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: 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,
	jh@suse.cz
Subject: Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop
Date: Sat, 21 Dec 2002 12:14:29 +0100

 > > The mainline regression reported in PR optimization/8492
 > > (an infinite loop in the compiler) showed up starting with
 > > this patch:
 > >
 > > Sun Jul 21 00:54:54 CEST 2002  Jan Hubicka  <jh@suse.cz>
 > >
 > >         * gcse.c: Include cselib.h
 > >         (constptop_register): Break out from ...
 > >         (cprop_insn): ... here; kill basic_block argument.
 > >         (do_local_cprop, local_cprop_pass): New functions.
 > >         (one_cprop_pass): Call local_cprop_pass.
 > >
 > 
 > Ha! I understand now... see the analysis:
 > http://gcc.gnu.org/ml/gcc/2002-12/msg00039.html
 > 
 > I think the CFG should be cleaned up between the local cprop pass and the 
 > global cprop pass, but I guess doing so won't particularly speed up the 
 > compiler, to say the least.
 I think deleting unreachable blocks is cheap enought to do in the case
 conditional jump was eliminated.
 Alternatively we may prevent first local cprop pass from modifying CFG.
 I will try to get into this tonight.  Thanks!
 
 Honza
 > 
 > -- 
 > Eric Botcazou