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perf: O(N²) → O(N) upvalue collection in closure handler #154

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Merged
davydog187 merged 1 commit into from
Feb 27, 2026
+7 −5
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perf: O(N²) → O(N) upvalue collection in closure handler #154

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12 changes: 7 additions & 5 deletions lib/lua/vm/executor.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -412,8 +412,9 @@ defmodule Lua.VM.Executor do
defp do_execute([{:closure, dest, proto_index} | rest], regs, upvalues, proto, state) do
nested_proto = Enum.at(proto.prototypes, proto_index)

# Capture upvalues based on descriptors, reusing open upvalue cells when available
{captured_upvalues, state} =
# Capture upvalues based on descriptors, reusing open upvalue cells when available.
# Accumulate in reverse (prepend) for O(N) collection, then reverse at the end.
{captured_upvalues_reversed, state} =
Enum.reduce(nested_proto.upvalue_descriptors, {[], state}, fn
{:parent_local, reg, _name}, {cells, state} ->
case Map.get(state.open_upvalues, reg) do
Expand All @@ -428,18 +429,19 @@ defmodule Lua.VM.Executor do
open_upvalues: Map.put(state.open_upvalues, reg, cell_ref)
}

{cells ++ [cell_ref], state}
{[cell_ref | cells], state}

existing_cell ->
# Reuse existing open upvalue cell
{cells ++ [existing_cell], state}
{[existing_cell | cells], state}
end

{:parent_upvalue, index, _name}, {cells, state} ->
# Share the parent's upvalue cell
{cells ++ [Enum.at(upvalues, index)], state}
{[Enum.at(upvalues, index) | cells], state}
end)

captured_upvalues = Enum.reverse(captured_upvalues_reversed)
closure = {:lua_closure, nested_proto, captured_upvalues}
regs = put_elem(regs, dest, closure)
do_execute(rest, regs, upvalues, proto, state)
Expand Down