When checking that the necessary bits are zero in

order to reduce ((x<<30)>>24) to x<<6, check the
correct bits.  PR 8547.

llvm-svn: 118665

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 012d238729a..9f7d98ed794 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -131,9 +131,9 @@ static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift,
     // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't
     // profitable unless we know the and'd out bits are already zero.
     if (CI->getZExtValue() > NumBits) {
-      unsigned HighBits = CI->getZExtValue() - NumBits;
+      unsigned LowBits = TypeWidth - CI->getZExtValue();
       if (MaskedValueIsZero(I->getOperand(0),
-                            APInt::getHighBitsSet(TypeWidth, HighBits)))
+                       APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
         return true;
     }