 = EDGE_SUCC (cond_block, 1)->dest;
> +      if (single_pred_p (bb1) && single_pred_p (bb2)
> +         && single_succ_p (bb1) && single_succ_p (bb2)
> +         && empty_block_p (bb1) && empty_block_p (bb2))
> +       deleteboth = true;
> +    }
>    else
>      gcc_unreachable ();
>
> @@ -148,6 +156,31 @@ replace_phi_edge_with_variable (basic_block cond_block,
>        e->probability = profile_probability::always ();
>        delete_basic_block (edge_to_remove->dest);
>
> +      /* Eliminate the COND_EXPR at the end of COND_BLOCK.  */
> +      gsi = gsi_last_bb (cond_block);
> +      gsi_remove (&gsi, true);
> +    }
> +  else if (deleteboth)
> +    {
> +      basic_block bb1 = EDGE_SUCC (cond_block, 0)->dest;
> +      basic_block bb2 = EDGE_SUCC (cond_block, 1)->dest;
> +
> +      edge newedge = redirect_edge_and_branch (keep_edge, bb);
> +
> +      /* The new edge should be the same. */
> +      gcc_assert (newedge == keep_edge);
> +
> +      keep_edge->flags |= EDGE_FALLTHRU;
> +      keep_edge->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
> +      keep_edge->probability = profile_probability::always ();
> +
> +      /* Copy the edge's phi entry from the old one. */
> +      copy_phi_arg_into_existing_phi (e, keep_edge);
> +
> +      /* Delete the old 2 empty basic blocks */
> +      delete_basic_block (bb1);
> +      delete_basic_block (bb2);
> +
>        /* Eliminate the COND_EXPR at the end of COND_BLOCK.  */
>        gsi = gsi_last_bb (cond_block);
>        gsi_remove (&gsi, true);
> --
> 2.31.1
>