[GlobalIsel] Speedup select to integer min/max

tschuett · tschuett · commit 699518f70029 · 2024-05-16T15:24:09.000+02:00
llvm#92309
diff --git a/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h b/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
@@ -822,6 +822,9 @@ class CombinerHelper {
   // Given a binop \p MI, commute operands 1 and 2.
   void applyCommuteBinOpOperands(MachineInstr &MI);
 
+  /// Combine select to integer min/max.
+  bool matchSelectIMinMax(const MachineOperand &MO, BuildFnTy &MatchInfo);
+
   /// Combine selects.
   bool matchSelect(MachineInstr &MI, BuildFnTy &MatchInfo);
 
@@ -962,9 +965,6 @@ class CombinerHelper {
 
   bool tryFoldSelectOfConstants(GSelect *Select, BuildFnTy &MatchInfo);
 
-  /// Try to fold (icmp X, Y) ? X : Y -> integer minmax.
-  bool tryFoldSelectToIntMinMax(GSelect *Select, BuildFnTy &MatchInfo);
-
   bool isOneOrOneSplat(Register Src, bool AllowUndefs);
   bool isZeroOrZeroSplat(Register Src, bool AllowUndefs);
   bool isConstantSplatVector(Register Src, int64_t SplatValue,
diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -1307,6 +1307,13 @@ def select_to_minmax: GICombineRule<
          [{ return Helper.matchSimplifySelectToMinMax(*${root}, ${info}); }]),
   (apply [{ Helper.applyBuildFn(*${root}, ${info}); }])>;
 
+def select_to_iminmax: GICombineRule<
+  (defs root:$root, build_fn_matchinfo:$info),
+  (match (G_ICMP $tst, $tst1, $x, $y),
+         (G_SELECT $root, $tst, $x, $y),
+         [{ return Helper.matchSelectIMinMax(${root}, ${info}); }]),
+  (apply [{ Helper.applyBuildFnMO(${root}, ${info}); }])>;
+
 def match_selects : GICombineRule<
   (defs root:$root, build_fn_matchinfo:$matchinfo),
   (match (wip_match_opcode G_SELECT):$root,
@@ -1670,7 +1677,7 @@ def phi_combines : GICombineGroup<[extend_through_phis]>;
 def bitreverse_shift : GICombineGroup<[bitreverse_shl, bitreverse_lshr]>;
 
 def select_combines : GICombineGroup<[select_undef_cmp, select_constant_cmp,
-                                      match_selects]>;
+                                      select_to_iminmax, match_selects]>;
 
 def trivial_combines : GICombineGroup<[copy_prop, mul_to_shl, add_p2i_to_ptradd,
                                        mul_by_neg_one, idempotent_prop]>;
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -6749,22 +6749,19 @@ bool CombinerHelper::tryFoldBoolSelectToLogic(GSelect *Select,
   return false;
 }
 
-bool CombinerHelper::tryFoldSelectToIntMinMax(GSelect *Select,
-                                              BuildFnTy &MatchInfo) {
+bool CombinerHelper::matchSelectIMinMax(const MachineOperand &MO,
+                                        BuildFnTy &MatchInfo) {
+  GSelect *Select = cast<GSelect>(MRI.getVRegDef(MO.getReg()));
+  GICmp *Cmp = cast<GICmp>(MRI.getVRegDef(Select->getCondReg()));
+
   Register DstReg = Select->getReg(0);
-  Register Cond = Select->getCondReg();
   Register True = Select->getTrueReg();
   Register False = Select->getFalseReg();
   LLT DstTy = MRI.getType(DstReg);
 
   if (DstTy.isPointer())
     return false;
 
-  // We need an G_ICMP on the condition register.
-  GICmp *Cmp = getOpcodeDef<GICmp>(Cond, MRI);
-  if (!Cmp)
-    return false;
-
   // We want to fold the icmp and replace the select.
   if (!MRI.hasOneNonDBGUse(Cmp->getReg(0)))
     return false;
@@ -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); };
+    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;
   }
-
-  return false;
 }
 
 bool CombinerHelper::matchSelect(MachineInstr &MI, BuildFnTy &MatchInfo) {
@@ -6842,9 +6823,6 @@ bool CombinerHelper::matchSelect(MachineInstr &MI, BuildFnTy &MatchInfo) {
   if (tryFoldBoolSelectToLogic(Select, MatchInfo))
     return true;
 
-  if (tryFoldSelectToIntMinMax(Select, MatchInfo))
-    return true;
-
   return false;
 }
 
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
@@ -896,3 +896,31 @@ body:             |
     RET_ReallyLR
 
 ...
+---
+# test failed_select icmp_sle f,t_t_f --> smin(t,f)
+name:            select_icmp_sle_f_t_t_f_smin_t_f
+body:             |
+  bb.1:
+    liveins: $x0, $x1, $x2
+    ; CHECK-LABEL: name: select_icmp_sle_f_t_t_f_smin_t_f
+    ; CHECK: liveins: $x0, $x1, $x2
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK-NEXT: %t1:_(s32) = G_TRUNC [[COPY]](s64)
+    ; 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: $q0 = COPY %sel(<4 x s32>)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %t1:_(s32) = G_TRUNC %0
+    %f1:_(s32) = G_TRUNC %1
+    %t:_(<4 x s32>) = G_BUILD_VECTOR %t1, %t1, %t1, %t1
+    %f:_(<4 x s32>) = G_BUILD_VECTOR %f1, %f1, %f1, %f1
+    %c:_(<4 x s32>) = G_ICMP intpred(sle), %f(<4 x s32>), %t(<4 x s32>)
+    %sel:_(<4 x s32>) = exact G_SELECT %c, %t, %f
+    $q0 = COPY %sel(<4 x s32>)
+...
