[NFC][LoopVectorize] Make the createStepForVF interface more caller-friendly

[david-arm]

Summary

The common use case for calling createStepForVF is currently something
like:

Value *Step = createStepForVF(Builder, ConstantInt::get(Ty, UF), VF);

and it makes more sense to reduce overall lines of code and change the
function to let it create the constant instead. With my patch this
becomes:

Value *Step = createStepForVF(Builder, Ty, VF, UF);

and the ConstantInt is created instead createStepForVF. A side-effect of
this is that the code in createStepForVF is also becomes simpler.

As part of this patch I've also replaced some calls to getRuntimeVF
with calls to createStepForVF, i.e.

getRuntimeVF(Builder, Count->getType(), VFactor * UFactor) ->
createStepForVF(Builder, Count->getType(), VFactor, UFactor)

because this feels semantically better.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

if (I) {
     if (I->getDebugLoc())
       DL = I->getDebugLoc();
   }
 
   return OptimizationRemarkAnalysis(PassName, RemarkName, DL, CodeRegion);
 }
 
 /// Return a value for Step multiplied by VF.
-static Value *createStepForVF(IRBuilder<> &B, Constant *Step, ElementCount VF) {
-  assert(isa<ConstantInt>(Step) && "Expected an integer step");
-  Constant *StepVal = ConstantInt::get(
-      Step->getType(),
-      cast<ConstantInt>(Step)->getSExtValue() * VF.getKnownMinValue());
+static Value *createStepForVF(IRBuilder<> &B, Type *Ty, ElementCount VF,
+                              int64_t Step) {
+  assert(Ty->isIntegerTy() && "Expected an integer step");
+  Constant *StepVal = ConstantInt::get(Ty, Step * VF.getKnownMinValue());
   return VF.isScalable() ? B.CreateVScale(StepVal) : StepVal;
 }
 
 namespace llvm {
 
 /// Return the runtime value for VF.
 Value *getRuntimeVF(IRBuilder<> &B, Type *Ty, ElementCount VF) {
   Constant *EC = ConstantInt::get(Ty, VF.getKnownMinValue());
void InnerLoopVectorizer::buildScalarSteps(Value *ScalarIV, Value *Step,
   if (!IsUniform && VF.isScalable()) {
     VecIVTy = VectorType::get(ScalarIVTy, VF);
     UnitStepVec = Builder.CreateStepVector(VectorType::get(IntStepTy, VF));
     SplatStep = Builder.CreateVectorSplat(VF, Step);
     SplatIV = Builder.CreateVectorSplat(VF, ScalarIV);
   }
 
   for (unsigned Part = 0; Part < UF; ++Part) {
-    Value *StartIdx0 =
-        createStepForVF(Builder, ConstantInt::get(IntStepTy, Part), VF);
+    Value *StartIdx0 = createStepForVF(Builder, IntStepTy, VF, Part);
 
     if (!IsUniform && VF.isScalable()) {
       auto *SplatStartIdx = Builder.CreateVectorSplat(VF, StartIdx0);
       auto *InitVec = Builder.CreateAdd(SplatStartIdx, UnitStepVec);
       if (ScalarIVTy->isFloatingPointTy())
         InitVec = Builder.CreateSIToFP(InitVec, VecIVTy);
       auto *Mul = Builder.CreateBinOp(MulOp, InitVec, SplatStep);
       auto *Add = Builder.CreateBinOp(AddOp, SplatIV, Mul);
if (Reverse) {
           cast<GetElementPtrInst>(Builder.CreateGEP(ScalarDataTy, Ptr, NumElt));
       PartPtr->setIsInBounds(InBounds);
       PartPtr = cast<GetElementPtrInst>(
           Builder.CreateGEP(ScalarDataTy, PartPtr, LastLane));
       PartPtr->setIsInBounds(InBounds);
       if (isMaskRequired) // Reverse of a null all-one mask is a null mask.
         BlockInMaskParts[Part] = reverseVector(BlockInMaskParts[Part]);
     } else {
-      Value *Increment = createStepForVF(Builder, Builder.getInt32(Part), VF);
+      Value *Increment =
+          createStepForVF(Builder, Builder.getInt32Ty(), VF, Part);
       PartPtr = cast<GetElementPtrInst>(
           Builder.CreateGEP(ScalarDataTy, Ptr, Increment));
       PartPtr->setIsInBounds(InBounds);
     }
 
     unsigned AddressSpace = Ptr->getType()->getPointerAddressSpace();
     return Builder.CreateBitCast(PartPtr, DataTy->getPointerTo(AddressSpace));
   };
Value *InnerLoopVectorizer::getOrCreateVectorTripCount(Loop *L) {
   if (VectorTripCount)
     return VectorTripCount;
 
   Value *TC = getOrCreateTripCount(L);
   IRBuilder<> Builder(L->getLoopPreheader()->getTerminator());
 
   Type *Ty = TC->getType();
   // This is where we can make the step a runtime constant.
-  Value *Step = createStepForVF(Builder, ConstantInt::get(Ty, UF), VF);
+  Value *Step = createStepForVF(Builder, Ty, VF, UF);
 
   // If the tail is to be folded by masking, round the number of iterations N
   // up to a multiple of Step instead of rounding down. This is done by first
   // adding Step-1 and then rounding down. Note that it's ok if this addition
   // overflows: the vector induction variable will eventually wrap to zero given
   // that it starts at zero and its Step is a power of two; the loop will then
   // exit, with the last early-exit vector comparison also producing all-true.
   if (Cost->foldTailByMasking()) {
void InnerLoopVectorizer::emitMinimumIterationCountCheck(Loop *L,
   // to the backedge-taken count overflowed leading to an incorrect trip count
   // of zero. In this case we will also jump to the scalar loop.
   auto P = Cost->requiresScalarEpilogue(VF) ? ICmpInst::ICMP_ULE
                                             : ICmpInst::ICMP_ULT;
 
   // If tail is to be folded, vector loop takes care of all iterations.
   Value *CheckMinIters = Builder.getFalse();
   if (!Cost->foldTailByMasking()) {
-    Value *Step =
-        createStepForVF(Builder, ConstantInt::get(Count->getType(), UF), VF);
+    Value *Step = createStepForVF(Builder, Count->getType(), VF, UF);
     CheckMinIters = Builder.CreateICmp(P, Count, Step, "min.iters.check");
   }
   // Create new preheader for vector loop.
   LoopVectorPreHeader =
       SplitBlock(TCCheckBlock, TCCheckBlock->getTerminator(), DT, LI, nullptr,
                  "vector.ph");
 
   assert(DT->properlyDominates(DT->getNode(TCCheckBlock),
(opt)  v      <-- edge from middle to exit iff epilogue is not required.
   //   - is the size of the widest induction variable type
   // then we create a new one.
   OldInduction = Legal->getPrimaryInduction();
   Type *IdxTy = Legal->getWidestInductionType();
   Value *StartIdx = ConstantInt::get(IdxTy, 0);
   // The loop step is equal to the vectorization factor (num of SIMD elements)
   // times the unroll factor (num of SIMD instructions).
   Builder.SetInsertPoint(&*Lp->getHeader()->getFirstInsertionPt());
-  Value *Step = createStepForVF(Builder, ConstantInt::get(IdxTy, UF), VF);
+  Value *Step = createStepForVF(Builder, IdxTy, VF, UF);
   Value *CountRoundDown = getOrCreateVectorTripCount(Lp);
   Induction =
       createInductionVariable(Lp, StartIdx, CountRoundDown, Step,
                               getDebugLocFromInstOrOperands(OldInduction));
 
   // Emit phis for the new starting index of the scalar loop.
   createInductionResumeValues(Lp, CountRoundDown);
 
if (Cost->isScalarAfterVectorization(P, State.VF)) {
       Value *UnitStepVec = nullptr, *PtrIndSplat = nullptr;
       if (NeedsVectorIndex) {
         Type *VecIVTy = VectorType::get(PtrInd->getType(), VF);
         UnitStepVec = Builder.CreateStepVector(VecIVTy);
         PtrIndSplat = Builder.CreateVectorSplat(VF, PtrInd);
       }
 
       for (unsigned Part = 0; Part < UF; ++Part) {
-        Value *PartStart = createStepForVF(
-            Builder, ConstantInt::get(PtrInd->getType(), Part), VF);
+        Value *PartStart =
+            createStepForVF(Builder, PtrInd->getType(), VF, Part);
 
         if (NeedsVectorIndex) {
           // Here we cache the whole vector, which means we can support the
           // extraction of any lane. However, in some cases the extractelement
           // instruction that is generated for scalar uses of this vector (e.g.
           // a load instruction) is not folded away. Therefore we still
           // calculate values for the first n lanes to avoid redundant moves
           // (when extracting the 0th element) and to produce scalar code (i.e.
BasicBlock *EpilogueVectorizerMainLoop::emitMinimumIterationCountCheck(
   IRBuilder<> Builder(TCCheckBlock->getTerminator());
 
   // Generate code to check if the loop's trip count is less than VF * UF of the
   // main vector loop.
   auto P = Cost->requiresScalarEpilogue(ForEpilogue ? EPI.EpilogueVF : VF) ?
       ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
 
   Value *CheckMinIters = Builder.CreateICmp(
-      P, Count, getRuntimeVF(Builder, Count->getType(), VFactor * UFactor),
+      P, Count, createStepForVF(Builder, Count->getType(), VFactor, UFactor),
       "min.iters.check");
 
   if (!ForEpilogue)
     TCCheckBlock->setName("vector.main.loop.iter.check");
 
   // Create new preheader for vector loop.
   LoopVectorPreHeader = SplitBlock(TCCheckBlock, TCCheckBlock->getTerminator(),
                                    DT, LI, nullptr, "vector.ph");
EpilogueVectorizerEpilogueLoop::emitMinimumVectorEpilogueIterCountCheck(
   IRBuilder<> Builder(Insert->getTerminator());
   Value *Count = Builder.CreateSub(TC, EPI.VectorTripCount, "n.vec.remaining");
 
   // Generate code to check if the loop's trip count is less than VF * UF of the
   // vector epilogue loop.
   auto P = Cost->requiresScalarEpilogue(EPI.EpilogueVF) ?
       ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
 
-  Value *CheckMinIters = Builder.CreateICmp(
-      P, Count,
-      getRuntimeVF(Builder, Count->getType(), EPI.EpilogueVF * EPI.EpilogueUF),
+  Value *CheckMinIters =
+      Builder.CreateICmp(P, Count,
+                         createStepForVF(Builder, Count->getType(),
+                                         EPI.EpilogueVF, EPI.EpilogueUF),
                          "min.epilog.iters.check");
 
   ReplaceInstWithInst(
       Insert->getTerminator(),
       BranchInst::Create(Bypass, LoopVectorPreHeader, CheckMinIters));
 
   LoopBypassBlocks.push_back(Insert);
   return Insert;
 }