Arithmetic compound assignment operators tests

test/libsolidity/smtCheckerTests/operators/compound_sub_array_index.sol

@@ -0,0 +1,15 @@
+pragma experimental SMTChecker;
+
+contract C
+{
+	uint[] array;
+	function f(uint x, uint p) public {
+		require(x < 100);
+		require(array[p] == 200);
+		array[p] -= array[p] - x;
+		assert(array[p] >= 0);
+		assert(array[p] < 90);
+	}
+}
+// ----
+// Warning: (201-222): Assertion violation happens here