[Bug c++/94957] New: Compilation slowww for simple code with -O1/2/3 and -g in GCC 8 and 9

[hehaochen at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94957

            Bug ID: 94957
           Summary: Compilation slowww for simple code with -O1/2/3 and -g
                    in GCC 8 and 9
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hehaochen at hotmail dot com
  Target Milestone: ---

code:

---------------------------------

class MyObject
    {
    public:
        MyObject() {}
    };

    class MyClassSlow
    {
        MyObject array[30000] {}; 
    };


    int main()
    {
        MyClassSlow slow;
    }

---------------------------------


run : 
   g++ -Ox -g -std=c++11 test.cpp
in
  gcc-7 gcc-8 gcc-9 with -O1/2/3 -g


#############
##
##   Hangs "forever"
##   gcc version 9.2.0 (GCC)
##
#############

  -O3

    real    0m1.299s
    user    0m0.910s
    sys 0m0.197s

  -O3 -g

    Forever... (kill after 15min)


#############
##
##   Hangs "forever"
##   gcc version 8.2.0 (GCC)
##
#############

  -O3

    real    0m1.434s
    user    0m1.062s
    sys     0m0.229s

  -O2 -g

    Forever... (kill after 15min)

#############
##
## Acceptable but still slow in
##   gcc version 7.4.0 (GCC)
##
#############


  -O0 -g 

    real    0m 3.892s
    user    0m 3.404s
    sys     0m 0.482s


  -O1 -g

    real    1m 6.103s
    user    1m 5.718s
    sys     0m 0.302s


  -O2 -g

    real    1m 23.666s
    user    1m 23.310s
    sys     0m 0.280s


  -O3

    real    0m 1.451s
    user    0m 1.229s
    sys     0m 0.221s

  -O3 -g

    real    1m 19.463s
    user    1m 19.037s
    sys     0m 0.349s


Execution times (seconds)
 phase opt and generate  :  84.89 (99%) usr   1.88 (90%) sys  86.89 (99%) wall 
139631 kB (65%) ggc
 trivially dead code     :  82.12 (96%) usr   0.00 ( 0%) sys  82.26 (94%) wall 
     0 kB ( 0%) ggc



#############
##
## OK in clang
##
#############

clang version 9.0.0-svn366056

root@c5c7aa8003d9:/downloads# time  clang++-9 -O3 -g test.cpp

  real    0m 0.176s
  user    0m 0.103s
  sys     0m 0.073s

root@c5c7aa8003d9:/downloads# time  clang++-9 -O3 test.cpp

  real    0m 0.165s
  user    0m 0.102s
  sys     0m 0.063s