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Re: Fix twolf -funroll-loops -O3 miscompilation (a semi-latent web.c bug)
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: Steven Bosscher <stevenb dot gcc at gmail dot com>
- Cc: gcc-patches at gcc dot gnu dot org, Paolo Bonzini <bonzini at gnu dot org>, Dominique Dhumieres <dominiq at lps dot ens dot fr>, hubicka at ucw dot cz, Richard Henderson <rth at redhat dot com>, Jeff Law <law at redhat dot com>
- Date: Mon, 03 Dec 2012 22:10:35 +0100
- Subject: Re: Fix twolf -funroll-loops -O3 miscompilation (a semi-latent web.c bug)
- References: <20121118231540.726263BABA@mailhost.lps.ens.fr> <8323491.RGjWGtIWxN@polaris> <CABu31nPTc7SKZBaUeEy=FsxrKMWzRNtg+D07hatOgrZK_+o-AQ@mail.gmail.com>
> You mean the patch at
> http://gcc.gnu.org/ml/gcc-patches/2012-11/msg02275.html right?
>
> I haven't tried that other patch. I'll test that one.
Yes, thanks.
> I suppose so. But this was all added before RTL fwprop and way before
> GIMPLE optimizations. Avoiding the self-referential case is just more
> difficult to do, quite expensive (have to scan the SET_SRC pattern),
> and AFAICT doesn't bring much pay-off.
>
> I'll prepare something to avoid the self-referential case, but I think
> we're making our lives complicated for no good reason.
Can't you just use the same best-effort approach used for fwprop.c here?
--
Eric Botcazou