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

Andrew Gontarek
2011-04-26T17:26:16Z

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