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feat(ir): absorb the magic-do thunk into early-split effect workers (#265)
An Effect/ST action of two or more real arguments is saturated at that arity before magic-do runs, so the uncurrying worker/wrapper split fires at the real arity and magic-do afterwards rewrites the worker's body into the nullary thunk an Effect value is. Every fully applied statement site then allocates that thunk and immediately forces it, two Lua calls with a closure in between. The late uncurry run cannot repair it: it splits manifest lambda chains, and the thunk is inside a worker that is already n-ary. absorbEffectThunk widens such a worker in place — the thunk's parameter joins its parameter list, its body becomes the worker's body — and rewrites every forced site w(a...)(run) to the single call w(a..., run), still an effect run by its trailing marker. Each wrapper delegating to the worker grows one parameter, which the delegate passes on, so a partial application still evaluates to a closure. The precondition is that every reference is a forced site or such a delegate, with at least one forced site: the Lua backend drops the worker's trailing unused parameter run, so any other reference the wider arity leaves under-applied would become a saturated Lua call and run the effect at construction time. Absorbing the marker also makes a recursive driver's self-call a genuine tail call, so the native-loop lowering turns it into a Lua while loop. Bench.EffectStep2 gains 1.22x under PUC Lua 5.1 and 1.28x under LuaJIT; Bench.EffectStep, whose two-argument driver is the same case, gains 1.10x/1.14x, and both trace reports lose their thunk-allocation aborts with the driver ending as a compiled ILOOP. The pass runs last, after the late uncurry run and the dce that follows it: nothing later moves a call, so the reference census is final, and the wrappers whose sites all went to their workers are already gone.
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15 files changed

Lines changed: 913 additions & 306 deletions

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‎bench/goldens/fnew_Bench.EffectStep.txt‎

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Bench.EffectStep.lua:11
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Bench.EffectStep.lua:11
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Bench.EffectStep.lua:32
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Bench.EffectStep.lua:43
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Bench.EffectStep.lua:46
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Bench.EffectStep.lua:55
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Bench.EffectStep.lua:49
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Bench.EffectStep.lua:48
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Bench.EffectStep.lua:58

‎bench/goldens/fnew_Bench.EffectStep2.txt‎

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Bench.EffectStep2.lua:9
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Bench.EffectStep2.lua:11
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Bench.EffectStep2.lua:29
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Bench.EffectStep2.lua:40
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Bench.EffectStep2.lua:44
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Bench.EffectStep2.lua:43
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Bench.EffectStep2.lua:49
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Bench.EffectStep2.lua:56
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Bench.EffectStep2.lua:52
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Bench.EffectStep2.lua:51
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Bench.EffectStep2.lua:59

‎bench/goldens/trace_effect_step.txt‎

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workload: n=100000 reps=4 result=1500000
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aborts (distinct site -- reason):
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Bench.EffectStep.lua:11 -- NYI: bytecode FNEW
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Bench.EffectStep.lua:43 -- NYI: bytecode FNEW
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Bench.EffectStep.lua:55 -- NYI: bytecode FNEW
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Bench.EffectStep.lua:58 -- NYI: bytecode FNEW
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Bench.EffectStep.lua:8 -- NYI: bytecode FNEW
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Bench.EffectStep.lua:9 -- NYI: bytecode FNEW
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bytecode end state (J*=compiled, I*=blacklisted):
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Bench.EffectStep.lua:10 IFUNCF
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Bench.EffectStep.lua:11 IFUNCF
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Bench.EffectStep.lua:11 JFUNCF
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Bench.EffectStep.lua:16 IFUNCF
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Bench.EffectStep.lua:35 IFUNCF
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Bench.EffectStep.lua:36 IFUNCF
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Bench.EffectStep.lua:35 ILOOP
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Bench.EffectStep.lua:8 JFUNCF
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Bench.EffectStep.lua:9 IFUNCF
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Bench.EffectStep.lua:9 JFUNCF
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counts: aborts=5 compiled=3 blacklisted=6
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counts: aborts=4 compiled=3 blacklisted=5

‎bench/goldens/trace_effect_step2.txt‎

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workload: n=100000 reps=4 result=1500000
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aborts (distinct site -- reason):
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Bench.EffectStep2.lua:11 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:29 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:40 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:56 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:59 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:8 -- NYI: bytecode FNEW
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Bench.EffectStep2.lua:9 -- NYI: bytecode FNEW
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bytecode end state (J*=compiled, I*=blacklisted):
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Bench.EffectStep2.lua:10 IFUNCF
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Bench.EffectStep2.lua:11 IFUNCF
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Bench.EffectStep2.lua:11 JFUNCF
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Bench.EffectStep2.lua:16 IFUNCF
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Bench.EffectStep2.lua:17 IFUNCF
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Bench.EffectStep2.lua:32 IFUNCF
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Bench.EffectStep2.lua:33 IFUNCF
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Bench.EffectStep2.lua:30 ILOOP
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Bench.EffectStep2.lua:8 JFUNCF
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Bench.EffectStep2.lua:9 IFUNCF
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Bench.EffectStep2.lua:9 JFUNCF
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counts: aborts=6 compiled=3 blacklisted=7
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counts: aborts=4 compiled=3 blacklisted=5

‎changelog.d/20260729_200000_unisay_absorb_effect_thunk.md‎

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### Added
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- Effect/ST actions of two or more arguments no longer allocate a closure
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per executed statement (#265). Such an action is already saturated at
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its real arity when the uncurrying worker/wrapper split measures it, so
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the split fires there and magic-do only afterwards rewrites the worker's
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body into the nullary thunk an Effect value is — leaving every fully
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applied statement site to allocate that thunk and immediately force it.
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The late uncurry run cannot repair this: it splits manifest lambda
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chains, and the thunk sits inside a worker that is already n-ary. The
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new `absorbEffectThunk` pass instead widens the worker in place, moving
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the thunk's parameter onto its parameter list, so the site is one n-ary
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call:
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```lua
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local Golden_EffectWorkerThunk_Test_report_S_w = function(tag, n)
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return function()
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local _ = Effect_Console_log(tag)()
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local _ = Effect_Console_log(Data_Show_showIntImpl(n))()
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return Effect_Console_log("-")()
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end
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end
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local _ = Golden_EffectWorkerThunk_Test_report_S_w("a", 1)()
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```
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becomes
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```lua
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local Golden_EffectWorkerThunk_Test_report_S_w = function(tag, n)
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local _ = Effect_Console_log(tag)()
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local _ = Effect_Console_log(Data_Show_showIntImpl(n))()
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return Effect_Console_log("-")()
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end
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local _ = Golden_EffectWorkerThunk_Test_report_S_w("a", 1)
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```
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The action's curried wrapper grows one parameter so a partial
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application still evaluates to a closure. Taking the run marker into
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the call also makes a recursive driver's self-call a genuine tail call,
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which the native-loop lowering then turns into a Lua `while` — the
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driver of `Bench.EffectStep` went from
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```lua
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local Bench_EffectStep_go_S_w
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Bench_EffectStep_go_S_w = function(i, ref)
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return function()
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local _ = Bench_EffectStep_step_S_w(ref)
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if i >= 1 and i ~= 1 then
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return Bench_EffectStep_go_S_w(i - 1, ref)()
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else
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return Control_Monad_ST_Internal_read(ref)()
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end
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end
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end
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```
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to
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```lua
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local Bench_EffectStep_go_S_w = function(i, ref)
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while true do
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local _ = Bench_EffectStep_step_S_w(ref)
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if i >= 1 and i ~= 1 then
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i, ref = i - 1, ref
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else
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return Control_Monad_ST_Internal_read(ref)()
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end
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end
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end
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```
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1.22× faster under PUC Lua 5.1 and 1.28× under LuaJIT on the new
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`Bench.EffectStep2` macrobenchmark, and 1.10×/1.14× on the pre-existing
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`Bench.EffectStep`, whose two-argument driver is the same case; that
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spec's trace report loses one `NYI: bytecode FNEW` abort and its driver
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ends compiled as an `ILOOP` instead of interpreted as an `IFUNCF`.
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A worker whose call is bound as an action value and run later keeps the
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call-then-force shape, as does any other reference the widened arity
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would leave under-applied: the Lua backend drops a trailing unused
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parameter run, so an under-applied worker call would run the effect at
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construction time. `Golden.EffectWorkerThunk` pins both sides, including
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a `let`-bound local worker.

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