From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id 645883858D20; Thu, 14 Sep 2023 13:27:09 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 645883858D20 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1694698029; bh=FPQYiXP8ehy6kj4agc6aCeIIBRi2Fx8qfRpQmGYY9AQ=; h=From:To:Subject:Date:From; b=vC3x7QLrgRtq6KdVR7gLz2l8KoeFNBmhHL0UlAtF2OotdGNWdZDGkZBBOvVnC0KJ5 7Cmn4RdqU2FF9HZ3ZNTioXFsQ9Quxfsmgbm8B/soApQCEFLBlAW1hU4zd/smzH2s2Z z9z6Nw7Mq4TdRtWneZtPl3gVmJCWHH0mCWhpKf00= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-3990] libstdc++: Remove some more unconditional uses of atomics X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: 8517317ce8e9fbea0b4c7a8f87a86d07d95dc8c7 X-Git-Newrev: b9b9d0a7db098e2b7e6894dca98ddd551067cad1 Message-Id: <20230914132709.645883858D20@sourceware.org> Date: Thu, 14 Sep 2023 13:27:09 +0000 (GMT) List-Id: https://gcc.gnu.org/g:b9b9d0a7db098e2b7e6894dca98ddd551067cad1 commit r14-3990-gb9b9d0a7db098e2b7e6894dca98ddd551067cad1 Author: Jonathan Wakely Date: Tue Sep 12 12:04:37 2023 +0100 libstdc++: Remove some more unconditional uses of atomics These atomics cause linker errors on arm4t where __sync_synchronize is not defined. For single-threaded targets we don't need the atomics. libstdc++-v3/ChangeLog: * include/experimental/io_context (io_context) [!_GLIBCXX_HAS_GTHREADS]: Use a plain integer for _M_work_count for single-threaded targets. * include/experimental/memory_resource (__get_default_resource) [!_GLIBCXX_HAS_GTHREADS]: Use unsynchronized type for single-threaded targets. * src/c++17/default_resource.h: Adjust preprocessor conditions to match memory_resource.cc. * src/c++17/memory_resource.cc [!_GLIBCXX_HAS_GTHREADS] (atomic_mem_res): Use unsynchronized type for single-threaded targets. Diff: --- libstdc++-v3/include/experimental/io_context | 4 +++ libstdc++-v3/include/experimental/memory_resource | 12 +++++++- libstdc++-v3/src/c++17/default_resource.h | 6 +++- libstdc++-v3/src/c++17/memory_resource.cc | 35 ++++++++++++----------- 4 files changed, 38 insertions(+), 19 deletions(-) diff --git a/libstdc++-v3/include/experimental/io_context b/libstdc++-v3/include/experimental/io_context index c59f8c8e73b..c878d5a7025 100644 --- a/libstdc++-v3/include/experimental/io_context +++ b/libstdc++-v3/include/experimental/io_context @@ -562,7 +562,11 @@ inline namespace v1 } }; +#ifdef _GLIBCXX_HAS_GTHREADS atomic _M_work_count; +#else + count_type _M_work_count; +#endif mutable execution_context::mutex_type _M_mtx; queue> _M_op; bool _M_stopped = false; diff --git a/libstdc++-v3/include/experimental/memory_resource b/libstdc++-v3/include/experimental/memory_resource index 9f1cb42373e..6f419a0a929 100644 --- a/libstdc++-v3/include/experimental/memory_resource +++ b/libstdc++-v3/include/experimental/memory_resource @@ -549,10 +549,20 @@ namespace pmr { // The default memory resource /// @cond undocumented - inline std::atomic& + inline auto& __get_default_resource() { +#ifndef _GLIBCXX_HAS_GTHREADS + struct type { + using value_type = memory_resource*; + explicit type(value_type __r) : _M_r(__r) { } + value_type _M_r; + value_type load() const { return _M_r; } + value_type exchange(value_type __r) { return std::__exchange(_M_r, __r); } + }; +#else using type = atomic; +#endif alignas(type) static unsigned char __buf[sizeof(type)]; static type* __r = new(__buf) type(new_delete_resource()); return *__r; diff --git a/libstdc++-v3/src/c++17/default_resource.h b/libstdc++-v3/src/c++17/default_resource.h index 522cee13b90..f8d03d7d3bc 100644 --- a/libstdc++-v3/src/c++17/default_resource.h +++ b/libstdc++-v3/src/c++17/default_resource.h @@ -2,7 +2,11 @@ // to suppress the warning caused by using a reserved init_priority. #pragma GCC system_header -#if ATOMIC_POINTER_LOCK_FREE == 2 || defined(__GTHREAD_MUTEX_INIT) +#ifndef _GLIBCXX_HAS_GTHREADS +# error "This file should not be included for this build" +#elif ATOMIC_POINTER_LOCK_FREE == 2 +# error "This file should not be included for this build" +#elif defined __GTHREAD_MUTEX_INIT # error "This file should not be included for this build" #endif diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc index c0c7cf0cf83..63856eadaf5 100644 --- a/libstdc++-v3/src/c++17/memory_resource.cc +++ b/libstdc++-v3/src/c++17/memory_resource.cc @@ -27,9 +27,9 @@ #include #include // has_single_bit, bit_ceil, bit_width #include +#include // std::__exchange #if ATOMIC_POINTER_LOCK_FREE != 2 # include // std::mutex, std::lock_guard -# include // std::__exchange #endif #if __has_cpp_attribute(clang::require_constant_initialization) @@ -94,56 +94,57 @@ namespace pmr __constinit constant_init newdel_res{}; __constinit constant_init null_res{}; -#if ATOMIC_POINTER_LOCK_FREE == 2 - using atomic_mem_res = atomic; + +#ifndef _GLIBCXX_HAS_GTHREADS # define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED -#elif defined(_GLIBCXX_HAS_GTHREADS) - // Can't use pointer-width atomics, define a type using a mutex instead: + // Single-threaded, no need for synchronization struct atomic_mem_res { -# ifdef __GTHREAD_MUTEX_INIT -# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED - // std::mutex has constexpr constructor constexpr -# endif atomic_mem_res(memory_resource* r) : val(r) { } - mutex mx; memory_resource* val; - memory_resource* load(std::memory_order) + memory_resource* load(std::memory_order) const { - lock_guard lock(mx); return val; } memory_resource* exchange(memory_resource* r, std::memory_order) { - lock_guard lock(mx); return std::__exchange(val, r); } }; -#else +#elif ATOMIC_POINTER_LOCK_FREE == 2 + using atomic_mem_res = atomic; # define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED - // Single-threaded, no need for synchronization +#else + // Can't use pointer-width atomics, define a type using a mutex instead: struct atomic_mem_res { +# ifdef __GTHREAD_MUTEX_INIT +# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED + // std::mutex has constexpr constructor constexpr +# endif atomic_mem_res(memory_resource* r) : val(r) { } + mutex mx; memory_resource* val; - memory_resource* load(std::memory_order) const + memory_resource* load(std::memory_order) { + lock_guard lock(mx); return val; } memory_resource* exchange(memory_resource* r, std::memory_order) { + lock_guard lock(mx); return std::__exchange(val, r); } }; -#endif // ATOMIC_POINTER_LOCK_FREE == 2 +#endif #ifdef _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED __constinit constant_init default_res{&newdel_res.obj};