From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 15 Jul 2018 17:06:59 +0000 (+0000)
Subject: [InstCombine] Corrections in comments for division transformation (NFC)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=597deb9284417718d5e1a3cea1f173a78b99732e;p=llvm

[InstCombine] Corrections in comments for division transformation (NFC)

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

Patch by Aaron Puchert!

Differential Revision: https://reviews.llvm.org/D49276


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337131 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a539f870aa2..d6adbec02ac 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -628,7 +628,7 @@ static bool multiplyOverflows(const APInt &C1, const APInt &C2, APInt &Product,
   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");
@@ -714,7 +714,7 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
       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));
@@ -722,7 +722,7 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
         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));