Re: [PATCH i386] Enable -freorder-blocks-and-partition

[Jan Hubicka <hubicka@ucw.cz>]

> On Wed, Dec 11, 2013 at 1:21 AM, Martin Liška <marxin.liska@gmail.com> wrote:
> > Hello,
> >    I prepared a collection of systemtap graphs for GIMP.
> >
> > 1) just my profile-based function reordering: 550 pages
> > 2) just -freorder-blocks-and-partitions: 646 pages
> > 3) just -fno-reorder-blocks-and-partitions: 638 pages
> >
> > Please see attached data.
> 
> Thanks for the data. A few observations/questions:
> 
> With both 1) (your (time-based?) reordering) and 2)
> (-freorder-blocks-and-partitions) there are a fair amount of accesses
> out of the cold section. I'm not seeing so many accesses out of the
> cold section in the apps I am looking at with splitting enabled. In

I see you already comitted the patch, so perhaps Martin's measurement assume
the pass is off by default?

I rebuilded GCC with profiledboostrap and with the linkerscript unmapping
text.unlikely.  I get ICE in:
(gdb) bt
#0  diagnostic_set_caret_max_width(diagnostic_context*, int) () at ../../gcc/diagnostic.c:108
#1  0x0000000000f68457 in diagnostic_initialize (context=0x18ae000 <global_diagnostic_context>, n_opts=n_opts@entry=1290) at ../../gcc/diagnostic.c:135
#2  0x000000000100050e in general_init (argv0=<optimized out>) at ../../gcc/toplev.c:1110
#3  toplev_main(int, char**) () at ../../gcc/toplev.c:1922
#4  0x00007ffff774cbe5 in __libc_start_main () from /lib64/libc.so.6
#5  0x0000000000f7898d in _start () at ../sysdeps/x86_64/start.S:122

That is relatively early in startup process. The function seems inlined and
it fails only on second invocation, did not have time to investigate further,
yet while without -fprofile-use it starts...

On our periodic testers I see off-noise improvement in crafty 2200->2300
and regression on Vortex, 2900->2800, plus code size increase.

Honza