[Bug target/72861] New: [7 Regression] 25% tramp3d-v4 performance regression on ppc64le

["trippels at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72861

            Bug ID: 72861
           Summary: [7 Regression] 25% tramp3d-v4 performance regression
                    on ppc64le
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: trippels at gcc dot gnu.org
  Target Milestone: ---
              Host: powerpc64le-unknown-linux-gnu
            Target: powerpc64le-unknown-linux-gnu
             Build: powerpc64le-unknown-linux-gnu

Performance of tramp3d-v4 regressed more than 25% compared to gcc-6
on ppc64le (gcc112):

gcc-6:

trippels@gcc2-power8 ~ % ~/gcc_6/usr/local/bin/g++ -w -Ofast -mlra -mcpu=power8
tramp3d-v4.cpp

 Performance counter stats for './a.out --cartvis 1.0 0.0 --rhomin 1e-8 -n 20'
(5 runs):

       1972.550946      task-clock (msec)         #    0.999 CPUs utilized     
      ( +-  0.22% )
               159      context-switches          #    0.081 K/sec             
      ( +-  0.90% )
                 0      cpu-migrations            #    0.000 K/sec              
             1,224      page-faults               #    0.621 K/sec             
      ( +-  0.02% )
     6,748,308,064      cycles                    #    3.421 GHz               
      ( +-  0.22% ) [66.46%]
       102,294,018      stalled-cycles-frontend   #    1.52% frontend cycles
idle     ( +-  3.23% ) [49.91%]
     4,241,962,795      stalled-cycles-backend    #   62.86% backend  cycles
idle     ( +-  0.42% ) [50.41%]
     7,902,269,951      instructions              #    1.17  insns per cycle    
                                                  #    0.54  stalled cycles per
insn  ( +-  0.17% ) [67.10%]
       740,198,353      branches                  #  375.249 M/sec             
      ( +-  0.12% ) [50.14%]
        12,209,406      branch-misses             #    1.65% of all branches   
      ( +-  0.25% ) [49.82%]

       1.973964281 seconds time elapsed                                        
 ( +-  0.22% )


gcc-7:

trippels@gcc2-power8 ~ % ~/gcc_7/usr/local/bin/g++ -w -Ofast -mlra -mcpu=power8
tramp3d-v4.cpp 

 Performance counter stats for './a.out --cartvis 1.0 0.0 --rhomin 1e-8 -n 20'
(5 runs):

       2677.865248      task-clock (msec)         #    0.999 CPUs utilized     
      ( +-  0.84% )
               163      context-switches          #    0.061 K/sec             
      ( +-  1.77% )
                 0      cpu-migrations            #    0.000 K/sec             
      ( +-100.00% )
             2,092      page-faults               #    0.781 K/sec             
      ( +-  0.03% )
     9,149,015,944      cycles                    #    3.417 GHz               
      ( +-  0.92% ) [66.65%]
       105,804,553      stalled-cycles-frontend   #    1.16% frontend cycles
idle     ( +-  5.21% ) [50.12%]
     6,383,265,282      stalled-cycles-backend    #   69.77% backend  cycles
idle     ( +-  1.30% ) [50.31%]
     8,980,496,614      instructions              #    0.98  insns per cycle    
                                                  #    0.71  stalled cycles per
insn  ( +-  0.32% ) [66.96%]
       682,369,238      branches                  #  254.818 M/sec             
      ( +-  0.25% ) [49.93%]
        10,159,864      branch-misses             #    1.49% of all branches   
      ( +-  0.61% ) [49.82%]

       2.679415575 seconds time elapsed                                        
 ( +-  0.84% )