Re: Use of FLAGS_REGNUM clashes with generates insn

["Paulo J. Matos" <paulo at matos-sorge dot com>]

On 23/09/11 08:21, Joern Rennecke wrote:
> Quoting "Paulo J. Matos" <paulo@matos-sorge.com>:
>
> > My addition instruction sets all the flags. So I have:
>
> This is annoying, but can be handled. Been there, done that.
> dse.c needs a small patch, which I intend to submit sometime in the future.

Ok. Actually I was quite happy with my solution too which avoided having 
to change the core. However, it was not heavily tested.

> > And all my (define_insn "*mov..." are tagged with a (clobber (reg:CC
> > RCC)). This generates all kinds of trouble since GCC generates moves
> > internally without the clobber that fail to match.
>
> I don't think that can be overcome without cc0. Unless you want to
> hide your flags register altogether.

That's seriously annoying. The idea was to ditch cc0 and explicitly 
represent CC in a register to perform optimizations like splitting add 
and addc for a double word addition. If by hiding my register flags 
means going back to cc0, then it seems that the only way to go unless I 
get it to work somehow. If you having anything else in mind to get it to 
work let me know.

What I currently have in mind is to have a backend macro listing all the 
move for which a move clobber CC_REG, then whenever GCC generates a 
move, it queries the macro to know if the move requires clobbering and 
emits the clobber if required. However, I am unsure how deep the rabbit 
hole goes.

--
PMatos