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* [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence @ 2012-10-08 21:21 ozabluda at gmail dot com 2012-10-08 21:27 ` [Bug libstdc++/54861] " redi at gcc dot gnu.org ` (5 more replies) 0 siblings, 6 replies; 7+ messages in thread From: ozabluda at gmail dot com @ 2012-10-08 21:21 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 Bug #: 54861 Summary: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned@gcc.gnu.org ReportedBy: ozabluda@gmail.com Host: x86_64-linux-gnu Target: x86_64-linux-gnu Build: x86_64-linux-gnu Created attachment 28394 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28394 Preprocessed source #include <atomic> void f() { std::atomic_signal_fence(std::memory_order_seq_cst); } f(): .LFB321: .cfi_startproc mfence # <== unnecessary mfence ret .cfi_endproc The reason is that std::atomic_signal_fence() (in bits/atomic_base.h) simply calls std::atomic_thread_fence(), where mfence is indeed necessary. C++11 29.8.8 says: extern "C" void atomic_signal_fence(memory_order order) noexcept; Effects: equivalent to atomic_thread_fence(order), except that the resulting ordering constraints are established only between a thread and a signal handler executed in the same thread. 8 Note: compiler optimizations and reorderings of loads and stores are inhibited in the same way as with atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would have inserted are not emitted. C11 7.17.4.2 has an identical language. =============================== $ g++-4.7 -v -save-temps --std=c++0x -O2 -c atomic_fences.cpp Using built-in specs. COLLECT_GCC=g++-4.7 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.7.0-7ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --disable-bootstrap --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.7.0 (Ubuntu/Linaro 4.7.0-7ubuntu3) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-O2' '-c' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.7/cc1plus -E -quiet -v -imultiarch x86_64-linux-gnu -D_GNU_SOURCE atomic_fences.cpp -mtune=generic -march=x86-64 -std=c++11 -O2 -fpch-preprocess -fstack-protector -o atomic_fences.ii ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/include/c++/4.7 /usr/include/c++/4.7/x86_64-linux-gnu /usr/include/c++/4.7/backward /usr/lib/gcc/x86_64-linux-gnu/4.7/include /usr/local/include /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed /usr/include/x86_64-linux-gnu /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-O2' '-c' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.7/cc1plus -fpreprocessed atomic_fences.ii -quiet -dumpbase atomic_fences.cpp -mtune=generic -march=x86-64 -auxbase atomic_fences -O2 -std=c++11 -version -fstack-protector -o atomic_fences.s GNU C++ (Ubuntu/Linaro 4.7.0-7ubuntu3) version 4.7.0 (x86_64-linux-gnu) compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++ (Ubuntu/Linaro 4.7.0-7ubuntu3) version 4.7.0 (x86_64-linux-gnu) compiled by GNU C version 4.6.3, GMP version 5.0.2, MPFR version 3.1.0-p3, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 33e4f0c75e4f7f1ac5eae22180dee261 COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-O2' '-c' '-shared-libgcc' '-mtune=generic' '-march=x86-64' as --64 -o atomic_fences.o atomic_fences.s COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.7/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++11' '-O2' '-c' '-shared-libgcc' '-mtune=generic' '-march=x86-64' ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com @ 2012-10-08 21:27 ` redi at gcc dot gnu.org 2012-10-09 18:34 ` amacleod at redhat dot com ` (4 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: redi at gcc dot gnu.org @ 2012-10-08 21:27 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Component|c++ |libstdc++ Severity|normal |enhancement ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com 2012-10-08 21:27 ` [Bug libstdc++/54861] " redi at gcc dot gnu.org @ 2012-10-09 18:34 ` amacleod at redhat dot com 2012-10-09 18:40 ` amacleod at redhat dot com ` (3 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: amacleod at redhat dot com @ 2012-10-09 18:34 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 Andrew Macleod <amacleod at redhat dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2012-10-09 AssignedTo|unassigned at gcc dot |amacleod at redhat dot com |gnu.org | Ever Confirmed|0 |1 --- Comment #1 from Andrew Macleod <amacleod at redhat dot com> 2012-10-09 18:34:08 UTC --- Created attachment 28402 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28402 patch to resolve the problem Just a typo in the header file where __atomic_thread_fence() built-in was being called instead of the __atomic_signal_fence() built-in function. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com 2012-10-08 21:27 ` [Bug libstdc++/54861] " redi at gcc dot gnu.org 2012-10-09 18:34 ` amacleod at redhat dot com @ 2012-10-09 18:40 ` amacleod at redhat dot com 2012-10-09 18:49 ` ozabluda at gmail dot com ` (2 subsequent siblings) 5 siblings, 0 replies; 7+ messages in thread From: amacleod at redhat dot com @ 2012-10-09 18:40 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 --- Comment #2 from Andrew Macleod <amacleod at redhat dot com> 2012-10-09 18:40:16 UTC --- Author: amacleod Date: Tue Oct 9 18:40:02 2012 New Revision: 192268 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=192268 Log: 2012-10-09 Andrew MacLeod <amacleod@redhat.com> PR libstdc++/54861 * include/bits/atomic_base.h (atomic_signal_fence): Call __atomic_signal_fence instead of __atomic_thread_fence. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/include/bits/atomic_base.h ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com ` (2 preceding siblings ...) 2012-10-09 18:40 ` amacleod at redhat dot com @ 2012-10-09 18:49 ` ozabluda at gmail dot com 2012-10-10 20:48 ` amacleod at redhat dot com 2013-11-19 14:03 ` glisse at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: ozabluda at gmail dot com @ 2012-10-09 18:49 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 --- Comment #3 from Oleg Zabluda <ozabluda at gmail dot com> 2012-10-09 18:48:56 UTC --- I can confirm that this fixes it in gcc 4.7.0. ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com ` (3 preceding siblings ...) 2012-10-09 18:49 ` ozabluda at gmail dot com @ 2012-10-10 20:48 ` amacleod at redhat dot com 2013-11-19 14:03 ` glisse at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: amacleod at redhat dot com @ 2012-10-10 20:48 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 --- Comment #4 from Andrew Macleod <amacleod at redhat dot com> 2012-10-10 20:47:48 UTC --- Author: amacleod Date: Wed Oct 10 20:47:39 2012 New Revision: 192332 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=192332 Log: 2012-10-10 Andrew MacLeod <amacleod@redhat.com> PR libstdc++/54861 * include/bits/atomic_base.h (atomic_signal_fence): Call __atomic_signal_fence instead of __atomic_thread_fence. Modified: branches/gcc-4_7-branch/libstdc++-v3/ChangeLog branches/gcc-4_7-branch/libstdc++-v3/include/bits/atomic_base.h ^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/54861] std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com ` (4 preceding siblings ...) 2012-10-10 20:48 ` amacleod at redhat dot com @ 2013-11-19 14:03 ` glisse at gcc dot gnu.org 5 siblings, 0 replies; 7+ messages in thread From: glisse at gcc dot gnu.org @ 2013-11-19 14:03 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54861 Marc Glisse <glisse at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |FIXED --- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> --- >From the comments, seems that this was fixed and Andrew just forgot to close the PR. ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2013-11-19 14:03 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-10-08 21:21 [Bug c++/54861] New: std::atomic_signal_fence(std::memory_order_seq_cst) issues unnecessary mfence ozabluda at gmail dot com 2012-10-08 21:27 ` [Bug libstdc++/54861] " redi at gcc dot gnu.org 2012-10-09 18:34 ` amacleod at redhat dot com 2012-10-09 18:40 ` amacleod at redhat dot com 2012-10-09 18:49 ` ozabluda at gmail dot com 2012-10-10 20:48 ` amacleod at redhat dot com 2013-11-19 14:03 ` glisse at gcc dot gnu.org
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