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Re: [cft] subreg validation patch
- From: Ulrich Weigand <Ulrich dot Weigand at de dot ibm dot com>
- To: Richard Henderson <rth at redhat dot com>
- Cc: ebotcazou at libertysurf dot fr, gcc at gcc dot gnu dot org, jh at suse dot cz
- Date: Mon, 15 Nov 2004 23:41:58 +0100
- Subject: Re: [cft] subreg validation patch
Richard Henderson <rth@redhat.com> wrote on 11/15/2004 11:02:32 PM:
> Hmm. How about lowpart_subreg? At least then we won't wind up
> with nested subregs.
src is guaranteed to satisfy REG_P at this point, so this shouldn't
be an issue. (Also, regmove.c already uses gen_lowpart_SUBREG at
another similar location.)
> Nope. On re-reading I don't see any such proscription. I still
> don't think it's a fantastic idea, but...
I'm not necessarily arguing that (subreg:DF (reg:TI) 0) is something
we need to support for its own sake. I'm only arguing that we need
clear rules, and preferably ones that are as simple as possible.
Given that I see no clear benefit to prohibiting that specific example,
simplicity of rules would appear to argue for allowing it ...
(In fact, for pseudos I would favor having no further restrictions
other than proper alignment at lowpart-of-subword boundary. Hard
regs may have further restrictions, but reload should do the right
thing here.)
Bye,
Ulrich