Re: asm clobbers, !SMALL_REGISTER_CLASSES patch.

[Geoffrey KEATING <geoffk@discus.anu.edu.au>]

> Cc: egcs@cygnus.com
> Date: Thu, 12 Feb 1998 23:10:32 -0500
> From: David Edelsohn <dje@watson.ibm.com>
> 
>         * stmt.c (expand_asm_operands): When an asm statement
>         clobbers a register that is in a class of its own, and there
>         is space remaining for an extra output, turn the clobber into
>         an output to a dummy pseudo.  At present, don't do this if
>         there are constraints that have alternatives.
> 
> 	This is a good effort and I am glad that you are continuing to
> pursue this needed feature, but I am curious why you are choosing to
> implement it this way instead of as a match_scratch of the appropriate
> register class?  I think that the correct solution is to turn the clobber
> of a named register into the equivalent that GCC uses internally for
> machine description files: match_scratch.  This patch probably works to
> some extent, but it simply lies to GCC by transforming the clobber -- and
> lying to GCC always causes problems in the long run.

I looked into this, and it seems that match_scratch in a MD file gets
turned into (i) a dummy pseudo and (ii) a constraint on the insn.  The
only way I can see to specify a constraint on an asm statement is like
this.

Of course, there might be someone out there who knows how this should
_really_ be done, in which case suggestions are welcomed.

--
Geoff Keating <Geoff.Keating@anu.edu.au>