[GlobalISel] Add support for most G_VECREDUCE_* operations to moreElementsVector

llvm/include/llvm/CodeGen/GlobalISel/LegalizerHelper.h

@@ -281,6 +281,10 @@ class LegalizerHelper {
                                          MachineInstr &MI,
                                          LostDebugLocObserver &LocObserver);
 
+  MachineInstrBuilder
+  getNeutralElementForVecReduce(unsigned Opcode, MachineIRBuilder &MIRBuilder,
+                                LLT Ty);
+
 public:
   /// Return the alignment to use for a stack temporary object with the given
   /// type.

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -5159,6 +5159,42 @@ LegalizerHelper::moreElementsVectorPhi(MachineInstr &MI, unsigned TypeIdx,
   return Legalized;
 }
 
+MachineInstrBuilder LegalizerHelper::getNeutralElementForVecReduce(
+    unsigned Opcode, MachineIRBuilder &MIRBuilder, LLT Ty) {
+  assert(Ty.isScalar() && "Expected scalar type to make neutral element for");
+
+  switch (Opcode) {
+  default:
+    return MIRBuilder.buildUndef(Ty);
+  case TargetOpcode::G_VECREDUCE_ADD:
+  case TargetOpcode::G_VECREDUCE_OR:
+  case TargetOpcode::G_VECREDUCE_XOR:
+  case TargetOpcode::G_VECREDUCE_UMAX:
+    return MIRBuilder.buildConstant(Ty, 0);
+  case TargetOpcode::G_VECREDUCE_MUL:
+    return MIRBuilder.buildConstant(Ty, 1);
+  case TargetOpcode::G_VECREDUCE_AND:
+  case TargetOpcode::G_VECREDUCE_UMIN:
+    return MIRBuilder.buildConstant(
+        Ty, APInt::getAllOnes(Ty.getScalarSizeInBits()));
+  case TargetOpcode::G_VECREDUCE_SMAX:
+    return MIRBuilder.buildConstant(
+        Ty, APInt::getSignedMinValue(Ty.getSizeInBits()));
+  case TargetOpcode::G_VECREDUCE_SMIN:
+    return MIRBuilder.buildConstant(
+        Ty, APInt::getSignedMaxValue(Ty.getSizeInBits()));
+  case TargetOpcode::G_VECREDUCE_FADD:
+    return MIRBuilder.buildFConstant(Ty, -0.0);
+  case TargetOpcode::G_VECREDUCE_FMUL:
+    return MIRBuilder.buildFConstant(Ty, 1.0);
+  case TargetOpcode::G_VECREDUCE_FMINIMUM:
+  case TargetOpcode::G_VECREDUCE_FMAXIMUM:
+    assert(false && "getNeutralElementForVecReduce unimplemented for "
+                    "G_VECREDUCE_FMINIMUM and G_VECREDUCE_FMAXIMUM!");
+  }
+  llvm_unreachable("switch expected to return!");
+}
+
 LegalizerHelper::LegalizeResult
 LegalizerHelper::moreElementsVector(MachineInstr &MI, unsigned TypeIdx,
                                     LLT MoreTy) {
@@ -5341,6 +5377,35 @@ LegalizerHelper::moreElementsVector(MachineInstr &MI, unsigned TypeIdx,
     Observer.changedInstr(MI);
     return Legalized;
   }
+  case TargetOpcode::G_VECREDUCE_FADD:
+  case TargetOpcode::G_VECREDUCE_FMUL:
+  case TargetOpcode::G_VECREDUCE_ADD:
+  case TargetOpcode::G_VECREDUCE_MUL:
+  case TargetOpcode::G_VECREDUCE_AND:
+  case TargetOpcode::G_VECREDUCE_OR:
+  case TargetOpcode::G_VECREDUCE_XOR:
+  case TargetOpcode::G_VECREDUCE_SMAX:
+  case TargetOpcode::G_VECREDUCE_SMIN:
+  case TargetOpcode::G_VECREDUCE_UMAX:
+  case TargetOpcode::G_VECREDUCE_UMIN: {
+    LLT OrigTy = MRI.getType(MI.getOperand(1).getReg());
+    MachineOperand &MO = MI.getOperand(1);
+    auto NewVec = MIRBuilder.buildPadVectorWithUndefElements(MoreTy, MO);
+    auto NeutralElement = getNeutralElementForVecReduce(
+        MI.getOpcode(), MIRBuilder, MoreTy.getElementType());
+    for (size_t i = OrigTy.getNumElements(), e = MoreTy.getNumElements();
+         i != e; i++) {
+      auto Idx = MIRBuilder.buildConstant(LLT::scalar(32), i);
+      NewVec = MIRBuilder.buildInsertVectorElement(MoreTy, NewVec,
+                                                   NeutralElement, Idx);
+    }
+
+    Observer.changingInstr(MI);
+    MO.setReg(NewVec.getReg(0));
+    Observer.changedInstr(MI);
+    return Legalized;
+  }
+
   default:
     return UnableToLegalize;
   }