[Bug ipa/79966] New: [6/7 Regression] run time more than twice slower when using -fipa-cp-clone

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79966

            Bug ID: 79966
           Summary: [6/7 Regression] run time more than twice slower when
                    using -fipa-cp-clone
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dominiq at lps dot ens.fr
  Target Milestone: ---

Created attachment 40927
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40927&action=edit
reduced test from pr79930

This PR is a sequel of pr79930. On gcc6 and trunk (7.0) the run time is more
than twice slower when the attached test is compiled with -fipa-cp-clone in
addition to -O2 -fpeel-loops -finline-functions:

% gfca sum_xy.f90 -O2 -fpeel-loops -finline-functions
% ./a.out
 Using SUM, time:          9.28960443E-02
 sum =  -19609.087488337318     
% gfca sum_xy.f90 -O2 -fpeel-loops -fipa-cp-clone -finline-functions
% ./a.out
 Using SUM, time:         0.264802039    
 sum =  -56108.398701889098     
% gfc6 sum_xy.f90 -O2 -fpeel-loops -finline-functions
% ./a.out
 Using SUM, time:          9.48660374E-02
 sum =  -27582.388828175150     
% gfc6 sum_xy.f90 -O2 -fpeel-loops -fipa-cp-clone -finline-functions
% ./a.out
 Using SUM, time:         0.279235005    
 sum =  -37131.668569316826     
% gfc5 sum_xy.f90 -O2 -fpeel-loops -finline-functions
% ./a.out
 Using SUM, time:         0.106678963    
 sum =   6552.5940282615447     
% gfc5 sum_xy.f90 -O2 -fpeel-loops -fipa-cp-clone -finline-functions
% ./a.out
 Using SUM, time:         0.104918003    
 sum =   28692.268429922191     

gfca is trunk at r245974, gfc6 is 6.3.1 at r245745, and gfc5 is 5.4.1 at
r245752.

Looking at my archives it seems that the regression appeared un gcc5 before
branching, but has been reverted since, while always being in the gcc6 branch.