Simplify (A & ~B) in icmp if A is a power of 2

The transform will execute like so:
(A & ~B) == 0 --> (A & B) != 0
(A & ~B) != 0 --> (A & B) == 0

llvm-svn: 179386

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 4d5fa8776e9..4c252c03d08 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2669,6 +2669,15 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   }
 
   { Value *A, *B;
+    // Transform (A & ~B) == 0 --> (A & B) != 0
+    // and       (A & ~B) != 0 --> (A & B) == 0
+    // if A is a power of 2.
+    if (match(Op0, m_And(m_Value(A), m_Not(m_Value(B)))) &&
+        match(Op1, m_Zero()) && isKnownToBeAPowerOfTwo(A) && I.isEquality())
+      return new ICmpInst(I.getInversePredicate(),
+                          Builder->CreateAnd(A, B),
+                          Op1);
+
     // ~x < ~y --> y < x
     // ~x < cst --> ~cst < x
     if (match(Op0, m_Not(m_Value(A)))) {