Author: Eli Friedman Date: 2026-07-22T13:43:38Z New Revision: 2cff4ff7a21c91b3493eb0fd8a7f072aee77fe7d
URL: https://github.com/llvm/llvm-project/commit/2cff4ff7a21c91b3493eb0fd8a7f072aee77fe7d DIFF: https://github.com/llvm/llvm-project/commit/2cff4ff7a21c91b3493eb0fd8a7f072aee77fe7d.diff LOG: Make ios_base::xalloc non-atomic with LIBCXX_ENABLE_THREADS=OFF. (#208356) 762b77a moved the definition of "xindex" out of the header, and in the process dropped the _LIBCPP_HAS_THREADS check. Re-add the check to maintain the status quo. The discussion on https://github.com/llvm/llvm-project/pull/198994 indicates it's not clear whether LIBCXX_ENABLE_THREADS=OFF is actually supposed to mean single-threaded. But it clearly does in practice: atomic_support.h uses non-atomic ops when threads are disabled, and a few other APIs have explicit non-atomic fallback paths. My team ran into this trying to run libc++ tests for a RISC-V core without the "a" extension. (cherry picked from commit 3eb929be5e17d66900020bd1caa7d2510d4f9601) Added: Modified: libcxx/src/ios.cpp Removed: ################################################################################ diff --git a/libcxx/src/ios.cpp b/libcxx/src/ios.cpp index 2e049098740dc..db6ca50f7f6ca 100644 --- a/libcxx/src/ios.cpp +++ b/libcxx/src/ios.cpp @@ -122,7 +122,14 @@ static size_t __ios_new_cap(size_t __req_size, size_t __current_cap) { // Precon } int ios_base::xalloc() { +#if _LIBCPP_HAS_THREADS constinit static atomic<int> xindex = 0; +#else + // If we don't have atomics, fall back to single-threaded implementation. + // FIXME: Should "single-threaded" be a separate option from + // _LIBCPP_HAS_THREADS? + static int xindex = 0; +#endif // _LIBCPP_HAS_THREADS return xindex++; } _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
