Re: [PATCH] tree-optimization/105142 - improve maybe_fold_comparisons_from_match_pd fix

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

On Tue, Jul 26, 2022 at 1:18 PM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The following improves on the fix for PR105142 which restricted the
> expression lookup used for maybe_fold_comparisons_from_match_pd to
> avoid picking up flow-sensitive info for use in places where guarding
> conditions do not hold.  Instead of not allowing to expand SSA
> definitions there the following temporarily clears flow-sensitive
> info on the SSA names and restores it when finished matching.
>
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Better late then never - I have now pushed this after re-bootstrapping
and testing this on x86_64-unknown-linux-gnu.

Richard.

>         PR tree-optimization/105142
>         * gimple-fold.cc (fosa_unwind): New global.
>         (follow_outer_ssa_edges): When the SSA definition to follow
>         is does not dominate fosa_bb, temporarily clear flow-sensitive
>         info.
>         (maybe_fold_comparisons_from_match_pd): Set up unwind stack
>         for follow_outer_ssa_edges and unwind flow-sensitive info
>         clearing after matching.
> ---
>  gcc/gimple-fold.cc | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
> index a1704784bc9..876ef45434e 100644
> --- a/gcc/gimple-fold.cc
> +++ b/gcc/gimple-fold.cc
> @@ -6886,6 +6886,7 @@ and_comparisons_1 (tree type, enum tree_code code1, tree op1a, tree op1b,
>  }
>
>  static basic_block fosa_bb;
> +static vec<std::pair<tree, void *> > *fosa_unwind;
>  static tree
>  follow_outer_ssa_edges (tree val)
>  {
> @@ -6899,7 +6900,15 @@ follow_outer_ssa_edges (tree val)
>               && (def_bb == fosa_bb
>                   || dominated_by_p (CDI_DOMINATORS, fosa_bb, def_bb))))
>         return val;
> -      return NULL_TREE;
> +      /* If the definition does not dominate fosa_bb temporarily reset
> +        flow-sensitive info.  */
> +      if (val->ssa_name.info.range_info)
> +       {
> +         fosa_unwind->safe_push (std::make_pair
> +                                   (val, val->ssa_name.info.range_info));
> +         val->ssa_name.info.range_info = NULL;
> +       }
> +      return val;
>      }
>    return val;
>  }
> @@ -6958,9 +6967,14 @@ maybe_fold_comparisons_from_match_pd (tree type, enum tree_code code,
>                       type, gimple_assign_lhs (stmt1),
>                       gimple_assign_lhs (stmt2));
>    fosa_bb = outer_cond_bb;
> +  auto_vec<std::pair<tree, void *>, 8> unwind_stack;
> +  fosa_unwind = &unwind_stack;
>    if (op.resimplify (NULL, (!outer_cond_bb
>                             ? follow_all_ssa_edges : follow_outer_ssa_edges)))
>      {
> +      fosa_unwind = NULL;
> +      for (auto p : unwind_stack)
> +       p.first->ssa_name.info.range_info = p.second;
>        if (gimple_simplified_result_is_gimple_val (&op))
>         {
>           tree res = op.ops[0];
> @@ -6982,6 +6996,9 @@ maybe_fold_comparisons_from_match_pd (tree type, enum tree_code code,
>           return build2 ((enum tree_code)op.code, op.type, op0, op1);
>         }
>      }
> +  fosa_unwind = NULL;
> +  for (auto p : unwind_stack)
> +    p.first->ssa_name.info.range_info = p.second;
>
>    return NULL_TREE;
>  }
> --
> 2.35.3