1 files changed, 13 insertions, 9 deletions
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 84ee8c0..11d8294 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -2854,14 +2854,18 @@ bool DependenceInfo::testMIV(const SCEV *Src, const SCEV *Dst,
          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 std::nullopt.
-static std::optional<APInt> getConstantPart(const SCEV *Expr) {
+/// Given a SCEVMulExpr, returns its first operand if its first operand is a
+/// constant and the product doesn't overflow in a signed sense. Otherwise,
+/// returns std::nullopt. For example, given (10 * X * Y)<nsw>, it returns 10.
+/// Notably, if it doesn't have nsw, the multiplication may overflow, and if
+/// so, it may not a multiple of 10.
+static std::optional<APInt> getConstanCoefficient(const SCEV *Expr) {
   if (const auto *Constant = dyn_cast<SCEVConstant>(Expr))
     return Constant->getAPInt();
   if (const auto *Product = dyn_cast<SCEVMulExpr>(Expr))
     if (const auto *Constant = dyn_cast<SCEVConstant>(Product->getOperand(0)))
-      return Constant->getAPInt();
+      if (Product->hasNoSignedWrap())
+        return Constant->getAPInt();
   return std::nullopt;
 }
 
@@ -2887,7 +2891,7 @@ bool DependenceInfo::accumulateCoefficientsGCD(const SCEV *Expr,
   if (AddRec->getLoop() == CurLoop) {
     CurLoopCoeff = Step;
   } else {
-    std::optional<APInt> ConstCoeff = getConstantPart(Step);
+    std::optional<APInt> ConstCoeff = getConstanCoefficient(Step);
 
     // If the coefficient is the product of a constant and other stuff, we can
     // use the constant in the GCD computation.
@@ -2940,7 +2944,7 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
     const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
     // If the coefficient is the product of a constant and other stuff,
     // we can use the constant in the GCD computation.
-    std::optional<APInt> ConstCoeff = getConstantPart(Coeff);
+    std::optional<APInt> ConstCoeff = getConstanCoefficient(Coeff);
     if (!ConstCoeff)
       return false;
     RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff->abs());
@@ -2958,7 +2962,7 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
     const SCEV *Coeff = AddRec->getStepRecurrence(*SE);
     // If the coefficient is the product of a constant and other stuff,
     // we can use the constant in the GCD computation.
-    std::optional<APInt> ConstCoeff = getConstantPart(Coeff);
+    std::optional<APInt> ConstCoeff = getConstanCoefficient(Coeff);
     if (!ConstCoeff)
       return false;
     RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ConstCoeff->abs());
@@ -2979,7 +2983,7 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
       } else if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Operand)) {
         // Search for constant operand to participate in GCD;
         // If none found; return false.
-        std::optional<APInt> ConstOp = getConstantPart(Product);
+        std::optional<APInt> ConstOp = getConstanCoefficient(Product);
         if (!ConstOp)
           return false;
         ExtraGCD = APIntOps::GreatestCommonDivisor(ExtraGCD, ConstOp->abs());
@@ -3032,7 +3036,7 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
     Delta = SE->getMinusSCEV(SrcCoeff, DstCoeff);
     // If the coefficient is the product of a constant and other stuff,
     // we can use the constant in the GCD computation.
-    std::optional<APInt> ConstCoeff = getConstantPart(Delta);
+    std::optional<APInt> ConstCoeff = getConstanCoefficient(Delta);
     if (!ConstCoeff)
       // The difference of the two coefficients might not be a product
       // or constant, in which case we give up on this direction.