[PATCH] D38128: Handle COPYs of physregs better (regalloc hints)

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa added a comment.

In https://reviews.llvm.org/D38128#904581, @efriedma wrote:

> > Not sure if it is clear that coalescing with %R8 is generally better than %R0.
>
> What do you mean, it isn't clear?  Is the performance problem not clear?  Or do you mean you're not sure how to detect this situation when you're sorting the hints?


I guess given your initial wording ("not great"), I was not sure if this is general and serious enough so that we really want to add an additional heuristic like "COPY to compare" on top of the sorting by weight. I suppose then there should be a flag like HasCompareUser which is then the tie-breaker when the weight is the same, or?


https://reviews.llvm.org/D38128