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Re: GCC hacking questions (peepholes etc.)
- To: Marek Michalkiewicz <marekm at linux dot org dot pl>
- Subject: Re: GCC hacking questions (peepholes etc.)
- From: Richard Henderson <rth at cygnus dot com>
- Date: Wed, 26 Jul 2000 21:41:01 -0700
- Cc: gcc at gcc dot gnu dot org
- References: <200007260709.JAA08151@marekm.home>
On Wed, Jul 26, 2000 at 09:09:59AM +0200, Marek Michalkiewicz wrote:
> - is it allowed to mix both define_peephole and define_peephole2 in
> one md file?
Yes.
> - if the answer to the above is "no", is it possible for define_peephole
> to request a scratch register (as documented for define_peephole2)?
No.
> - how to tell GCC that it is cheaper to load constants to a certain
> register class (r16-r31) than to other registers (r0-r15)?
Use "?" or "!" in the constraint string. Probably "?" is enough
deprecation.
> - is it safe to use a constraint letter for which REG_CLASS_FROM_LETTER
> returns either GENERAL_REGS or NO_REGS depending on target_flags, to
> optionally enable some alternatives in a define_insn?
Yes.
r~