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Auto merge of #117905 - RalfJung:no-const-mut, r=lcnr

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revert stabilization of const_intrinsic_copy

`@rust-lang/wg-const-eval`  I don't know what we were thinking when we approved https://github.com/rust-lang/rust/pull/97276... const-eval isn't supposed to be able to mutate anything yet! It's also near impossible to actually call `copy` in const on stable since `&mut` expressions are generally unstable. However, there's one exception...

```rust
static mut INT: i32 = unsafe {
    let val = &mut [1]; // `&mut` on arrays is allowed in `static mut`
    (val as *mut [i32; 1]).copy_from(&[42], 1);
    val[0]
};

fn main() { unsafe {
    dbg!(INT);
} }
```

Inside `static mut`, we accept some `&mut` since ~forever, to make `static mut FOO: &mut [T] = &mut [...];` work. We reject any attempt to actually write to that mutable reference though... except for the `copy` functions.

I think we should revert stabilizing these functions that take `*mut`, and then re-stabilize them together with `ptr.write` once mutable references are stable.

(This will likely fail on PowerPC until https://github.com/rust-lang/stdarch/pull/1497 lands. But we'll need a crater run first anyway.)
This commit is contained in:
bors 2024-02-06 21:43:11 +00:00
commit 256b6fb19a
7 changed files with 18 additions and 13 deletions
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8
library/core/src/intrinsics.rs
View File

@ -2749,13 +2749,13 @@ pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -
#[doc(alias = "memcpy")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules]
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[rustc_diagnostic_item = "ptr_copy_nonoverlapping"]
pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
extern "rust-intrinsic" {
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[rustc_nounwind]
pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
}
@ -2845,13 +2845,13 @@ pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -
#[doc(alias = "memmove")]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_allowed_through_unstable_modules]
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[rustc_diagnostic_item = "ptr_copy"]
pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
extern "rust-intrinsic" {
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[rustc_nounwind]
fn copy<T>(src: *const T, dst: *mut T, count: usize);
}

1
library/core/src/lib.rs
View File

@ -135,6 +135,7 @@
#![feature(const_hint_assert_unchecked)]
#![feature(const_index_range_slice_index)]
#![feature(const_int_unchecked_arith)]
#![feature(const_intrinsic_copy)]
#![feature(const_intrinsic_forget)]
#![feature(const_ipv4)]
#![feature(const_ipv6)]

4
library/core/src/ptr/const_ptr.rs
View File

@ -1284,7 +1284,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy`] for safety concerns and examples.
///
/// [`ptr::copy`]: crate::ptr::copy()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@ -1304,7 +1304,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
///
/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces

7
library/core/src/ptr/mod.rs
View File

@ -1176,7 +1176,6 @@ macro_rules! attempt_swap_as_chunks {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
#[rustc_allow_const_fn_unstable(const_mut_refs, const_maybe_uninit_as_mut_ptr)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[rustc_diagnostic_item = "ptr_read"]
pub const unsafe fn read<T>(src: *const T) -> T {
@ -1294,7 +1293,11 @@ macro_rules! attempt_swap_as_chunks {
#[inline]
#[stable(feature = "ptr_unaligned", since = "1.17.0")]
#[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
#[rustc_allow_const_fn_unstable(const_mut_refs, const_maybe_uninit_as_mut_ptr)]
#[rustc_allow_const_fn_unstable(
const_mut_refs,
const_maybe_uninit_as_mut_ptr,
const_intrinsic_copy
)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[rustc_diagnostic_item = "ptr_read_unaligned"]
pub const unsafe fn read_unaligned<T>(src: *const T) -> T {

8
library/core/src/ptr/mut_ptr.rs
View File

@ -1385,7 +1385,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy`] for safety concerns and examples.
///
/// [`ptr::copy`]: crate::ptr::copy()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@ -1405,7 +1405,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
///
/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@ -1425,7 +1425,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy`] for safety concerns and examples.
///
/// [`ptr::copy`]: crate::ptr::copy()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@ -1445,7 +1445,7 @@ pub unsafe fn read_volatile(self) -> T
/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
///
/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
#[stable(feature = "pointer_methods", since = "1.26.0")]
#[inline(always)]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces

1
library/core/tests/lib.rs
View File

@ -14,6 +14,7 @@
#![feature(const_cell_into_inner)]
#![feature(const_hash)]
#![feature(const_heap)]
#![feature(const_intrinsic_copy)]
#![feature(const_maybe_uninit_as_mut_ptr)]
#![feature(const_nonnull_new)]
#![feature(const_pointer_is_aligned)]

2
tests/ui/consts/const-eval/raw-pointer-ub.rs
View File

@ -1,4 +1,4 @@
#![feature(const_mut_refs)]
#![feature(const_mut_refs, const_intrinsic_copy)]
const MISALIGNED_LOAD: () = unsafe {