[PATCH] Bug 12705: Extremely poor performance when printing large arrays

[Andrew Gontarek <andrewg@cray.com>]

Hello,

I noticed that when I wanted to print out a very large array, the
performance
was unbearably slow. This can be observed by setting print repeats and print
elements to 0 (unlimited) and then attempting to print a large array.

set print repeats 0
set print elements 0

I discovered this behavior while attempting to directly parse a very large
array's value directly using gdb/mi with the command
-data-evaluate-expression.

The following is a patch which fixes this issue:

Index: valprint.c

===================================================================

RCS file: /cvs/src/src/gdb/valprint.c,v

retrieving revision 1.110

diff -c -p -r1.110 valprint.c

*** valprint.c  14 Feb 2011 11:35:45 -0000      1.110

--- valprint.c  26 Apr 2011 16:57:39 -0000

*************** val_print_array_elements (struct type *t

*** 1247,1261 ****



        rep1 = i + 1;

        reps = 1;

!       while (rep1 < len

             && value_available_contents_eq (val,

                                             embedded_offset + i *
eltlen,
                                             val,

                                             embedded_offset + rep1 *
eltlen,
                                             eltlen))

!       {

!         ++reps;

!         ++rep1;

        }



        if (reps > options->repeat_count_threshold)
--- 1247,1267 ----

        rep1 = i + 1;
        reps = 1;
!
!       /* Only check for reps if repeat_count_threshold is not set to
!          UINT_MAX (unlimited) */
!       if (options->repeat_count_threshold < UINT_MAX)
!         {
!           while (rep1 < len
             && value_available_contents_eq (val,
                                             embedded_offset + i * eltlen,
                                             val,
                                             embedded_offset + rep1 *
eltlen,
                                             eltlen))
!           {
!             ++reps;
!             ++rep1;
!           }
        }

        if (reps > options->repeat_count_threshold)

Index: ChangeLog
===================================================================
RCS file: /cvs/src/src/gdb/ChangeLog,v
retrieving revision 1.12951
diff -c -p -r1.12951 ChangeLog
*** ChangeLog   26 Apr 2011 15:40:56 -0000      1.12951
--- ChangeLog   26 Apr 2011 17:13:39 -0000
***************
*** 1,3 ****
--- 1,9 ----
+ 2011-04-26  Andrew Gontarek  <andrewg@cray.com>
+
+       * valprint.c (val_print_array_elements): Fixed poor performance
+       of printing very large arrays with repeat_count_threshold set
+       to unlimited. New comment.
+
  2011-04-26  Michael Walle  <michael@walle.cc>

        * remote.c (remote_start_remote): Ack packet after sending the
-- 
Andrew Gontarek
PE debugger development at CRAY
Ph: 651-605-9176