https://gcc.gnu.org/g:0804fea06587c55f09aaf9b9a11ad1724ec7389e
commit 0804fea06587c55f09aaf9b9a11ad1724ec7389e
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'.
(cherry picked from commit 059b5509c14904b55c37f659170240ae0d2c1c8e)
Diff:
---
libstdc++-v3/ChangeLog.omp | 10 ++++++++++
libstdc++-v3/acinclude.m4 | 7 ++++---
libstdc++-v3/configure | 11 ++++++-----
libstdc++-v3/configure.host | 11 +++++++++++
4 files changed, 31 insertions(+), 8 deletions(-)
diff --git a/libstdc++-v3/ChangeLog.omp b/libstdc++-v3/ChangeLog.omp
index daca152e84a5..a704e56156fe 100644
--- a/libstdc++-v3/ChangeLog.omp
+++ b/libstdc++-v3/ChangeLog.omp
@@ -1,5 +1,15 @@
2025-04-17 Thomas Schwinge <tschwi...@baylibre.com>
+ Backported from trunk:
+ 2025-04-07 Thomas Schwinge <tschwi...@baylibre.com>
+
+ PR target/119645
+ * 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'.
+
Backported from trunk:
2025-04-03 Thomas Schwinge <tschwi...@baylibre.com>
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 1c6d725a1359..453e231c7ec1 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -4023,10 +4023,11 @@ AC_DEFUN([GLIBCXX_ENABLE_LOCK_POLICY], [
dnl Why don't we check 8-byte CAS for sparc64, where _Atomic_word is long?!
dnl New targets should only check for CAS for the _Atomic_word type.
AC_TRY_COMPILE([
- #if defined __riscv
+ #if defined __AMDGCN__ || defined __nvptx__
+ /* Yes, please. */
+ #elif defined __riscv
# error "Defaulting to mutex-based locks for ABI compatibility"
- #endif
- #if ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
+ #elif ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
# error "No 2-byte compare-and-swap"
#elif ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
# error "No 4-byte compare-and-swap"
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 789c3929f4a5..377a788300c6 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -16394,10 +16394,11 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
- #if defined __riscv
+ #if defined __AMDGCN__ || defined __nvptx__
+ /* Yes, please. */
+ #elif defined __riscv
# error "Defaulting to mutex-based locks for ABI compatibility"
- #endif
- #if ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
+ #elif ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
# error "No 2-byte compare-and-swap"
#elif ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
# error "No 4-byte compare-and-swap"
@@ -16444,7 +16445,7 @@ $as_echo "mutex" >&6; }
# unnecessary for this test.
cat > conftest.$ac_ext << EOF
-#line 16447 "configure"
+#line 16448 "configure"
int main()
{
_Decimal32 d1;
@@ -16486,7 +16487,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
# unnecessary for this test.
cat > conftest.$ac_ext << EOF
-#line 16489 "configure"
+#line 16490 "configure"
template<typename T1, typename T2>
struct same
{ typedef T2 type; };
diff --git a/libstdc++-v3/configure.host b/libstdc++-v3/configure.host
index 8375764bf4dc..253e5a9ad0db 100644
--- a/libstdc++-v3/configure.host
+++ b/libstdc++-v3/configure.host
@@ -370,10 +370,21 @@ case "${host}" in
;;
esac
;;
+ amdgcn-*-amdhsa)
+ # To avoid greater pain elsewhere, force use of '__atomic' builtins,
+ # regardless of the outcome of 'configure' checks; see PR119645
+ # "GCN, nvptx: libstdc++ 'checking for atomic builtins [...]... no'".
+ atomicity_dir=cpu/generic/atomicity_builtins
+ ;;
arm*-*-freebsd*)
port_specific_symbol_files="\$(srcdir)/../config/os/gnu-linux/arm-eabi-extra.ver"
;;
nvptx-*-none)
+ # To avoid greater pain elsewhere, force use of '__atomic' builtins,
+ # regardless of the outcome of 'configure' checks; see PR119645
+ # "GCN, nvptx: libstdc++ 'checking for atomic builtins [...]... no'".
+ atomicity_dir=cpu/generic/atomicity_builtins
+
# For 'make all-target-libstdc++-v3', re 'alloca'/VLA usage:
EXTRA_CFLAGS="${EXTRA_CFLAGS} -mfake-ptx-alloca"
OPTIMIZE_CXXFLAGS="${OPTIMIZE_CXXFLAGS} -mfake-ptx-alloca"
