[Bug fortran/91512] [10 Regression] Fortran compile time regression.

[skpgkp2 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91512

--- Comment #4 from Sunil Pandey <skpgkp2 at gmail dot com> ---
(In reply to Thomas Koenig from comment #3)
> (In reply to Sunil Pandey from comment #2)
> 
> >  phase opt and generate             :  47.72 ( 97%)   0.24 ( 77%)  48.04 (
> > 96%)  118205 kB ( 89%)
> 
> So, phase_opt_and_generate appears to be something strange.
> 
> What the patch did was to change the way for subarrays that are
> packed because they are passed to an old-style argument, like this:
> 
> module x
>   implicit none
> contains
>   subroutine bar(a, n)
>     integer, intent(in) :: n
>     integer, intent(in), dimension(n) :: a
>     print *,a
>   end subroutine bar
> end module x
> 
> program main
>   use x
>   implicit none
>   integer, parameter :: n = 10
>   integer, dimension(n) :: a
>   integer :: i
>   a = [(i,i=1,n)]
>   call bar(a(n:1:-1),n)
> end program main
> 
> After the patch, the packing is done in the front end, which
> means that the optimizers can see through it and possibly inline
> the procedures, or do other optimizations.  If these optimizations
> hit some quadratic (or worse) behavior, this could lead to long
> compilation times.
> 
> I would assume that your code has a lot of places where code like
> the above occurs, is that the case?

Actually it is spec cpu 2017 521.wrf benchmark getting this problem while
compiling. Compilation taking forever, you can see while compiling file
module_first_rk_step_part1.fppized.f90 as a representative.