[Bug debug/37738] New: Fortran DW_TAG_common_block has incorrect placement/scope

[Bug debug/37738] New: Fortran DW_TAG_common_block has incorrect placement/scope

[jan dot kratochvil at redhat dot com]

gfortran:
(1) Merges all common blocks into a single one.
(2) Places this single common block into the first subroutine where it was
used.

Fix:
(1) The scope of the common block is only the subroutine where it is present.
    Each subroutine should have its own DW_TAG_common_block.
    Accessing variable imported by a common block in different subroutine does
    not access the common block - it creates a local variable there.
(2) (Placing the common block directly under CU not discussed - IMO wrong.)

Intel Fortran compiler IMO does it right.


subroutine a
  INTEGER*4 a_i
  common /block/a_i
  a_i = 1
end subroutine a
subroutine b
  INTEGER*4 b_i
  common /block/b_i
  a_i = 3
  b_i = 2
end subroutine b
subroutine c
  INTEGER*4 a_i
  common /block/a_i
  if (a_i .ne. 2) call abort
end subroutine c
program abc
  call a
  call b
  call c
end program abc


/opt/intel/fce/10.1.008/bin/ifort

<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
 <1><68>: Abbrev Number: 3 (DW_TAG_subprogram)
  <2><8a>: Abbrev Number: 4 (DW_TAG_common_block)
   <3><a0>: Abbrev Number: 5 (DW_TAG_variable)
 <1><c8>: Abbrev Number: 3 (DW_TAG_subprogram)
  <2><ea>: Abbrev Number: 6 (DW_TAG_variable)
  <2><fa>: Abbrev Number: 4 (DW_TAG_common_block)
   <3><110>: Abbrev Number: 5 (DW_TAG_variable)
 <1><135>: Abbrev Number: 3 (DW_TAG_subprogram)
  <2><157>: Abbrev Number: 4 (DW_TAG_common_block)
   <3><16d>: Abbrev Number: 5 (DW_TAG_variable)
 <1><187>: Abbrev Number: 7 (DW_TAG_subprogram)

The section .debug_info contains:
 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
     DW_AT_language    : 14     (Fortran 95)
     DW_AT_name        : abc.f90
     DW_AT_producer    : Intel (R) Fortran Compiler Fixes RangesRelative
 <1><68>: Abbrev Number: 3 (DW_TAG_subprogram)
     DW_AT_name        : a
 <2><8a>: Abbrev Number: 4 (DW_TAG_common_block)
     DW_AT_name        : block_
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <3><a0>: Abbrev Number: 5 (DW_TAG_variable)
     DW_AT_name        : a_i
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <1><c8>: Abbrev Number: 3 (DW_TAG_subprogram)
     DW_AT_name        : b
 <2><ea>: Abbrev Number: 6 (DW_TAG_variable)
     DW_AT_name        : a_i
     DW_AT_location    : 2 byte block: 76 70    (DW_OP_breg6: -16)
 <2><fa>: Abbrev Number: 4 (DW_TAG_common_block)
     DW_AT_name        : block_
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <3><110>: Abbrev Number: 5 (DW_TAG_variable)
     DW_AT_name        : b_i
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <1><135>: Abbrev Number: 3 (DW_TAG_subprogram)
     DW_AT_name        : c
 <2><157>: Abbrev Number: 4 (DW_TAG_common_block)
     DW_AT_name        : block_
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <3><16d>: Abbrev Number: 5 (DW_TAG_variable)
     DW_AT_name        : a_i
     DW_AT_location    : 9 byte block: 3 70 45 68 0 0 0 0 0     (DW_OP_addr:
684570)
 <1><187>: Abbrev Number: 7 (DW_TAG_subprogram)
     DW_AT_calling_convention: 2        (program)
     DW_AT_name        : abc


GNU Fortran (GCC) version 4.4.0 20081005 (experimental)
(x86_64-unknown-linux-gnu)
        compiled by GNU C version 4.4.0 20081005 (experimental), GMP version
4.2.2, MPFR version 2.3.1.

<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
 <1><2d>: Abbrev Number: 2 (DW_TAG_subprogram)
  <2><4b>: Abbrev Number: 3 (DW_TAG_common_block)
   <3><5c>: Abbrev Number: 4 (DW_TAG_variable)
   <3><72>: Abbrev Number: 4 (DW_TAG_variable)
   <3><88>: Abbrev Number: 4 (DW_TAG_variable)
 <1><a7>: Abbrev Number: 2 (DW_TAG_subprogram)
  <2><c5>: Abbrev Number: 6 (DW_TAG_variable)
 <1><db>: Abbrev Number: 7 (DW_TAG_subprogram)

The section .debug_info contains:
 <0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
    < c>   DW_AT_producer    : (indirect string, offset: 0x1e): GNU Fortran
4.4.0 20081005 (experimental)
    <10>   DW_AT_language    : 14       (Fortran 95)
    <11>   DW_AT_name        : (indirect string, offset: 0x0): abc.f90
 <1><2d>: Abbrev Number: 2 (DW_TAG_subprogram)
    <2f>   DW_AT_name        : a
 <2><4b>: Abbrev Number: 3 (DW_TAG_common_block)
    <4c>   DW_AT_name        : (indirect string, offset: 0x8): block
    <52>   DW_AT_location    : 9 byte block: 3 0 c 60 0 0 0 0 0        
(DW_OP_addr: 600c00)
 <3><5c>: Abbrev Number: 4 (DW_TAG_variable)
    <5d>   DW_AT_name        : a_i
    <68>   DW_AT_location    : 9 byte block: 3 0 c 60 0 0 0 0 0        
(DW_OP_addr: 600c00)
 <3><72>: Abbrev Number: 4 (DW_TAG_variable)
    <73>   DW_AT_name        : b_i
    <7e>   DW_AT_location    : 9 byte block: 3 0 c 60 0 0 0 0 0        
(DW_OP_addr: 600c00)
 <3><88>: Abbrev Number: 4 (DW_TAG_variable)
    <89>   DW_AT_name        : a_i
    <94>   DW_AT_location    : 9 byte block: 3 0 c 60 0 0 0 0 0        
(DW_OP_addr: 600c00)
 <1><a7>: Abbrev Number: 2 (DW_TAG_subprogram)
    <a9>   DW_AT_name        : b
 <2><c5>: Abbrev Number: 6 (DW_TAG_variable)
    <c6>   DW_AT_name        : a_i
    <d0>   DW_AT_location    : 2 byte block: 91 6c      (DW_OP_fbreg: -20)
 <1><db>: Abbrev Number: 7 (DW_TAG_subprogram)
    <dd>   DW_AT_name        : c
 <1><f5>: Abbrev Number: 8 (DW_TAG_subprogram)
    <f7>   DW_AT_name        : abc
    <111>   DW_AT_calling_convention: 2 (program)


-- 
           Summary: Fortran DW_TAG_common_block has incorrect
                    placement/scope
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jan dot kratochvil at redhat dot com
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[jan dot kratochvil at redhat dot com]

------- Comment #1 from jan dot kratochvil at redhat dot com  2008-10-05 15:33 -------
Saw there also needless DW_OP_plus_uconst - it could be single DW_OP_addr for
all the common block variables (which would make the GDB support a bit easier).

program a2
  INTEGER*4 a
  INTEGER*4 b
  common /block/a,b
  a = 1
  a = 2
end program a2

 <2><4d>: Abbrev Number: 3 (DW_TAG_common_block)
    <4e>   DW_AT_name        : (indirect string, offset: 0x46): block
    <54>   DW_AT_location    : 9 byte block: 3 e0 a 60 0 0 0 0 0       
(DW_OP_addr: 600ae0)
 <3><5e>: Abbrev Number: 4 (DW_TAG_variable)
    <5f>   DW_AT_name        : a
    <68>   DW_AT_location    : 9 byte block: 3 e0 a 60 0 0 0 0 0       
(DW_OP_addr: 600ae0)
 <3><72>: Abbrev Number: 4 (DW_TAG_variable)
    <73>   DW_AT_name        : b
    <7c>   DW_AT_location    : 11 byte block: 3 e0 a 60 0 0 0 0 0 23 4 
(DW_OP_addr: 600ae0; DW_OP_plus_uconst: 4)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-10-06 15:11:07
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2008-10-07 18:15 -------
Subject: Bug 37738

Author: jakub
Date: Tue Oct  7 18:14:16 2008
New Revision: 140944

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=140944
Log:
        PR debug/37738
        * dwarf2out.c (common_block_die_table): New variable.
        (common_block_die_table_hash, common_block_die_table_eq): New
        functions.
        (gen_variable_die): Look up a DW_TAG_common_block die for a particular
        COMMON block in the current scope rather than globally.  Optimize
        DW_OP_addr SYMBOL_REF DW_OP_plus_uconst off into
        DW_OP_addr SYMBOL_REF+off.

        * gfortran.dg/debug/pr37738.f: New test.

Added:
    trunk/gcc/testsuite/gfortran.dg/debug/pr37738.f
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/dwarf2out.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[mikael at gcc dot gnu dot org]

------- Comment #3 from mikael at gcc dot gnu dot org  2008-12-08 22:23 -------
Is it fixed?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2008-12-08 22:42 -------
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[robert dot mance at intel dot com]

------- Comment #5 from robert dot mance at intel dot com  2009-08-18 21:01 -------
(In reply to comment #4)
> Fixed.

Could you please tell me what version of gfortran this is fixed in?  I'm
working the Intel Fortran compiler debug information at the moment regarding a
request to add DW_AT_common_inclusion to our output.  Seems like gfortran has
actually decided to move in Intel's direction here.  I'd like to see the output
that gfortran is now creating, and be able to run that version of gfortran
here.

Thanks.

Bob


-- 

robert dot mance at intel dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |robert dot mance at intel
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2009-08-18 21:17 -------
GCC 4.4.0/4.4.1 have it, as well as GCC trunk.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[robert dot mance at intel dot com]

------- Comment #7 from robert dot mance at intel dot com  2009-08-19 21:28 -------
I've managed to download and install 4.4.5 of gfortran and can verify that what
you're doing here is just about identical to what ifort is doing.  

I have a request to emit a DW_TAG_common_inclusion record in our dwarf output
for Fortran named commons.  As you probably know, DW_TAG_common_inclusion would
contain a DW_AT_reference entry that would refer to a single
DW_TAG_common_block that would be shared by all of the common users.  

While that sounds good, it seems at best impractical, and at worse, impossible.
 Users of commons are free to map them as they like.  Declaring a single common
block that would satisfy all users of the common would be tricky, and perhaps
impossible, if two such users both declared a variable with the same name, but
with different types and locations in the common.

It gets worse when you consider multiple subroutines including the common in
separately compiled programs.

The only potential use here maybe when an include statement is used to bring a
named common into multiple subroutines.  We currently don't know that is
happening (in debug info output), but given enough time and code, might be able
to do that.

I'm just curious about views on this and if gfortran has any plans to implement
support for DW_TAG_common_inclusion.

Thanks.

Bob


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738

[Bug debug/37738] Fortran DW_TAG_common_block has incorrect placement/scope

[burnus at gcc dot gnu dot org]

------- Comment #8 from burnus at gcc dot gnu dot org  2009-08-21 18:16 -------
(In reply to comment #7)
> I have a request to emit a DW_TAG_common_inclusion record in our dwarf output
> for Fortran named commons.  [...]
> I'm just curious about views on this and if gfortran has any plans to implement
> support for DW_TAG_common_inclusion.

Currently, there no plan to implement it; simply because there was no request
for it and other items seem to be more important. I create PR 41143 to track
this, but I do not think that anyone will do much about it any time soon - that
includes thinking about how and whether to implement it. (But I might be wrong
and it might get implemented/considered sooner than I think.)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37738