On Wed, 5 Oct 2016 23:33:49 +1300, Bruce Hoult wrote: > On Wed, Oct 5, 2016 at 7:46 AM, Tim Northover via llvm-dev < > [email protected]> wrote: > > > Hi Emilio, > > > > On 4 October 2016 at 11:14, Emilio Pozuelo Monfort via llvm-dev > > <[email protected]> wrote: > > > In file included from /«PKGBUILDDIR»/lib/Support/ThreadPool.cpp:14:0: > > > /«PKGBUILDDIR»/include/llvm/Support/ThreadPool.h: In member function > > > 'std::shared_future<void> llvm::ThreadPool::async(Function&&, Args&& > > ...)': > > > /«PKGBUILDDIR»/include/llvm/Support/ThreadPool.h:78:77: error: return > > type > > > 'class std::shared_future<void>' is incomplete > > > inline std::shared_future<VoidTy> async(Function &&F, Args &&... > > ArgList) { > > > > > ^ > > > > > > Any idea about this failure? > > > > > > For the Debian armel porters, we're switching to LLVM 3.8, so this > > failure > > > (which happens on 3.8, 3.9 and llvm-toolchain-snapshot) is likely going > > to cause > > > some package removals on armel as we try to get rid of older LLVM > > versions. > > > Helping fixing this issue would be appreciated to prevent that. > > > > This looks like the kind of failure you get when your host toolchain > > doesn't support C++11 properly (specifically lock-free atomics in this > > case). When I've seen it before GCC was defaulting to a CPU that's > > too old to do atomics properly, and that configuration is very > > unlikely to be supported by LLVM ever (any more). > > > > This seems bogus. > > C++11 allows atomic variables to be implemented using mutexes if the CPU > doesn't support atomic operations on a given data type in some other way. > > If you don't call atomic_is_lock_free(&var) then everything should work > correctly, albeit perhaps more slowly than you might like. > > It seems to me that atomic_is_lock_free() (or precomputed shortcuts such as > ATOMIC_INT_LOCK_FREE) is there to enable you the possibility to use a > different algorithm (if one is available), not to throw up your hands and > say you don't support that architecture at all! > > If it's the standard library going out of its way to > check ATOMIC_INT_LOCK_FREE and then throwing up its hands and giving up > then I'd say that's a bug. Simply taking out that check should produce > working, correct code on anything that supports mutexes at all.
Attached patch to debian libstdc++ package is supposed to fix clang compilation.I'm still waiting compilation to complete before I can test it. The compilation will take long time in an armel vm. I decided to share it in case someone else has faster test environment than I have. The patch has extra src directory that needs to be striped with s/\([ab]\)\/src/\1/g if someone tries to apply it to upstream sources. Pauli
From 805f44b797bf23b1c2cd95ab8cd9c748c7bdb8ea Mon Sep 17 00:00:00 2001 From: Pauli <[email protected]> Date: Sat, 5 Nov 2016 17:33:20 +0200 Subject: [PATCH] libstdc++: Fix future header for targets without atomic int instructions --- libstdc++-v3/include/std/future | 4 +--- libstdc++-v3/libsupc++/eh_ptr.cc | 28 ++++++++++++++++------------ libstdc++-v3/libsupc++/exception | 3 +-- libstdc++-v3/libsupc++/exception_ptr.h | 4 ---- libstdc++-v3/libsupc++/nested_exception.cc | 2 -- libstdc++-v3/libsupc++/nested_exception.h | 4 ---- 6 files changed, 18 insertions(+), 27 deletions(-) Index: gcc-6-6.2.0/src/libstdc++-v3/include/std/future =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/include/std/future +++ gcc-6-6.2.0/src/libstdc++-v3/include/std/future @@ -182,8 +182,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION future<__async_result_of<_Fn, _Args...>> async(_Fn&& __fn, _Args&&... __args); -#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) \ - && (ATOMIC_INT_LOCK_FREE > 1) +#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1) /// Base class and enclosing scope. struct __future_base @@ -1745,7 +1744,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #endif // _GLIBCXX_ASYNC_ABI_COMPAT #endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1 - // && ATOMIC_INT_LOCK_FREE // @} group futures _GLIBCXX_END_NAMESPACE_VERSION Index: gcc-6-6.2.0/src/libstdc++-v3/libsupc++/eh_ptr.cc =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/libsupc++/eh_ptr.cc +++ gcc-6-6.2.0/src/libstdc++-v3/libsupc++/eh_ptr.cc @@ -23,14 +23,12 @@ // <http://www.gnu.org/licenses/>. #include <bits/c++config.h> -#include <bits/atomic_lockfree_defines.h> - -#if ATOMIC_INT_LOCK_FREE > 1 #define _GLIBCXX_EH_PTR_COMPAT #include <exception> #include <bits/exception_ptr.h> +#include <ext/atomicity.h> #include "unwind-cxx.h" using namespace __cxxabiv1; @@ -103,7 +101,9 @@ std::__exception_ptr::exception_ptr::_M_ { __cxa_refcounted_exception *eh = __get_refcounted_exception_header_from_obj (_M_exception_object); - __atomic_add_fetch (&eh->referenceCount, 1, __ATOMIC_ACQ_REL); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&eh->referenceCount); + __gnu_cxx::__atomic_add_dispatch(&eh->referenceCount, 1); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&eh->referenceCount); } } @@ -114,11 +114,13 @@ std::__exception_ptr::exception_ptr::_M_ if (_M_exception_object) { __cxa_refcounted_exception *eh = - __get_refcounted_exception_header_from_obj (_M_exception_object); - if (__atomic_sub_fetch (&eh->referenceCount, 1, __ATOMIC_ACQ_REL) == 0) + __get_refcounted_exception_header_from_obj (_M_exception_object); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&eh->referenceCount); + if (__gnu_cxx::__exchange_and_add_dispatch(&eh->referenceCount, -1) == 1) { - if (eh->exc.exceptionDestructor) - eh->exc.exceptionDestructor (_M_exception_object); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&eh->referenceCount); + if (eh->exc.exceptionDestructor) + eh->exc.exceptionDestructor (_M_exception_object); __cxa_free_exception (_M_exception_object); _M_exception_object = 0; @@ -219,8 +221,10 @@ __gxx_dependent_exception_cleanup(_Unwin __cxa_free_dependent_exception (dep); - if (__atomic_sub_fetch (&header->referenceCount, 1, __ATOMIC_ACQ_REL) == 0) + _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&header->referenceCount); + if (__gnu_cxx::__exchange_and_add_dispatch(&header->referenceCount, -1) == 1) { + _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&header->referenceCount); if (header->exc.exceptionDestructor) header->exc.exceptionDestructor (header + 1); @@ -238,7 +242,9 @@ std::rethrow_exception(std::exception_pt __cxa_dependent_exception *dep = __cxa_allocate_dependent_exception (); dep->primaryException = obj; - __atomic_add_fetch (&eh->referenceCount, 1, __ATOMIC_ACQ_REL); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_BEFORE(&eh->referenceCount); + __gnu_cxx::__atomic_add_dispatch(&eh->referenceCount, 1); + _GLIBCXX_SYNCHRONIZATION_HAPPENS_AFTER(&eh->referenceCount); dep->unexpectedHandler = get_unexpected (); dep->terminateHandler = get_terminate (); @@ -260,5 +266,3 @@ std::rethrow_exception(std::exception_pt } #undef _GLIBCXX_EH_PTR_COMPAT - -#endif Index: gcc-6-6.2.0/src/libstdc++-v3/libsupc++/exception =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/libsupc++/exception +++ gcc-6-6.2.0/src/libstdc++-v3/libsupc++/exception @@ -35,7 +35,6 @@ #pragma GCC visibility push(default) #include <bits/c++config.h> -#include <bits/atomic_lockfree_defines.h> extern "C++" { @@ -166,7 +165,7 @@ _GLIBCXX_END_NAMESPACE_VERSION #pragma GCC visibility pop -#if (__cplusplus >= 201103L) && (ATOMIC_INT_LOCK_FREE > 1) +#if (__cplusplus >= 201103L) #include <bits/exception_ptr.h> #include <bits/nested_exception.h> #endif Index: gcc-6-6.2.0/src/libstdc++-v3/libsupc++/exception_ptr.h =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/libsupc++/exception_ptr.h +++ gcc-6-6.2.0/src/libstdc++-v3/libsupc++/exception_ptr.h @@ -36,10 +36,6 @@ #include <bits/c++config.h> #include <bits/exception_defines.h> -#if ATOMIC_INT_LOCK_FREE < 2 -# error This platform does not support exception propagation. -#endif - extern "C++" { namespace std Index: gcc-6-6.2.0/src/libstdc++-v3/libsupc++/nested_exception.cc =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/libsupc++/nested_exception.cc +++ gcc-6-6.2.0/src/libstdc++-v3/libsupc++/nested_exception.cc @@ -25,7 +25,5 @@ namespace std { -#if ATOMIC_INT_LOCK_FREE > 1 nested_exception::~nested_exception() noexcept = default; -#endif } // namespace std Index: gcc-6-6.2.0/src/libstdc++-v3/libsupc++/nested_exception.h =================================================================== --- gcc-6-6.2.0.orig/src/libstdc++-v3/libsupc++/nested_exception.h +++ gcc-6-6.2.0/src/libstdc++-v3/libsupc++/nested_exception.h @@ -39,10 +39,6 @@ #include <bits/c++config.h> #include <bits/move.h> -#if ATOMIC_INT_LOCK_FREE < 2 -# error This platform does not support exception propagation. -#endif - extern "C++" { namespace std
