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Rollup merge of #132423 - RalfJung:const-eval-align-offset, r=dtolnay

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remove const-support for align_offset and is_aligned

As part of the recent discussion to stabilize `ptr.is_null()` in const context, the general vibe was that it's okay for a const function to panic when the same operation would work at runtime (that's just a case of "dynamically detecting that something is not supported as a const operation"), but it is *not* okay for a const function to just return a different result.

Following that, `is_aligned` and `is_aligned_to` have their const status revoked in this PR, since they do return actively wrong results at const time. In the future we can consider having a new intrinsic or so that can check whether a pointer is "guaranteed to be aligned", but the current implementation based on `align_offset` does not have the behavior we want.

In fact `align_offset` itself behaves quite strangely in const, and that support needs a bunch of special hacks. That doesn't seem worth it. Instead, the users that can fall back to a different implementation should just use const_eval_select directly, and everything else should not be made const-callable. So this PR does exactly that, and entirely removes const support for align_offset.

Closes some tracking issues by removing the associated features:
Closes https://github.com/rust-lang/rust/issues/90962
Closes https://github.com/rust-lang/rust/issues/104203

Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
This commit is contained in:
Jubilee 2024-11-03 20:08:13 -08:00 committed by GitHub
commit 3313e760d0
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16 changed files with 185 additions and 1022 deletions
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3
compiler/rustc_const_eval/messages.ftl
View File

@ -1,9 +1,6 @@
const_eval_address_space_full =
there are no more free addresses in the address space
const_eval_align_offset_invalid_align =
`align_offset` called with non-power-of-two align: {$target_align}
const_eval_alignment_check_failed =
{$msg ->
[AccessedPtr] accessing memory

88
compiler/rustc_const_eval/src/const_eval/machine.rs
View File

@ -1,7 +1,6 @@
use std::borrow::{Borrow, Cow};
use std::fmt;
use std::hash::Hash;
use std::ops::ControlFlow;
use rustc_abi::{Align, ExternAbi, Size};
use rustc_ast::Mutability;
@ -10,7 +9,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{self as hir, CRATE_HIR_ID, LangItem};
use rustc_middle::mir::AssertMessage;
use rustc_middle::query::TyCtxtAt;
use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::{bug, mir};
use rustc_span::Span;
@ -22,9 +21,9 @@ use crate::errors::{LongRunning, LongRunningWarn};
use crate::fluent_generated as fluent;
use crate::interpret::{
self, AllocId, AllocRange, ConstAllocation, CtfeProvenance, FnArg, Frame, GlobalAlloc, ImmTy,
InterpCx, InterpResult, MPlaceTy, OpTy, Pointer, PointerArithmetic, RangeSet, Scalar,
StackPopCleanup, compile_time_machine, interp_ok, throw_exhaust, throw_inval, throw_ub,
throw_ub_custom, throw_unsup, throw_unsup_format,
InterpCx, InterpResult, MPlaceTy, OpTy, Pointer, RangeSet, Scalar, compile_time_machine,
interp_ok, throw_exhaust, throw_inval, throw_ub, throw_ub_custom, throw_unsup,
throw_unsup_format,
};
/// When hitting this many interpreted terminators we emit a deny by default lint
@ -226,8 +225,8 @@ impl<'tcx> CompileTimeInterpCx<'tcx> {
&mut self,
instance: ty::Instance<'tcx>,
args: &[FnArg<'tcx>],
dest: &MPlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
_dest: &MPlaceTy<'tcx>,
_ret: Option<mir::BasicBlock>,
) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
let def_id = instance.def_id();
@ -259,85 +258,10 @@ impl<'tcx> CompileTimeInterpCx<'tcx> {
);
return interp_ok(Some(new_instance));
} else if self.tcx.is_lang_item(def_id, LangItem::AlignOffset) {
let args = self.copy_fn_args(args);
// For align_offset, we replace the function call if the pointer has no address.
match self.align_offset(instance, &args, dest, ret)? {
ControlFlow::Continue(()) => return interp_ok(Some(instance)),
ControlFlow::Break(()) => return interp_ok(None),
}
}
interp_ok(Some(instance))
}
/// `align_offset(ptr, target_align)` needs special handling in const eval, because the pointer
/// may not have an address.
///
/// If `ptr` does have a known address, then we return `Continue(())` and the function call should
/// proceed as normal.
///
/// If `ptr` doesn't have an address, but its underlying allocation's alignment is at most
/// `target_align`, then we call the function again with an dummy address relative to the
/// allocation.
///
/// If `ptr` doesn't have an address and `target_align` is stricter than the underlying
/// allocation's alignment, then we return `usize::MAX` immediately.
fn align_offset(
&mut self,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
dest: &MPlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
) -> InterpResult<'tcx, ControlFlow<()>> {
assert_eq!(args.len(), 2);
let ptr = self.read_pointer(&args[0])?;
let target_align = self.read_scalar(&args[1])?.to_target_usize(self)?;
if !target_align.is_power_of_two() {
throw_ub_custom!(
fluent::const_eval_align_offset_invalid_align,
target_align = target_align,
);
}
match self.ptr_try_get_alloc_id(ptr, 0) {
Ok((alloc_id, offset, _extra)) => {
let (_size, alloc_align, _kind) = self.get_alloc_info(alloc_id);
if target_align <= alloc_align.bytes() {
// Extract the address relative to the allocation base that is definitely
// sufficiently aligned and call `align_offset` again.
let addr = ImmTy::from_uint(offset.bytes(), args[0].layout).into();
let align = ImmTy::from_uint(target_align, args[1].layout).into();
let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
// Push the stack frame with our own adjusted arguments.
self.init_stack_frame(
instance,
self.load_mir(instance.def, None)?,
fn_abi,
&[FnArg::Copy(addr), FnArg::Copy(align)],
/* with_caller_location = */ false,
dest,
StackPopCleanup::Goto { ret, unwind: mir::UnwindAction::Unreachable },
)?;
interp_ok(ControlFlow::Break(()))
} else {
// Not alignable in const, return `usize::MAX`.
let usize_max = Scalar::from_target_usize(self.target_usize_max(), self);
self.write_scalar(usize_max, dest)?;
self.return_to_block(ret)?;
interp_ok(ControlFlow::Break(()))
}
}
Err(_addr) => {
// The pointer has an address, continue with function call.
interp_ok(ControlFlow::Continue(()))
}
}
}
/// See documentation on the `ptr_guaranteed_cmp` intrinsic.
fn guaranteed_cmp(&mut self, a: Scalar, b: Scalar) -> InterpResult<'tcx, u8> {
interp_ok(match (a, b) {

3
compiler/rustc_hir/src/lang_items.rs
View File

@ -348,9 +348,6 @@ language_item_table! {
MaybeUninit, sym::maybe_uninit, maybe_uninit, Target::Union, GenericRequirement::None;
/// Align offset for stride != 1; must not panic.
AlignOffset, sym::align_offset, align_offset_fn, Target::Fn, GenericRequirement::None;
Termination, sym::termination, termination, Target::Trait, GenericRequirement::None;
Try, sym::Try, try_trait, Target::Trait, GenericRequirement::None;

1
compiler/rustc_span/src/symbol.rs
View File

@ -378,7 +378,6 @@ symbols! {
aggregate_raw_ptr,
alias,
align,
align_offset,
alignment,
all,
alloc,

2
library/core/src/lib.rs
View File

@ -112,7 +112,6 @@
#![feature(asm_experimental_arch)]
#![feature(const_align_of_val)]
#![feature(const_align_of_val_raw)]
#![feature(const_align_offset)]
#![feature(const_alloc_layout)]
#![feature(const_black_box)]
#![feature(const_char_encode_utf16)]
@ -123,7 +122,6 @@
#![feature(const_nonnull_new)]
#![feature(const_option_ext)]
#![feature(const_pin_2)]
#![feature(const_pointer_is_aligned)]
#![feature(const_ptr_is_null)]
#![feature(const_ptr_sub_ptr)]
#![feature(const_raw_ptr_comparison)]

192
library/core/src/ptr/const_ptr.rs
View File

@ -1358,15 +1358,6 @@ impl<T: ?Sized> *const T {
/// beyond the allocation that the pointer points into. It is up to the caller to ensure that
/// the returned offset is correct in all terms other than alignment.
///
/// When this is called during compile-time evaluation (which is unstable), the implementation
/// may return `usize::MAX` in cases where that can never happen at runtime. This is because the
/// actual alignment of pointers is not known yet during compile-time, so an offset with
/// guaranteed alignment can sometimes not be computed. For example, a buffer declared as `[u8;
/// N]` might be allocated at an odd or an even address, but at compile-time this is not yet
/// known, so the execution has to be correct for either choice. It is therefore impossible to
/// find an offset that is guaranteed to be 2-aligned. (This behavior is subject to change, as usual
/// for unstable APIs.)
///
/// # Panics
///
/// The function panics if `align` is not a power-of-two.
@ -1395,8 +1386,7 @@ impl<T: ?Sized> *const T {
#[must_use]
#[inline]
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
pub const fn align_offset(self, align: usize) -> usize
pub fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
@ -1431,94 +1421,10 @@ impl<T: ?Sized> *const T {
/// assert!(ptr.is_aligned());
/// assert!(!ptr.wrapping_byte_add(1).is_aligned());
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// is never aligned if cast to a type with a stricter alignment than the reference's
/// underlying allocation.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let data = AlignedI32(42);
/// let ptr = &data as *const AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(!ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
/// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.cast::<AlignedI64>().is_aligned(),
/// runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let ptr = 40 as *const AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // For pointers with a known address, runtime and compiletime behavior are identical.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[stable(feature = "pointer_is_aligned", since = "1.79.0")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned(self) -> bool
pub fn is_aligned(self) -> bool
where
T: Sized,
{
@ -1555,105 +1461,15 @@ impl<T: ?Sized> *const T {
///
/// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// cannot be stricter aligned than the reference's underlying allocation.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// const _: () = {
/// let data = AlignedI32(42);
/// let ptr = &data as *const AlignedI32;
///
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
///
/// // At compiletime, we know for sure that the pointer isn't aligned to 8.
/// assert!(!ptr.is_aligned_to(8));
/// assert!(!ptr.wrapping_add(1).is_aligned_to(8));
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
/// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.is_aligned_to(8),
/// runtime_ptr.wrapping_add(1).is_aligned_to(8),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// const _: () = {
/// let ptr = 40 as *const u8;
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
/// assert!(ptr.is_aligned_to(8));
/// assert!(!ptr.is_aligned_to(16));
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[unstable(feature = "pointer_is_aligned_to", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned_to(self, align: usize) -> bool {
pub fn is_aligned_to(self, align: usize) -> bool {
if !align.is_power_of_two() {
panic!("is_aligned_to: align is not a power-of-two");
}
#[inline]
fn runtime_impl(ptr: *const (), align: usize) -> bool {
ptr.addr() & (align - 1) == 0
}
#[inline]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
const fn const_impl(ptr: *const (), align: usize) -> bool {
// We can't use the address of `self` in a `const fn`, so we use `align_offset` instead.
ptr.align_offset(align) == 0
}
// The cast to `()` is used to
// 1. deal with fat pointers; and
// 2. ensure that `align_offset` (in `const_impl`) doesn't actually try to compute an offset.
const_eval_select((self.cast::<()>(), align), const_impl, runtime_impl)
self.addr() & (align - 1) == 0
}
}

10
library/core/src/ptr/mod.rs
View File

@ -1852,9 +1852,7 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
///
/// Any questions go to @nagisa.
#[allow(ptr_to_integer_transmute_in_consts)]
#[lang = "align_offset"]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
pub(crate) const unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
// FIXME(#75598): Direct use of these intrinsics improves codegen significantly at opt-level <=
// 1, where the method versions of these operations are not inlined.
use intrinsics::{
@ -1915,11 +1913,7 @@ pub(crate) const unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usiz
let stride = mem::size_of::<T>();
// SAFETY: This is just an inlined `p.addr()` (which is not
// a `const fn` so we cannot call it).
// During const eval, we hook this function to ensure that the pointer never
// has provenance, making this sound.
let addr: usize = unsafe { mem::transmute(p) };
let addr: usize = p.addr();
// SAFETY: `a` is a power-of-two, therefore non-zero.
let a_minus_one = unsafe { unchecked_sub(a, 1) };

186
library/core/src/ptr/mut_ptr.rs
View File

@ -1,6 +1,5 @@
use super::*;
use crate::cmp::Ordering::{Equal, Greater, Less};
use crate::intrinsics::const_eval_select;
use crate::mem::SizedTypeProperties;
use crate::slice::{self, SliceIndex};
@ -1636,8 +1635,7 @@ impl<T: ?Sized> *mut T {
#[must_use]
#[inline]
#[stable(feature = "align_offset", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
pub const fn align_offset(self, align: usize) -> usize
pub fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
@ -1675,95 +1673,10 @@ impl<T: ?Sized> *mut T {
/// assert!(ptr.is_aligned());
/// assert!(!ptr.wrapping_byte_add(1).is_aligned());
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// is never aligned if cast to a type with a stricter alignment than the reference's
/// underlying allocation.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(!ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// // Also, note that mutable references are not allowed in the final value of constants.
/// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
/// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.cast::<AlignedI64>().is_aligned(),
/// runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let ptr = 40 as *mut AlignedI32;
/// assert!(ptr.is_aligned());
///
/// // For pointers with a known address, runtime and compiletime behavior are identical.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
/// assert!(ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[stable(feature = "pointer_is_aligned", since = "1.79.0")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned(self) -> bool
pub fn is_aligned(self) -> bool
where
T: Sized,
{
@ -1800,106 +1713,15 @@ impl<T: ?Sized> *mut T {
///
/// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// cannot be stricter aligned than the reference's underlying allocation.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// const _: () = {
/// let mut data = AlignedI32(42);
/// let ptr = &mut data as *mut AlignedI32;
///
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
///
/// // At compiletime, we know for sure that the pointer isn't aligned to 8.
/// assert!(!ptr.is_aligned_to(8));
/// assert!(!ptr.wrapping_add(1).is_aligned_to(8));
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// // Also, note that mutable references are not allowed in the final value of constants.
/// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
/// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.is_aligned_to(8),
/// runtime_ptr.wrapping_add(1).is_aligned_to(8),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// const _: () = {
/// let ptr = 40 as *mut u8;
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
/// assert!(ptr.is_aligned_to(8));
/// assert!(!ptr.is_aligned_to(16));
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[must_use]
#[inline]
#[unstable(feature = "pointer_is_aligned_to", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned_to(self, align: usize) -> bool {
pub fn is_aligned_to(self, align: usize) -> bool {
if !align.is_power_of_two() {
panic!("is_aligned_to: align is not a power-of-two");
}
#[inline]
fn runtime_impl(ptr: *mut (), align: usize) -> bool {
ptr.addr() & (align - 1) == 0
}
#[inline]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
const fn const_impl(ptr: *mut (), align: usize) -> bool {
// We can't use the address of `self` in a `const fn`, so we use `align_offset` instead.
ptr.align_offset(align) == 0
}
// The cast to `()` is used to
// 1. deal with fat pointers; and
// 2. ensure that `align_offset` (in `const_impl`) doesn't actually try to compute an offset.
const_eval_select((self.cast::<()>(), align), const_impl, runtime_impl)
self.addr() & (align - 1) == 0
}
}

170
library/core/src/ptr/non_null.rs
View File

@ -1192,8 +1192,7 @@ impl<T: ?Sized> NonNull<T> {
#[inline]
#[must_use]
#[stable(feature = "non_null_convenience", since = "1.80.0")]
#[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
pub const fn align_offset(self, align: usize) -> usize
pub fn align_offset(self, align: usize) -> usize
where
T: Sized,
{
@ -1224,98 +1223,10 @@ impl<T: ?Sized> NonNull<T> {
/// assert!(ptr.is_aligned());
/// assert!(!NonNull::new(ptr.as_ptr().wrapping_byte_add(1)).unwrap().is_aligned());
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// is never aligned if cast to a type with a stricter alignment than the reference's
/// underlying allocation.
///
/// ```
/// #![feature(const_nonnull_new)]
/// #![feature(const_pointer_is_aligned)]
/// use std::ptr::NonNull;
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let data = [AlignedI32(42), AlignedI32(42)];
/// let ptr = NonNull::<AlignedI32>::new(&data[0] as *const _ as *mut _).unwrap();
/// assert!(ptr.is_aligned());
///
/// // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = unsafe { ptr.add(1).cast::<AlignedI64>() };
/// assert!(!ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
/// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.cast::<AlignedI64>().is_aligned(),
/// runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(const_pointer_is_aligned)]
/// #![feature(const_nonnull_new)]
/// use std::ptr::NonNull;
///
/// // On some platforms, the alignment of primitives is less than their size.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
/// #[repr(align(8))]
/// struct AlignedI64(i64);
///
/// const _: () = {
/// let ptr = NonNull::new(40 as *mut AlignedI32).unwrap();
/// assert!(ptr.is_aligned());
///
/// // For pointers with a known address, runtime and compiletime behavior are identical.
/// let ptr1 = ptr.cast::<AlignedI64>();
/// let ptr2 = NonNull::new(ptr.as_ptr().wrapping_add(1)).unwrap().cast::<AlignedI64>();
/// assert!(ptr1.is_aligned());
/// assert!(!ptr2.is_aligned());
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[inline]
#[must_use]
#[stable(feature = "pointer_is_aligned", since = "1.79.0")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned(self) -> bool
pub fn is_aligned(self) -> bool
where
T: Sized,
{
@ -1352,85 +1263,10 @@ impl<T: ?Sized> NonNull<T> {
///
/// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
/// ```
///
/// # At compiletime
/// **Note: Alignment at compiletime is experimental and subject to change. See the
/// [tracking issue] for details.**
///
/// At compiletime, the compiler may not know where a value will end up in memory.
/// Calling this function on a pointer created from a reference at compiletime will only
/// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
/// cannot be stricter aligned than the reference's underlying allocation.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// const _: () = {
/// let data = AlignedI32(42);
/// let ptr = &data as *const AlignedI32;
///
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
///
/// // At compiletime, we know for sure that the pointer isn't aligned to 8.
/// assert!(!ptr.is_aligned_to(8));
/// assert!(!ptr.wrapping_add(1).is_aligned_to(8));
/// };
/// ```
///
/// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
/// pointer is aligned, even if the compiletime pointer wasn't aligned.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// // On some platforms, the alignment of i32 is less than 4.
/// #[repr(align(4))]
/// struct AlignedI32(i32);
///
/// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
/// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
/// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
/// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
///
/// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
/// let runtime_ptr = COMPTIME_PTR;
/// assert_ne!(
/// runtime_ptr.is_aligned_to(8),
/// runtime_ptr.wrapping_add(1).is_aligned_to(8),
/// );
/// ```
///
/// If a pointer is created from a fixed address, this function behaves the same during
/// runtime and compiletime.
///
/// ```
/// #![feature(pointer_is_aligned_to)]
/// #![feature(const_pointer_is_aligned)]
///
/// const _: () = {
/// let ptr = 40 as *const u8;
/// assert!(ptr.is_aligned_to(1));
/// assert!(ptr.is_aligned_to(2));
/// assert!(ptr.is_aligned_to(4));
/// assert!(ptr.is_aligned_to(8));
/// assert!(!ptr.is_aligned_to(16));
/// };
/// ```
///
/// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
#[inline]
#[must_use]
#[unstable(feature = "pointer_is_aligned_to", issue = "96284")]
#[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
pub const fn is_aligned_to(self, align: usize) -> bool {
pub fn is_aligned_to(self, align: usize) -> bool {
self.pointer.is_aligned_to(align)
}
}

157
library/core/src/slice/ascii.rs
View File

@ -3,6 +3,7 @@
use core::ascii::EscapeDefault;
use crate::fmt::{self, Write};
use crate::intrinsics::const_eval_select;
use crate::{ascii, iter, mem, ops};
#[cfg(not(test))]
@ -346,89 +347,93 @@ pub const fn is_ascii_simple(mut bytes: &[u8]) -> bool {
/// If any of these loads produces something for which `contains_nonascii`
/// (above) returns true, then we know the answer is false.
#[inline]
#[rustc_allow_const_fn_unstable(const_raw_ptr_comparison, const_pointer_is_aligned)] // only in a debug assertion
#[rustc_allow_const_fn_unstable(const_align_offset)] // behavior does not change when `align_offset` fails
#[rustc_allow_const_fn_unstable(const_eval_select)] // fallback impl has same behavior
const fn is_ascii(s: &[u8]) -> bool {
const USIZE_SIZE: usize = mem::size_of::<usize>();
// The runtime version behaves the same as the compiletime version, it's
// just more optimized.
return const_eval_select((s,), compiletime, runtime);
let len = s.len();
let align_offset = s.as_ptr().align_offset(USIZE_SIZE);
// If we wouldn't gain anything from the word-at-a-time implementation, fall
// back to a scalar loop.
//
// We also do this for architectures where `size_of::<usize>()` isn't
// sufficient alignment for `usize`, because it's a weird edge case.
if len < USIZE_SIZE || len < align_offset || USIZE_SIZE < mem::align_of::<usize>() {
return is_ascii_simple(s);
const fn compiletime(s: &[u8]) -> bool {
is_ascii_simple(s)
}
// We always read the first word unaligned, which means `align_offset` is
// 0, we'd read the same value again for the aligned read.
let offset_to_aligned = if align_offset == 0 { USIZE_SIZE } else { align_offset };
#[inline]
fn runtime(s: &[u8]) -> bool {
const USIZE_SIZE: usize = mem::size_of::<usize>();
let start = s.as_ptr();
// SAFETY: We verify `len < USIZE_SIZE` above.
let first_word = unsafe { (start as *const usize).read_unaligned() };
let len = s.len();
let align_offset = s.as_ptr().align_offset(USIZE_SIZE);
if contains_nonascii(first_word) {
return false;
}
// We checked this above, somewhat implicitly. Note that `offset_to_aligned`
// is either `align_offset` or `USIZE_SIZE`, both of are explicitly checked
// above.
debug_assert!(offset_to_aligned <= len);
// SAFETY: word_ptr is the (properly aligned) usize ptr we use to read the
// middle chunk of the slice.
let mut word_ptr = unsafe { start.add(offset_to_aligned) as *const usize };
// `byte_pos` is the byte index of `word_ptr`, used for loop end checks.
let mut byte_pos = offset_to_aligned;
// Paranoia check about alignment, since we're about to do a bunch of
// unaligned loads. In practice this should be impossible barring a bug in
// `align_offset` though.
// While this method is allowed to spuriously fail in CTFE, if it doesn't
// have alignment information it should have given a `usize::MAX` for
// `align_offset` earlier, sending things through the scalar path instead of
// this one, so this check should pass if it's reachable.
debug_assert!(word_ptr.is_aligned_to(mem::align_of::<usize>()));
// Read subsequent words until the last aligned word, excluding the last
// aligned word by itself to be done in tail check later, to ensure that
// tail is always one `usize` at most to extra branch `byte_pos == len`.
while byte_pos < len - USIZE_SIZE {
// Sanity check that the read is in bounds
debug_assert!(byte_pos + USIZE_SIZE <= len);
// And that our assumptions about `byte_pos` hold.
debug_assert!(matches!(
word_ptr.cast::<u8>().guaranteed_eq(start.wrapping_add(byte_pos)),
// These are from the same allocation, so will hopefully always be
// known to match even in CTFE, but if it refuses to compare them
// that's ok since it's just a debug check anyway.
None | Some(true),
));
// SAFETY: We know `word_ptr` is properly aligned (because of
// `align_offset`), and we know that we have enough bytes between `word_ptr` and the end
let word = unsafe { word_ptr.read() };
if contains_nonascii(word) {
return false;
// If we wouldn't gain anything from the word-at-a-time implementation, fall
// back to a scalar loop.
//
// We also do this for architectures where `size_of::<usize>()` isn't
// sufficient alignment for `usize`, because it's a weird edge case.
if len < USIZE_SIZE || len < align_offset || USIZE_SIZE < mem::align_of::<usize>() {
return is_ascii_simple(s);
}
byte_pos += USIZE_SIZE;
// SAFETY: We know that `byte_pos <= len - USIZE_SIZE`, which means that
// after this `add`, `word_ptr` will be at most one-past-the-end.
word_ptr = unsafe { word_ptr.add(1) };
// We always read the first word unaligned, which means `align_offset` is
// 0, we'd read the same value again for the aligned read.
let offset_to_aligned = if align_offset == 0 { USIZE_SIZE } else { align_offset };
let start = s.as_ptr();
// SAFETY: We verify `len < USIZE_SIZE` above.
let first_word = unsafe { (start as *const usize).read_unaligned() };
if contains_nonascii(first_word) {
return false;
}
// We checked this above, somewhat implicitly. Note that `offset_to_aligned`
// is either `align_offset` or `USIZE_SIZE`, both of are explicitly checked
// above.
debug_assert!(offset_to_aligned <= len);
// SAFETY: word_ptr is the (properly aligned) usize ptr we use to read the
// middle chunk of the slice.
let mut word_ptr = unsafe { start.add(offset_to_aligned) as *const usize };
// `byte_pos` is the byte index of `word_ptr`, used for loop end checks.
let mut byte_pos = offset_to_aligned;
// Paranoia check about alignment, since we're about to do a bunch of
// unaligned loads. In practice this should be impossible barring a bug in
// `align_offset` though.
// While this method is allowed to spuriously fail in CTFE, if it doesn't
// have alignment information it should have given a `usize::MAX` for
// `align_offset` earlier, sending things through the scalar path instead of
// this one, so this check should pass if it's reachable.
debug_assert!(word_ptr.is_aligned_to(mem::align_of::<usize>()));
// Read subsequent words until the last aligned word, excluding the last
// aligned word by itself to be done in tail check later, to ensure that
// tail is always one `usize` at most to extra branch `byte_pos == len`.
while byte_pos < len - USIZE_SIZE {
// Sanity check that the read is in bounds
debug_assert!(byte_pos + USIZE_SIZE <= len);
// And that our assumptions about `byte_pos` hold.
debug_assert!(word_ptr.cast::<u8>() == start.wrapping_add(byte_pos));
// SAFETY: We know `word_ptr` is properly aligned (because of
// `align_offset`), and we know that we have enough bytes between `word_ptr` and the end
let word = unsafe { word_ptr.read() };
if contains_nonascii(word) {
return false;
}
byte_pos += USIZE_SIZE;
// SAFETY: We know that `byte_pos <= len - USIZE_SIZE`, which means that
// after this `add`, `word_ptr` will be at most one-past-the-end.
word_ptr = unsafe { word_ptr.add(1) };
}
// Sanity check to ensure there really is only one `usize` left. This should
// be guaranteed by our loop condition.
debug_assert!(byte_pos <= len && len - byte_pos <= USIZE_SIZE);
// SAFETY: This relies on `len >= USIZE_SIZE`, which we check at the start.
let last_word = unsafe { (start.add(len - USIZE_SIZE) as *const usize).read_unaligned() };
!contains_nonascii(last_word)
}
// Sanity check to ensure there really is only one `usize` left. This should
// be guaranteed by our loop condition.
debug_assert!(byte_pos <= len && len - byte_pos <= USIZE_SIZE);
// SAFETY: This relies on `len >= USIZE_SIZE`, which we check at the start.
let last_word = unsafe { (start.add(len - USIZE_SIZE) as *const usize).read_unaligned() };
!contains_nonascii(last_word)
}

95
library/core/src/slice/memchr.rs
View File

@ -1,6 +1,7 @@
// Original implementation taken from rust-memchr.
// Copyright 2015 Andrew Gallant, bluss and Nicolas Koch
use crate::intrinsics::const_eval_select;
use crate::mem;
const LO_USIZE: usize = usize::repeat_u8(0x01);
@ -50,58 +51,66 @@ const fn memchr_naive(x: u8, text: &[u8]) -> Option<usize> {
None
}
#[rustc_allow_const_fn_unstable(const_cmp)]
#[rustc_allow_const_fn_unstable(const_align_offset)]
#[rustc_allow_const_fn_unstable(const_eval_select)] // fallback impl has same behavior
#[cfg_attr(bootstrap, rustc_const_stable(feature = "const_memchr", since = "1.65.0"))]
const fn memchr_aligned(x: u8, text: &[u8]) -> Option<usize> {
// Scan for a single byte value by reading two `usize` words at a time.
//
// Split `text` in three parts
// - unaligned initial part, before the first word aligned address in text
// - body, scan by 2 words at a time
// - the last remaining part, < 2 word size
// The runtime version behaves the same as the compiletime version, it's
// just more optimized.
return const_eval_select((x, text), compiletime, runtime);
// search up to an aligned boundary
let len = text.len();
let ptr = text.as_ptr();
let mut offset = ptr.align_offset(USIZE_BYTES);
if offset > 0 {
// FIXME(const-hack, fee1-dead): replace with min
offset = if offset < len { offset } else { len };
// FIXME(const-hack, fee1-dead): replace with range slicing
// SAFETY: offset is within bounds
let slice = unsafe { super::from_raw_parts(text.as_ptr(), offset) };
if let Some(index) = memchr_naive(x, slice) {
return Some(index);
}
const fn compiletime(x: u8, text: &[u8]) -> Option<usize> {
memchr_naive(x, text)
}
// search the body of the text
let repeated_x = usize::repeat_u8(x);
while offset <= len - 2 * USIZE_BYTES {
// SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes
// between the offset and the end of the slice.
unsafe {
let u = *(ptr.add(offset) as *const usize);
let v = *(ptr.add(offset + USIZE_BYTES) as *const usize);
#[inline]
fn runtime(x: u8, text: &[u8]) -> Option<usize> {
// Scan for a single byte value by reading two `usize` words at a time.
//
// Split `text` in three parts
// - unaligned initial part, before the first word aligned address in text
// - body, scan by 2 words at a time
// - the last remaining part, < 2 word size
// break if there is a matching byte
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
// search up to an aligned boundary
let len = text.len();
let ptr = text.as_ptr();
let mut offset = ptr.align_offset(USIZE_BYTES);
if offset > 0 {
offset = offset.min(len);
let slice = &text[..offset];
if let Some(index) = memchr_naive(x, slice) {
return Some(index);
}
}
offset += USIZE_BYTES * 2;
}
// Find the byte after the point the body loop stopped.
// FIXME(const-hack): Use `?` instead.
// FIXME(const-hack, fee1-dead): use range slicing
// SAFETY: offset is within bounds
let slice = unsafe { super::from_raw_parts(text.as_ptr().add(offset), text.len() - offset) };
if let Some(i) = memchr_naive(x, slice) { Some(offset + i) } else { None }
// search the body of the text
let repeated_x = usize::repeat_u8(x);
while offset <= len - 2 * USIZE_BYTES {
// SAFETY: the while's predicate guarantees a distance of at least 2 * usize_bytes
// between the offset and the end of the slice.
unsafe {
let u = *(ptr.add(offset) as *const usize);
let v = *(ptr.add(offset + USIZE_BYTES) as *const usize);
// break if there is a matching byte
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
}
}
offset += USIZE_BYTES * 2;
}
// Find the byte after the point the body loop stopped.
// FIXME(const-hack): Use `?` instead.
// FIXME(const-hack, fee1-dead): use range slicing
let slice =
// SAFETY: offset is within bounds
unsafe { super::from_raw_parts(text.as_ptr().add(offset), text.len() - offset) };
if let Some(i) = memchr_naive(x, slice) { Some(offset + i) } else { None }
}
}
/// Returns the last index matching the byte `x` in `text`.

1
library/core/src/str/converts.rs
View File

@ -82,7 +82,6 @@ use crate::{mem, ptr};
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_stable(feature = "const_str_from_utf8_shared", since = "1.63.0")]
#[rustc_allow_const_fn_unstable(str_internals)]
#[rustc_diagnostic_item = "str_from_utf8"]
pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> {
// FIXME(const-hack): This should use `?` again, once it's `const`

26
library/core/src/str/validations.rs
View File

@ -1,6 +1,7 @@
//! Operations related to UTF-8 validation.
use super::Utf8Error;
use crate::intrinsics::const_eval_select;
use crate::mem;
/// Returns the initial codepoint accumulator for the first byte.
@ -122,15 +123,28 @@ const fn contains_nonascii(x: usize) -> bool {
/// Walks through `v` checking that it's a valid UTF-8 sequence,
/// returning `Ok(())` in that case, or, if it is invalid, `Err(err)`.
#[inline(always)]
#[rustc_const_unstable(feature = "str_internals", issue = "none")]
#[rustc_allow_const_fn_unstable(const_eval_select)] // fallback impl has same behavior
pub(super) const fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
let mut index = 0;
let len = v.len();
let usize_bytes = mem::size_of::<usize>();
let ascii_block_size = 2 * usize_bytes;
const USIZE_BYTES: usize = mem::size_of::<usize>();
let ascii_block_size = 2 * USIZE_BYTES;
let blocks_end = if len >= ascii_block_size { len - ascii_block_size + 1 } else { 0 };
let align = v.as_ptr().align_offset(usize_bytes);
let align = {
const fn compiletime(_v: &[u8]) -> usize {
usize::MAX
}
fn runtime(v: &[u8]) -> usize {
v.as_ptr().align_offset(USIZE_BYTES)
}
// Below, we safely fall back to a slower codepath if the offset is `usize::MAX`,
// so the end-to-end behavior is the same at compiletime and runtime.
const_eval_select((v,), compiletime, runtime)
};
while index < len {
let old_offset = index;
@ -209,11 +223,11 @@ pub(super) const fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
// Ascii case, try to skip forward quickly.
// When the pointer is aligned, read 2 words of data per iteration
// until we find a word containing a non-ascii byte.
if align != usize::MAX && align.wrapping_sub(index) % usize_bytes == 0 {
if align != usize::MAX && align.wrapping_sub(index) % USIZE_BYTES == 0 {
let ptr = v.as_ptr();
while index < blocks_end {
// SAFETY: since `align - index` and `ascii_block_size` are
// multiples of `usize_bytes`, `block = ptr.add(index)` is
// multiples of `USIZE_BYTES`, `block = ptr.add(index)` is
// always aligned with a `usize` so it's safe to dereference
// both `block` and `block.add(1)`.
unsafe {

14
library/core/src/ub_checks.rs
View File

@ -120,7 +120,19 @@ pub(crate) const fn check_language_ub() -> bool {
#[inline]
#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize, is_zst: bool) -> bool {
ptr.is_aligned_to(align) && (is_zst || !ptr.is_null())
#[inline]
fn runtime(ptr: *const (), align: usize, is_zst: bool) -> bool {
ptr.is_aligned_to(align) && (is_zst || !ptr.is_null())
}
#[inline]
#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
const fn comptime(ptr: *const (), _align: usize, is_zst: bool) -> bool {
is_zst || !ptr.is_null()
}
// This is just for safety checks so we can const_eval_select.
const_eval_select((ptr, align, is_zst), comptime, runtime)
}
#[inline]

2
library/core/tests/lib.rs
View File

@ -16,14 +16,12 @@
#![feature(cell_update)]
#![feature(clone_to_uninit)]
#![feature(const_align_of_val_raw)]
#![feature(const_align_offset)]
#![feature(const_black_box)]
#![feature(const_eval_select)]
#![feature(const_heap)]
#![feature(const_nonnull_new)]
#![feature(const_option_ext)]
#![feature(const_pin_2)]
#![feature(const_pointer_is_aligned)]
#![feature(const_three_way_compare)]
#![feature(const_trait_impl)]
#![feature(core_intrinsics)]

257
library/core/tests/ptr.rs
View File

@ -359,22 +359,6 @@ fn align_offset_zst() {
}
}
#[test]
fn align_offset_zst_const() {
const {
// For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
// all, because no amount of elements will align the pointer.
let mut p = 1;
while p < 1024 {
assert!(ptr::without_provenance::<()>(p).align_offset(p) == 0);
if p != 1 {
assert!(ptr::without_provenance::<()>(p + 1).align_offset(p) == !0);
}
p = (p + 1).next_power_of_two();
}
}
}
#[test]
fn align_offset_stride_one() {
// For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
@ -396,25 +380,6 @@ fn align_offset_stride_one() {
}
}
#[test]
fn align_offset_stride_one_const() {
const {
// For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
// number of bytes.
let mut align = 1;
while align < 1024 {
let mut ptr = 1;
while ptr < 2 * align {
let expected = ptr % align;
let offset = if expected == 0 { 0 } else { align - expected };
assert!(ptr::without_provenance::<u8>(ptr).align_offset(align) == offset);
ptr += 1;
}
align = (align + 1).next_power_of_two();
}
}
}
#[test]
fn align_offset_various_strides() {
unsafe fn test_stride<T>(ptr: *const T, align: usize) -> bool {
@ -495,192 +460,6 @@ fn align_offset_various_strides() {
assert!(!x);
}
#[test]
fn align_offset_various_strides_const() {
const unsafe fn test_stride<T>(ptr: *const T, numptr: usize, align: usize) {
let mut expected = usize::MAX;
// Naive but definitely correct way to find the *first* aligned element of stride::<T>.
let mut el = 0;
while el < align {
if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
expected = el;
break;
}
el += 1;
}
let got = ptr.align_offset(align);
assert!(got == expected);
}
const {
// For pointers of stride != 1, we verify the algorithm against the naivest possible
// implementation
let mut align = 1;
let limit = 32;
while align < limit {
let mut ptr = 1;
while ptr < 4 * align {
unsafe {
#[repr(packed)]
struct A3(#[allow(dead_code)] u16, #[allow(dead_code)] u8);
test_stride::<A3>(ptr::without_provenance::<A3>(ptr), ptr, align);
struct A4(#[allow(dead_code)] u32);
test_stride::<A4>(ptr::without_provenance::<A4>(ptr), ptr, align);
#[repr(packed)]
struct A5(#[allow(dead_code)] u32, #[allow(dead_code)] u8);
test_stride::<A5>(ptr::without_provenance::<A5>(ptr), ptr, align);
#[repr(packed)]
struct A6(#[allow(dead_code)] u32, #[allow(dead_code)] u16);
test_stride::<A6>(ptr::without_provenance::<A6>(ptr), ptr, align);
#[repr(packed)]
struct A7(
#[allow(dead_code)] u32,
#[allow(dead_code)] u16,
#[allow(dead_code)] u8,
);
test_stride::<A7>(ptr::without_provenance::<A7>(ptr), ptr, align);
#[repr(packed)]
struct A8(#[allow(dead_code)] u32, #[allow(dead_code)] u32);
test_stride::<A8>(ptr::without_provenance::<A8>(ptr), ptr, align);
#[repr(packed)]
struct A9(
#[allow(dead_code)] u32,
#[allow(dead_code)] u32,
#[allow(dead_code)] u8,
);
test_stride::<A9>(ptr::without_provenance::<A9>(ptr), ptr, align);
#[repr(packed)]
struct A10(
#[allow(dead_code)] u32,
#[allow(dead_code)] u32,
#[allow(dead_code)] u16,
);
test_stride::<A10>(ptr::without_provenance::<A10>(ptr), ptr, align);
test_stride::<u32>(ptr::without_provenance::<u32>(ptr), ptr, align);
test_stride::<u128>(ptr::without_provenance::<u128>(ptr), ptr, align);
}
ptr += 1;
}
align = (align + 1).next_power_of_two();
}
}
}
#[test]
fn align_offset_with_provenance_const() {
const {
// On some platforms (e.g. msp430-none-elf), the alignment of `i32` is less than 4.
#[repr(align(4))]
struct AlignedI32(i32);
let data = AlignedI32(42);
// `stride % align == 0` (usual case)
let ptr: *const i32 = &data.0;
assert!(ptr.align_offset(1) == 0);
assert!(ptr.align_offset(2) == 0);
assert!(ptr.align_offset(4) == 0);
assert!(ptr.align_offset(8) == usize::MAX);
assert!(ptr.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr.wrapping_byte_add(1).align_offset(2) == usize::MAX);
assert!(ptr.wrapping_byte_add(2).align_offset(1) == 0);
assert!(ptr.wrapping_byte_add(2).align_offset(2) == 0);
assert!(ptr.wrapping_byte_add(2).align_offset(4) == usize::MAX);
assert!(ptr.wrapping_byte_add(3).align_offset(1) == 0);
assert!(ptr.wrapping_byte_add(3).align_offset(2) == usize::MAX);
assert!(ptr.wrapping_add(42).align_offset(4) == 0);
assert!(ptr.wrapping_add(42).align_offset(8) == usize::MAX);
let ptr1: *const i8 = ptr.cast();
assert!(ptr1.align_offset(1) == 0);
assert!(ptr1.align_offset(2) == 0);
assert!(ptr1.align_offset(4) == 0);
assert!(ptr1.align_offset(8) == usize::MAX);
assert!(ptr1.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr1.wrapping_byte_add(1).align_offset(2) == 1);
assert!(ptr1.wrapping_byte_add(1).align_offset(4) == 3);
assert!(ptr1.wrapping_byte_add(1).align_offset(8) == usize::MAX);
assert!(ptr1.wrapping_byte_add(2).align_offset(1) == 0);
assert!(ptr1.wrapping_byte_add(2).align_offset(2) == 0);
assert!(ptr1.wrapping_byte_add(2).align_offset(4) == 2);
assert!(ptr1.wrapping_byte_add(2).align_offset(8) == usize::MAX);
assert!(ptr1.wrapping_byte_add(3).align_offset(1) == 0);
assert!(ptr1.wrapping_byte_add(3).align_offset(2) == 1);
assert!(ptr1.wrapping_byte_add(3).align_offset(4) == 1);
assert!(ptr1.wrapping_byte_add(3).align_offset(8) == usize::MAX);
let ptr2: *const i16 = ptr.cast();
assert!(ptr2.align_offset(1) == 0);
assert!(ptr2.align_offset(2) == 0);
assert!(ptr2.align_offset(4) == 0);
assert!(ptr2.align_offset(8) == usize::MAX);
assert!(ptr2.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr2.wrapping_byte_add(1).align_offset(2) == usize::MAX);
assert!(ptr2.wrapping_byte_add(2).align_offset(1) == 0);
assert!(ptr2.wrapping_byte_add(2).align_offset(2) == 0);
assert!(ptr2.wrapping_byte_add(2).align_offset(4) == 1);
assert!(ptr2.wrapping_byte_add(2).align_offset(8) == usize::MAX);
assert!(ptr2.wrapping_byte_add(3).align_offset(1) == 0);
assert!(ptr2.wrapping_byte_add(3).align_offset(2) == usize::MAX);
let ptr3: *const i64 = ptr.cast();
assert!(ptr3.align_offset(1) == 0);
assert!(ptr3.align_offset(2) == 0);
assert!(ptr3.align_offset(4) == 0);
assert!(ptr3.align_offset(8) == usize::MAX);
assert!(ptr3.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr3.wrapping_byte_add(1).align_offset(2) == usize::MAX);
// `stride % align != 0` (edge case)
let ptr4: *const [u8; 3] = ptr.cast();
assert!(ptr4.align_offset(1) == 0);
assert!(ptr4.align_offset(2) == 0);
assert!(ptr4.align_offset(4) == 0);
assert!(ptr4.align_offset(8) == usize::MAX);
assert!(ptr4.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr4.wrapping_byte_add(1).align_offset(2) == 1);
assert!(ptr4.wrapping_byte_add(1).align_offset(4) == 1);
assert!(ptr4.wrapping_byte_add(1).align_offset(8) == usize::MAX);
assert!(ptr4.wrapping_byte_add(2).align_offset(1) == 0);
assert!(ptr4.wrapping_byte_add(2).align_offset(2) == 0);
assert!(ptr4.wrapping_byte_add(2).align_offset(4) == 2);
assert!(ptr4.wrapping_byte_add(2).align_offset(8) == usize::MAX);
assert!(ptr4.wrapping_byte_add(3).align_offset(1) == 0);
assert!(ptr4.wrapping_byte_add(3).align_offset(2) == 1);
assert!(ptr4.wrapping_byte_add(3).align_offset(4) == 3);
assert!(ptr4.wrapping_byte_add(3).align_offset(8) == usize::MAX);
let ptr5: *const [u8; 5] = ptr.cast();
assert!(ptr5.align_offset(1) == 0);
assert!(ptr5.align_offset(2) == 0);
assert!(ptr5.align_offset(4) == 0);
assert!(ptr5.align_offset(8) == usize::MAX);
assert!(ptr5.wrapping_byte_add(1).align_offset(1) == 0);
assert!(ptr5.wrapping_byte_add(1).align_offset(2) == 1);
assert!(ptr5.wrapping_byte_add(1).align_offset(4) == 3);
assert!(ptr5.wrapping_byte_add(1).align_offset(8) == usize::MAX);
assert!(ptr5.wrapping_byte_add(2).align_offset(1) == 0);
assert!(ptr5.wrapping_byte_add(2).align_offset(2) == 0);
assert!(ptr5.wrapping_byte_add(2).align_offset(4) == 2);
assert!(ptr5.wrapping_byte_add(2).align_offset(8) == usize::MAX);
assert!(ptr5.wrapping_byte_add(3).align_offset(1) == 0);
assert!(ptr5.wrapping_byte_add(3).align_offset(2) == 1);
assert!(ptr5.wrapping_byte_add(3).align_offset(4) == 1);
assert!(ptr5.wrapping_byte_add(3).align_offset(8) == usize::MAX);
}
}
#[test]
fn align_offset_issue_103361() {
#[cfg(target_pointer_width = "64")]
@ -693,23 +472,6 @@ fn align_offset_issue_103361() {
let _ = ptr::without_provenance::<HugeSize>(SIZE).align_offset(SIZE);
}
#[test]
fn align_offset_issue_103361_const() {
#[cfg(target_pointer_width = "64")]
const SIZE: usize = 1 << 47;
#[cfg(target_pointer_width = "32")]
const SIZE: usize = 1 << 30;
#[cfg(target_pointer_width = "16")]
const SIZE: usize = 1 << 13;
struct HugeSize(#[allow(dead_code)] [u8; SIZE - 1]);
const {
assert!(ptr::without_provenance::<HugeSize>(SIZE - 1).align_offset(SIZE) == SIZE - 1);
assert!(ptr::without_provenance::<HugeSize>(SIZE).align_offset(SIZE) == 0);
assert!(ptr::without_provenance::<HugeSize>(SIZE + 1).align_offset(SIZE) == 1);
}
}
#[test]
fn is_aligned() {
let data = 42;
@ -726,25 +488,6 @@ fn is_aligned() {
assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
}
#[test]
fn is_aligned_const() {
const {
let data = 42;
let ptr: *const i32 = &data;
assert!(ptr.is_aligned());
assert!(ptr.is_aligned_to(1));
assert!(ptr.is_aligned_to(2));
assert!(ptr.is_aligned_to(4));
assert!(ptr.wrapping_byte_add(2).is_aligned_to(1));
assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
// At comptime neither `ptr` nor `ptr+1` is aligned to 8.
assert!(!ptr.is_aligned_to(8));
assert!(!ptr.wrapping_add(1).is_aligned_to(8));
}
}
#[test]
fn offset_from() {
let mut a = [0; 5];