https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119645
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Thomas Schwinge <tschwi...@gcc.gnu.org>: https://gcc.gnu.org/g:059b5509c14904b55c37f659170240ae0d2c1c8e commit r15-9256-g059b5509c14904b55c37f659170240ae0d2c1c8e Author: Thomas Schwinge <tschwi...@baylibre.com> Date: Sat Apr 5 23:11:23 2025 +0200 GCN, nvptx libstdc++: Force use of '__atomic' builtins [PR119645] For both GCN, nvptx, this gets rid of 'configure'-time: configure: WARNING: No native atomic operations are provided for this platform. configure: WARNING: They will be faked using a mutex. configure: WARNING: Performance of certain classes will degrade as a result. ..., and changes: -checking for lock policy for shared_ptr reference counts... mutex +checking for lock policy for shared_ptr reference counts... atomic That means, '[...]/[target]/libstdc++-v3/', 'Makefile's change: -ATOMICITY_SRCDIR = config/cpu/generic/atomicity_mutex +ATOMICITY_SRCDIR = config/cpu/generic/atomicity_builtins ..., and '[...]/[target]/libstdc++-v3/config.h' changes: /* Defined if shared_ptr reference counting should use atomic operations. */ -/* #undef HAVE_ATOMIC_LOCK_POLICY */ +#define HAVE_ATOMIC_LOCK_POLICY 1 /* Define if the compiler supports C++11 atomics. */ -/* #undef _GLIBCXX_ATOMIC_BUILTINS */ +#define _GLIBCXX_ATOMIC_BUILTINS 1 ..., and '[...]/[target]/libstdc++-v3/include/[target]/bits/c++config.h' changes: /* Defined if shared_ptr reference counting should use atomic operations. */ -/* #undef _GLIBCXX_HAVE_ATOMIC_LOCK_POLICY */ +#define _GLIBCXX_HAVE_ATOMIC_LOCK_POLICY 1 /* Define if the compiler supports C++11 atomics. */ -/* #undef _GLIBCXX_ATOMIC_BUILTINS */ +#define _GLIBCXX_ATOMIC_BUILTINS 1 This means that '[...]/[target]/libstdc++-v3/libsupc++/atomicity.cc', '[...]/[target]/libstdc++-v3/libsupc++/atomicity.o' then uses atomic instructions for synchronization instead of C++ static local variables, which in turn for their guard variables, via 'libstdc++-v3/libsupc++/guard.cc', used 'libgcc/gthr.h' recursive mutexes, which currently are unsupported for GCN. For GCN, this turns ~500 libstdc++ execution test FAILs into PASSes, and also progresses: PASS: g++.dg/tree-ssa/pr20458.C -std=gnu++17 (test for excess errors) [-FAIL:-]{+PASS:+} g++.dg/tree-ssa/pr20458.C -std=gnu++17 execution test PASS: g++.dg/tree-ssa/pr20458.C -std=gnu++26 (test for excess errors) [-FAIL:-]{+PASS:+} g++.dg/tree-ssa/pr20458.C -std=gnu++26 execution test UNSUPPORTED: g++.dg/tree-ssa/pr20458.C -std=gnu++98: exception handling not supported (For nvptx, there is no effective change, due to other misconfiguration.) PR target/119645 libstdc++-v3/ * acinclude.m4 (GLIBCXX_ENABLE_LOCK_POLICY) [GCN, nvptx]: Hard-code results. * configure: Regenerate. * configure.host [GCN, nvptx] (atomicity_dir): Set to 'cpu/generic/atomicity_builtins'.
