From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x229.google.com (mail-lj1-x229.google.com [IPv6:2a00:1450:4864:20::229]) by sourceware.org (Postfix) with ESMTPS id 9BF5F3858CDA for ; Thu, 14 Sep 2023 07:43:57 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 9BF5F3858CDA Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=linaro.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=linaro.org Received: by mail-lj1-x229.google.com with SMTP id 38308e7fff4ca-2bfb17435e4so9762171fa.0 for ; Thu, 14 Sep 2023 00:43:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1694677436; x=1695282236; darn=gcc.gnu.org; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=k8jYTyLJfwcmmCJZB0mCyq84bT8FvmNe18DVJN7hTH0=; b=j4VztPztXpngv19PYjShiEUUmdwWHVkJJpQQprnOsmm6Q8AVOA+rJZR7B6dVEgPRgl vk7qMiuqnRB1szUOqVoPc2/sBcC0kmudcVlfxUnsQ83qWZzWVITMLUWKLgdfjAkLMpeP 474/0DNu080RW+5R4+yhHeH1JW8zxYws5n/3uDgYaJdhR5aGY0GeivedmRb14DPpKjZR /gzheQJqjFPqpAXrU1h3BYp/xXzYqYH/Dy6q1WhMOgvadBPQogC+3WPmiypXFDAzB5qw 83SjQdWI/JYZdv1t/rbRpfxBO4t3gCL4Wa6v352gNxGxRVoFblA+e5eWI+WNbPFU9oJX /icQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1694677436; x=1695282236; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=k8jYTyLJfwcmmCJZB0mCyq84bT8FvmNe18DVJN7hTH0=; b=YOW3mmUSmZum6gm9cnp/kDxH7i7QDzs3AyphR9v+1t1zsZfTJ1QgrtuWOUzCQQfjd2 ZjVtn0Om2+UVgAyylGawFViG5cHfJTTWrqeNPKiloIWF043qDTKCkiDHyMs/qL+xM4xn gEh9fDEjXbMgI18YgoDzrzBip2vQ4h35sDvRhg/PzUzgCFbO9atpkBLN2YLQLEktP7QR jP8J/UNdd7hKA3/LBuo/t8K/gTgz0sPUmtIC/icE7PFa973YlaudrRMuvWMYpLNgQAE7 52R96DWD975oBcFY/sLtQVDcj8ycZGWzbak5FFumxzAervEXiJ4Wsrdzug/SoiihsvVq USgw== X-Gm-Message-State: AOJu0YyJGNQjTJKKhHwDkc2KgjAbu5/wOK8Te4bbwdNgq+/ieFMJwdCb ufwruDdJUbtAR47NyZTltTFhp8PKM0qPd9myeZhZBqMNReMyB1uvi7Xqtw== X-Google-Smtp-Source: AGHT+IH6JPVxn8GP4LaKq4Gjhyld3as/HDnuSSya2FYOb7l6g0thuFNZRlBb5eKFK0mzfVXKjVIa9NjljyqZCAYdNZ0= X-Received: by 2002:a2e:9099:0:b0:2bc:dd96:147c with SMTP id l25-20020a2e9099000000b002bcdd96147cmr4132646ljg.34.1694677436064; Thu, 14 Sep 2023 00:43:56 -0700 (PDT) MIME-Version: 1.0 References: <20230913123226.2083892-1-jwakely@redhat.com> In-Reply-To: <20230913123226.2083892-1-jwakely@redhat.com> From: Christophe Lyon Date: Thu, 14 Sep 2023 09:43:44 +0200 Message-ID: Subject: Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics To: Jonathan Wakely Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Content-Type: multipart/alternative; boundary="000000000000960a6106054cd62c" X-Spam-Status: No, score=-9.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,HTML_MESSAGE,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: --000000000000960a6106054cd62c Content-Type: text/plain; charset="UTF-8" Hi, On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely wrote: > Tested x86_64-linux and aarch64-linux. I intend to push this to trunk. > > -- >8 -- > > These atomics cause linker errors on arm4t where __sync_synchronize is > not defined. For single-threaded targets we don't need the atomics. > > I ran the tests on arm-eabi default config (so, armv4t) with this patch, and here is the list of remaining UNRESOLVED tests: 29_atomics/atomic/compare_exchange_padding.cc 29_atomics/atomic/cons/value_init.cc 29_atomics/atomic_float/value_init.cc 29_atomics/atomic_integral/cons/value_init.cc 29_atomics/atomic_ref/compare_exchange_padding.cc 29_atomics/atomic_ref/generic.cc 29_atomics/atomic_ref/integral.cc 29_atomics/atomic_ref/pointer.cc experimental/polymorphic_allocator/construct_pair.cc all of them are due to undefined reference to __sync_synchronize (some also reference __atomic_compare_exchange_4, etc...) IIUC, this should not be the case for experimental/polymorphic_allocator/construct_pair.cc ? The reference for __sync_synchronize is near the beginning of test0[123] from a call to __atomic_load_n line 835 of atomic_base.h not sure where it comes from, the .loc directive indicates line 28 of the testcase which is the opening brace HTH Christophe libstdc++-v3/ChangeLog: > > * include/experimental/io_context (io_context) > [!_GLIBCXX_HAS_GTHREADS]: > Use a plain integer for _M_work_count for single-threaded > targets. > * src/c++17/memory_resource.cc [!_GLIBCXX_HAS_GTHREADS] > (atomic_mem_res): Use unsynchronized type for single-threaded > targets. > --- > libstdc++-v3/include/experimental/io_context | 4 ++ > libstdc++-v3/src/c++17/memory_resource.cc | 49 ++++++++++---------- > 2 files changed, 29 insertions(+), 24 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/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) > @@ -94,10 +94,31 @@ namespace pmr > > __constinit constant_init newdel_res{}; > __constinit constant_init null_res{}; > -#if ATOMIC_POINTER_LOCK_FREE == 2 > + > +#ifndef _GLIBCXX_HAS_GTHREADS > +# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED > + // Single-threaded, no need for synchronization > + struct atomic_mem_res > + { > + constexpr > + atomic_mem_res(memory_resource* r) : val(r) { } > + > + memory_resource* val; > + > + memory_resource* load(std::memory_order) const > + { > + return val; > + } > + > + memory_resource* exchange(memory_resource* r, std::memory_order) > + { > + return std::__exchange(val, r); > + } > + }; > +#elif ATOMIC_POINTER_LOCK_FREE == 2 > using atomic_mem_res = atomic; > # define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED > -#elif defined(_GLIBCXX_HAS_GTHREADS) > +#else > // Can't use pointer-width atomics, define a type using a mutex > instead: > struct atomic_mem_res > { > @@ -123,27 +144,7 @@ namespace pmr > return std::__exchange(val, r); > } > }; > -#else > -# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED > - // Single-threaded, no need for synchronization > - struct atomic_mem_res > - { > - constexpr > - atomic_mem_res(memory_resource* r) : val(r) { } > - > - memory_resource* val; > - > - memory_resource* load(std::memory_order) const > - { > - return val; > - } > - > - memory_resource* exchange(memory_resource* r, std::memory_order) > - { > - 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}; > -- > 2.41.0 > > --000000000000960a6106054cd62c--