[PATCH] D156491: [RA] Split a virtual register in cold blocks if it is not assigned preferred physical register

[Guozhi Wei via Phabricator via llvm-commits]

Carrot added inline comments.


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Comment at: llvm/lib/CodeGen/RegAllocGreedy.cpp:2404
+  if (!NewVRegs.empty())
+    return 0;
 
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qcolombet wrote:
> qcolombet wrote:
> > Splitting decisions are supposed to be taken later (`trySplit`), this breaks the general algorithm's flow.
> Concretely, I'm asking if you could do this kind of splitting in the splitting heuristic.
> You may want to add a new stage in the algorithm (and that'll come at a compile time cost.)
The problem is we need to decide between a physical register and split, if we move it to trySplit, we will miss the possibility of assigning a physical register to the whole virtual register. trySplit compares splits against different physical registers, we need to compare split against non-split.
Function tryAssignCSRFirstTime does similar thing. trySplitAroundHintReg is even more special because it tries to split against only 1 physical register.



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https://reviews.llvm.org/D156491