[llvm] [GlobalIsel] Combine select to integer min max more (PR #92570)

[Thorsten Schütt via llvm-commits]

https://github.com/tschuett created https://github.com/llvm/llvm-project/pull/92570

None

>From 445f918f01f1fb4a3034884a6b0a336902c91813 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thorsten=20Sch=C3=BCtt?= <schuett at gmail.com>
Date: Fri, 17 May 2024 18:09:53 +0200
Subject: [PATCH] [GlobalIsel] Combine select to integer min max more

---
 .../include/llvm/Target/GlobalISel/Combine.td |  2 +-
 .../lib/CodeGen/GlobalISel/CombinerHelper.cpp | 84 +++++++++++--------
 .../AArch64/GlobalISel/combine-select.mir     |  3 +-
 3 files changed, 52 insertions(+), 37 deletions(-)

diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
index a1d39d910bc8e..5d4b5a2479f6a 100644
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -1309,7 +1309,7 @@ def select_to_minmax: GICombineRule<
 
 def select_to_iminmax: GICombineRule<
   (defs root:$root, build_fn_matchinfo:$info),
-  (match (G_ICMP $tst, $tst1, $x, $y),
+  (match (G_ICMP $tst, $tst1, $a, $b),
          (G_SELECT $root, $tst, $x, $y),
          [{ return Helper.matchSelectIMinMax(${root}, ${info}); }]),
   (apply [{ Helper.applyBuildFnMO(${root}, ${info}); }])>;
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index a87a26d72b452..0d2e59541b05a 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -6772,46 +6772,62 @@ bool CombinerHelper::matchSelectIMinMax(const MachineOperand &MO,
   if (CmpInst::isEquality(Pred))
     return false;
 
-  [[maybe_unused]] Register CmpLHS = Cmp->getLHSReg();
-  [[maybe_unused]] Register CmpRHS = Cmp->getRHSReg();
+  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);
+  }
 
   // (icmp X, Y) ? X : Y -> integer minmax.
   // see matchSelectPattern in ValueTracking.
   // Legality between G_SELECT and integer minmax can differ.
-  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); };
-    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}))
+  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:
       return false;
-    MatchInfo = [=](MachineIRBuilder &B) { B.buildSMin(DstReg, True, False); };
-    return true;
-  }
-  default:
-    return false;
+    }
   }
+
+  return false;
 }
 
 bool CombinerHelper::matchSelect(MachineInstr &MI, BuildFnTy &MatchInfo) {
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
index 8d9ad8d7cacaf..353c1550d6974 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
@@ -911,8 +911,7 @@ body:             |
     ; CHECK-NEXT: %f1:_(s32) = G_TRUNC [[COPY1]](s64)
     ; CHECK-NEXT: %t:_(<4 x s32>) = G_BUILD_VECTOR %t1(s32), %t1(s32), %t1(s32), %t1(s32)
     ; CHECK-NEXT: %f:_(<4 x s32>) = G_BUILD_VECTOR %f1(s32), %f1(s32), %f1(s32), %f1(s32)
-    ; CHECK-NEXT: %c:_(<4 x s32>) = G_ICMP intpred(sle), %f(<4 x s32>), %t
-    ; CHECK-NEXT: %sel:_(<4 x s32>) = exact G_SELECT %c(<4 x s32>), %t, %f
+    ; CHECK-NEXT: %sel:_(<4 x s32>) = G_SMAX %t, %f
     ; CHECK-NEXT: $q0 = COPY %sel(<4 x s32>)
     %0:_(s64) = COPY $x0
     %1:_(s64) = COPY $x1