[PATCH] D96015: [RegAllocFast] Handle case where operand of copy cannot be assigned.

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D96015#2573571 <https://reviews.llvm.org/D96015#2573571>, @qcolombet wrote:

>> It sounds like we need to have the fast-RA be able to defer to the more sophisticated allocators in certain cases.
>
> That's a good idea! We could do something similar to what we do with GISel: set some function attributes to inform the other allocators whether or not they have something to do.

I think this is actually a problem GlobalISel does have since it doesn't have the DAG scheduler/linearizer to minimize physical register live ranges. We need an MI equivalent pass to do this


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