[LV] Add setStartValue to VPWidenIntOrFPInductionRecipe

[michaelmaitland]

Summary

VPWidenIntOrFPInductionRecipe is casted to VPHeaderPHIRecipe even
though it is not a VPHeaderPHIRecipe. Then setStartValue is called
on the VPWidenIntOrFPInductionRecipe which was casted to a class
that it does not inherit from. This bug was not caught because
VPHeaderPHIRecipe::setStartValue has the same body that *should*
have existed in VPWidenIntOrFPInductionRecipe. This patch
casts to the correct Recipe type and calls the correct
setStartValue function.

[michaelmaitland]

Abandon in favor of https://reviews.llvm.org/D144125

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

if (!VectorizeLoop) {
               ID = &WidenInd->getInductionDescriptor();
             }
 
             ResumeV = MainILV.createInductionResumeValue(
                 IndPhi, *ID, {EPI.MainLoopIterationCountCheck});
           }
           assert(ResumeV && "Must have a resume value");
           VPValue *StartVal = BestEpiPlan.getOrAddExternalDef(ResumeV);
-          cast<VPHeaderPHIRecipe>(&R)->setStartValue(StartVal);
+          if (auto *PhiR = dyn_cast<VPHeaderPHIRecipe>(&R))
+            PhiR->setStartValue(StartVal);
+          else if (auto *PhiR = dyn_cast<VPWidenIntOrFpInductionRecipe>(&R))
+            PhiR->setStartValue(StartVal);
         }
 
         LVP.executePlan(EPI.EpilogueVF, EPI.EpilogueUF, BestEpiPlan, EpilogILV,
                         DT, true);
         ++LoopsEpilogueVectorized;
 
         if (!MainILV.areSafetyChecksAdded())
           DisableRuntimeUnroll = true;

llvm/lib/Transforms/Vectorize/VPlan.h

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
   void print(raw_ostream &O, const Twine &Indent,
              VPSlotTracker &SlotTracker) const override;
 #endif
 
   /// Returns the start value of the induction.
   VPValue *getStartValue() { return getOperand(0); }
   const VPValue *getStartValue() const { return getOperand(0); }
 
+  /// Sets the start value of the induction
+  void setStartValue(VPValue *V) { setOperand(0, V); }
+
   /// Returns the step value of the induction.
   VPValue *getStepValue() { return getOperand(1); }
   const VPValue *getStepValue() const { return getOperand(1); }
 
   /// Returns the first defined value as TruncInst, if it is one or nullptr
   /// otherwise.
   TruncInst *getTruncInst() {
     return dyn_cast_or_null<TruncInst>(getVPValue(0)->getUnderlyingValue());