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

[Arnaud A. de Grandmaison]

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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