[llvm] [GlobalIsel] Speedup select to integer min/max (PR #92378)

[Jay Foad via llvm-commits]

================
@@ -6743,62 +6740,46 @@ bool CombinerHelper::tryFoldSelectToIntMinMax(GSelect *Select,
   if (CmpInst::isEquality(Pred))
     return false;
 
-  Register CmpLHS = Cmp->getLHSReg();
-  Register CmpRHS = Cmp->getRHSReg();
-
-  // We can swap CmpLHS and CmpRHS for higher hitrate.
-  if (True == CmpRHS && False == CmpLHS) {
-    std::swap(CmpLHS, CmpRHS);
-    Pred = CmpInst::getSwappedPredicate(Pred);
-  }
+  [[maybe_unused]] Register CmpLHS = Cmp->getLHSReg();
+  [[maybe_unused]] Register CmpRHS = Cmp->getRHSReg();
 
   // (icmp X, Y) ? X : Y -> integer minmax.
   // see matchSelectPattern in ValueTracking.
   // Legality between G_SELECT and integer minmax can differ.
-  if (True == CmpLHS && False == CmpRHS) {
-    switch (Pred) {
-    case ICmpInst::ICMP_UGT:
-    case ICmpInst::ICMP_UGE: {
-      if (!isLegalOrBeforeLegalizer({TargetOpcode::G_UMAX, DstTy}))
-        return false;
-      MatchInfo = [=](MachineIRBuilder &B) {
-        B.buildUMax(DstReg, True, False);
-      };
-      return true;
-    }
-    case ICmpInst::ICMP_SGT:
-    case ICmpInst::ICMP_SGE: {
-      if (!isLegalOrBeforeLegalizer({TargetOpcode::G_SMAX, DstTy}))
-        return false;
-      MatchInfo = [=](MachineIRBuilder &B) {
-        B.buildSMax(DstReg, True, False);
-      };
-      return true;
-    }
-    case ICmpInst::ICMP_ULT:
-    case ICmpInst::ICMP_ULE: {
-      if (!isLegalOrBeforeLegalizer({TargetOpcode::G_UMIN, DstTy}))
-        return false;
-      MatchInfo = [=](MachineIRBuilder &B) {
-        B.buildUMin(DstReg, True, False);
-      };
-      return true;
-    }
-    case ICmpInst::ICMP_SLT:
-    case ICmpInst::ICMP_SLE: {
-      if (!isLegalOrBeforeLegalizer({TargetOpcode::G_SMIN, DstTy}))
-        return false;
-      MatchInfo = [=](MachineIRBuilder &B) {
-        B.buildSMin(DstReg, True, False);
-      };
-      return true;
-    }
-    default:
+  assert(True == CmpLHS && False == CmpRHS && "unexpected MIR pattern");
----------------
jayfoad wrote:

Sure, either write two patterns or move the `True == CmpLHS` checks back into C++ code. I don't think it's OK to regress functionality, just to make the pattern matching neater.

https://github.com/llvm/llvm-project/pull/92378