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

[Pierre van Houtryve via llvm-commits]

Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/92378 at github.com>


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@@ -6775,62 +6772,46 @@ 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");
+
+  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); };
----------------
Pierre-vh wrote:

> e.g. allowing the user to write their own combined "match+apply" function in the first place.

Can you open an issue to track this idea? I'm not sure I like it yet, i'd need to think about how the TableGen would look.

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