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The new graph structure replaces the node and edge linked lists with vectors. Free lists (well, free vectors) are used for fast insertion/deletion. The ultimate aim is to make PBQP graphs cheap to clone. The motivation is that the PBQP solver destructively consumes input graphs while computing a solution, forcing the graph to be fully reconstructed for each round of PBQP. This imposes a high cost on large functions, which often require several rounds of solving/spilling to find a final register allocation. If we can cheaply clone the PBQP graph and incrementally update it between rounds then hopefully we can reduce this cost. Further, once we begin pooling matrix/vector values (future work), we can cache some PBQP solver metadata and share it between cloned graphs, allowing the PBQP solver to re-use some of the computation done in earlier rounds. For now this is just a data structure update. The allocator and solver still use the graph the same way as before, fully reconstructing it between each round. I expect no material change from this update, although it may change the iteration order of the nodes, causing ties in the solver to break in different directions, and this could perturb the generated allocations (hopefully in a completely benign way). Thanks very much to Arnaud Allard de Grandmaison for encouraging me to get back to work on this, and for a lot of discussion and many useful PBQP test cases. llvm-svn: 194300 |
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