add test that checks overflows on arithmetic operators

src/test/ui/consts/const-int-arithmetic-overflow.rs

@@ -0,0 +1,26 @@
+// run-pass
+// compile-flags: -O
+#![allow(const_err)]
+
+// Make sure arithmetic unary/binary ops actually return the right result, even when overflowing.
+// We have to put them in `const fn` and turn on optimizations to avoid overflow checks.
+
+const fn add(x: i8, y: i8) -> i8 { x+y }
+const fn sub(x: i8, y: i8) -> i8 { x-y }
+const fn mul(x: i8, y: i8) -> i8 { x*y }
+// div and rem are always checked, so we cannot test their result in case of oveflow.
+const fn neg(x: i8) -> i8 { -x }
+
+fn main() {
+    const ADD_OFLOW: i8 = add(100, 100);
+    assert_eq!(ADD_OFLOW, -56);
+
+    const SUB_OFLOW: i8 = sub(100, -100);
+    assert_eq!(SUB_OFLOW, -56);
+
+    const MUL_OFLOW: i8 = mul(-100, -2);
+    assert_eq!(MUL_OFLOW, -56);
+
+    const NEG_OFLOW: i8 = neg(-128);
+    assert_eq!(NEG_OFLOW, -128);
+}