Auto merge of #122582 - scottmcm:swap-intrinsic-v2, r=oli-obk

Let codegen decide when to `mem::swap` with immediates

Making `libcore` decide this is silly; the backend has so much better information about when it's a good idea.

Thus this PR introduces a new `typed_swap` intrinsic with a fallback body, and replaces that fallback implementation when swapping immediates or scalar pairs.

r? oli-obk

Replaces #111744, and means we'll never need more libs PRs like #111803 or #107140

Author: bors

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

@@ -0,0 +1,19 @@
+#![feature(core_intrinsics)]
+#![feature(rustc_attrs)]
+
+use std::intrinsics::typed_swap;
+use std::ptr::addr_of_mut;
+
+fn invalid_array() {
+    let mut a = [1_u8; 100];
+    let mut b = [2_u8; 100];
+    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
+    }
+}
+
+fn main() {
+    invalid_array();
+}

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

@@ -0,0 +1,20 @@
+error: Undefined Behavior: constructing invalid value at [0]: encountered 0x02, but expected a boolean
+  --> $DIR/typed-swap-invalid-array.rs:LL:CC
+   |
+LL |         typed_swap(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
+   = note: BACKTRACE:
+   = note: inside `invalid_array` at $DIR/typed-swap-invalid-array.rs:LL:CC
+note: inside `main`
+  --> $DIR/typed-swap-invalid-array.rs:LL:CC
+   |
+LL |     invalid_array();
+   |     ^^^^^^^^^^^^^^^
+
+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

@@ -0,0 +1,19 @@
+#![feature(core_intrinsics)]
+#![feature(rustc_attrs)]
+
+use std::intrinsics::typed_swap;
+use std::ptr::addr_of_mut;
+
+fn invalid_scalar() {
+    let mut a = 1_u8;
+    let mut b = 2_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
+    }
+}
+
+fn main() {
+    invalid_scalar();
+}

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

@@ -0,0 +1,20 @@
+error: Undefined Behavior: constructing invalid value: encountered 0x02, but expected a boolean
+  --> $DIR/typed-swap-invalid-scalar.rs:LL:CC
+   |
+LL |         typed_swap(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
+   = note: BACKTRACE:
+   = note: inside `invalid_scalar` at $DIR/typed-swap-invalid-scalar.rs:LL:CC
+note: inside `main`
+  --> $DIR/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
+