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Re: dangerous cleverness? ppc int<->float conversions, subreg
- To: aoliva at redhat dot com, zack at codesourcery dot com
- Subject: Re: dangerous cleverness? ppc int<->float conversions, subreg
- From: mike stump <mrs at windriver dot com>
- Date: Mon, 5 Nov 2001 10:31:02 -0800 (PST)
- Cc: gcc at gcc dot gnu dot org, rth at redhat dot com
> To: Zack Weinberg <zack@codesourcery.com>
> Cc: Richard Henderson <rth@redhat.com>, gcc@gcc.gnu.org
> From: Alexandre Oliva <aoliva@redhat.com>
> Date: 04 Nov 2001 06:31:47 -0200
> So I had to come up with separate patters to make sure the register
> allocator wouldn't even consider assigning pseudos to FP registers,
> and there goes your platform-independence :-(
One can DO things like FIRST_FP_REGISTER, LAST_FP_REGISTER, or
IS_FP_REGISTER and then in the mi parts of the compiler, use that to
dissuade the allocator from using those resources in certain cases.
That restores the MIness of most of the code, and expresses the
minimal amount of md code that I think one needs in the end.
Playing games with patterns, the more I think about it, the more I
hate it.
Any rule that says, take all your patterns, and then double them, and
then modify them in this systematic way, has got to be the wrong way.
:-(
Sure would be nice for gcc to deliver on the promise of one
instruction, one pattern.