Re: middle-end/6566: sparc64-unknown-netbsd-gcc loops consuming memory

[Jan Hubicka <jh@suse.cz>]

The following reply was made to PR middle-end/6566; it has been noted by GNATS.

From: Jan Hubicka <jh@suse.cz>
To: davem@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
	hubicka@gcc.gnu.org, nobody@gcc.gnu.org, thorpej@wasabisystems.com,
	gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: middle-end/6566: sparc64-unknown-netbsd-gcc loops consuming memory
Date: Fri, 7 Jun 2002 13:22:22 +0200

 > Synopsis: sparc64-unknown-netbsd-gcc loops consuming memory
 > 
 > Responsible-Changed-From-To: unassigned->hubicka
 > Responsible-Changed-By: davem
 > Responsible-Changed-When: Fri Jun  7 01:32:16 2002
 > Responsible-Changed-Why:
 >     Jan can you take a look at this?  The problem is
 >     calculate_global_regs_live() is what is looping.
 >     Every iteration, right before qhead gets to qtail
 >     in the main loop, we advance qtail almost through
 >     the whole queue.  This process repeats forever.
 >     Any target crossed to sparc64-netbsd will be able
 >     to reproduce this so it should be easy for you to
 >     work on it.
 >     Thanks.
 > State-Changed-From-To: open->analyzed
 > State-Changed-By: davem
 > State-Changed-When: Fri Jun  7 01:32:16 2002
 > State-Changed-Why:
 >     calculate_global_regs_live loops forever never making
 >     forward progress
 
 This has been discussed on the list briefly.  The problem is that
 iterative dataflow is not guaranteed to terminate when the starting
 sollution is not strictly bellow the correct one.
 
 We commonly do that and situation got worse after the renumbering
 changes, but really it just makes latent bug to happen more often.
 
 I want to take a look at it today or tomorrow.  My plan is to turn
 dataflow into hybrid search, as df.c does, so we save some bits and
 create extra bitmap for each basic block noting changes in the liveness.
 When we change liveness of given pseudo twice, we wipe all the liveness
 bits of it and re-start relaxation.
 Not perfect sollution, but should work in practice.  I am still looking
 for hints in the literatue, but most of it does appear to suggest that
 inverval analysis is the proper way to go.
 
 Honza
 > 
 > http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6566