[llvm-commits] [PATCH] Prevent the mixing of S and D registers for vsqrt/vdiv instructions on A15

[Jakob Stoklund Olesen]

On Sep 25, 2012, at 7:25 AM, Tim Northover <t.p.northover at gmail.com> wrote:

> Hi all,
> 
>> The attached patch prevents the mixing of D and S registers for vsqrt/vdiv
>> instructions when using neonfp on A15. This is necessary since single
>> precision math instructions use D registers when using neonfp, and there
>> are no equivalent instructions for vsqrt and vdiv.
> 
> I've taken a look at the patch, and while the extra duplicated
> instruction to support this is rather a hack, I can't see any other
> way to enforce the allocation constraints in that pattern.
> 
> This is  probably a necessary evil.

It's not clear why the extra instruction is required. Could you elaborate, please?

/jakob