[Bug target/91875] Performance drop with mt19937 with -O2/-O3/-Ofast compared to -O1

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91875

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |marxin at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Well, using a native ISA (-march=native) gives me on znver1 following numbers
for GCC 9.2.0:

marxin@marxinbox:~/Programming/testcases> g++ pr91875.cc -O1 -march=native &&
./a.out 
float_default: 48.716
float_mt: 33.531
float_mt_64: 81.984
marxin@marxinbox:~/Programming/testcases> g++ pr91875.cc -O1 && ./a.out 
float_default: 48.484
float_mt: 32.037
float_mt_64: 82.632
marxin@marxinbox:~/Programming/testcases> g++ pr91875.cc -Ofast -march=native
&& ./a.out 
float_default: 46.845
float_mt: 20.189
float_mt_64: 66.006