Simplify memory ordering intrinsics

[m-ou-se]

This changes the names of the atomic intrinsics to always fully include their memory ordering arguments.

- atomic_cxchg
+ atomic_cxchg_seqcst_seqcst

- atomic_cxchg_acqrel
+ atomic_cxchg_acqrel_release

- atomic_cxchg_acqrel_failrelaxed
+ atomic_cxchg_acqrel_relaxed

// And so on.

• seqcst is no longer implied
• The failure ordering on chxchg is no longer implied in some cases, but now always explicitly part of the name.
• release is no longer shortened to just rel. That was especially confusing, since relaxed also starts with rel.
• acquire is no longer shortened to just acq, such that the names now all match the std::sync::atomic::Ordering variants exactly.
• This now allows for more combinations on the compare exchange operations, such as atomic_cxchg_acquire_release, which is necessary for Lift unnecessary restriction on CAS failure ordering #68464.
• This PR only exposes the new possibilities through unstable intrinsics, but not yet through the stable API. That's for a separate PR that requires an FCP.

Suffixes for operations with a single memory order:

Order	Before	After
Relaxed	_relaxed	_relaxed
Acquire	_acq	_acquire
Release	_rel	_release
AcqRel	_acqrel	_acqrel
SeqCst	(none)	_seqcst

Suffixes for compare-and-exchange operations with two memory orderings:

Success	Failure	Before	After
Relaxed	Relaxed	_relaxed	_relaxed_relaxed
Relaxed	Acquire	❌	_relaxed_acquire
Relaxed	SeqCst	❌	_relaxed_seqcst
Acquire	Relaxed	_acq_failrelaxed	_acquire_relaxed
Acquire	Acquire	_acq	_acquire_acquire
Acquire	SeqCst	❌	_acquire_seqcst
Release	Relaxed	_rel	_release_relaxed
Release	Acquire	❌	_release_acquire
Release	SeqCst	❌	_release_seqcst
AcqRel	Relaxed	_acqrel_failrelaxed	_acqrel_relaxed
AcqRel	Acquire	_acqrel	_acqrel_acquire
AcqRel	SeqCst	❌	_acqrel_seqcst
SeqCst	Relaxed	_failrelaxed	_seqcst_relaxed
SeqCst	Acquire	_failacq	_seqcst_acquire
SeqCst	SeqCst	(none)	_seqcst_seqcst

[rust-highfive]

r? @kennytm

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[m-ou-se]

cc @tmiasko

[m-ou-se]

This updates the stdarch submodule to include rust-lang/stdarch@dc4b2e2, which isn't merged in stdarch's main branch yet, since that change needs to happen at the same time as the rest of this PR.

[tmiasko]

Looks good to me. Thanks!

r=me with commits squashed.

[m-ou-se]

This updates the stdarch submodule to include rust-lang/stdarch@dc4b2e2, which isn't merged in stdarch's main branch yet, since that change needs to happen at the same time as the rest of this PR.

cc @Amanieu for stdarch ^

[tmiasko]

This updates the stdarch submodule to include rust-lang/stdarch@dc4b2e2, which isn't merged in stdarch's main branch yet, since that change needs to happen at the same time as the rest of this PR.

Since the core_arch uses intrinsics declared in the core, for the not(bootstrap) case we can also add re-exports under old name for those handful of intrinsics that are still required, and update stdarch using the usual process at some later point.

[m-ou-se]

Oops, got distracted.

I've updated the PR following your suggestion. :)

[tmiasko]

@bors r+

[bors]

📌 Commit 2d02416 has been approved by tmiasko

[m-ou-se]

@bors r=tmiasko

[bors]

📌 Commit 4982a59 has been approved by tmiasko

[kkysen]

It seems that the error messages for these updated intrinsics are out-of-date with the new names, as they say similarly named function `{old_instrinsic_name}` defined here while pointing to the definition of the new intrinsic name. For example,

error[E0425]: cannot find function `atomic_xchg_acq` in module `core::intrinsics`
   --> src/atomics.rs:167:33
    |
167 |         ) = ::core::intrinsics::atomic_xchg_acq(&mut x, 33 as libc::c_int);
    |                                 ^^^^^^^^^^^^^^^ help: a function with a similar name exists: `atomic_cxchg_acq`
    |
   ::: /home/kkysen/.rustup/toolchains/nightly-2022-08-08-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/intrinsics.rs:320:5
    |
320 |     pub fn atomic_cxchg_acquire_acquire<T: Copy>(dst: *mut T, old: T, src: T) -> (T, bool);
    |     -------------------------------------------------------------------------------------- similarly named function `atomic_cxchg_acq` defined here

error[E0425]: cannot find function `atomic_store_rel` in module `core::intrinsics`
   --> src/atomics.rs:171:25
    |
171 |     ::core::intrinsics::atomic_store_rel(&mut x, 0);
    |                         ^^^^^^^^^^^^^^^^ help: a function with a similar name exists: `atomic_store`
    |
   ::: /home/kkysen/.rustup/toolchains/nightly-2022-08-08-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/intrinsics.rs:523:5
    |
523 |     pub fn atomic_store_seqcst<T: Copy>(dst: *mut T, val: T);
    |     -------------------------------------------------------- similarly named function `atomic_store` defined here