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'.
(cherry picked from commit
059b5509c14904b55c37f659170240ae0d2c1c8e)