On Tue, 2024-01-16 at 17:53 +0800, xndcn wrote:
> Thanks, so I add a test: atomic_float/compare_exchange_padding.cc,
> which will fail due to timeout without the patch.
Please resend in plain text instead of HTML. Sending in HTML causes the
patch mangled.
And libstdc++ patches should CC libstd...@gcc.gnu.org, in addition to
gcc-patches@gcc.gnu.org.
> ---
> libstdc++-v3/ChangeLog:
>
> * include/bits/atomic_base.h: add __builtin_clear_padding in __atomic_float
> constructor.
> * testsuite/lib/dg-options.exp: enable libatomic for IA32 and X86-64.
> * testsuite/29_atomics/atomic_float/compare_exchange_padding.cc: New test.
> ---
> libstdc++-v3/include/bits/atomic_base.h | 7 ++-
> .../atomic_float/compare_exchange_padding.cc | 50 +++++++++++++++++++
> libstdc++-v3/testsuite/lib/dg-options.exp | 1 +
> 3 files changed, 57 insertions(+), 1 deletion(-)
> create mode 100644
> libstdc++-v3/testsuite/29_atomics/atomic_float/compare_exchange_padding.cc
>
> diff --git a/libstdc++-v3/include/bits/atomic_base.h
> b/libstdc++-v3/include/bits/atomic_base.h
> index d3a2c4f3805..cbe3749e17f 100644
> --- a/libstdc++-v3/include/bits/atomic_base.h
> +++ b/libstdc++-v3/include/bits/atomic_base.h
> @@ -1283,7 +1283,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> constexpr
> __atomic_float(_Fp __t) : _M_fp(__t)
> - { }
> + {
> +#if __cplusplus >= 201402L && __has_builtin(__builtin_clear_padding)
> + if _GLIBCXX17_CONSTEXPR (__atomic_impl::__maybe_has_padding<_Fp>())
> + __builtin_clear_padding(std::__addressof(_M_fp));
> +#endif
> + }
>
> __atomic_float(const __atomic_float&) = delete;
> __atomic_float& operator=(const __atomic_float&) = delete;
> diff --git
> a/libstdc++-v3/testsuite/29_atomics/atomic_float/compare_exchange_padding.cc
> b/libstdc++-v3/testsuite/29_atomics/atomic_float/compare_exchange_padding.cc
> new file mode 100644
> index 00000000000..9376ab22850
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/29_atomics/atomic_float/compare_exchange_padding.cc
> @@ -0,0 +1,50 @@
> +// { dg-do run { target c++20 } }
> +// { dg-options "-O0" }
> +// { dg-timeout 10 }
> +// { dg-additional-options "-mlong-double-80" { target x86_64-*-* } }
> +// { dg-do run { target { ia32 || x86_64-*-* } } }
> +// { dg-add-options libatomic }
> +
> +#include <atomic>
> +#include <testsuite_hooks.h>
> +
> +template<typename T>
> +void __attribute__((noinline,noipa))
> +fill_padding(T& f)
> +{
> + T mask;
> + __builtin_memset(&mask, 0xff, sizeof(T));
> + __builtin_clear_padding(&mask);
> + unsigned char* ptr_f = (unsigned char*)&f;
> + unsigned char* ptr_mask = (unsigned char*)&mask;
> + for (int i = 0; i < sizeof(T); i++)
> + {
> + if (ptr_mask[i] == 0x00)
> + {
> + ptr_f[i] = 0xff;
> + }
> + }
> +}
> +
> +void
> +test01()
> +{
> + long double f = 0.5f; // long double may contains padding on X86
> + fill_padding(f);
> + std::atomic<long double> as{ f }; // padding cleared on constructor
> + long double t = 1.5;
> +
> + as.fetch_add(t);
> + long double s = f + t;
> + t = as.load();
> + VERIFY(s == t); // padding ignored on float comparing
> + fill_padding(s);
> + VERIFY(as.compare_exchange_weak(s, f)); // padding cleared on cmpexchg
> + fill_padding(f);
> + VERIFY(as.compare_exchange_strong(f, t)); // padding cleared on cmpexchg
> +}
> +
> +int main()
> +{
> + test01();
> +}
> diff --git a/libstdc++-v3/testsuite/lib/dg-options.exp
> b/libstdc++-v3/testsuite/lib/dg-options.exp
> index bc387d17ed7..d9a19dadd7f 100644
> --- a/libstdc++-v3/testsuite/lib/dg-options.exp
> +++ b/libstdc++-v3/testsuite/lib/dg-options.exp
> @@ -337,6 +337,7 @@ proc add_options_for_libatomic { flags } {
> || ([istarget powerpc*-*-*] && [check_effective_target_ilp32])
> || [istarget riscv*-*-*]
> || ([istarget sparc*-*-linux-gnu] && [check_effective_target_ilp32])
> + || ([istarget i?86-*-*] || [istarget x86_64-*-*])
This seems too overkill as "dg-add-options libatomic" is not intended to
handle 16-byte atomics. Maybe we can fork this to a new dg-add-options
like "add_options_for_libatomic_16b"?
> } {
> global TOOL_OPTIONS
>
> --
> 2.25.1
--
Xi Ruoyao <xry...@xry111.site>
School of Aerospace Science and Technology, Xidian University
