[llvm] [X86] Fast AVX-512-VNNI vpdpwssd tuning (PR #85033)

[Simon Pilgrim via llvm-commits]

================
@@ -10572,18 +10572,23 @@ bool X86InstrInfo::getMachineCombinerPatterns(
   case X86::VPDPWSSDrm:
   case X86::VPDPWSSDYrr:
   case X86::VPDPWSSDYrm: {
-    Patterns.push_back(MachineCombinerPattern::DPWSSD);
-    return true;
+    if (!Subtarget.hasFastPWSSD()) {
----------------
RKSimon wrote:

Can you remove the default, break if we don't use the MachineCombinerPattern::DPWSSD pattern and move this to after the switch:
```
return TargetInstrInfo::getMachineCombinerPatterns(Root, Patterns, DoRegPressureReduce);
```

https://github.com/llvm/llvm-project/pull/85033