Add new testcase for arithmetic shr of -1

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4069 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/shift.ll

@@ -37,3 +37,8 @@ uint %test6(uint %A) {
 	%B = shl uint %A, ubyte 1   ;; convert to an add instruction
 	ret uint %B
 }
+
+int %test7(ubyte %A) {
+	%B = shr int -1, ubyte %A   ;; Always equal to -1
+	ret int %B
+}