[MicroPerf] Reverse instead of sort already-ordered branch fixups in IL writer - #20349
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origReqdBrFixups is recorded by prepending at strictly-increasing code positions, so it always arrives strictly descending by fixupLoc with no ties. The stable List.sortBy is therefore exactly List.rev. Output is byte-for-byte identical. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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…dBrFixups Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Output-identical: emitted IL and metadata are byte-for-byte unchanged on every workload checked.
applyBrFixupsstable-sorted the required branch fixups by code offset once per emitted method body. Fixups are recorded by prepending at the current code position as the stream is emitted linearly, so the list always arrives strictly descending by offset with no ties — the sort is exactly a reverse. ReplacedList.sortBywithList.rev.Measured over a 65,880-LOC / 120-file compile (net11 Release; ~46,465 calls/compile, 88% empty lists, longest 25): 0.595 ms → 0.240 ms and 1444 KB → 634 KB allocated per compile for this step. Isolated microbench on the same call-length distribution is ~3× faster at ~2.3× less allocation, and beats a packed-
int64Array.Sortand every other candidate tried.Equivalence was checked by computing both orderings for every emitted method during a full compile and comparing element-for-element: 139,370 method bodies, 0 mismatches (and every list confirmed strictly descending, 0 ties).