From fe7fccff11dd78a126199a35b428537385d316a2 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sat, 11 Oct 2014 10:20:04 +0000
Subject: InstCombine: Don't fold (X <<s log(INT_MIN)) /s INT_MIN to X

Consider the case where X is 2.  (2 <<s 31)/s-2147483648 is zero but we
would fold to X.  Note that this is valid when we are in the unsigned
domain because we require NUW: 2 <<u 31 results in poison.

This fixes PR21245.

llvm-svn: 219568
---
 llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'llvm/lib/Transforms')

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 8d004f2a0a2..b09198afff2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -762,7 +762,8 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
           }
         }
 
-        if ((IsSigned && match(LHS, m_NSWShl(m_Value(X), m_APInt(C1)))) ||
+        if ((IsSigned && match(LHS, m_NSWShl(m_Value(X), m_APInt(C1))) &&
+             *C1 != C1->getBitWidth() - 1) ||
             (!IsSigned && match(LHS, m_NUWShl(m_Value(X), m_APInt(C1))))) {
           APInt Quotient(C1->getBitWidth(), /*Val=*/0ULL, IsSigned);
           APInt C1Shifted = APInt::getOneBitSet(
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