Re: [PATCH, rs6000] power8 patches, patch #4 (revised), new power8 builtins

[Segher Boessenkool <segher at kernel dot crashing dot org>]

> I also wonder whether it would be useful to have 32-bit do the  
> vector logical
> ops in gprs as well.  At the moment, the patches don't allow it  
> (vector types
> must be done in the altivec/vsx registers, an TImode is done by  
> splitting the
> operation into 4 separate categories).  On the 64-bit side, having  
> __int128_t
> passed in GPRs, means you want to avoid ping-ponging between the  
> GPRs and VSX
> registers.  In addition, the atomic quad word support (patch #7)  
> has to run in
> GPRs, so we need add/subtract/logical to have versions that run in  
> GPRs.

It might work better if you added a mode V1TI for TI in vector
regs, and then used plain TI only for GPRs.  It certainly will
make things a lot more regular; whether it actually works better,
I have no idea.

The way you have things now, only after reload the vector patterns
are split to GPR patterns; much too late to do most optimisations
on it.  On the other hand, deciding early what register set some
op should go to isn't too pleasant either; is it always the best
choice to use the vector regs when possible?


Segher