From 43b40a4620c155c73ac71b48472ea2411d7c35da Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Tue, 4 Jan 2011 18:19:15 +0000
Subject: fix an off-by-one bug that caused a crash analyzing ashr's with huge
 shift amounts, PR8896

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122814 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'lib/Analysis/ValueTracking.cpp')

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6f58afe..e2d7e92 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -337,7 +337,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     // (ashr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
     if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
       // Compute the new bits that are at the top now.
-      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
+      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
       
       // Signed shift right.
       APInt Mask2(Mask.shl(ShiftAmt));
-- 
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