It would be great if this can make into gcc4.8. The patch has close to 0 impact on code stability.
David On Fri, Dec 28, 2012 at 11:32 AM, Rong Xu <x...@google.com> wrote: > Hi Honza, > > In the other thread of discussion (similar patch in google-4_7 > branch), you said you were thinking if to let this patch into trunk in > stage 3. Can you give some update? > > Thanks, > > -Rong > > On Fri, Dec 21, 2012 at 10:37 AM, Rong Xu <x...@google.com> wrote: >> On Fri, Dec 21, 2012 at 1:25 AM, Jan Hubicka <hubi...@ucw.cz> wrote: >>>> Hi, >>>> >>>> This patch adds support of atomic update of profiles counters. The goal is >>>> to improve >>>> the poor counter values for highly thread programs. >>>> >>>> The atomic update is under a new option -fprofile-gen-atomic=<N> >>>> N=0: default, no atomic update >>>> N=1: atomic update edge counters. >>>> N=2: atomic update some of value profile counters (currently indirect-call >>>> and one value profile). >>>> N=3: both edge counter and the above value profile counters. >>>> Other value: fall back to the default. >>>> >>>> This patch is a simple porting of the version in google-4_7 branch. It >>>> uses __atomic_fetch_add >>>> based on Andrew Pinski's suggestion. Note I did not apply to all the value >>>> profiles as >>>> the indirect-call profile is the most relevant one here. >>>> >>>> Test with bootstrap. >>>> >>>> Comments and suggestions are welcomed. >>>> >>>> Thanks, >>>> >>>> -Rong >>>> >>>> >>>> 2012-12-20 Rong Xu <x...@google.com> >>>> >>>> * libgcc/libgcov.c (__gcov_one_value_profiler_body_atomic): New >>>> function. Atomic update profile counters. >>>> (__gcov_one_value_profiler_atomic): Ditto. >>>> (__gcov_indirect_call_profiler_atomic): Ditto. >>>> * gcc/gcov-io.h: Macros for atomic update. >>>> * gcc/common.opt: New option. >>>> * gcc/tree-profile.c (gimple_init_edge_profiler): Atomic >>>> update profile counters. >>>> (gimple_gen_edge_profiler): Ditto. >>> >>> The patch looks resonable. Eventually we probably should provide rest of >>> the value counters >>> in thread safe manner. What happens on targets not having atomic >>> operations? >> >> From >> http://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#_005f_005fsync-Builtins, >> it says: >> "If a particular operation cannot be implemented on the target >> processor, a warning is generated and a call an external function is >> generated. " >> >> So I think there will be a warning and eventually a link error of unsat. >> >> Thanks, >> >> -Rong >> >> >>> >>> Honza
