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Make core::slice::from_raw_parts[_mut] const

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This commit is contained in:
Maybe Waffle 2021-10-28 17:15:25 +03:00
parent 4e0d3973fa
commit 991a296ce7
2 changed files with 42 additions and 14 deletions
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1
library/core/src/lib.rs
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@ -105,6 +105,7 @@
#![feature(const_caller_location)]
#![feature(const_cell_into_inner)]
#![feature(const_discriminant)]
#![cfg_attr(not(bootstrap), feature(const_eval_select))]
#![feature(const_float_bits_conv)]
#![feature(const_float_classify)]
#![feature(const_fmt_arguments_new)]

55
library/core/src/slice/raw.rs
View file

@ -1,8 +1,6 @@
//! Free functions to create `&[T]` and `&mut [T]`.
use crate::array;
use crate::intrinsics::is_aligned_and_not_null;
use crate::mem;
use crate::ptr;
/// Forms a slice from a pointer and a length.
@ -85,12 +83,10 @@ use crate::ptr;
/// [`NonNull::dangling()`]: ptr::NonNull::dangling
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
debug_assert!(is_aligned_and_not_null(data), "attempt to create unaligned or null slice");
debug_assert!(
mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize,
"attempt to create slice covering at least half the address space"
);
#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "none")]
pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
debug_check_data_len(data, len);
// SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
unsafe { &*ptr::slice_from_raw_parts(data, len) }
}
@ -126,16 +122,47 @@ pub unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
/// [`NonNull::dangling()`]: ptr::NonNull::dangling
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
debug_assert!(is_aligned_and_not_null(data), "attempt to create unaligned or null slice");
debug_assert!(
mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize,
"attempt to create slice covering at least half the address space"
);
#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "none")]
pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
debug_check_data_len(data as _, len);
// SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
unsafe { &mut *ptr::slice_from_raw_parts_mut(data, len) }
}
// In debug builds checks that `data` pointer is aligned and non-null and that slice with given `len` would cover less than half the address space
#[cfg(all(not(bootstrap), debug_assertions))]
#[unstable(feature = "const_slice_from_raw_parts", issue = "none")]
#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "none")]
const fn debug_check_data_len<T>(data: *const T, len: usize) {
fn rt_check<T>(data: *const T) {
use crate::intrinsics::is_aligned_and_not_null;
assert!(is_aligned_and_not_null(data), "attempt to create unaligned or null slice");
}
const fn ctfe_check<T>(_data: *const T) {
// It's impossible to check alignment in const fn.
//
// CTFE engine checks that the pointer is aligned and not null.
}
// SAFETY:
// - `calling from_raw_parts[_mut]` with arguments that fail to fulfil checks made here is UB, so unless UB is already triggered this is noop
// - CTFE makes the same checks as `rt_check`, so behavior change is not observable due to compilation error
unsafe {
crate::intrinsics::const_eval_select((data,), ctfe_check, rt_check);
}
assert!(
crate::mem::size_of::<T>().saturating_mul(len) <= isize::MAX as usize,
"attempt to create slice covering at least half the address space"
);
}
#[cfg(not(all(not(bootstrap), debug_assertions)))]
const fn debug_check_data_len<T>(_data: *const T, _len: usize) {}
/// Converts a reference to T into a slice of length 1 (without copying).
#[stable(feature = "from_ref", since = "1.28.0")]
#[rustc_const_unstable(feature = "const_slice_from_ref", issue = "90206")]