Fold ((1 << a) & 1) to (a == 0).

llvm-svn: 53276

2 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 675f7ec5714..27af3c397a1 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3473,6 +3473,18 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
         }
 
         break;
+
+      case Instruction::Shl:
+      case Instruction::LShr:
+        // (1 << x) & 1 --> zext(x == 0)
+        // (1 >> x) & 1 --> zext(x == 0)
+        if (AndRHSMask.getLimitedValue() == 1 && Op0LHS == AndRHS) {
+          Instruction *NewICmp = new ICmpInst(ICmpInst::ICMP_EQ, Op0RHS,
+                                           Constant::getNullValue(I.getType()));
+          InsertNewInstBefore(NewICmp, I);
+          return new ZExtInst(NewICmp, I.getType());
+        }
+        break;
       }
 
       if (ConstantInt *Op0CI = dyn_cast<ConstantInt>(Op0I->getOperand(1)))
diff --git a/llvm/test/Transforms/InstCombine/2008-07-08-ShiftOneAndOne.ll b/llvm/test/Transforms/InstCombine/2008-07-08-ShiftOneAndOne.ll
new file mode 100644
index 00000000000..956b9a6ae2e
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/2008-07-08-ShiftOneAndOne.ll
@@ -0,0 +1,10 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {icmp ne i32 \%a}
+; PR2330
+
+define i1 @foo(i32 %a) nounwind  {
+entry:
+	%tmp15 = shl i32 1, %a		; <i32> [#uses=1]
+	%tmp237 = and i32 %tmp15, 1		; <i32> [#uses=1]
+	%toBool = icmp eq i32 %tmp237, 0		; <i1> [#uses=1]
+	ret i1 %toBool
+}