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Re: RFC: subreg fixing (extract_bit_field or simplify_subreg)
- From: "Ulrich Weigand" <weigand at i1 dot informatik dot uni-erlangen dot de>
- To: aldyh at redhat dot com (Aldy Hernandez)
- Cc: weigand at i1 dot informatik dot uni-erlangen dot de (Ulrich Weigand), rth at redhat dot com, gcc at gcc dot gnu dot org
- Date: Thu, 28 Oct 2004 20:43:48 +0200 (CEST)
- Subject: Re: RFC: subreg fixing (extract_bit_field or simplify_subreg)
Aldy Hernandez wrote:
> The RTL is invalid because you can't have a SI subreg of a DF value.
Why do you think so?
The only general restriction I'm aware of is that you cannot switch
between different floating point modes using subreg. Interpreting a
floating point mode as integer mode using subreg is OK.
There are additional restrictions for hard registers; a subreg
is only OK if it can be expressed as a single machine register.
These restrictions do not apply to pseudos, however. It would
be the task of reload to ensure subregs of pseudos are lowered
correctly into valid hard registers and/or subregs.
Bye,
Ulrich
--
Dr. Ulrich Weigand
weigand@informatik.uni-erlangen.de