[DemandedBits] Fix computation of demanded bits for ICmps

The computation of ICmp demanded bits is independent of the individual operand being evaluated. We simply return a mask consisting of the minimum leading zeroes of both operands.

We were incorrectly passing "I" to ComputeKnownBits - this should be "UserI->getOperand(0)". In cases where we were evaluating the 1th operand, we were taking the minimum leading zeroes of it and itself.

This should fix PR26266.

llvm-svn: 258690

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/DemandedBits.cpp b/llvm/lib/Analysis/DemandedBits.cpp
index 912c5ceb754..143d0b79f18 100644
--- a/llvm/lib/Analysis/DemandedBits.cpp
+++ b/llvm/lib/Analysis/DemandedBits.cpp
@@ -244,7 +244,7 @@ void DemandedBits::determineLiveOperandBits(
     break;
   case Instruction::ICmp:
     // Count the number of leading zeroes in each operand.
-    ComputeKnownBits(BitWidth, I, UserI->getOperand(1));
+    ComputeKnownBits(BitWidth, UserI->getOperand(0), UserI->getOperand(1));
     auto NumLeadingZeroes = std::min(KnownZero.countLeadingOnes(),
                                      KnownZero2.countLeadingOnes());
     AB = ~APInt::getHighBitsSet(BitWidth, NumLeadingZeroes);