JIT: Cache start of cold section for reuse in 3-opt layout #111365
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cc @dotnet/jit-contrib, @AndyAyersMS PTAL. Diffs are from |
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Follow-up to #111365. Instead of allocating a separate ordinal array, track each block's ordinal by overwriting its bbPostorderNum. We can check if a given block is in the candidate set of blocks being reordered if its ordinal is less than the number of hot blocks, and if the block at the given ordinal in blockOrder matches the block in question (i.e. the same implementation as FlowGraphDfsTree::Contains).
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During cold code motion, if
fgMoveColdBlocksfinds a call-finally pair that begins with a cold block, it will try to move the entire pair, regardless of whether the tail is cold or not. If the tail isn't cold, 3-opt layout's detection of the last hot block may terminate early, causing the cold part of an EH region to also be considered for reordering. Because 3-opt expects each EH subregion being reordered to be contiguous, this split causes asserts. Caching the cold region start point infgMoveColdBlocksmeans we don't need to find the first cold block in 3-opt, thus removing the potential of getting it wrong.While I was here, I decided to enhance
fgMoveColdBlocksso that it can move cold call-finally pairs at the end of the hot main method body, and clean up 3-opt's initialization logic to reduce its allocation sizes. Fixes #111207.