swap_typed_nonoverlapping: properly detect overlap even when swapping scalar values

Author: RalfJung

tests/fail/intrinsics/typed-swap-invalid-scalar.stderr renamed to tests/fail/intrinsics/typed-swap-invalid-scalar.left.stderr

@@ -0,0 +1,20 @@
+error: Undefined Behavior: constructing invalid value: encountered 0x03, but expected a boolean
+  --> tests/fail/intrinsics/typed-swap-invalid-scalar.rs:LL:CC
+   |
+LL |         typed_swap_nonoverlapping(a, b);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x03, but expected a boolean
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `invalid_scalar` at tests/fail/intrinsics/typed-swap-invalid-scalar.rs:LL:CC
+note: inside `main`
+  --> tests/fail/intrinsics/typed-swap-invalid-scalar.rs:LL:CC
+   |
+LL |     invalid_scalar();
+   |     ^^^^^^^^^^^^^^^^
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

tests/fail/intrinsics/typed-swap-invalid-scalar.right.stderr

@@ -1,12 +1,14 @@
+//@revisions: left right
 #![feature(core_intrinsics)]
 #![feature(rustc_attrs)]
 
 use std::intrinsics::typed_swap_nonoverlapping;
 use std::ptr::addr_of_mut;
 
 fn invalid_scalar() {
-    let mut a = 1_u8;
-    let mut b = 2_u8;
+    // We run the test twice, with either the left or the right side being invalid.
+    let mut a = if cfg!(left) { 2_u8} else { 1_u8 };
+    let mut b = if cfg!(right) { 3_u8} else { 1_u8 };
     unsafe {
         let a = addr_of_mut!(a).cast::<bool>();
         let b = addr_of_mut!(b).cast::<bool>();

tests/fail/intrinsics/typed-swap-invalid-scalar.rs

@@ -5,7 +5,7 @@ use std::intrinsics::typed_swap_nonoverlapping;
 use std::ptr::addr_of_mut;
 
 fn main() {
-    let mut a = [0_u8; 100];
+    let mut a = 0_u8;
     unsafe {
         let a = addr_of_mut!(a);
         typed_swap_nonoverlapping(a, a); //~ERROR: called on overlapping ranges