Added a codegen test for a recent optimization for overflow-checks=on

src/test/codegen/integer-overflow.rs

@@ -0,0 +1,26 @@
+// no-system-llvm
+// compile-flags: -O -C overflow-checks=on
+
+#![crate_type = "lib"]
+
+
+pub struct S1<'a> {
+    data: &'a [u8],
+    position: usize,
+}
+
+// CHECK-LABEL: @slice_no_index_order
+#[no_mangle]
+pub fn slice_no_index_order<'a>(s: &'a mut S1, n: usize) -> &'a [u8] {
+    // CHECK-NOT: slice_index_order_fail
+    let d = &s.data[s.position..s.position+n];
+    s.position += n;
+    return d;
+}
+
+// CHECK-LABEL: @test_check
+#[no_mangle]
+pub fn test_check<'a>(s: &'a mut S1, x: usize, y: usize) -> &'a [u8] {
+    // CHECK: slice_index_order_fail
+    &s.data[x..y]
+}