[llvm-commits] [PATCH] Remove redundant register copies when inserting to Q registers on ARM

[Jakob Stoklund Olesen]

On Sep 4, 2012, at 9:31 AM, James Molloy <James.Molloy at arm.com> wrote:

> Hi Jakob,
> 
> +      unsigned DReg = TRI->getSubReg(QReg, ARM::dsub_0 +
> +                                     ((QLane >> LaneShift) &
> LaneMask));
> 
> You're quite right; This should be:
> 
> +      unsigned DReg = TRI->getSubReg(QReg, ARM::dsub_0 +
> +                                     ((QLane >> LaneShift) & 1));
> 
> LaneMask is a mask to get the right lane number (either 0..1 or 0..3)
> but the DPR it applies to is always in the range 0..1.
> 
> I'll add some more comments hopefully tomorrow (I'm in training, so not
> at my PC) in addition to correcting this if you wish?

Yes, please.

Add some comments explaining the range and meaning of the immediates and lane numbers etc. That way, a bug like the one above should become obvious to anyone reading the code.

Thanks,
/jakob