[PATCH][AArch64] Separate shrink wrapping hooks implementation

[Segher Boessenkool]

On Thu, Nov 17, 2016 at 04:50:46PM +0000, Kyrill Tkachov wrote:
> >>Is loading/storing a pair as cheap as loading/storing a single register?
> >>In that case you could shrink-wrap per pair of registers instead.
> >
> >I suppose it can vary by microarchitecture. For the purposes of codegen 
> >I'd say
> >it's more expensive than load/storing a single register (as there's more 
> >memory bandwidth required after all)
> >but cheaper than two separate loads stores (alignment quirks 
> >notwithstanding).
> >Interesting idea. That could help with code size too. I'll try it out.
> 
> I'm encountering some difficulties implementing this idea.
> I want to still keep the per-register structures across the hooks but 
> basically restrict the number
> of components in a basic block to an even number of FPRs and GPRs. I tried 
> doing this in COMPONENTS_FOR_BB

So your COMPONENTS_FOR_BB returns both components in a pair whenever one
of those is needed?  That should work afaics.

> but apparently this ended up not saving/restoring some of the registers at 
> all because the components that were
> "filtered out" that way still made their way to the bitmap passed into 
> SET_HANDLED_COMPONENTS and so the normal
> prologue/epilogue didn't end up saving and restoring them.

I am not sure what this means?  "filtered out"?


Segher