[PATCH 3/4] Try inverted comparison for match_simplify in phiopt

Richard Biener richard.guenther@gmail.com
Mon Jun 28 08:44:18 GMT 2021


On Mon, Jun 28, 2021 at 1:28 AM apinski--- via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> Since match and simplify does not have all of the inverted
> comparison patterns, it make sense to just have
> phi-opt try to do the inversion and try match and simplify again.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu.

OK with the comment fix suggested by Bernhard.  I think
if the match fails you have to somewhere discard the
sequence, since it can still end up with partly pushed
stmts - otherwise you'll slowly leak SSA names.  Theres
gimple_seq_discard () for this.  It's probably best to do it
in gimple_simplify_phiopt after each failed try.

Richard.

> Thanks,
> Andrew Pinski
>
> gcc/ChangeLog:
>
>         * tree-ssa-phiopt.c (gimple_simplify_phiopt):
>         If "A ? B : C" fails to simplify, try "(!A) ? C : B".
> ---
>  gcc/tree-ssa-phiopt.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
> index 17bc597851b..9bda1b2a397 100644
> --- a/gcc/tree-ssa-phiopt.c
> +++ b/gcc/tree-ssa-phiopt.c
> @@ -836,7 +836,8 @@ phiopt_early_allow (enum tree_code code)
>     with parts pushed if EARLY_P was true. Also rejects non allowed tree code
>     if EARLY_P is set.
>     Takes the comparison from COMP_STMT and two args, ARG0 and ARG1 and tries
> -   to simplify CMP ? ARG0 : ARG1.  */
> +   to simplify CMP ? ARG0 : ARG1.
> +   Also try to simplify (!CMP) ? ARG0 : ARG1 if the non-inverse failed.  */
>  static tree
>  gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
>                         tree arg0, tree arg1,
> @@ -869,6 +870,30 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple *comp_stmt,
>             return result;
>         }
>      }
> +  /* Try the inverted comparison, that is !COMP ? ARG1 : ARG0. */
> +  comp_code = invert_tree_comparison (comp_code, HONOR_NANS (cmp0));
> +
> +  if (comp_code == ERROR_MARK)
> +    return NULL;
> +
> +  cond = build2_loc (loc,
> +                    comp_code, boolean_type_node,
> +                    cmp0, cmp1);
> +  gimple_match_op op1 (gimple_match_cond::UNCOND,
> +                      COND_EXPR, type, cond, arg1, arg0);
> +
> +  if (op1.resimplify (early_p ? NULL : seq, follow_all_ssa_edges))
> +    {
> +      /* Early we want only to allow some generated tree codes. */
> +      if (!early_p
> +         || op1.code.is_tree_code ()
> +         || phiopt_early_allow ((tree_code)op1.code))
> +       {
> +         result = maybe_push_res_to_seq (&op1, seq);
> +         if (result)
> +           return result;
> +       }
> +    }
>
>    return NULL;
>  }
> --
> 2.27.0
>


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