[Bug fortran/22244] New: dimension information is lost for multi-dimension array

["woodzltc at sources dot redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Please have a look at the following source, variable "a" is a two-dimension 
array (5 X 5):

       program array2
       integer a(5, 5)

       do i = 1, 5
         do j = 1, 5
           a(i, j) = i * j
           write (*, *) a(i, j)
         end do
       end do

       end program

After using gfortran to compile it, use "readelf -wi array2" to see the 
outputed debuginfo:

 <2><89>: Abbrev Number: 3 (DW_TAG_variable)
     DW_AT_name        : a
     DW_AT_decl_file   : 1
     DW_AT_decl_line   : 2
     DW_AT_type        : <be>
     DW_AT_location    : 3 byte block: 75 94 7f         (DW_OP_breg5: -108)

 ...
 <1><be>: Abbrev Number: 7 (DW_TAG_array_type)
     DW_AT_type        : <b6>
 <2><c3>: Abbrev Number: 8 (DW_TAG_subrange_type)
     DW_AT_type        : <b6>
     DW_AT_lower_bound : 0
     DW_AT_upper_bound : 24
     
>From the above, we can see that two-dimension array a(5, 5) is flatten to
a one-dimension array with 25 elements (0 - 24).  This will hinder GDB from 
correctly inteprete "a". 

This might also has some other negative impacts.  Feng Wang ever said that (I 
put him in the CC list): 

It's not only gdb problem, but also affects performance and optimization on the
tree-level. We lose the dimension infomation and can not get correct data
dependency. This limits many optimizations like loop interchange and loop
distribution, etc.

-- 
           Summary: dimension information is lost for multi-dimension array
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: woodzltc at sources dot redhat dot com
                CC: gcc-bugs at gcc dot gnu dot org,wf_cs at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22244