[Bug tree-optimization/80980] New: -Os generates larger code than -O1 because loop is not removed

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80980

            Bug ID: 80980
           Summary: -Os generates larger code than -O1 because loop is not
                    removed
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

$ cat foo.f90
program main
  integer :: i
  do i=1,1
    print *,i
  end do
end program main
$ gfortran -o os.s -S -Os foo.f90 
$ gfortran -o o1.s -S -O1 foo.f90 
$ wc -l os.s
82 os.s
$ wc -l o1.s
63 o1.s

This is probably due to -Os not removing the loop.
The -fdump-tree-optimized dump shows for -Os

  <bb 2> [15.00%]:
  i = 1;

  <bb 3> [100.00%]:
  i.2_1 = i;
  if (i.2_1 > 1)
    goto <bb 5>; [15.00%]
  else
    goto <bb 4>; [85.00%]

and for -O1

  <bb 2> [15.00%]:
  i = 1;

$ gfortran -v
Es werden eingebaute Spezifikationen verwendet.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/home/ig25/lib/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Ziel: x86_64-pc-linux-gnu
Konfiguriert mit: ../trunk/configure --prefix=/home/ig25
--enable-languages=c,c++,fortran --enable-maintainer-mode
Thread-Modell: posix
gcc-Version 8.0.0 20170525 (experimental) (GCC)