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Remove restrictions on compare-exchange memory ordering. #1315

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Jul 18, 2022
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Remove restrictions on compare-exchange memory ordering. #1315

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16 changes: 11 additions & 5 deletions crates/core_arch/src/x86_64/cmpxchg16b.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,7 @@ use stdarch_test::assert_instr;
/// support `cmpxchg16b` and the program enters an execution path that
/// eventually would reach this function the behavior is undefined.
///
/// The `success` ordering must also be stronger or equal to `failure`, or this
/// The failure ordering must be [`SeqCst`], [`Acquire`] or [`Relaxed`], or this
/// function call is undefined. See the `Atomic*` documentation's
/// `compare_exchange` function for more information. When `compare_exchange`
/// panics, this is undefined behavior. Currently this function aborts the
Expand All @@ -54,15 +54,21 @@ pub unsafe fn cmpxchg16b(
debug_assert!(dst as usize % 16 == 0);

let (val, _ok) = match (success, failure) {
(Acquire, Acquire) => intrinsics::atomic_cxchg_acquire_acquire(dst, old, new),
(Release, Relaxed) => intrinsics::atomic_cxchg_release_relaxed(dst, old, new),
(AcqRel, Acquire) => intrinsics::atomic_cxchg_acqrel_acquire(dst, old, new),
(Relaxed, Relaxed) => intrinsics::atomic_cxchg_relaxed_relaxed(dst, old, new),
(SeqCst, SeqCst) => intrinsics::atomic_cxchg_seqcst_seqcst(dst, old, new),
(Relaxed, Acquire) => intrinsics::atomic_cxchg_relaxed_acquire(dst, old, new),
(Relaxed, SeqCst) => intrinsics::atomic_cxchg_relaxed_seqcst(dst, old, new),
(Acquire, Relaxed) => intrinsics::atomic_cxchg_acquire_relaxed(dst, old, new),
(Acquire, Acquire) => intrinsics::atomic_cxchg_acquire_acquire(dst, old, new),
(Acquire, SeqCst) => intrinsics::atomic_cxchg_acquire_seqcst(dst, old, new),
(Release, Relaxed) => intrinsics::atomic_cxchg_release_relaxed(dst, old, new),
(Release, Acquire) => intrinsics::atomic_cxchg_release_acquire(dst, old, new),
(Release, SeqCst) => intrinsics::atomic_cxchg_release_seqcst(dst, old, new),
(AcqRel, Relaxed) => intrinsics::atomic_cxchg_acqrel_relaxed(dst, old, new),
(AcqRel, Acquire) => intrinsics::atomic_cxchg_acqrel_acquire(dst, old, new),
(AcqRel, SeqCst) => intrinsics::atomic_cxchg_acqrel_seqcst(dst, old, new),
(SeqCst, Relaxed) => intrinsics::atomic_cxchg_seqcst_relaxed(dst, old, new),
(SeqCst, Acquire) => intrinsics::atomic_cxchg_seqcst_acquire(dst, old, new),
(SeqCst, SeqCst) => intrinsics::atomic_cxchg_seqcst_seqcst(dst, old, new),

// The above block is all copied from libcore, and this statement is
// also copied from libcore except that it's a panic in libcore and we
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