[InstCombine] Corrections in comments for division transformation

[aaronpuchert]

Summary

The actual code seems to be correct, but the comments were misleading.

[spatel]

LGTM.

[aaronpuchert]

Thanks for the review. Could you commit this for me (Aaron Puchert <[e-mail]>)?

lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

 /// True if the multiply can not be expressed in an int this size.
 static bool multiplyOverflows(const APInt &C1, const APInt &C2, APInt &Product,
                               bool IsSigned) {
   bool Overflow;
   Product = IsSigned ? C1.smul_ov(C2, Overflow) : C1.umul_ov(C2, Overflow);
   return Overflow;
 }
 
-/// True if C2 is a multiple of C1. Quotient contains C2/C1.
+/// True if C1 is a multiple of C2. Quotient contains C1/C2.
 static bool isMultiple(const APInt &C1, const APInt &C2, APInt &Quotient,
                        bool IsSigned) {
   assert(C1.getBitWidth() == C2.getBitWidth() && "Constant widths not equal");
 
   // Bail if we will divide by zero.
   if (C2.isNullValue())
     return false;
 
if (match(Op1, m_APInt(C2))) {
 
     if ((IsSigned && match(Op0, m_NSWShl(m_Value(X), m_APInt(C1))) &&
          *C1 != C1->getBitWidth() - 1) ||
         (!IsSigned && match(Op0, m_NUWShl(m_Value(X), m_APInt(C1))))) {
       APInt Quotient(C1->getBitWidth(), /*Val=*/0ULL, IsSigned);
       APInt C1Shifted = APInt::getOneBitSet(
           C1->getBitWidth(), static_cast<unsigned>(C1->getLimitedValue()));
 
-      // (X << C1) / C2 -> X / (C2 >> C1) if C2 is a multiple of C1.
+      // (X << C1) / C2 -> X / (C2 >> C1) if C2 is a multiple of 1 << C1.
       if (isMultiple(*C2, C1Shifted, Quotient, IsSigned)) {
         auto *BO = BinaryOperator::Create(I.getOpcode(), X,
                                           ConstantInt::get(Ty, Quotient));
         BO->setIsExact(I.isExact());
         return BO;
       }
 
-      // (X << C1) / C2 -> X * (C2 >> C1) if C1 is a multiple of C2.
+      // (X << C1) / C2 -> X * ((1 << C1) / C2) if 1 << C1 is a multiple of C2.
       if (isMultiple(C1Shifted, *C2, Quotient, IsSigned)) {
         auto *Mul = BinaryOperator::Create(Instruction::Mul, X,
                                            ConstantInt::get(Ty, Quotient));
         auto *OBO = cast<OverflowingBinaryOperator>(Op0);
         Mul->setHasNoUnsignedWrap(!IsSigned && OBO->hasNoUnsignedWrap());
         Mul->setHasNoSignedWrap(OBO->hasNoSignedWrap());
         return Mul;
       }