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Re: [PATCH][AArch64] Separate shrink wrapping hooks implementation
On Fri, Nov 18, 2016 at 09:29:13AM +0000, Kyrill Tkachov wrote:
> >So your COMPONENTS_FOR_BB returns both components in a pair whenever one
> >of those is needed? That should work afaics.
>
> I mean I still want to have one component per register and since
> emit_{prologue,epilogue}_components knows how to form pairs from the
> components passed down to it I just need to restrict the number of
> components in any particular basic block to an even number.
> So say a function can wrap 5 registers: x22,x23,x24,x25,x26.
> I want get_separate_components to return 5 components since in that hook
> we don't know how these registers are distributed across each basic block.
> components_for_bb has that information.
> In components_for_bb I want to restrict the components for a basic block to
> an even number, so if normally all 5 registers would be valid for wrapping
> in that bb I'd only choose 4 so I could form 2 pairs. But selecting only 4
> of the 5 registers, say only x22,x23,x24,x25 leads to x26 not being saved
> or restored at all, even during the normal prologue and epilogue because
> x26 was marked as a component in components_for_bb and therefore omitted
> from
> the prologue and epilogue.
> So I'm thinking x26 should be removed from the wrappable components of
> a basic block by disqualify_components. I'm trying that approach now.
My suggestion was, in components_for_bb, whenever you mark x22 as needed
you also mark x23 as needed, and whenever you mark x23 as needed you also
mark x22. I think this is a lot simpler?
Segher