1 files changed, 7 insertions, 1 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 1085be6..2862e42 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2884,7 +2884,13 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
       return XKnown.isNonZero() ||
              isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);
 
-    return KnownBits::mul(XKnown, YKnown).isNonZero();
+    // If there exists any subset of X (sX) and subset of Y (sY) s.t sX * sY is
+    // non-zero, then X * Y is non-zero. We can find sX and sY by just taking
+    // the the lowest known One of X and Y. If they are non-zero, the result
+    // must be non-zero. We can check if LSB(X) * LSB(Y) != 0 by doing
+    // X.CountLeadingZeros + Y.CountLeadingZeros < BitWidth.
+    return (XKnown.countMaxTrailingZeros() + YKnown.countMaxTrailingZeros()) <
+           BitWidth;
   }
   case Instruction::Select:
     // (C ? X : Y) != 0 if X != 0 and Y != 0.