[PATCH] [Statepoints] Reuse stack slots for assignment idioms

[Philip Reames]

@Igor - Your restatement is correct.  I like your idea of renaming the method, but I hadn't really come up with a great name.  As your follow on question about PHIs points out, the current notion is actually stronger than just "preferred".  It's more like "preferred so strongly that there can't be a better slot to pick".

Hm, I think I just understood your question about phis after writing that.  Were you intending to say that we could special case PHIs where exactly one input had a spill slot assigned and that input's only use is the phi?  That avoids the problem of picking one spill slot when multiple are available.  Might be worth exploring in a future change.

w.r.t. your comments about DSE, no, I'm not really sure.  :)  I may be utterly wrong in fact.  Having said that, non of the existing test cases break with this change and I didn't see any differences in codegen for the example I happened to look at.  I'll revert this part of the patch, but I'll have to introduce another data structure to do it.  Can I ask you to submit a test which would have caught this?


http://reviews.llvm.org/D10402

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