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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53276 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 675f7ec57146f76f99546b59dbe799c4ccac9878..27af3c397a1685f2cd85a99314e13fb15636c889 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/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/test/Transforms/InstCombine/2008-07-08-ShiftOneAndOne.ll b/test/Transforms/InstCombine/2008-07-08-ShiftOneAndOne.ll
new file mode 100644 (file)
index 0000000..956b9a6
--- /dev/null
+++ b/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
+}