Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop

[Jan Hubicka <jh@suse.cz>]

The following reply was made to PR optimization/8492; it has been noted by GNATS.

From: Jan Hubicka <jh@suse.cz>
To: Eric Botcazou <ebotcazou@libertysurf.fr>
Cc: Jan Hubicka <jh@suse.cz>, janis187@us.ibm.com,
	gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org, gcc-bugs@gcc.gnu.org,
	nobody@gcc.gnu.org, thorpej@shagadelic.org
Subject: Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop
Date: Sun, 22 Dec 2002 00:43:50 +0100

 > > I think deleting unreachable blocks is cheap enought to do in the case
 > > conditional jump was eliminated.
 > 
 > Ok. But then the GCSE code needs to be (at least partially) re-initialized 
 > because the number of basic blocks may change. I've attached a naive patch I 
 > wrote some time ago: while fixing the PR (and doing some housekeeping work), 
 > it introduces many regressions because of this problem.
 > 
 > > Alternatively we may prevent first local cprop pass from modifying CFG.
 > 
 > I don't know enough of the global organization of optimization passes to 
 > comment. Will the optimizations missed at that point be caught elsewhere ?
 
 Yes, there are examples where removing the conditional would allow more
 PRE to happen, but I guess it is not that common.  We already disable
 the transformation for global CPROP and in fact I am quite surprised
 that I didn't the same for local pass.  I guess I just forgot about
 that.
 
 Honza
 > 
 > -- 
 > Eric Botcazou