<atomic>: make compare_exchange_weak really weak on ARM64
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- C++
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Description
From https://github.com/microsoft/STL/pull/694#issuecomment-622441925:
LL/SC machines are the motivation for compare_exchange_weak existing in the C++ standard. Other compilers like GCC and clang know the difference and emit non-looping code for CAS_weak.
Apparently it cannot be done without compiler support by having more ARM intrinsics exposed.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reading the linked discussion in microsoft/STL#694 and comparing how GCC and Clang implement weak compare-exchange on ARM64. Investigate the ARM intrinsics and compiler support mentioned in the issue. Done means the STL emits genuinely non-looping code for compare_exchange_weak on ARM64 while preserving the required behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- performance
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100