[VPlan] Check VPValue step in isCanonical (NFCI).

Update the isCanonical() implementations to check the VPValue step
operand instead of the step in the induction descriptor.

At the moment this is NFC, but it enables further optimizations if the
step is replaced by a constant in D147783.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D147891

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -33,6 +33,7 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/ADT/ilist.h"
 #include "llvm/ADT/ilist_node.h"
+#include "llvm/Analysis/IVDescriptors.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/VectorUtils.h"
 #include "llvm/IR/DebugLoc.h"
@@ -47,7 +48,6 @@ namespace llvm {
 
 class BasicBlock;
 class DominatorTree;
-class InductionDescriptor;
 class InnerLoopVectorizer;
 class IRBuilderBase;
 class LoopInfo;
@@ -1848,9 +1848,11 @@ class VPCanonicalIVPHIRecipe : public VPHeaderPHIRecipe {
     return true;
   }
 
-  /// Check if the induction described by \p ID is canonical, i.e.  has the same
-  /// start, step (of 1), and type as the canonical IV.
-  bool isCanonical(const InductionDescriptor &ID, Type *Ty) const;
+  /// Check if the induction described by \p Kind, /p Start and \p Step is
+  /// canonical, i.e.  has the same start, step (of 1), and type as the
+  /// canonical IV.
+  bool isCanonical(InductionDescriptor::InductionKind Kind, VPValue *Start,
+                   VPValue *Step, Type *Ty) const;
 };
 
 /// A recipe for generating the active lane mask for the vector loop that is

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -735,8 +735,13 @@ void VPWidenIntOrFpInductionRecipe::print(raw_ostream &O, const Twine &Indent,
 #endif
 
 bool VPWidenIntOrFpInductionRecipe::isCanonical() const {
+  // The step may be defined by a recipe in the preheader (e.g. if it requires
+  // SCEV expansion), but for the canonical induction the step is required to be
+  // 1, which is represented as live-in.
+  if (getStepValue()->getDefiningRecipe())
+    return false;
+  auto *StepC = dyn_cast<ConstantInt>(getStepValue()->getLiveInIRValue());
   auto *StartC = dyn_cast<ConstantInt>(getStartValue()->getLiveInIRValue());
-  auto *StepC = dyn_cast<SCEVConstant>(getInductionDescriptor().getStep());
   return StartC && StartC->isZero() && StepC && StepC->isOne();
 }
 
@@ -1091,20 +1096,22 @@ void VPCanonicalIVPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 }
 #endif
 
-bool VPCanonicalIVPHIRecipe::isCanonical(const InductionDescriptor &ID,
-                                         Type *Ty) const {
-  if (Ty != getScalarType())
+bool VPCanonicalIVPHIRecipe::isCanonical(
+    InductionDescriptor::InductionKind Kind, VPValue *Start, VPValue *Step,
+    Type *Ty) const {
+  // The types must match and it must be an integer induction.
+  if (Ty != getScalarType() || Kind != InductionDescriptor::IK_IntInduction)
+    return false;
+  // Start must match the start value of this canonical induction.
+  if (Start != getStartValue())
     return false;
-  // The start value of ID must match the start value of this canonical
-  // induction.
-  if (getStartValue()->getLiveInIRValue() != ID.getStartValue())
+
+  // If the step is defined by a recipe, it is not a ConstantInt.
+  if (Step->getDefiningRecipe())
     return false;
 
-  ConstantInt *Step = ID.getConstIntStepValue();
-  // ID must also be incremented by one. IK_IntInduction always increment the
-  // induction by Step, but the binary op may not be set.
-  return ID.getKind() == InductionDescriptor::IK_IntInduction && Step &&
-         Step->isOne();
+  ConstantInt *StepC = dyn_cast<ConstantInt>(Step->getLiveInIRValue());
+  return StepC && StepC->isOne();
 }
 
 bool VPWidenPointerInductionRecipe::onlyScalarsGenerated(ElementCount VF) {

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -520,7 +520,8 @@ void VPlanTransforms::optimizeInductions(VPlan &Plan, ScalarEvolution &SE) {
     VPValue *Step =
         vputils::getOrCreateVPValueForSCEVExpr(Plan, ID.getStep(), SE);
     VPValue *BaseIV = CanonicalIV;
-    if (!CanonicalIV->isCanonical(ID, ResultTy)) {
+    if (!CanonicalIV->isCanonical(ID.getKind(), WideIV->getStartValue(), Step,
+                                  ResultTy)) {
       BaseIV = new VPDerivedIVRecipe(ID, WideIV->getStartValue(), CanonicalIV,
                                      Step, ResultTy);
       HeaderVPBB->insert(BaseIV->getDefiningRecipe(), IP);