Process current bucket instead of parent's bucket when starting loop for dominators. #111596
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☔ The latest upstream changes (presumably #111585) made this pull request unmergeable. Please resolve the merge conflicts. |
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Good catch! I thought I transcribed the impl pretty closely, but I must've missed something in this bit. I think this looks right to me though. @bors r+ |
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Finished benchmarking commit (25f084d): comparison URL. Overall result: no relevant changes - no action needed@rustbot label: -perf-regression Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)ResultsThis is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
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The linked paper by Georgiadis suggests in §2.2.3 to process
bucket[w]when beginning the loop, instead ofbucket[parent[w]]when finishing it.In the test case, we correctly computed
idom[2] = 0andsdom[3] = 1, but the algorithm returnedidom[3] = 1, instead of the correct value 0, because of the path 0-7-2-3.This provoked LLVM ICE in #111061 (comment). LLVM checks that SSA assignments dominate uses using its own implementation of Lengauer-Tarjan, and saw case where rustc was breaking the dominance property.
r? @Mark-Simulacrum