aco: don't try to form load+store clauses

fossil-db (gfx1100):
Totals from 79 (0.06% of 133428) affected shaders:
MaxWaves: 1484 -> 1408 (-5.12%)
Instrs: 216290 -> 216255 (-0.02%); split: -0.04%, +0.03%
CodeSize: 1149288 -> 1149148 (-0.01%); split: -0.03%, +0.02%
VGPRs: 7384 -> 7840 (+6.18%)
Latency: 3303521 -> 3305077 (+0.05%); split: -0.05%, +0.10%
InvThroughput: 2716621 -> 2719973 (+0.12%); split: -0.01%, +0.13%
VClause: 5605 -> 6170 (+10.08%)
SClause: 3005 -> 2983 (-0.73%); split: -0.77%, +0.03%
Copies: 33428 -> 33490 (+0.19%); split: -0.07%, +0.26%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23505>

src/amd/compiler/aco_ir.cpp

@@ -1277,6 +1277,9 @@ wait_imm::empty() const
 bool
 should_form_clause(const Instruction* a, const Instruction* b)
 {
+   if (a->definitions.empty() != b->definitions.empty())
+      return false;
+
    if (a->format != b->format)
       return false;