On Fri, Jul 10, 2026 at 6:03 AM Richard Biener
<[email protected]> wrote:
>
> On Wed, Jul 8, 2026 at 10:20 AM Andrew 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.
> >
> > 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: Andrew Pinski <[email protected]>
> > ---
> > gcc/tree-ssa-phiopt.cc | 48 ++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 48 insertions(+)
> >
> > diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> > index e12dc7a8b0c..fd173ec01f4 100644
> > --- a/gcc/tree-ssa-phiopt.cc
> > +++ b/gcc/tree-ssa-phiopt.cc
> > @@ -688,6 +688,52 @@ 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;
> > +
> > + /* 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;
> > + for (unsigned i = 0; i < op.num_ops; i++)
> > + {
> > + tree use = op.ops[i];
> > + if (TREE_CODE (use) == SSA_NAME)
> > + bitmap_set_bit (uses, SSA_NAME_VERSION (use));
> > + }
> > + 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)))
> > + {
> > + for (unsigned i = 0; i < gimple_num_ops (s); i++)
> > + {
> > + tree use = gimple_op (s, i);
> > + if (TREE_CODE (use) == SSA_NAME)
> > + bitmap_set_bit (uses, SSA_NAME_VERSION (use));
>
> I think this doesn't work on REALPART_EXPR and friends,
> nor on &a[i_3]. Not sure the latter will appear, but for sure
> the former will.
>
> Walking SSA operands w/o SSA operands is ... hard (you
> might want to dig out removed vectorizer code that needed
> to do this for pattern stmts).
Yes you are correct I didn't think of REALPART_EXPR; though I don't
think it shows up in any pattern used with cond currently which is why
I didn't see an issue here.
I don't think `&a[i_3]` will show up but yes it is never too safe to be sorry.
> Maybe use operands_scanner from tree-ssa-operands.cc and
> expose the parse_ssa_operands method?
Yes I will look into that when I get back from vacation.
>
> > + }
> > + gsi_prev (&gsi);
> > + continue;
> > + }
> > + gsi_remove (&gsi, true);
> > + release_defs (s);
> > + ggc_free (s);
> > + /* If this was the last statement, 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
> > @@ -729,6 +775,7 @@ 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))
> > @@ -783,6 +830,7 @@ 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
> >
