> On 8 Sep 2026, at 15:21, Richard Biener <[email protected]> wrote:
>
> On Mon, 7 Sep 2026, [email protected] wrote:
>
>> From: Kyrylo Tkachov <[email protected]>
>>
>> genmatch can leave the iterators of a named match unexpanded. Code
>> generation
>> emits COND_EXPR conditions in opcode switches. Overlapping delayed iterator
>> sets can then emit duplicate case labels.
>
> Can you show an example pattern?
Patch 3/3 is enabled by this. I want to write:
(for cmp (ge gt)
(match (unsigned_integer_sat_add @0 @1)
(cond^ (cmp:c (bit_not @1) @0)
(plus:c @0 @1) integer_minus_onep)))
(for cmp (lt le)
(match (unsigned_integer_sat_add @0 @1)
(cond^ (cmp:c (bit_not @1) @0)
integer_minus_onep (plus:c @0 @1))))
The :c modifier also generates the comparison with swapped operands:
• (ge gt) produces direct GE/GT and commuted LE/LT.
• (lt le) produces direct LT/LE and commuted GT/GE.
Without this patch genmatch emits this:
switch (gimple_assign_rhs_code (_a2))
{
case GE_EXPR:
case GT_EXPR:
{ ... }
case LE_EXPR:
case LT_EXPR:
{ ... }
case LT_EXPR: /* Duplicate. */
case LE_EXPR: /* Duplicate. */
{ ... }
case GT_EXPR: /* Duplicate. */
case GE_EXPR: /* Duplicate. */
{ ... }
}
Thanks,
Kyrill
>
>> Substitute a group before decision-tree insertion when one of its iterators
>> occurs in a COND_EXPR condition. The existing eager path keeps the
>> substitutions aligned and lets the decision tree merge common concrete
>> operations. Other named matches keep delayed substitution.
>>
>> A reduced GIMPLE and GENERIC matcher with overlapping iterator sets fails to
>> compile before this change. Both forms compile after the change.
>> This is needed to accept the patterns in patch 3/3.
>>
>> Bootstrapped and tested on aarch64-none-linux-gnu.
>>
>> Ok for trunk?
>> Thanks,
>> Kyrill
>>
>> gcc/ChangeLog:
>>
>> * genmatch.cc (cond_expr_condition_contains_id): New function.
>> (lower_for): Expand iterators used in COND_EXPR conditions.
>> (lower): Update comment.
>>
>> Signed-off-by: Kyrylo Tkachov <[email protected]>
>> ---
>> gcc/genmatch.cc | 44 ++++++++++++++++++++++++++++++++++++++++----
>> 1 file changed, 40 insertions(+), 4 deletions(-)
>>
>> diff --git a/gcc/genmatch.cc b/gcc/genmatch.cc
>> index 1bc5875d7dd..c4bb1c12400 100644
>> --- a/gcc/genmatch.cc
>> +++ b/gcc/genmatch.cc
>> @@ -2159,6 +2159,26 @@ contains_id (operand *o, user_id *id)
>> return false;
>> }
>>
>> +/* Return true if O contains a COND_EXPR condition that refers to ID. */
>> +
>> +static bool
>> +cond_expr_condition_contains_id (operand *o, user_id *id)
>> +{
>> + if (capture *c = dyn_cast <capture *> (o))
>> + return c->what && cond_expr_condition_contains_id (c->what, id);
>> +
>> + if (expr *e = dyn_cast <expr *> (o))
>> + {
>> + if (*e->operation == COND_EXPR && contains_id (e->ops[0], id))
>> + return true;
>> + for (unsigned i = 0; i < e->ops.length (); ++i)
>> + if (cond_expr_condition_contains_id (e->ops[i], id))
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>>
>> /* In AST operand O replace operator ID with operator WITH. */
>>
>> @@ -2304,9 +2324,24 @@ lower_for (simplify *sin, vec<simplify *>&
>> simplifiers)
>> else
>> can_delay_subst = false;
>> }
>> - if (sin->kind == simplify::MATCH
>> - && can_delay_subst)
>> - continue;
>> + /* Code generation emits COND_EXPR conditions in opcode switches.
>> + Substitute iterators in these conditions before inserting the patterns
>> + into the decision tree. Overlapping iterator sets could otherwise
>> + emit duplicate case labels. */
>> + if (sin->kind == simplify::MATCH && can_delay_subst)
>> + {
>> + for (unsigned si = worklist_start;
>> + si < worklist.length () && can_delay_subst; ++si)
>> + for (unsigned i = 0; i < n_ids; ++i)
>> + if (cond_expr_condition_contains_id (worklist[si]->match,
>> + ids[i]))
>> + {
>> + can_delay_subst = false;
>> + break;
>> + }
>> + if (can_delay_subst)
>> + continue;
>> + }
>>
>> unsigned worklist_end = worklist.length ();
>> for (unsigned si = worklist_start; si < worklist_end; ++si)
>> @@ -2374,7 +2409,8 @@ lower (vec<simplify *>& simplifiers, bool gimple)
>> /* Lower for needs to happen before lowering cond
>> to support (for cnd (cond vec_cond)). This is
>> safe as substitution delay does not happen for
>> - cond or vec_cond. */
>> + cond or vec_cond, or for iterators used in a
>> + COND_EXPR condition. */
>> out_simplifiers.truncate (0);
>> for (auto s: simplifiers)
>> lower_for (s, out_simplifiers);
>>
>
> --
> Richard Biener <[email protected]>
> SUSE Software Solutions Germany GmbH,
> Frankenstrasse 146, 90461 Nuernberg, Germany;
> GF: Jochen Jaser, Andrew McDonald, Abhinav Puri; (HRB 36809, AG Nuernberg)
