Re: [Qemu-devel] [PATCH 2/4] tcg/aarch64: implement new TCG target for aarch64

[Peter Maydell]

On 24 May 2013 18:02, Richard Henderson <address@hidden> wrote:
> On 05/24/2013 01:53 AM, Claudio Fontana wrote:
>> We use FP to point to the callee_saved registers, and to move to/from them
>> in the tcg_out_store_pair and tcg_out_load_pair functions.
>
> I hadn't noticed you'd hard-coded FP into the load/store_pair functions.
> Let's *really* not do that.  Even if we decide to continue using it, let's
> pass it in explicitly.
>
> But I don't see that you're really gaining anything in the prologue from
> using FP instead of SP.  It seems like a waste of a register to me.

Where's the waste? The procedure calling standard mandates that we
set FP up, so it's not like we can use it as a general purpose
register anywhere. I agree that we shouldn't hardcode tcg_out_store_pair
to use FP as a base, but there's no particular reason not to use
it at this point in the prologue since it happens to be convenient.

thanks
-- PMM