[Bug debug/55579] New: SRA doesn't create debug stmts when they would be useful

[Bug debug/55579] New: SRA doesn't create debug stmts when they would be useful

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

             Bug #: 55579
           Summary: SRA doesn't create debug stmts when they would be
                    useful
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: jamborm@gcc.gnu.org


Consider -g -O2:
struct S { int a; char b; char c; short d; };

int
foo (int x)
{
  struct S s = { x + 1, x + 2, x + 3, x + 4 };
  char *p = &s.c;
  return x;
}
Unfortunately, SRA doesn't add here any debug stmts and everything is DSEd
later on.
*.esra dump says:
Candidate (1722): s
Marking s offset: 0, size: 32  to be replaced with debug statements.
Marking s offset: 32, size: 8  to be replaced with debug statements.
Marking s offset: 40, size: 8  to be replaced with debug statements.
Marking s offset: 48, size: 16  to be replaced with debug statements.
! Disqualifying s - No scalar replacements to be created.

If there are just debug replacements, no normal ones, and the aggregate still
has been candidate for SRA (i.e. no address escape, etc.), it would be nice if
the debug replacements could be emitted anyway.  CDDCE or DSE will then remove
the actual stmts, but debug info will be accurate.

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-12-04
     Ever Confirmed|0                           |1
           Severity|normal                      |enhancement

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-04 09:38:41 UTC ---
Confirmed.

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |jamborm at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #2 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-12-06 16:58:58 UTC ---
Mine.

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

--- Comment #3 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-12-07 14:59:43 UTC ---
Created attachment 28896
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28896
Untested patch

I'm bootstrapping and testing this patch.

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #28896|0                           |1
        is obsolete|                            |

--- Comment #4 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-12-14 11:46:16 UTC ---
Created attachment 28954
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28954
Another untested fix

Unfortunately, the previous patch had problems with debug comparisons.
At the moment I'm bootstrapping the new attached variant which
hopefully does not have this problem and which I'd like to then
submit for 4.8.

In the next stage1 I'd like to go a step further and not mark all
variables as disqualified candidates when analyze_access_trees decides
there are not replacements to be made for them which should make
access structures available to the function modification phase which
then can remove s few more assignments (e.g. to variables or parts of
variables which are never read).  But I'm still only experimenting
with that.

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[aoliva at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

--- Comment #5 from Alexandre Oliva <aoliva at gcc dot gnu.org> 2012-12-21 01:41:18 UTC ---
FWIW, the patch in comment 4 makes sense to me.  Thanks!

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-p
                   |                            |atches/2013-01/msg00180.htm
                   |                            |l

--- Comment #6 from Martin Jambor <jamborm at gcc dot gnu.org> 2013-01-04 13:02:25 UTC ---
Patch posted to the mailing list:
http://gcc.gnu.org/ml/gcc-patches/2013-01/msg00180.html

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

--- Comment #7 from Martin Jambor <jamborm at gcc dot gnu.org> 2013-01-08 14:10:52 UTC ---
Author: jamborm
Date: Tue Jan  8 14:10:44 2013
New Revision: 195015

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195015
Log:
2013-01-08  Martin Jambor  <mjambor@suse.cz>

    PR debug/55579
    * tree-sra.c (analyze_access_subtree): Return true also after
    potentially creating a debug-only replacement.

testsuite/
    * gcc.dg/tree-ssa/pr55579.c: New test.


Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr55579.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-sra.c

[Bug debug/55579] SRA doesn't create debug stmts when they would be useful

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55579

Martin Jambor <jamborm at gcc dot gnu.org> changed:

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

--- Comment #8 from Martin Jambor <jamborm at gcc dot gnu.org> 2013-01-08 14:14:49 UTC ---
Patch committed