The application performance built from gcc 7.1 is very worse compared to gcc 6.3

[Nan Xiao]

Hi all,

Greetings from me!

My OS is ArchLinux, and on this Monday, I upgrade gcc from 6.3.1 to
7.1.1 (both packages are released by ArchLinux). But after rebuilding
my program, I find the performance downgrades drastically.

For single-thread version, the program which is built with "gcc 6.3.1"
would use ~85 seconds to process a transaction; while with "7.1.1", it
grows to ~115 seconds.
For multiple-thread version using OpenMP, the  program which is built
with "gcc 6.3.1" would use  only ~11 seconds to process a transaction;
while with "7.1.1", it grows to ~50 seconds.

The compile and link flags are " -g -O2 -fopenmp -fprofile-arcs
-ftest-coverage -fPIC   -std=gnu++11 ".

I also download and build gcc 7.1 myself from
https://gcc.gnu.org/gcc-7/, the single-thread program can use ~95
seconds, while OpenMP version still consumes ~50 seconds. So compared
to program built using gcc 6.3, the performance is very worse.

I have checked the release note of gcc
(https://gcc.gnu.org/gcc-7/changes.html), but can't find some valuable
information.

Could anyone give some comments? Thanks very much in advance!

Best Regards
Nan Xiao