On Fri, Nov 13, 2026 at 8:33 AM Andrea Pinski
<[email protected]> wrote:
>
> Since match and simplify can add unused statements to the sequence
> in some cases, we should remove them before call phiopt_early_allow.
> This is needed for 2 future patches. One is to allowing of comparisons,
> optionally with a cast and optional with a negative expression.
> The other is about supporting a way to handling
> cond_removal_in_builtin_zero_pattern in match and also adding a new match
> pattern to fix PR 126035 (ctz split back into one).
>
> Bootstrapped and tested on x86_64-linux-gnu.
>
> Changes since v1:
> * v2: Use walk_gimple_op/walk_tree instead of assuming the operands
> are simple.
>
> gcc/ChangeLog:
>
> * tree-ssa-phiopt.cc (remove_unused_stmts): New function.
> (gimple_simplify_phiopt): Call remove_unused_stmts before
> phiopt_early_allow.
>
> Signed-off-by: Andrea Pinski <[email protected]>
> ---
> gcc/tree-ssa-phiopt.cc | 55 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index 875f8e4af34..43317213fa9 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -56,6 +56,7 @@ along with GCC; see the file COPYING3. If not see
> #include "gimple-predict.h"
> #include "alias.h"
> #include "tree-ssa-threadedge.h"
> +#include "gimple-walk.h"
>
> /* Return the singleton PHI in the SEQ of PHIs for edges E0 and E1. */
>
> @@ -707,6 +708,58 @@ phiopt_early_allow (gimple_seq &seq, gimple_match_op &op)
> }
> }
>
> +/* Remove unused statements in SEQ. That are used in OP.
> + This is needed for the way resimplify/match and simplify
> + works as it will place some unneeded statements in the sequence
> + which can get in the way of handling phiopt_early_allow. */
> +
> +static void
> +remove_unused_stmts (gimple_seq *seq, const gimple_match_op &op)
> +{
> + if (*seq == nullptr)
> + return;
> +
> + walk_stmt_info wi = {};
> +
> + /* Since the sequence of statements are not part of
> + a basic block yet, have to manually go through the operands
> + to mark the uses. */
> + auto_bitmap uses;
> + wi.info = (bitmap)uses;
> + auto fn = [](tree *tp, int *, void *data) -> tree
> + {
> + walk_stmt_info *wi = (walk_stmt_info*)data;
> + bitmap uses = (bitmap)wi->info;
> + tree use = *tp;
> + if (TREE_CODE (use) == SSA_NAME)
> + bitmap_set_bit (uses, SSA_NAME_VERSION (use));
> + return NULL_TREE;
> + };
I just noticed that this callback function does not ignore lhs like it
was doing previously. It might be ok not to ignore the lhs as we
check the lhs before doing the walk. But it is just better to ignore
it.
I will have a fixed up patch this afternoon.
Thanks,
Andrea
> + for (unsigned i = 0; i < op.num_ops; i++)
> + {
> + tree use = op.ops[i];
> + walk_tree (&use, fn, &wi, nullptr);
> + }
> + gimple_stmt_iterator gsi = gsi_last (*seq);
> + while (!gsi_end_p (gsi))
> + {
> + gimple *s = *gsi;
> + tree lhs = gimple_get_lhs (s);
> + if (bitmap_bit_p (uses, SSA_NAME_VERSION (lhs)))
> + {
> + walk_gimple_op (s, fn, &wi);
> + gsi_prev (&gsi);
> + continue;
> + }
> + gsi_remove (&gsi, true);
> + release_defs (s);
> + ggc_free (s);
> + /* gsi_remove goes to the next stmt so start over. */
> + if (gsi_end_p (gsi))
> + gsi = gsi_last (*seq);
> + }
> +}
> +
> /* gimple_simplify_phiopt is like gimple_simplify but designed for PHIOPT.
> Return NULL if nothing can be simplified or the resulting simplified value
> with parts pushed if EARLY_P was true. Also rejects non allowed tree code
> @@ -748,6 +801,7 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple
> *comp_stmt,
>
> if (op.resimplify (&seq1, follow_all_ssa_edges))
> {
> + remove_unused_stmts (&seq1, op);
> bool allowed = !early_p || phiopt_early_allow (seq1, op);
> tree result = maybe_push_res_to_seq (&op, &seq1);
> if (dump_file && (dump_flags & TDF_FOLDING))
> @@ -802,6 +856,7 @@ gimple_simplify_phiopt (bool early_p, tree type, gimple
> *comp_stmt,
>
> if (op1.resimplify (&seq1, follow_all_ssa_edges))
> {
> + remove_unused_stmts (&seq1, op1);
> bool allowed = !early_p || phiopt_early_allow (seq1, op1);
> tree result = maybe_push_res_to_seq (&op1, &seq1);
> if (dump_file && (dump_flags & TDF_FOLDING))
> --
> 2.43.0
>
