From: Nick Lewycky <nicholas@mxc.ca>
Date: Mon, 21 Mar 2011 21:40:32 +0000 (+0000)
Subject: Fix INT_MIN gotcha pointed out by Eli Friedman.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=1f7bc701b030f5b01553f306cc975eeac1e4d99b;p=oota-llvm.git

Fix INT_MIN gotcha pointed out by Eli Friedman.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128028 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index c36f68c2aeb..0f4bfb7b0d9 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -725,9 +725,10 @@ bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) {
       isPowerOfTwo(SI->getFalseValue(), TD, Depth);
 
   // An exact divide or right shift can only shift off zero bits, so the result
-  // is a power of two only if the first operand is a power of two.
-  if (match(V, m_Shr(m_Value(), m_Value())) ||
-      match(V, m_IDiv(m_Value(), m_Value()))) {
+  // is a power of two only if the first operand is a power of two and not
+  // copying a sign bit (sdiv int_min, 2).
+  if (match(V, m_LShr(m_Value(), m_Value())) ||
+      match(V, m_UDiv(m_Value(), m_Value()))) {
     BinaryOperator *BO = cast<BinaryOperator>(V);
     if (BO->isExact())
       return isPowerOfTwo(BO->getOperand(0), TD, Depth);