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Commitae08c58

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Rollup merge ofrust-lang#126213 - zachs18:atomicbool-u8-i8-from-ptr-alignment, r=Nilstrieb
Update docs for AtomicBool/U8/I8 with regard to alignmentFixesrust-lang#126084.Since `AtomicBool`/`AtomicU8`/`AtomicI8` are guaranteed to have size == 1, and Rust guarantees that `size % align == 0`, they also must have alignment equal to 1, so some current docs are contradictory/confusing when describing their alignment requirements.Specifically:* Fix `AtomicBool::from_ptr` claiming that `align_of::<AtomicBool>() > align_of::<bool>()` on some platforms. (same for `AtomicU8::from_ptr`/`AtomicI8::from_ptr`)* Explicitly state that `AtomicU8`/`AtomicI8` have the same alignment as `u8`/`i8` (in addition to size and bit validity)* (internal) Change the `if_not_8_bit` macro to be `if_8_bit` and to allow an "if-else"-like structure, instead of just "if"-like.---I opted to leave the "`ptr` must be aligned" wording in `from_ptr`'s docs and just clarify that it is always satsified, instead of just removing the wording entirely. If that is instead preferred I can do that.
2 parentsc26bd79 +5840184 commitae08c58

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‎core/src/sync/atomic.rs‎

Lines changed: 33 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -443,8 +443,8 @@ impl AtomicBool {
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///
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/// # Safety
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///
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/// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note thaton some platforms this can
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///be bigger than`align_of::<bool>()`).
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/// * `ptr` must be aligned to `align_of::<AtomicBool>()` (note thatthis is always true, since
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/// `align_of::<AtomicBool>() == 1`).
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/// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
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/// * You must adhere to the [Memory model for atomic accesses]. In particular, it is not
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/// allowed to mix atomic and non-atomic accesses, or atomic accesses of different sizes,
@@ -2091,10 +2091,10 @@ impl<T> From<*mut T> for AtomicPtr<T> {
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}
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#[allow(unused_macros)]// This macro ends up being unused on some architectures.
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macro_rules!if_not_8_bit{
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(u8, $($tt:tt)*)=>{""};
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(i8, $($tt:tt)*)=>{""};
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($_:ident, $($tt:tt)*)=>{ $($tt)*};
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macro_rules!if_8_bit{
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(u8, $( yes =[$($yes:tt)*],)? $( no =[$($no:tt)*],)?)=>{concat!("", $($($yes)*)?)};
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(i8, $( yes =[$($yes:tt)*],)? $( no =[$($no:tt)*],)?)=>{concat!("", $($($yes)*)?)};
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($_:ident, $( yes =[$($yes:tt)*],)? $( no =[$($no:tt)*],)?)=>{concat!("",$($($no)*)?)};
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}
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#[cfg(target_has_atomic_load_store)]
@@ -2116,18 +2116,24 @@ macro_rules! atomic_int {
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$int_type:ident $atomic_type:ident) =>{
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/// An integer type which can be safely shared between threads.
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///
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/// This type has the same size and bit validity as the underlying
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/// integer type, [`
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/// This type has the same
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#[doc = if_8_bit!(
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$int_type,
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yes =["size, alignment, and bit validity"],
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no =["size and bit validity"],
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)]
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/// as the underlying integer type, [`
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#[doc = $s_int_type]
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/// `].
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#[doc =if_not_8_bit!{
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#[doc =if_8_bit!{
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$int_type,
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concat!(
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no =[
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"However, the alignment of this type is always equal to its ",
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"size, even on targets where [`", $s_int_type,"`] has a ",
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"lesser alignment."
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)
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],
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}]
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///
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/// For more about the differences between atomic types and
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/// non-atomic types as well as information about the portability of
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/// this type, please see the [module-level documentation].
@@ -2220,9 +2226,19 @@ macro_rules! atomic_int {
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///
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/// # Safety
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///
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#[doc = concat!(" * `ptr` must be aligned to\
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`align_of::<", stringify!($atomic_type),">()` (note that on some platforms this\
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can be bigger than `align_of::<", stringify!($int_type),">()`).")]
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/// * `ptr` must be aligned to
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#[doc = concat!(" `align_of::<", stringify!($atomic_type),">()`")]
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#[doc = if_8_bit!{
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$int_type,
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yes =[
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" (note that this is always true, since `align_of::<",
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stringify!($atomic_type),">() == 1`)."
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],
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no =[
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" (note that on some platforms this can be bigger than `align_of::<",
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stringify!($int_type),">()`)."
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],
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}]
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/// * `ptr` must be [valid] for both reads and writes for the whole lifetime `'a`.
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/// * You must adhere to the [Memory model for atomic accesses]. In particular, it is not
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/// allowed to mix atomic and non-atomic accesses, or atomic accesses of different sizes,
@@ -2261,12 +2277,12 @@ macro_rules! atomic_int {
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#[doc = concat!("Get atomic access to a `&mut ", stringify!($int_type),"`.")]
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///
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#[doc =if_not_8_bit!{
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#[doc =if_8_bit!{
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$int_type,
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concat!(
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no =[
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"**Note:** This function is only available on targets where `",
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stringify!($int_type),"` has an alignment of ", $align," bytes."
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)
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],
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}]
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///
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/// # Examples

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