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

[Quentin Colombet via Phabricator via llvm-commits]

qcolombet added a comment.

> 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

That's a good point. I've been advocating for this for years, if not publicly at least internally. Without a sort of scheduler in the pipeline, on targets like x86, we would generate awful code whenever we carry around flags, since so many instructions would clobber them. Currently, I believe we would just spill the flags!


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  https://reviews.llvm.org/D96015/new/

https://reviews.llvm.org/D96015