[Bug target/86448] GCC 9 compiler generates slower code for spec 2006 milc on a power9 using -mcpu=power9 than using -mcpu=power8

[kelvin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86448

--- Comment #4 from kelvin at gcc dot gnu.org ---

There are aspects of Michael's recent comment that I may not fully understand.

I checked the source for milc, and it is C, so I added -fgnu89-inline to the
list of OPTIMIZE options.  Then I reran my tests with gcc8 (svn version 262483)
on a DD2.2 power9 machine.


OPTIMIZE        = -O3 -fpeel-loops -funroll-loops -ftree-vectorize
-fvect-cost-\
model -fno-strict-aliasing -msave-toc-indirect
-mno-pointers-to-nested-function\
s -fno-aggressive-loop-optimizations -ffast-math -mveclibabi=mass
-mrecip=rsqrt\
 -fgnu89-inline -mcpu=power9 (vs. -mcpu=power8)
LDOPT           = -m64 -Wl,-q  -Wl,-rpath=%{BASE_DIR}/lib64

I'm still not seeing the performance degradation Michael saw.  Here are my most
recent results:

        gcc8            gcc9                    

        28.79           28.14                   
        29.01           28.84                   
        28.51           28.5                    
        28.55           28.39                   
        29.02           29.07                   
        29.1            28.51                   
                                        delta   % delta
average 28.83           28.575          0.255   0.88%

Does anyone see anything I may be doing wrong?