[patch 3.3/3.4/3.5] Fix PR bootstrap/14671

[John David Anglin]

> > Zdenek Dvorak wrote:
> > 
> > >Almost definitely not; it probably just exposes the problem by changing
> > >the memory consumption and consequently the time when garbage
> > >collections are triggered.
> > 
> > Even if that is so, it is still your responsibility to look into it.
> > 
> > Would you please help J. David to track down what's going on?
> 
> I believe that the problem should be fixed by the inclusion of GTY
> markers on the reg_known_value (which probably should be added to
> whatever other branches contain the fix for PR12440).

The good news is that Richard's patch fixes the problem.  The bad
news is that the patch uses ggc_free which isn't in 3.3 and 3.4.
Implementing ggc_free looks like it would require back porting
3 or 4 more patches.

Richard wrote in
<http://gcc.gnu.org/ml/gcc-patches/2004-03/msg02057.html>:

  No idea why this is happening now, and apparently only to me, but
  the fact is that data gets put into reg_known_value and a call to
  ggc_collect happens before end_alias_analysis.  The call to collect
  happens during CSE, and is protected by a ggc_push_context, but it
  still doesn't seem terribly safe.

Thus, it would seem that the push and pop fix isn't safe.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)