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Re: scheduling cc0
- From: Steven Bosscher <stevenb at suse dot de>
- To: gcc at gcc dot gnu dot org, Miles Bader <miles at gnu dot org>
- Date: Wed, 2 Feb 2005 11:52:11 +0100
- Subject: Re: scheduling cc0
- Organization: SUSE Labs
- References: <buomzuns0wk.fsf@mctpc71.ucom.lsi.nec.co.jp>
On Wednesday 02 February 2005 11:37, Miles Bader wrote:
> This approach seems to work well in practice, but can anyone see any
> potential problems with it?
Well, isn't it a potential problem that lots of places in the compiler
expect that the cc0 setter is right before the cc0-using insn? And if
you do this kind of scheduling before reload, what happens if reload
has to insert insns that set cc0?
> Is this a reasonable way to do things?
The "recommended practice" of today is to use a fake hard register for
the CC reg, always, instead of cc0.
See e.g. "http://gcc.gnu.org/wiki/general backend cleanup", under
"Convert md files that use CC0 so they don't anymore."
Unfortunately the v850 targets is one of the few GCC targets that still
use cc0 for the condition code, see http://gcc.gnu.org/backends.html.
Gr.
Steven