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Re: Projects for beginners
- To: Hans-Peter Nilsson <hans-peter dot nilsson at axis dot com>
- Subject: Re: Projects for beginners
- From: Michael Matz <matzmich at cs dot tu-berlin dot de>
- Date: Thu, 1 Feb 2001 18:28:33 +0100 (MET)
- cc: zackw at Stanford dot EDU, gcc at gcc dot gnu dot org
Hi,
On Wed, 31 Jan 2001, Hans-Peter Nilsson wrote:
> > This is where I admit that I have never been able to understand any of
> > the multiple different ways of handling condition codes in GCC.
> > There's the pure cc0 approach, the every-insn's-a-parallel approach
> > taken by the x86 back end, the cbranch stuff which I totally agree
> > needs more documentation, and the pure flag registers approach which
> > apparently only works on machines where that is the hardware.
>
> You could change cc0-ports to the flags-register approach (as
> was done with x86), but your .md would be cluttered with
> clobbers for insns that affect cc0 on your machine. This is
> somewhat seen in the x86 back-end, though "luckily" it seems
> it's mostly arithmetic insns that set its cc0 (now expressed as
> (reg:CC 17)).
A very unfortunate side-effect of this PARALLEL wrapping of insns is, that
GCSE doesn't look into stuff in parallel's at all.
Ciao,
Michael.