Skip to content

[only tests] Add tests for current read/write unaligned behaviour #158341

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
scottmcm wants to merge 2 commits into from
Closed

[only tests] Add tests for current read/write unaligned behaviour #158341

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
4eb7436
Use `transmute_neo` in `assume_init`
scottmcm Jun 24, 2026
6308be0
Add a test for current read/write unaligned behaviour
scottmcm Jun 21, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 3 additions & 3 deletions library/core/src/mem/maybe_uninit.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
use crate::any::type_name;
use crate::clone::TrivialClone;
use crate::marker::Destruct;
use crate::mem::ManuallyDrop;
use crate::mem::{ManuallyDrop, transmute_neo};
use crate::{fmt, intrinsics, ptr, slice};

/// A wrapper type to construct uninitialized instances of `T`.
Expand Down Expand Up @@ -724,9 +724,9 @@ impl<T> MaybeUninit<T> {
// This also means that `self` must be a `value` variant.
unsafe {
intrinsics::assert_inhabited::<T>();
// We do this via a raw ptr read instead of `ManuallyDrop::into_inner` so that there's
// We do this via a transmute instead of `ManuallyDrop::into_inner` so that there's
// no trace of `ManuallyDrop` in Miri's error messages here.
(&raw const self.value).cast::<T>().read()
transmute_neo(self)
}
}

Expand Down
5 changes: 5 additions & 0 deletions library/core/src/mem/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1196,6 +1196,9 @@ pub const unsafe fn transmute_prefix<Src, Dst>(src: Src) -> Dst {
/// New version of `transmute`, exposed under this name so it can be iterated upon
/// without risking breakage to uses of "real" transmute.
///
/// Uses a `const`-`assert` to check the sizes instead of typeck hacks,
/// but is semantially identical to `transmute` otherwise.
///
/// It will not be stabilized under this name.
///
/// # Examples
Expand All @@ -1214,6 +1217,8 @@ pub const unsafe fn transmute_prefix<Src, Dst>(src: Src) -> Dst {
/// unsafe { transmute_neo::<u32, u16>(123) };
/// ```
#[unstable(feature = "transmute_neo", issue = "155079")]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
#[inline]
pub const unsafe fn transmute_neo<Src, Dst>(src: Src) -> Dst {
const { assert!(Src::SIZE == Dst::SIZE) };

Expand Down
71 changes: 71 additions & 0 deletions tests/codegen-llvm/read_write_unaligned.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,71 @@
//@ compile-flags: -Copt-level=3
//@ only-64bit

#![crate_type = "lib"]

use std::num::NonZero;
use std::ptr::NonNull;

// CHECK-LABEL: nonnull ptr @read_unaligned_ptr(ptr{{.+}}%ptr)
#[no_mangle]
unsafe fn read_unaligned_ptr(ptr: *const NonNull<i16>) -> NonNull<i16> {
// CHECK: start:
// CHECK-NEXT: [[TEMP:%.+]] = load ptr, ptr %ptr, align 1
// CHECK-SAME: !nonnull
// CHECK-SAME: !noundef
// CHECK-NEXT: ret ptr [[TEMP]]
ptr.read_unaligned()
}

// CHECK-LABEL: range(i16 1, 0) i16 @read_unaligned_i16(ptr{{.+}}%ptr)
#[no_mangle]
unsafe fn read_unaligned_i16(ptr: *const NonZero<i16>) -> NonZero<i16> {
// CHECK: start:
// CHECK-NEXT: [[TEMP:%.+]] = load i16, ptr %ptr, align 1
// CHECK-NOT: !noundef
// CHECK-NOT: !range
// CHECK-NEXT: ret i16 [[TEMP]]
ptr.read_unaligned()
}

// CHECK-LABEL: void @typed_copy_unaligned_i32(ptr{{.+}}%src, ptr{{.+}}%dst)
#[no_mangle]
unsafe fn typed_copy_unaligned_i32(src: *const NonZero<i32>, dst: *mut NonZero<i32>) {
// CHECK: start:
// CHECK-NEXT: [[TEMP:%.+]] = load i32, ptr %src, align 1
// CHECK-NOT: !noundef
// CHECK-NOT: !range
// CHECK-NEXT: store i32 [[TEMP]], ptr %dst, align 1
// CHECK-NEXT: ret void
dst.write_unaligned(src.read_unaligned())
}

// CHECK-LABEL: void @write_unaligned_i64(ptr{{.+}}%ptr, i64{{.+}}%val)
#[no_mangle]
unsafe fn write_unaligned_i64(ptr: *mut NonZero<i64>, val: NonZero<i64>) {
// CHECK: start:
// CHECK-NEXT: store i64 %val, ptr %ptr, align 1
// CHECK-NEXT: ret void
ptr.write_unaligned(val)
}

#[repr(align(128))]
struct HugeBuffer([u64; 1 << 10]);

// CHECK-LABEL: void @read_unaligned_huge(ptr{{.+}}%_0, ptr{{.+}}%ptr)
#[no_mangle]
unsafe fn read_unaligned_huge(ptr: *const HugeBuffer) -> HugeBuffer {
// CHECK: start:
// CHECK-NEXT: call void @llvm.memcpy{{.+}} align 128 dereferenceable(8192) %_0, {{.+}} align 1 dereferenceable(8192) %ptr, i64 8192,
// CHECK-NEXT: ret void
ptr.read_unaligned()
}

// CHECK-LABEL: void @write_unaligned_huge(ptr{{.+}}%ptr, ptr{{.+}}%val)
#[no_mangle]
unsafe fn write_unaligned_huge(ptr: *mut HugeBuffer, val: HugeBuffer) {
// CHECK: start:
// CHECK-NEXT: call void @llvm.memcpy{{.+}} align 1 dereferenceable(8192) %ptr, {{.+}} align 128 dereferenceable(8192) %val, i64 8192,
// CHECK-NEXT: ret void
ptr.write_unaligned(val)
}
37 changes: 37 additions & 0 deletions tests/mir-opt/pre-codegen/unaligned.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
//@ compile-flags: -O -Zmir-opt-level=2
//@ ignore-std-debug-assertions (there's one in `ptr::read` via `MaybeUninit::assume_init`)

#![crate_type = "lib"]

// EMIT_MIR unaligned.unaligned_copy_manual.runtime-optimized.after.mir
pub unsafe fn unaligned_copy_manual(src: *const u128, dst: *mut u128) {
#[repr(packed)]
struct Packed<T>(T);

// CHECK-LABEL: fn unaligned_copy_manual(_1: *const u128, _2: *mut u128) -> ()
// CHECK: [[SRCU:_.+]] = copy _1 as *const unaligned_copy_manual::Packed<u128> (PtrToPtr);
// CHECK: [[DSTU:_.+]] = copy _2 as *mut unaligned_copy_manual::Packed<u128> (PtrToPtr);
// CHECK: [[TEMP:_.+]] = copy ((*[[SRCU]]).0: u128);
// ((*[[DSTU]]).0: u128) = move [[TEMP]];
let src = src.cast::<Packed<u128>>();
let dst = dst.cast::<Packed<u128>>();
unsafe { (*dst).0 = (*src).0 };
}

// EMIT_MIR unaligned.unaligned_copy_generic.runtime-optimized.after.mir
pub unsafe fn unaligned_copy_generic<T>(src: *const T, dst: *mut T) {
// CHECK-LABEL: fn unaligned_copy_generic(
// CHECK: debug src => _1;
// CHECK: debug dst => _2;
// CHECK: debug val => [[VAL:_.+]];
// CHECK: copy _1 as *const u8 (PtrToPtr);
// CHECK: &raw mut
// CHECK: copy_nonoverlapping{{.+}}count = const <T as std::mem::SizedTypeProperties>::SIZE
// CHECK: &raw const
// CHECK: copy _2 as *mut u8 (PtrToPtr);
// CHECK: copy_nonoverlapping{{.+}}count = const <T as std::mem::SizedTypeProperties>::SIZE
unsafe {
let val = std::ptr::read_unaligned(src);
std::ptr::write_unaligned(dst, val);
}
}
99 changes: 99 additions & 0 deletions tests/mir-opt/pre-codegen/unaligned.unaligned_copy_generic.runtime-optimized.after.mir
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,99 @@
// MIR for `unaligned_copy_generic` after runtime-optimized

fn unaligned_copy_generic(_1: *const T, _2: *mut T) -> () {
debug src => _1;
debug dst => _2;
let mut _0: ();
let _9: T;
let mut _10: T;
scope 1 {
debug val => _9;
scope 14 (inlined #[track_caller] write_unaligned::<T>) {
let mut _11: *const T;
let mut _12: *const u8;
let mut _13: *mut u8;
scope 15 (inlined std::mem::size_of::<T>) {
}
scope 16 (inlined std::ptr::copy_nonoverlapping::<u8>) {
scope 17 (inlined core::ub_checks::check_language_ub) {
scope 18 (inlined core::ub_checks::check_language_ub::runtime) {
}
}
scope 19 (inlined std::mem::size_of::<u8>) {
}
scope 20 (inlined std::mem::align_of::<u8>) {
}
}
}
}
scope 2 (inlined #[track_caller] read_unaligned::<T>) {
let mut _3: std::mem::MaybeUninit<T>;
let mut _4: *const u8;
let mut _6: *mut u8;
let mut _7: std::mem::MaybeUninit<T>;
scope 3 {
scope 5 (inlined MaybeUninit::<T>::as_mut_ptr) {
let mut _5: *mut std::mem::MaybeUninit<T>;
}
scope 6 (inlined std::mem::size_of::<T>) {
}
scope 7 (inlined std::ptr::copy_nonoverlapping::<u8>) {
scope 8 (inlined core::ub_checks::check_language_ub) {
scope 9 (inlined core::ub_checks::check_language_ub::runtime) {
}
}
scope 10 (inlined std::mem::size_of::<u8>) {
}
scope 11 (inlined std::mem::align_of::<u8>) {
}
}
scope 12 (inlined #[track_caller] MaybeUninit::<T>::assume_init) {
let _8: ();
scope 13 (inlined transmute_neo::<MaybeUninit<T>, T>) {
}
}
}
scope 4 (inlined MaybeUninit::<T>::uninit) {
}
}

bb0: {
StorageLive(_9);
StorageLive(_5);
StorageLive(_3);
_3 = MaybeUninit::<T> { uninit: const () };
StorageLive(_4);
_4 = copy _1 as *const u8 (PtrToPtr);
StorageLive(_6);
_5 = &raw mut _3;
_6 = copy _5 as *mut u8 (PtrToPtr);
copy_nonoverlapping(dst = copy _6, src = copy _4, count = const <T as std::mem::SizedTypeProperties>::SIZE);
StorageDead(_6);
StorageDead(_4);
StorageLive(_7);
_7 = move _3;
_8 = assert_inhabited::<T>() -> [return: bb1, unwind unreachable];
}

bb1: {
_9 = copy _7 as T (Transmute);
StorageDead(_7);
StorageDead(_3);
StorageDead(_5);
StorageLive(_10);
_10 = move _9;
StorageLive(_11);
StorageLive(_12);
_11 = &raw const _10;
_12 = copy _11 as *const u8 (PtrToPtr);
StorageLive(_13);
_13 = copy _2 as *mut u8 (PtrToPtr);
copy_nonoverlapping(dst = copy _13, src = copy _12, count = const <T as std::mem::SizedTypeProperties>::SIZE);
StorageDead(_13);
StorageDead(_12);
StorageDead(_11);
StorageDead(_10);
StorageDead(_9);
return;
}
}
34 changes: 34 additions & 0 deletions tests/mir-opt/pre-codegen/unaligned.unaligned_copy_manual.runtime-optimized.after.mir
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
// MIR for `unaligned_copy_manual` after runtime-optimized

fn unaligned_copy_manual(_1: *const u128, _2: *mut u128) -> () {
debug src => _1;
debug dst => _2;
let mut _0: ();
let _3: *const unaligned_copy_manual::Packed<u128>;
let mut _5: u128;
scope 1 {
debug src => _3;
let _4: *mut unaligned_copy_manual::Packed<u128>;
scope 2 {
debug dst => _4;
}
scope 4 (inlined std::ptr::mut_ptr::<impl *mut u128>::cast::<Packed<u128>>) {
}
}
scope 3 (inlined std::ptr::const_ptr::<impl *const u128>::cast::<Packed<u128>>) {
}

bb0: {
StorageLive(_3);
_3 = copy _1 as *const unaligned_copy_manual::Packed<u128> (PtrToPtr);
StorageLive(_4);
_4 = copy _2 as *mut unaligned_copy_manual::Packed<u128> (PtrToPtr);
StorageLive(_5);
_5 = copy ((*_3).0: u128);
((*_4).0: u128) = move _5;
StorageDead(_5);
StorageDead(_4);
StorageDead(_3);
return;
}
}
Loading