Init implement TU select

Author: Mel-Chen

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1262,6 +1262,9 @@ class VPInstruction : public VPRecipeWithIRFlags {
     // operand). Only generates scalar values (either for the first lane only or
     // for all lanes, depending on its uses).
     PtrAdd,
+    // Selects elements from two vectors (second and third operand) based on a
+    // condition vector (first operand) and a pivot index (fourth operand).
+    MergeUntilPivot,
   };
 
 private:

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -144,6 +144,7 @@ bool VPRecipeBase::mayHaveSideEffects() const {
     case VPInstruction::FirstOrderRecurrenceSplice:
     case VPInstruction::LogicalAnd:
     case VPInstruction::PtrAdd:
+    case VPInstruction::MergeUntilPivot:
       return false;
     default:
       return true;
@@ -673,7 +674,18 @@ Value *VPInstruction::generatePerPart(VPTransformState &State, unsigned Part) {
     }
     return NewPhi;
   }
+  case VPInstruction::MergeUntilPivot: {
+    assert(Part == 0 && "No unrolling expected for predicated vectorization.");
+    Value *Cond = State.get(getOperand(0), Part);
+    Value *OnTrue = State.get(getOperand(1), Part);
+    Value *OnFalse = State.get(getOperand(2), Part);
+    Value *Pivot = State.get(getOperand(3), VPIteration(0, 0));
+    assert(Pivot->getType()->isIntegerTy() && "Pivot should be an integer.");
 
+    return Builder.CreateIntrinsic(Intrinsic::vp_merge, {OnTrue->getType()},
+                                   {Cond, OnTrue, OnFalse, Pivot}, nullptr,
+                                   Name);
+  }
   default:
     llvm_unreachable("Unsupported opcode for instruction");
   }
@@ -764,6 +776,9 @@ bool VPInstruction::onlyFirstLaneUsed(const VPValue *Op) const {
   case VPInstruction::BranchOnCond:
   case VPInstruction::ResumePhi:
     return true;
+  case VPInstruction::MergeUntilPivot:
+    // Pivot must be an integer.
+    return Op == getOperand(3);
   };
   llvm_unreachable("switch should return");
 }
@@ -782,6 +797,7 @@ bool VPInstruction::onlyFirstPartUsed(const VPValue *Op) const {
   case VPInstruction::BranchOnCount:
   case VPInstruction::BranchOnCond:
   case VPInstruction::CanonicalIVIncrementForPart:
+  case VPInstruction::MergeUntilPivot:
     return true;
   };
   llvm_unreachable("switch should return");
@@ -848,6 +864,9 @@ void VPInstruction::print(raw_ostream &O, const Twine &Indent,
   case VPInstruction::PtrAdd:
     O << "ptradd";
     break;
+  case VPInstruction::MergeUntilPivot:
+    O << "merge-until-pivot";
+    break;
   default:
     O << Instruction::getOpcodeName(getOpcode());
   }