Re: [PATCH] libstdc++: Use RAII in std::vector::_M_realloc_insert

[Jonathan Wakely <jwakely@redhat.com>]

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On Wed, 28 Jun 2023 at 08:56, Jan Hubicka wrote:

> > I think the __throw_bad_alloc() and __throw_bad_array_new_length()
> > functions should always be rare, so marking them cold seems fine (users
> who
> > define their own allocators that want to throw bad_alloc "often" will
> > probably throw it directly, they shouldn't be using our
> __throw_bad_alloc()
> > function anyway). I don't think __throw_bad_exception is ever used, so
> that
> > doesn't matter (we could remove it from the header and just keep its
> > definition in the library, but there's no big advantage to doing that).
> > Others like __throw_length_error() should also be very very rare, and
> could
> > be marked cold.
> >
> > Maybe we should just mark everything in <bits/functexcept.h> as cold. If
> > users want to avoid the cost of calls to those functions they can do so
> by
> > checking function preconditions/arguments to avoid the exceptions. There
> > are very few places where a throwing libstdc++ API doesn't have a way to
> > avoid the exception. The only one that isn't easily avoidable is
> > __throw_bad_alloc but OOM should be rare.
>
> Hi,
> this marks everything in functexcept.h as cold and I also noticed that
> we probably want to mark as such terminate.
>
> With fix to 110436 and -O3 we now inline _M_realloc_insert, yay :)
>
> tested on x86_64-linux, OK?
>

OK for trunk, thanks.


>
>         * include/bits/c++config (std::__terminate): Mark cold.
>         * include/bits/functexcept.h: Mark everything as cold.
>         * libsupc++/exception: Mark terminate and unexpected as cold.
> diff --git a/libstdc++-v3/include/bits/c++config
> b/libstdc++-v3/include/bits/c++config
> index 009a017b048..dd47f274d5f 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -320,7 +320,7 @@ namespace std
>    extern "C++" __attribute__ ((__noreturn__, __always_inline__))
>    inline void __terminate() _GLIBCXX_USE_NOEXCEPT
>    {
> -    void terminate() _GLIBCXX_USE_NOEXCEPT __attribute__ ((__noreturn__));
> +    void terminate() _GLIBCXX_USE_NOEXCEPT __attribute__
> ((__noreturn__,__cold__));
>      terminate();
>    }
>  #pragma GCC visibility pop
> diff --git a/libstdc++-v3/include/bits/functexcept.h
> b/libstdc++-v3/include/bits/functexcept.h
> index 2765f7865df..a2e97413661 100644
> --- a/libstdc++-v3/include/bits/functexcept.h
> +++ b/libstdc++-v3/include/bits/functexcept.h
> @@ -57,61 +57,61 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>    // Helper for exception objects in <typeinfo>
>    void
> -  __throw_bad_cast(void) __attribute__((__noreturn__));
> +  __throw_bad_cast(void) __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_bad_typeid(void) __attribute__((__noreturn__));
> +  __throw_bad_typeid(void) __attribute__((__noreturn__,__cold__));
>
>    // Helpers for exception objects in <stdexcept>
>    void
> -  __throw_logic_error(const char*) __attribute__((__noreturn__));
> +  __throw_logic_error(const char*) __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_domain_error(const char*) __attribute__((__noreturn__));
> +  __throw_domain_error(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_invalid_argument(const char*) __attribute__((__noreturn__));
> +  __throw_invalid_argument(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_length_error(const char*) __attribute__((__noreturn__));
> +  __throw_length_error(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_out_of_range(const char*) __attribute__((__noreturn__));
> +  __throw_out_of_range(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_out_of_range_fmt(const char*, ...) __attribute__((__noreturn__))
> +  __throw_out_of_range_fmt(const char*, ...)
> __attribute__((__noreturn__,__cold__))
>      __attribute__((__format__(__gnu_printf__, 1, 2)));
>
>    void
> -  __throw_runtime_error(const char*) __attribute__((__noreturn__));
> +  __throw_runtime_error(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_range_error(const char*) __attribute__((__noreturn__));
> +  __throw_range_error(const char*) __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_overflow_error(const char*) __attribute__((__noreturn__));
> +  __throw_overflow_error(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_underflow_error(const char*) __attribute__((__noreturn__));
> +  __throw_underflow_error(const char*)
> __attribute__((__noreturn__,__cold__));
>
>    // Helpers for exception objects in <ios>
>    void
> -  __throw_ios_failure(const char*) __attribute__((__noreturn__));
> +  __throw_ios_failure(const char*) __attribute__((__noreturn__,__cold__));
>
>    void
> -  __throw_ios_failure(const char*, int) __attribute__((__noreturn__));
> +  __throw_ios_failure(const char*, int)
> __attribute__((__noreturn__,__cold__));
>
>    // Helpers for exception objects in <system_error>
>    void
> -  __throw_system_error(int) __attribute__((__noreturn__));
> +  __throw_system_error(int) __attribute__((__noreturn__,__cold__));
>
>    // Helpers for exception objects in <future>
>    void
> -  __throw_future_error(int) __attribute__((__noreturn__));
> +  __throw_future_error(int) __attribute__((__noreturn__,__cold__));
>
>    // Helpers for exception objects in <functional>
>    void
> -  __throw_bad_function_call() __attribute__((__noreturn__));
> +  __throw_bad_function_call() __attribute__((__noreturn__,__cold__));
>
>  #else // ! HOSTED
>
> diff --git a/libstdc++-v3/libsupc++/exception
> b/libstdc++-v3/libsupc++/exception
> index a34386e6026..00a6347ebe5 100644
> --- a/libstdc++-v3/libsupc++/exception
> +++ b/libstdc++-v3/libsupc++/exception
> @@ -75,7 +75,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
>
>    /** The runtime will call this function if %exception handling must be
>     *  abandoned for any reason.  It can also be called by the user.  */
> -  void terminate() _GLIBCXX_USE_NOEXCEPT __attribute__ ((__noreturn__));
> +  void terminate() _GLIBCXX_USE_NOEXCEPT __attribute__
> ((__noreturn__,__cold__));
>
>  #if __cplusplus < 201703L || (__cplusplus <= 202002L &&
> _GLIBCXX_USE_DEPRECATED)
>    /// If you write a replacement %unexpected handler, it must be of this
> type.
> @@ -104,7 +104,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
>     * @deprecated Removed from the C++ standard in C++17
>     */
>    _GLIBCXX11_DEPRECATED
> -  void unexpected() __attribute__ ((__noreturn__));
> +  void unexpected() __attribute__ ((__noreturn__,__cold__));
>  #endif
>
>    /** [18.6.4]/1:  'Returns true after completing evaluation of a
>
>