InstSimplify: shl nsw/nuw undef, %V -> undef

We can always choose an value for undef which might cause %V to shift
out an important bit except for one case, when %V is zero.

However, shl behaves like an identity function when the right hand side
is zero.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224405 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstSimplify/undef.ll

@@ -216,3 +216,31 @@ define i32 @test27() {
   %b = shl i32 0, undef
   ret i32 %b
 }
+
+; CHECK-LABEL: @test28
+; CHECK: ret i32 undef
+define i32 @test28(i32 %a) {
+  %b = shl nsw i32 undef, %a
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test29
+; CHECK: ret i32 undef
+define i32 @test29(i32 %a) {
+  %b = shl nuw i32 undef, %a
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test30
+; CHECK: ret i32 undef
+define i32 @test30(i32 %a) {
+  %b = shl nsw nuw i32 undef, %a
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test31
+; CHECK: ret i32 0
+define i32 @test31(i32 %a) {
+  %b = shl i32 undef, %a
+  ret i32 %b
+}