InstSimplify: [al]shr exact undef, %X -> undef
Exact shifts always keep the non-zero bits of their input. This means
it keeps it's undef bits.
llvm-svn: 223923
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 767b42b..1c5a917 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1387,8 +1387,10 @@
return V;
// undef >>l X -> 0
+ // undef >>l X -> undef (if it's exact)
if (match(Op0, m_Undef()))
- return Constant::getNullValue(Op0->getType());
+ return isExact ? UndefValue::get(Op0->getType())
+ : Constant::getNullValue(Op0->getType());
// (X << A) >> A -> X
Value *X;
@@ -1421,8 +1423,10 @@
return Op0;
// undef >>a X -> all ones
+ // undef >>a X -> undef (if it's exact)
if (match(Op0, m_Undef()))
- return Constant::getAllOnesValue(Op0->getType());
+ return isExact ? UndefValue::get(Op0->getType())
+ : Constant::getAllOnesValue(Op0->getType());
// (X << A) >> A -> X
Value *X;
diff --git a/llvm/test/Transforms/InstSimplify/undef.ll b/llvm/test/Transforms/InstSimplify/undef.ll
index a6ae7a9..3742d74 100644
--- a/llvm/test/Transforms/InstSimplify/undef.ll
+++ b/llvm/test/Transforms/InstSimplify/undef.ll
@@ -174,3 +174,17 @@
%b = sdiv i32 %a, 0
ret i32 %b
}
+
+; CHECK-LABEL: @test22
+; CHECK: ret i32 undef
+define i32 @test22(i32 %a) {
+ %b = ashr exact i32 undef, %a
+ ret i32 %b
+}
+
+; CHECK-LABEL: @test23
+; CHECK: ret i32 undef
+define i32 @test23(i32 %a) {
+ %b = lshr exact i32 undef, %a
+ ret i32 %b
+}