1 files changed, 17 insertions, 3 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 3ba56bbe53e..b9be41840ff 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -922,10 +922,24 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *Cmp, ZExtInst &Zext,
     }
   }
 
-  // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
-  // It is also profitable to transform icmp eq into not(xor(A, B)) because that
-  // may lead to additional simplifications.
   if (Cmp->isEquality() && Zext.getType() == Cmp->getOperand(0)->getType()) {
+    // Test if a bit is clear/set using a shifted-one mask:
+    // zext (icmp eq (and X, (1 << ShAmt)), 0) --> and (lshr (not X), ShAmt), 1
+    // zext (icmp ne (and X, (1 << ShAmt)), 0) --> and (lshr X, ShAmt), 1
+    Value *X, *ShAmt;
+    if (Cmp->hasOneUse() && match(Cmp->getOperand(1), m_ZeroInt()) &&
+        match(Cmp->getOperand(0),
+              m_OneUse(m_c_And(m_Shl(m_One(), m_Value(ShAmt)), m_Value(X))))) {
+      if (Cmp->getPredicate() == ICmpInst::ICMP_EQ)
+        X = Builder.CreateNot(X);
+      Value *Lshr = Builder.CreateLShr(X, ShAmt);
+      Value *And1 = Builder.CreateAnd(Lshr, ConstantInt::get(X->getType(), 1));
+      return replaceInstUsesWith(Zext, And1);
+    }
+
+    // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
+    // It is also profitable to transform icmp eq into not(xor(A, B)) because
+    // that may lead to additional simplifications.
     if (IntegerType *ITy = dyn_cast<IntegerType>(Zext.getType())) {
       Value *LHS = Cmp->getOperand(0);
       Value *RHS = Cmp->getOperand(1);