Re: Does IRA support spilling to registers instead of stack?

[Don Padgett <dpadgett_mail-000 at yahoo dot com>]

Thanks.  I'll pursue specifying a more detailed cost model using existing hooks to see if I can get the desired behavior.

Don

--- On Tue, 7/19/11, Vladimir Makarov <vmakarov@redhat.com> wrote:

> From: Vladimir Makarov <vmakarov@redhat.com>
> Subject: Re: Does IRA support spilling to registers instead of stack?
> To: dpadgett_mail-000@yahoo.com
> Cc: gcc@gcc.gnu.org
> Date: Tuesday, July 19, 2011, 8:33 AM
> On 07/18/2011 05:20 PM, dpadgett_mail-000@yahoo.com
> wrote:
> > Hello,
> > 
> > Does gcc IRA provide a mechanism to support spilling
> to registers instead of the stack?? For the particular
> target I'm looking at, there are some non-general-purpose
> registers that can be copied to and from more quickly than
> the stack, so would be preferable to use as a form of
> shareable spill slot in some cases.? One limitation,
> which is perhaps a significant one, is that these registers
> are not callee save, so one would only want to save to and
> restore from them when there is no intervening function
> call. If there is no current support for such a mechanism,
> any opinions on the value and practicality of adding one
> would be much appreciated.
> > 
> > Thanks, Don
> It might work for new IRA without cover classes.
> 
> Pseudos will have classes containing usual registers and
> these special registers because they are really less costly
> than memory.? If a pseudo crosses a call, the special
> registers could be more costly than memory.
> 
> All you need is to define the right costs for register and
> memory move cost hooks to achieve better costs for regular
> registers, worse costs for the special registers, and the
> worst cost for memory.? If the pseudo intersects the
> call, the worst cost should be for the special
> registers.? It can be achieved by right definition of
> move cost between special registers and memory.
>