[Bug gcov-profile/67463] PGO (Profile Guided Optimizations) are not applied with gcc-5.2.1 (they are fine on gcc-4.9.x)

[shlomif at shlomifish dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67463

--- Comment #3 from Shlomi Fish <shlomif at shlomifish dot org> ---
Hi Martin, thanks for returning to me.

(In reply to Martin Liška from comment #2)
> Hi.
> 
> Sorry for waiting for some time. I tested your benchmark, where I had to
> disable tcmalloc as I can't link it with GCC 4.9, caused by C++ abi change.
> I also enhanced dump output to print total time spent (when function
> FCS_PRINT_FINISHED is called):
> 
> 4.9.4:
> Finished in 3.607
> Finished in 3.613
> Finished in 3.621
> Finished in 3.662
> 
> 5.4.0:
> Finished in 3.643
> Finished in 3.636
> Finished in 3.630
> Finished in 3.708
> 
> 6.3.0:
> Finished in 3.618
> Finished in 3.618
> Finished in 3.627
> Finished in 3.652
> 
> Tested on my desktop machine with Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz.
> That mentioned, I cannot see the regression, all numbers look within noise
> level.
> The regression you reported is very small (~3%) and it would be very hard to
> compare generated assembly to find different decisions made by GCC. Please
> try to
> test GCC 6 and possible GCC 7 (which will be released in couple of weeks)
> and if seen
> a significant regress, please reopen the issue.

Thanks! I'll try.