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Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop
- From: Jan Hubicka <jh at suse dot cz>
- To: Eric Botcazou <ebotcazou at libertysurf dot fr>
- Cc: janis187 at us dot ibm dot com, gcc-gnats at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org,gcc-bugs at gcc dot gnu dot org, nobody at gcc dot gnu dot org, thorpej at shagadelic dot org,jh at suse dot cz
- Date: Sat, 21 Dec 2002 12:14:29 +0100
- Subject: Re: optimization/8492: [3.3 regression] GCC spins forever compiling loop
- References: <3E039EF3.A9E5C688@us.ibm.com> <200212211154.46318.ebotcazou@libertysurf.fr>
> > 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