[Bug lto/45375] [meta-bug] Issues with building Mozilla with LTO

[tejohnson at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45375

--- Comment #156 from Teresa Johnson <tejohnson at google dot com> 2012-12-12 00:00:17 UTC ---
On Tue, Dec 11, 2012 at 2:57 PM, markus at trippelsdorf dot de
<gcc-bugzilla@gcc.gnu.org> wrote:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45375
>
> --- Comment #155 from Markus Trippelsdorf <markus at trippelsdorf dot de> 2012-12-11 22:57:14 UTC ---
> (In reply to comment #154)
>> What was the size of the gcc lto/pgo binary before the change to use the
>> histogram? Was it close to the gcc 4.7 lto/pgo size? In that case that is a
>> very large increase, ~25%.
>
> With revision 193914 (before the change) the lto/pgo size is 42115424 bytes.
> So it looks like Theresa is off the hook.

Unfortunately, I am still possibly on the hook since the main suspect
change is r193747 (committed by Honza with changes made by him and I
to use the histogram instead of a hard limit for determining bb
hotness). Between then and when I committed fixes for this under LTO
(r193999) I would expect that the code size might have been worse
temporarily because everything looked hot since the histogram was not
being streamed through the LTO files properly, and so inlining could
have gotten excessive.

>
>> Markus, could you attach to the bug one of the gcda files so that I can see the
>> program summary and figure out how far off the old hot bb threshold is from the
>> new histogram-based one? Also, it would be good to see the -fdump-ipa-inline
>> dumps before and after the regression (if necessary, the before one could be
>> from 4_7).
>
> Will try to post them tomorrow .

Ok thanks.
Teresa

>
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Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413