Auto merge of #134757 - RalfJung:const_swap, r=scottmcm

stabilize const_swap

libs-api FCP passed in rust-lang/rust#83163.

However, I only just realized that this actually involves an intrinsic. The intrinsic could be implemented entirely with existing stable const functionality, but we choose to make it a primitive to be able to detect more UB. So nominating for `@rust-lang/lang`  to make sure they are aware; I leave it up to them whether they want to FCP this.

While at it I also renamed the intrinsic to make the "nonoverlapping" constraint more clear.

Fixes #83163

Author: bors

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

@@ -1,7 +1,7 @@
 #![feature(core_intrinsics)]
 #![feature(rustc_attrs)]
 
-use std::intrinsics::typed_swap;
+use std::intrinsics::typed_swap_nonoverlapping;
 use std::ptr::addr_of_mut;
 
 fn invalid_array() {
@@ -10,7 +10,7 @@ fn invalid_array() {
     unsafe {
         let a = addr_of_mut!(a).cast::<[bool; 100]>();
         let b = addr_of_mut!(b).cast::<[bool; 100]>();
-        typed_swap(a, b); //~ERROR: constructing invalid value
+        typed_swap_nonoverlapping(a, b); //~ERROR: constructing invalid value
     }
 }
 

tests/fail/intrinsics/typed-swap-invalid-array.stderr

@@ -1,8 +1,8 @@
 error: Undefined Behavior: constructing invalid value at [0]: encountered 0x02, but expected a boolean
   --> tests/fail/intrinsics/typed-swap-invalid-array.rs:LL:CC
    |
-LL |         typed_swap(a, b);
-   |         ^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered 0x02, but expected a boolean
+LL |         typed_swap_nonoverlapping(a, b);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered 0x02, 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

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

@@ -1,8 +1,8 @@
 error: Undefined Behavior: constructing invalid value: encountered 0x02, but expected a boolean
   --> tests/fail/intrinsics/typed-swap-invalid-scalar.rs:LL:CC
    |
-LL |         typed_swap(a, b);
-   |         ^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x02, but expected a boolean
+LL |         typed_swap_nonoverlapping(a, b);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered 0x02, 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

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

@@ -1,16 +1,18 @@
+//@revisions: left right
 #![feature(core_intrinsics)]
 #![feature(rustc_attrs)]
 
-use std::intrinsics::typed_swap;
+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>();
-        typed_swap(a, b); //~ERROR: constructing invalid value
+        typed_swap_nonoverlapping(a, b); //~ERROR: constructing invalid value
     }
 }
 

tests/fail/intrinsics/typed-swap-overlap.rs

@@ -0,0 +1,13 @@
+#![feature(core_intrinsics)]
+#![feature(rustc_attrs)]
+
+use std::intrinsics::typed_swap_nonoverlapping;
+use std::ptr::addr_of_mut;
+
+fn main() {
+    let mut a = 0_u8;
+    unsafe {
+        let a = addr_of_mut!(a);
+        typed_swap_nonoverlapping(a, a); //~ERROR: called on overlapping ranges
+    }
+}

tests/fail/intrinsics/typed-swap-overlap.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: `copy_nonoverlapping` called on overlapping ranges
+  --> tests/fail/intrinsics/typed-swap-overlap.rs:LL:CC
+   |
+LL |         typed_swap_nonoverlapping(a, a);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `copy_nonoverlapping` called on overlapping ranges
+   |
+   = 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 `main` at tests/fail/intrinsics/typed-swap-overlap.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+