[LLVMdev] [PBQP] Are edges between nodes from totally disjoint register classes necessary ?

[Lang Hames]

Hi Arnaud,

That sounds good to me. If you send me the patch I'd like to have a look
too.

Cheers,
Lang.


On Tue, Feb 3, 2015 at 4:06 PM, Arnaud A. de Grandmaison <
arnaud.degrandmaison at arm.com> wrote:

> Hi Lang,
>
>
>
> While working on improving the debug dumps of the PBQP graphs, I found out
> that we can have some edges between nodes which belong to totally disjoint
> register classes (for example, on AArch64, this would be an int and a
> floating point register). Although it is true those 2 registers interferes,
> in the sense they are alive at the same time, they never have any physical
> interference, and this shows up as a zero matrix.
>
>
>
> I was wondering if it could make sense to skip adding such edges to the
> graph, as they do not add useful information, they increases the nodes
> degrees … and ultimately make the allocation take longer time.
>
>
>
> I have a patch ready prototyping this. It unfortunately breaks with the
> last fix you made (@ r227942), but if I revert it, it just works fine. if
> you believe this could be worth it, then I will investigate where the
> failure comes from.
>
>
>
> Cheers,
>
> --
>
> Arnaud A. de Grandmaison
>
>
>
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