[InstCombine] Handle assume(X & Pow2 != 0) in computeKnownBits()

If we know that X & Pow2 != 0, then the bit at that position is
known one.

Differential Revision: https://reviews.llvm.org/D140851

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 7c37b89..e49183d 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -940,6 +940,14 @@ static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known,
           Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros());
       }
       break;
+    case ICmpInst::ICMP_NE: {
+      // assume (v & b != 0) where b is a power of 2
+      const APInt *BPow2;
+      if (match(Cmp, m_ICmp(Pred, m_c_And(m_V, m_Power2(BPow2)), m_Zero())) &&
+          isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+        Known.One |= BPow2->zextOrTrunc(BitWidth);
+      }
+    } break;
     }
   }