From 40ccf16b92f20c3a21cef5e9a07285f4721cd545 Mon Sep 17 00:00:00 2001
From: Jingyue Wu <jingyue@google.com>
Date: Thu, 18 Jun 2015 03:35:57 +0000
Subject: [PATCH] [NFC] more comments in SLSR

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239984 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/StraightLineStrengthReduce.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp b/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
index 8e5cf46263e..f32769c2411 100644
--- a/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
@@ -632,6 +632,15 @@ void StraightLineStrengthReduce::rewriteCandidateWithBasis(
       // trivially dead.
       RecursivelyDeleteTriviallyDeadInstructions(Bump);
     } else {
+      // It's tempting to preserve nsw on Bump and/or Reduced. However, it's
+      // usually unsound, e.g.,
+      //
+      // X = (-2 +nsw 1) *nsw INT_MAX
+      // Y = (-2 +nsw 3) *nsw INT_MAX
+      //   =>
+      // Y = X + 2 * INT_MAX
+      //
+      // Neither + and * in the resultant expression are nsw.
       Reduced = Builder.CreateAdd(Basis.Ins, Bump);
     }
     break;
-- 
2.34.1