[Bug debug/101669] New: error reading variable from debug information when compiling with -O2

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101669

            Bug ID: 101669
           Summary: error reading variable from debug information when
                    compiling with -O2
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: guojiufu at gcc dot gnu.org
  Target Milestone: ---

For below case:
----------gdb.f90
  integer :: a(10), b(12)
  call sub (a, 10)
  call sub (b, 12)
  write (*,*) a, b
end

subroutine sub (a, n)
  integer :: a(n), n
  integer(kind=8) nl, i
  nl = n

  do i = 1, nl
    a(i) = i
  end do
  write (*,*) a                                                  
end subroutine
------------
At -O2, using command "gfortran -O2 -g ~/temp/gdb.f90 -o arg1.exe" to compile,
when debugger it with gdb, there is log:
a=<error reading variable: dwarf2_find_location_expression: Corrupted DWARF
expression.>

$ gdb arg1.exe
...
(gdb) b sub
Breakpoint 1 at 0x400710: file /home/guojiufu/temp/gdb.f90, line 7.
(gdb) r
Starting program: /home/guojiufu/gcc/build/gcc-mainline-base/arg1.exe 

Breakpoint 1, sub (a=<error reading variable: dwarf2_find_location_expression:
Corrupted DWARF expression.>, 
    n=10) at /home/guojiufu/temp/gdb.f90:7
7       subroutine sub (a, n)

This msg does not occur when compiling with -O3 -g.

This issue can be reproduced on x86/ppc64le with the latest trunk, and also
occur in gcc11.