Cranelift: use a BTreeMap for JITModule code ranges#13710
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Reasonable change and looks good -- thanks! (FWIW this is more or less how Wasmtime's address map data structures work so it's neat to see cranelift-jit have convergent evolution here.)
Just some style notes re: the comments below, then happy to merge.
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`JITModule` resolves a PC back to its defining function (for exception unwinding) via a `Vec<(start, end, FuncId)>` that was re-sorted in full on every `finalize_definitions` call. Code that defines and finalizes functions one at a time therefore paid an O(n) sort per finalize, i.e. O(n^2) overall. Replace the vector with a `BTreeMap` keyed on the start address. Inserts stay sorted incrementally (O(log n)) and the lookup becomes an O(log n) range query, so finalizing is linear in the number of functions with no sort.
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Let's make cranelift a little faster when booting JITed linux :)
Currently
JITModuleresolves a PC back to its defining function (for exception unwinding) via aVec<(start, end, FuncId)>that was re-sorted in full on everyfinalize_definitionscall. Code that defines and finalizes functions one at a time therefore paid an O(n) sort per finalize, i.e. O(n^2) overall.I replace the vector with a
BTreeMapkeyed on the start address. Inserts stay sorted incrementally (O(log n)) and the lookup becomes an O(log n) range query, so finalizing is linear in the number of functions with no sort.Noticible speedup is observed without any (obvious) problems. I think the change makes sense and I don't see why it wouldn't simply just get rid of O(n^2) complexity without any other issues.