ConstantFold: Shifting undef by zero results in undef

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224553 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp
index 31e962a..9176bf2 100644 (file)
--- a/lib/IR/ConstantFold.cpp
+++ b/lib/IR/ConstantFold.cpp
@@ -956,12 +956,18 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
       // X >>l undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef >>l 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // undef >>l X -> 0
       return Constant::getNullValue(C1->getType());
     case Instruction::AShr:
       // X >>a undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef >>a 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // TODO: undef >>a X -> undef if the shift is exact
       // undef >>a X -> 0
       return Constant::getNullValue(C1->getType());
@@ -969,6 +975,9 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
       // X << undef -> undef
       if (isa<UndefValue>(C2))
         return C2;
+      // undef << 0 -> undef
+      if (match(C2, m_Zero()))
+        return C1;
       // undef << X -> 0
       return Constant::getNullValue(C1->getType());
     }

diff --git a/test/Transforms/InstSimplify/undef.ll b/test/Transforms/InstSimplify/undef.ll
index bf64317..e8b49b6 100644 (file)
--- a/test/Transforms/InstSimplify/undef.ll
+++ b/test/Transforms/InstSimplify/undef.ll
@@ -244,3 +244,24 @@ define i32 @test31(i32 %a) {
   %b = shl i32 undef, %a
   ret i32 %b
 }
+
+; CHECK-LABEL: @test32
+; CHECK: ret i32 undef
+define i32 @test32(i32 %a) {
+  %b = shl i32 undef, 0
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test33
+; CHECK: ret i32 undef
+define i32 @test33(i32 %a) {
+  %b = ashr i32 undef, 0
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test34
+; CHECK: ret i32 undef
+define i32 @test34(i32 %a) {
+  %b = lshr i32 undef, 0
+  ret i32 %b
+}