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perf: reuse pre-allocated arrays in TailCall trampoline #1119

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perf: reuse pre-allocated arrays in TailCall trampoline #1119

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20 changes: 17 additions & 3 deletions sjsonnet/src/sjsonnet/Evaluator.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,17 @@ class Evaluator(
private val maxStack: Int = settings.maxStack
private[sjsonnet] var profiler: Profiler = _

// Rotating arg buffers for TailCall creation (zero-alloc trampoline).
// Safety: Func.apply copies Eval refs out of the buffer (extendSimple/arraycopy)
// before evalRhs can produce the next TailCall, so no slot is overwritten while live.
private var tailCallBufIdx: Int = 0
private val tailCallArgBuf1: Array[Array[Eval]] = Array.fill(4)(new Array[Eval](1))
private val tailCallArgBuf2: Array[Array[Eval]] = Array.fill(4)(new Array[Eval](2))
private val tailCallArgBuf3: Array[Array[Eval]] = Array.fill(4)(new Array[Eval](3))
@inline private def nextTailCallBufIdx(): Int = {
val i = tailCallBufIdx; tailCallBufIdx = (i + 1) & 3; i
}

@inline private[sjsonnet] final def checkStackDepth(pos: Position): Unit = {
stackDepth += 1
if (debugStats != null && stackDepth > debugStats.maxStackDepth)
Expand Down Expand Up @@ -1694,15 +1705,17 @@ class Evaluator(
val isStrict = e.isStrict
val func = visitExpr(e.value).cast[Val.Func]
val arg: Eval = if (!isStrict) visitAsLazy(e.a1) else visitExpr(e.a1)
new TailCall(func, Array[Eval](arg), null, e, strict = isStrict)
val buf = tailCallArgBuf1(nextTailCallBufIdx()); buf(0) = arg
new TailCall(func, buf, null, e, strict = isStrict)
} catch Error.withStackFrame(e)
case e: Apply2 =>
try {
val isStrict = e.isStrict
val func = visitExpr(e.value).cast[Val.Func]
val a1: Eval = if (!isStrict) visitAsLazy(e.a1) else visitExpr(e.a1)
val a2: Eval = if (!isStrict) visitAsLazy(e.a2) else visitExpr(e.a2)
new TailCall(func, Array[Eval](a1, a2), null, e, strict = isStrict)
val buf = tailCallArgBuf2(nextTailCallBufIdx()); buf(0) = a1; buf(1) = a2
new TailCall(func, buf, null, e, strict = isStrict)
} catch Error.withStackFrame(e)
case e: Apply3 =>
try {
Expand All @@ -1711,7 +1724,8 @@ class Evaluator(
val a1: Eval = if (!isStrict) visitAsLazy(e.a1) else visitExpr(e.a1)
val a2: Eval = if (!isStrict) visitAsLazy(e.a2) else visitExpr(e.a2)
val a3: Eval = if (!isStrict) visitAsLazy(e.a3) else visitExpr(e.a3)
new TailCall(func, Array[Eval](a1, a2, a3), null, e, strict = isStrict)
val buf = tailCallArgBuf3(nextTailCallBufIdx()); buf(0) = a1; buf(1) = a2; buf(2) = a3
new TailCall(func, buf, null, e, strict = isStrict)
} catch Error.withStackFrame(e)
case _ => visitExpr(e)
}
Expand Down
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