[NFC][DA] Remove duplicate code in checkSrcSubscript and checkDstSubscript

[zhongduo]

Summary

[DA] Move common code in checkSrcSubscript and checkDstSubscript to a
new function checkSubscript. This avoids duplicate code and possible
out of sync in the future.

[zhongduo]

@sebpop and @jmolloy can you please review the change?

[sebpop]

This cleanup looks good to me.

llvm/include/llvm/Analysis/DependenceAnalysis.h

private:
 
     /// updateDirection - Update direction vector entry
     /// based on the current constraint.
     void updateDirection(Dependence::DVEntry &Level,
                          const Constraint &CurConstraint) const;
 
     bool tryDelinearize(Instruction *Src, Instruction *Dst,
                         SmallVectorImpl<Subscript> &Pair);
+
+  private:
+    /// checkSubscript - Helper function for checkSrcSubscript and
+    /// checkDstSubscript to avoid duplicate code
+    bool checkSubscript(const SCEV *Expr, const Loop *LoopNest,
+                        SmallBitVector &Loops, bool IsSrc);
   }; // class DependenceInfo
 
   /// AnalysisPass to compute dependence information in a function
   class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
   public:
     typedef DependenceInfo Result;
     Result run(Function &F, FunctionAnalysisManager &FAM);
 

llvm/lib/Analysis/DependenceAnalysis.cpp

if ((isa<SCEVZeroExtendExpr>(Src) && isa<SCEVZeroExtendExpr>(Dst)) ||
     const SCEV *DstCastOp = DstCast->getOperand();
     if (SrcCastOp->getType() == DstCastOp->getType()) {
       Pair->Src = SrcCastOp;
       Pair->Dst = DstCastOp;
     }
   }
 }
 
-
 // Examine the scev and return true iff it's linear.
 // Collect any loops mentioned in the set of "Loops".
-bool DependenceInfo::checkSrcSubscript(const SCEV *Src, const Loop *LoopNest,
-                                       SmallBitVector &Loops) {
-  const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Src);
+bool DependenceInfo::checkSubscript(const SCEV *Expr, const Loop *LoopNest,
+                                    SmallBitVector &Loops, bool IsSrc) {
+  const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Expr);
   if (!AddRec)
-    return isLoopInvariant(Src, LoopNest);
+    return isLoopInvariant(Expr, LoopNest);
   const SCEV *Start = AddRec->getStart();
   const SCEV *Step = AddRec->getStepRecurrence(*SE);
   const SCEV *UB = SE->getBackedgeTakenCount(AddRec->getLoop());
   if (!isa<SCEVCouldNotCompute>(UB)) {
     if (SE->getTypeSizeInBits(Start->getType()) <
         SE->getTypeSizeInBits(UB->getType())) {
       if (!AddRec->getNoWrapFlags())
         return false;
     }
   }
   if (!isLoopInvariant(Step, LoopNest))
     return false;
+  if (IsSrc)
     Loops.set(mapSrcLoop(AddRec->getLoop()));
-  return checkSrcSubscript(Start, LoopNest, Loops);
+  else
+    Loops.set(mapDstLoop(AddRec->getLoop()));
+  return checkSubscript(Start, LoopNest, Loops, IsSrc);
 }
 
-
+// Examine the scev and return true iff it's linear.
+// Collect any loops mentioned in the set of "Loops".
+bool DependenceInfo::checkSrcSubscript(const SCEV *Src, const Loop *LoopNest,
+                                       SmallBitVector &Loops) {
+  return checkSubscript(Src, LoopNest, Loops, true);
+}
 
 // Examine the scev and return true iff it's linear.
 // Collect any loops mentioned in the set of "Loops".
 bool DependenceInfo::checkDstSubscript(const SCEV *Dst, const Loop *LoopNest,
                                        SmallBitVector &Loops) {
-  const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Dst);
-  if (!AddRec)
-    return isLoopInvariant(Dst, LoopNest);
-  const SCEV *Start = AddRec->getStart();
-  const SCEV *Step = AddRec->getStepRecurrence(*SE);
-  const SCEV *UB = SE->getBackedgeTakenCount(AddRec->getLoop());
-  if (!isa<SCEVCouldNotCompute>(UB)) {
-    if (SE->getTypeSizeInBits(Start->getType()) <
-        SE->getTypeSizeInBits(UB->getType())) {
-      if (!AddRec->getNoWrapFlags())
-        return false;
-    }
-  }
-  if (!isLoopInvariant(Step, LoopNest))
-    return false;
-  Loops.set(mapDstLoop(AddRec->getLoop()));
-  return checkDstSubscript(Start, LoopNest, Loops);
+  return checkSubscript(Dst, LoopNest, Loops, false);
 }
 
 
 // Examines the subscript pair (the Src and Dst SCEVs)
 // and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
 // Collects the associated loops in a set.
 DependenceInfo::Subscript::ClassificationKind
 DependenceInfo::classifyPair(const SCEV *Src, const Loop *SrcLoopNest,