266649 2023-12-19 11:15:14 -0800 Failure memory order cannot be release or acq_rel. 2023-12-22 13:05:13 -0800 1 1 1 Unclassified WebKit Platform WebKit Nightly Build Unspecified Unspecified RESOLVED FIXED InRadar P2 Normal --- 1 gfunni234 webkit-unassigned mark.lam webkit-bug-importer oldest_to_newest 2000789 0 gfunni234 2023-12-19 11:15:14 -0800 It is undefined behavior and clang now enforces this. 2001089 1 ap 2023-12-20 09:59:46 -0800 https://github.com/WebKit/WebKit/pull/22049 2001095 2 mark.lam 2023-12-20 10:14:46 -0800 (In reply to Seija K. from comment #0) > It is undefined behavior and clang now enforces this. Can you please point us to the C++ spec where it says that using release or acq_rel for the failure memory order is undefined behavior? Thanks. 2001592 3 webkit-bug-importer 2023-12-22 08:29:21 -0800 <rdar://problem/120047049> 2001593 4 mark.lam 2023-12-22 08:32:03 -0800 (In reply to Mark Lam from comment #2) > Can you please point us to the C++ spec where it says that using release or > acq_rel for the failure memory order is undefined behavior? Thanks. From https://en.cppreference.com/w/cpp/atomic/atomic/compare_exchange: ``` If failure is stronger than success or(until C++17) is one of std::memory_order_release and std::memory_order_acq_rel, the behavior is undefined. ``` Also, from that link, there's a table that says for `compare_exchange_strong`'s "load operation" in the failure mode, to use: ``` * std::memory_order_acquire if order is std::memory_order_acq_rel * std::memory_order_relaxed if order is std::memory_order_release * otherwise order ``` 2001638 5 ews-feeder 2023-12-22 13:05:12 -0800 Committed 272461@main (d2ba4a07e209): <https://commits.webkit.org/272461@main> Reviewed commits have been landed. Closing PR #22049 and removing active labels.