[Bug c++/80952] New: gcc 7.1.1 has a drastic performance downgrade using "-fprofile-arcs" compared to 6.3.1 version

[xiaonan830818 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80952

            Bug ID: 80952
           Summary: gcc 7.1.1 has a drastic performance downgrade using
                    "-fprofile-arcs" compared to 6.3.1 version
           Product: gcc
           Version: 7.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xiaonan830818 at gmail dot com
  Target Milestone: ---

Created attachment 41448
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41448&action=edit
Test program

Hi all,

My testbed is ArchLinux, X86_64, 32 cores, and I use the attached file to test
performance.

(1) Use the newest gcc 7.1.1, and build without "-fprofile-arcs" compile option
and run program:

$ g++ -fopenmp -g -O2 parallel.cpp
$ ./a.out
Function consume: 0.743077 s.

Then build with "-fprofile-arcs" compile option:

$ g++ -fopenmp -fprofile-arcs -g -O2 parallel.cpp
$ ./a.out
Function consume: 208 s.

We can see the performance gap is too large.

(2) While use gcc 6.3.1, without "-fprofile-arcs":  

$ g++ -fopenmp -g -O2 parallel.cpp
$ ./a.out
Function consume: 0.77169 s.

use it:  

$ g++ -fopenmp -fprofile-arcs -g -O2 parallel.cpp
$ ./a.out
Function consume: 0.746134 s.

We can see the performance is very near.