* [PATCH] libstdc++: Remove some more unconditional uses of atomics
@ 2023-09-13 12:31 Jonathan Wakely
2023-09-14 7:43 ` Christophe Lyon
0 siblings, 1 reply; 6+ messages in thread
From: Jonathan Wakely @ 2023-09-13 12:31 UTC (permalink / raw)
To: libstdc++, gcc-patches; +Cc: Christophe Lyon
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.
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<count_type> _M_work_count;
+#else
+ count_type _M_work_count;
+#endif
mutable execution_context::mutex_type _M_mtx;
queue<function<void()>> _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 <atomic>
#include <bit> // has_single_bit, bit_ceil, bit_width
#include <new>
+#include <bits/move.h> // std::__exchange
#if ATOMIC_POINTER_LOCK_FREE != 2
# include <bits/std_mutex.h> // std::mutex, std::lock_guard
-# include <bits/move.h> // std::__exchange
#endif
#if __has_cpp_attribute(clang::require_constant_initialization)
@@ -94,10 +94,31 @@ namespace pmr
__constinit constant_init<newdel_res_t> newdel_res{};
__constinit constant_init<null_res_t> 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<memory_resource*>;
# 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<atomic_mem_res> default_res{&newdel_res.obj};
--
2.41.0
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics
2023-09-13 12:31 [PATCH] libstdc++: Remove some more unconditional uses of atomics Jonathan Wakely
@ 2023-09-14 7:43 ` Christophe Lyon
2023-09-14 8:17 ` Jonathan Wakely
0 siblings, 1 reply; 6+ messages in thread
From: Christophe Lyon @ 2023-09-14 7:43 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 5091 bytes --]
Hi,
On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com> 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<count_type> _M_work_count;
> +#else
> + count_type _M_work_count;
> +#endif
> mutable execution_context::mutex_type _M_mtx;
> queue<function<void()>> _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 <atomic>
> #include <bit> // has_single_bit, bit_ceil,
> bit_width
> #include <new>
> +#include <bits/move.h> // std::__exchange
> #if ATOMIC_POINTER_LOCK_FREE != 2
> # include <bits/std_mutex.h> // std::mutex, std::lock_guard
> -# include <bits/move.h> // std::__exchange
> #endif
>
> #if __has_cpp_attribute(clang::require_constant_initialization)
> @@ -94,10 +94,31 @@ namespace pmr
>
> __constinit constant_init<newdel_res_t> newdel_res{};
> __constinit constant_init<null_res_t> 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<memory_resource*>;
> # 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<atomic_mem_res>
> default_res{&newdel_res.obj};
> --
> 2.41.0
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics
2023-09-14 7:43 ` Christophe Lyon
@ 2023-09-14 8:17 ` Jonathan Wakely
2023-09-14 8:41 ` Christophe Lyon
0 siblings, 1 reply; 6+ messages in thread
From: Jonathan Wakely @ 2023-09-14 8:17 UTC (permalink / raw)
To: Christophe Lyon; +Cc: libstdc++, gcc-patches
On Thu, 14 Sept 2023 at 08:44, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>
> Hi,
>
>
> On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com> 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
Doh, I removed the atomics from <memory_resource> but this is
<experimental/memory_resource>, which has a separate implementation.
I'll make a change to <experimental/memory_resource> as well, thanks
for catching my silly mistake.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics
2023-09-14 8:17 ` Jonathan Wakely
@ 2023-09-14 8:41 ` Christophe Lyon
2023-09-14 9:06 ` Jonathan Wakely
0 siblings, 1 reply; 6+ messages in thread
From: Christophe Lyon @ 2023-09-14 8:41 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 1939 bytes --]
On Thu, 14 Sept 2023 at 10:17, Jonathan Wakely <jwakely@redhat.com> wrote:
> On Thu, 14 Sept 2023 at 08:44, Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
> >
> > Hi,
> >
> >
> > On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com>
> 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
>
> Doh, I removed the atomics from <memory_resource> but this is
> <experimental/memory_resource>, which has a separate implementation.
>
> I'll make a change to <experimental/memory_resource> as well, thanks
> for catching my silly mistake.
>
>
You're welcome.
So I'll shrink my patch and add dg-require-thread-fence only to the few
29_atomics tests listed above.
Christophe
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics
2023-09-14 8:41 ` Christophe Lyon
@ 2023-09-14 9:06 ` Jonathan Wakely
2023-09-14 9:11 ` Christophe Lyon
0 siblings, 1 reply; 6+ messages in thread
From: Jonathan Wakely @ 2023-09-14 9:06 UTC (permalink / raw)
To: Christophe Lyon; +Cc: libstdc++, gcc-patches
On Thu, 14 Sept 2023 at 09:41, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>
>
>
> On Thu, 14 Sept 2023 at 10:17, Jonathan Wakely <jwakely@redhat.com> wrote:
>>
>> On Thu, 14 Sept 2023 at 08:44, Christophe Lyon
>> <christophe.lyon@linaro.org> wrote:
>> >
>> > Hi,
>> >
>> >
>> > On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com> 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
>>
>> Doh, I removed the atomics from <memory_resource> but this is
>> <experimental/memory_resource>, which has a separate implementation.
>>
>> I'll make a change to <experimental/memory_resource> as well, thanks
>> for catching my silly mistake.
>>
>
> You're welcome.
> So I'll shrink my patch and add dg-require-thread-fence only to the few 29_atomics tests listed above.
Great, thanks. That's approved for trunk then.
N.B. if you'd prefer to add { dg-require-effective-target thread_fence
} instead of { dg-require-thread-fence "" } then that's fine, just
note that the effective target uses an underscore not a hyphen. The
dg-require-thread-fence proc just uses the proc that checks the
thread_fence effective target, so both forms do the same thing.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] libstdc++: Remove some more unconditional uses of atomics
2023-09-14 9:06 ` Jonathan Wakely
@ 2023-09-14 9:11 ` Christophe Lyon
0 siblings, 0 replies; 6+ messages in thread
From: Christophe Lyon @ 2023-09-14 9:11 UTC (permalink / raw)
To: Jonathan Wakely; +Cc: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 2788 bytes --]
On Thu, 14 Sept 2023 at 11:06, Jonathan Wakely <jwakely@redhat.com> wrote:
> On Thu, 14 Sept 2023 at 09:41, Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
> >
> >
> >
> > On Thu, 14 Sept 2023 at 10:17, Jonathan Wakely <jwakely@redhat.com>
> wrote:
> >>
> >> On Thu, 14 Sept 2023 at 08:44, Christophe Lyon
> >> <christophe.lyon@linaro.org> wrote:
> >> >
> >> > Hi,
> >> >
> >> >
> >> > On Wed, 13 Sept 2023 at 14:32, Jonathan Wakely <jwakely@redhat.com>
> 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
> >>
> >> Doh, I removed the atomics from <memory_resource> but this is
> >> <experimental/memory_resource>, which has a separate implementation.
> >>
> >> I'll make a change to <experimental/memory_resource> as well, thanks
> >> for catching my silly mistake.
> >>
> >
> > You're welcome.
> > So I'll shrink my patch and add dg-require-thread-fence only to the few
> 29_atomics tests listed above.
>
> Great, thanks. That's approved for trunk then.
>
> N.B. if you'd prefer to add { dg-require-effective-target thread_fence
> } instead of { dg-require-thread-fence "" } then that's fine, just
> note that the effective target uses an underscore not a hyphen. The
> dg-require-thread-fence proc just uses the proc that checks the
> thread_fence effective target, so both forms do the same thing.
>
> Ha! Just sent v2, I kept dg-require-thread-fence, because it was used
elsewhere in the libstsdc++ testsuite.
Thanks,
Christophe
^ permalink raw reply [flat|nested] 6+ messages in thread
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2023-09-13 12:31 [PATCH] libstdc++: Remove some more unconditional uses of atomics Jonathan Wakely
2023-09-14 7:43 ` Christophe Lyon
2023-09-14 8:17 ` Jonathan Wakely
2023-09-14 8:41 ` Christophe Lyon
2023-09-14 9:06 ` Jonathan Wakely
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