On Mon, Aug 9, 2021 at 10:01 AM Sebastian Huber
<sebastian.hu...@embedded-brains.de> wrote:
>
> If get_gcov_type() returns a 64-bit type, then 64-bit atomic operations in
> hardware are required for the "atomic" method. Add a new method to force
> atomic operations even if a library implementation (libatomic) must be used.
I do wonder about the =atomic behavior here - I'd expected that to
be equivalent to force-atomic...
With =force-atomic the user will need to eventually link to -latomic
himself, correct? What happens for targets that do not have libatomic support?
See libatomic/configure.tgt - is that something we can test for and error/warn?
Thanks,
Richard.
> gcc/
>
> * common.opt (fprofile-update): Add force-atomic method.
> * coretypes.h (profile_update): Add PROFILE_UPDATE_FORCE_ATOMIC.
> * doc/invoke.texi (fprofile-update): Document force-atomic method.
> * tree-profile.c (tree_profiling): Support force-atomic method.
> ---
> gcc/common.opt | 5 ++++-
> gcc/coretypes.h | 3 ++-
> gcc/doc/invoke.texi | 14 +++++++++-----
> gcc/tree-profile.c | 2 ++
> 4 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/gcc/common.opt b/gcc/common.opt
> index d9da1131eda..ea887c987af 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -2247,7 +2247,7 @@ Enable correction of flow inconsistent profile data
> input.
>
> fprofile-update=
> Common Joined RejectNegative Enum(profile_update) Var(flag_profile_update)
> Init(PROFILE_UPDATE_SINGLE)
> --fprofile-update=[single|atomic|prefer-atomic] Set the profile update method.
> +-fprofile-update=[single|atomic|prefer-atomic|force-atomic] Set the
> profile update method.
>
> fprofile-filter-files=
> Common Joined RejectNegative Var(flag_profile_filter_files)
> @@ -2285,6 +2285,9 @@ Enum(profile_update) String(atomic)
> Value(PROFILE_UPDATE_ATOMIC)
> EnumValue
> Enum(profile_update) String(prefer-atomic)
> Value(PROFILE_UPDATE_PREFER_ATOMIC)
>
> +EnumValue
> +Enum(profile_update) String(force-atomic) Value(PROFILE_UPDATE_FORCE_ATOMIC)
> +
> fprofile-prefix-path=
> Common Joined RejectNegative Var(profile_prefix_path)
> Remove prefix from absolute path before mangling name for
> -fprofile-generate= and -fprofile-use=.
> diff --git a/gcc/coretypes.h b/gcc/coretypes.h
> index 406572e947d..ded8e718994 100644
> --- a/gcc/coretypes.h
> +++ b/gcc/coretypes.h
> @@ -209,7 +209,8 @@ enum offload_abi {
> enum profile_update {
> PROFILE_UPDATE_SINGLE,
> PROFILE_UPDATE_ATOMIC,
> - PROFILE_UPDATE_PREFER_ATOMIC
> + PROFILE_UPDATE_PREFER_ATOMIC,
> + PROFILE_UPDATE_FORCE_ATOMIC
> };
>
> /* Type of profile reproducibility methods. */
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index a64cec5387e..df920545ac1 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -14905,11 +14905,11 @@ part of the path and keep all file names relative
> to the main build directory.
> @item -fprofile-update=@var{method}
> @opindex fprofile-update
>
> -Alter the update method for an application instrumented for profile
> -feedback based optimization. The @var{method} argument should be one of
> -@samp{single}, @samp{atomic} or @samp{prefer-atomic}.
> -The first one is useful for single-threaded applications,
> -while the second one prevents profile corruption by emitting thread-safe
> code.
> +Alter the update method for an application instrumented for profile feedback
> +based optimization or code-coverage. The @var{method} argument should be one
> +of @samp{single}, @samp{atomic}, @samp{prefer-atomic} or @samp{force-atomic}.
> +The first one is useful for single-threaded applications, while the second
> one
> +prevents profile corruption by emitting thread-safe code.
>
> @strong{Warning:} When an application does not properly join all threads
> (or creates an detached thread), a profile file can be still corrupted.
> @@ -14919,6 +14919,10 @@ when supported by a target, or to @samp{single}
> otherwise. The GCC driver
> automatically selects @samp{prefer-atomic} when @option{-pthread}
> is present in the command line.
>
> +Using @samp{force-atomic} forces the use of an @samp{atomic} method even if
> the
> +target does not support it directly in hardware and a library implementation
> +must be used instead.
> +
> @item -fprofile-filter-files=@var{regex}
> @opindex fprofile-filter-files
>
> diff --git a/gcc/tree-profile.c b/gcc/tree-profile.c
> index 5a74cc96e13..ac2ef4ccdf2 100644
> --- a/gcc/tree-profile.c
> +++ b/gcc/tree-profile.c
> @@ -718,6 +718,8 @@ tree_profiling (void)
> else if (flag_profile_update == PROFILE_UPDATE_PREFER_ATOMIC)
> flag_profile_update = can_support_atomic
> ? PROFILE_UPDATE_ATOMIC : PROFILE_UPDATE_SINGLE;
> + else if (flag_profile_update == PROFILE_UPDATE_FORCE_ATOMIC)
> + flag_profile_update = PROFILE_UPDATE_ATOMIC;
>
> /* This is a small-ipa pass that gets called only once, from
> cgraphunit.c:ipa_passes(). */
> --
> 2.26.2
>
