Commit e8a900fc authored by Bill Wendling's avatar Bill Wendling
Browse files

Merging r155818: 

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r155818 | baldrick | 2012-04-30 04:56:58 -0700 (Mon, 30 Apr 2012) | 3 lines

Just mark the sign bit as known zero, rather than any other irrelevant bits
known zero in the LHS.  Fixes PR12541.

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llvm-svn: 155827
parent 2fe44613

llvm/lib/Analysis/ValueTracking.cpp

+1 −1
Original line number Diff line number Diff line
@@ -564,7 +564,7 @@ void llvm::ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne, 
                        Depth+1);

      // If it's known zero, our sign bit is also zero.

      if (LHSKnownZero.isNegative())

        KnownZero |= LHSKnownZero;

        KnownZero.setBit(BitWidth - 1);

    }



    break;

llvm/test/Transforms/InstCombine/2012-04-30-SRem.ll

0 → 100644
+12 −0
Original line number Diff line number Diff line 
; RUN: opt -instcombine -S < %s | FileCheck %s

; PR12541



define i32 @foo(i32 %x) {

  %y = xor i32 %x, 3

  %z = srem i32 1656690544, %y

  %sext = shl i32 %z, 24

  %s = ashr exact i32 %sext, 24

  ret i32 %s

; CHECK-NOT: and

; The shifts were wrongly being turned into an and with 112

}