Re: [Xen-devel] [PATCH] xen: arm: let the compiler choose the dummy register for TLB flush asm

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-04-24 at 16:14 +0100, Ian Campbell wrote:
> On Wed, 2013-04-24 at 15:17 +0100, Tim Deegan wrote:
> > At 14:21 +0100 on 24 Apr (1366813285), Ian Campbell wrote:
> > > While staring at some disassembly I noticed that the compiler was jumping
> > > through hoops to preserve the function argument (in r0) simply so it 
> > > could use
> > > r0 as the dummy argument to the tlb flush cp register writes.
> > > 
> > > Remove the enforced use of r0 and use an output constraint for the dummy
> > > register so there is no need to initialise the dummy.
> > 
> > Since we don't care about the register's contents and it's not changed,
> > can we just drop the variable and constraint entirely?
> 
> and just hard code the r0? I hadn't though of that, I suppose we could
> yes.

Scuppered because our clever STORE_CP32 macros add % to their argument.
I don't really want to change those macros, I suppose I could add
DUMMY_CP32 which just takes a name and inputs a dummy reigster.

Ian


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