[DependenceAnalysis] Refactor uses of getConstantPart. NFC.

[bcahoon]

Summary

Rather than checking for the SCEV type prior to calling getContantPart, perform the checks in the function. This reduces the number of places where the checks have been added.

This was a suggestion made during the review for http://reviews.llvm.org/D18718

[sanjoy]

lgtm with comments inline

lib/Analysis/DependenceAnalysis.cpp

2260

Use auto * here and below.

2263

Can you just check the first operand? Operands should be ordered by complexity, so if there is a SCEVConstant operand it should come first.

lib/Analysis/DependenceAnalysis.cpp

bool DependenceAnalysis::testMIV(const SCEV *Src,
   return gcdMIVtest(Src, Dst, Result) ||
     banerjeeMIVtest(Src, Dst, Loops, Result);
 }
 
 
 // Given a product, e.g., 10*X*Y, returns the first constant operand,
 // in this case 10. If there is no constant part, returns NULL.
 static
-const SCEVConstant *getConstantPart(const SCEVMulExpr *Product) {
-  for (unsigned Op = 0, Ops = Product->getNumOperands(); Op < Ops; Op++) {
-    if (const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Product->getOperand(Op)))
+const SCEVConstant *getConstantPart(const SCEV *Expr) {
+  if (const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Expr))
+    return Constant;
+  else if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Expr))
+    for (unsigned Op = 0, Ops = Product->getNumOperands(); Op < Ops; Op++)
+      if (const SCEVConstant *Constant =
+              dyn_cast<SCEVConstant>(Product->getOperand(Op)))
         return Constant;
-  }
   return nullptr;
 }
 
 
 //===----------------------------------------------------------------------===//
 // gcdMIVtest -
 // Tests an MIV subscript pair for dependence.
 // Returns true if any possible dependence is disproved.
bool DependenceAnalysis::gcdMIVtest(const SCEV *Src,
   // Examine Src coefficients.
   // Compute running GCD and record source constant.
   // Because we're looking for the constant at the end of the chain,
   // we can't quit the loop just because the GCD == 1.
   const SCEV *Coefficients = Src;
   while (const SCEVAddRecExpr *AddRec =
          dyn_cast<SCEVAddRecExpr>(Coefficients)) {
     const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
-    const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Coeff);
-    if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Coeff))
-      // If the coefficient is the product of a constant and other stuff,
-      // we can use the constant in the GCD computation.
-      Constant = getConstantPart(Product);
+    const SCEVConstant *Constant = getConstantPart(Coeff);
     if (!Constant)
       return false;
     APInt ConstCoeff = Constant->getAPInt();
     RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff.abs());
     Coefficients = AddRec->getStart();
   }
   const SCEV *SrcConst = Coefficients;
 
   // Examine Dst coefficients.
   // Compute running GCD and record destination constant.
   // Because we're looking for the constant at the end of the chain,
   // we can't quit the loop just because the GCD == 1.
   Coefficients = Dst;
   while (const SCEVAddRecExpr *AddRec =
          dyn_cast<SCEVAddRecExpr>(Coefficients)) {
     const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
-    const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Coeff);
-    if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Coeff))
-      // If the coefficient is the product of a constant and other stuff,
-      // we can use the constant in the GCD computation.
-      Constant = getConstantPart(Product);
+    const SCEVConstant *Constant = getConstantPart(Coeff);
     if (!Constant)
       return false;
     APInt ConstCoeff = Constant->getAPInt();
     RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff.abs());
     Coefficients = AddRec->getStart();
   }
   const SCEV *DstConst = Coefficients;
 
while (const SCEVAddRecExpr *AddRec =
     const SCEV *DstCoeff = SE->getMinusSCEV(SrcCoeff, SrcCoeff);
     const SCEV *Inner = Src;
     while (RunningGCD != 1 && isa<SCEVAddRecExpr>(Inner)) {
       AddRec = cast<SCEVAddRecExpr>(Inner);
       const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
       if (CurLoop == AddRec->getLoop())
         ; // SrcCoeff == Coeff
       else {
-        if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Coeff))
-          // If the coefficient is the product of a constant and other stuff,
-          // we can use the constant in the GCD computation.
-          Constant = getConstantPart(Product);
-        else
-          Constant = cast<SCEVConstant>(Coeff);
+        Constant = getConstantPart(Coeff);
         if (!Constant)
           return false;
         APInt ConstCoeff = Constant->getAPInt();
         RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff.abs());
       }
       Inner = AddRec->getStart();
     }
     Inner = Dst;
     while (RunningGCD != 1 && isa<SCEVAddRecExpr>(Inner)) {
       AddRec = cast<SCEVAddRecExpr>(Inner);
       const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
       if (CurLoop == AddRec->getLoop())
         DstCoeff = Coeff;
       else {
-        if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Coeff))
-          // If the coefficient is the product of a constant and other stuff,
-          // we can use the constant in the GCD computation.
-          Constant = getConstantPart(Product);
-        else
-          Constant = cast<SCEVConstant>(Coeff);
+        Constant = getConstantPart(Coeff);
         if (!Constant)
           return false;
         APInt ConstCoeff = Constant->getAPInt();
         RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff.abs());
       }
       Inner = AddRec->getStart();
     }
     Delta = SE->getMinusSCEV(SrcCoeff, DstCoeff);
-    if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Delta))
-      // If the coefficient is the product of a constant and other stuff,
-      // we can use the constant in the GCD computation.
-      Constant = getConstantPart(Product);
-    else if (isa<SCEVConstant>(Delta))
-      Constant = cast<SCEVConstant>(Delta);
-    else {
+    Constant = getConstantPart(Delta);
+    if (!Constant)
       // The difference of the two coefficients might not be a product
       // or constant, in which case we give up on this direction.
       continue;
-    }
-    if (!Constant)
-      continue;
     APInt ConstCoeff = Constant->getAPInt();
     RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff.abs());
     DEBUG(dbgs() << "\tRunningGCD = " << RunningGCD << "\n");
     if (RunningGCD != 0) {
       Remainder = ConstDelta.srem(RunningGCD);
       DEBUG(dbgs() << "\tRemainder = " << Remainder << "\n");
       if (Remainder != 0) {
         unsigned Level = mapSrcLoop(CurLoop);