[VectorUtils][VPlan] Consolidate VPWidenIntrinsicRecipe::onlyFirstLaneUsed and isVectorIntrinsicWithScalarOpAtArg

We can reuse isVectorIntrinsicWithScalarOpAtArg in VectorUtils to determine if only the first lane will be used for a VPWidenIntrinsicRecipe, provided that we also move the VP EVL operand check into it.

This was needed by a local patch I was working on that created a VPWidenIntrinsicRecipe with a VP intrinsic, and prevents the need to update the scalar arguments in two places.

Author: lukel97

llvm/lib/Analysis/VectorUtils.cpp

@@ -149,6 +149,11 @@ bool llvm::isVectorIntrinsicWithScalarOpAtArg(Intrinsic::ID ID,
   if (TTI && Intrinsic::isTargetIntrinsic(ID))
     return TTI->isTargetIntrinsicWithScalarOpAtArg(ID, ScalarOpdIdx);
 
+  // Vector predication intrinsics only demand the the first lane the last
+  // operand (the EVL operand).
+  if (VPIntrinsic::getVectorLengthParamPos(ID) == ScalarOpdIdx)
+    return true;
+
   switch (ID) {
   case Intrinsic::abs:
   case Intrinsic::vp_abs:
@@ -166,7 +171,7 @@ bool llvm::isVectorIntrinsicWithScalarOpAtArg(Intrinsic::ID ID,
   case Intrinsic::umul_fix_sat:
     return (ScalarOpdIdx == 2);
   case Intrinsic::experimental_vp_splice:
-    return ScalarOpdIdx == 2 || ScalarOpdIdx == 4 || ScalarOpdIdx == 5;
+    return ScalarOpdIdx == 2 || ScalarOpdIdx == 4;
   default:
     return false;
   }

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -1373,10 +1373,8 @@ StringRef VPWidenIntrinsicRecipe::getIntrinsicName() const {
 
 bool VPWidenIntrinsicRecipe::onlyFirstLaneUsed(const VPValue *Op) const {
   assert(is_contained(operands(), Op) && "Op must be an operand of the recipe");
-  // Vector predication intrinsics only demand the the first lane the last
-  // operand (the EVL operand).
-  return VPIntrinsic::isVPIntrinsic(VectorIntrinsicID) &&
-         Op == getOperand(getNumOperands() - 1);
+  unsigned Idx = std::distance(op_begin(), find(operands(), Op));
+  return isVectorIntrinsicWithScalarOpAtArg(VectorIntrinsicID, Idx, nullptr);
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)