big optimization round

docs/parallelism.md

@@ -204,4 +204,18 @@ Flows allow easy transforming of any [Iterable]. See how the standard Lyng libra
     }
 
 
-[Iterable]: Iterable.md
+[Iterable]: Iterable.md
+
+## Scope frame pooling (JVM)
+
+Lyng includes an optional optimization for function/method calls on JVM: scope frame pooling, toggled by the runtime flag `PerfFlags.SCOPE_POOL`.
+
+- Default: `SCOPE_POOL` is OFF on JVM.
+- Rationale: the current `ScopePool` implementation is not thread‑safe. Lyng targets multi‑threaded execution on most platforms, therefore we keep pooling disabled by default until a thread‑safe design is introduced.
+- When safe to enable: single‑threaded runs (e.g., micro‑benchmarks or scripts executed on a single worker) where no scopes are shared across threads.
+- How to toggle at runtime (Kotlin/JVM tests):
+  - `PerfFlags.SCOPE_POOL = true` to enable.
+  - `PerfFlags.SCOPE_POOL = false` to disable.
+- Expected effect (from our JVM micro‑benchmarks): in deep call loops, enabling pooling reduced total time by about 1.38× in a dedicated pooling benchmark; mileage may vary depending on workload.
+
+Future work: introduce thread‑safe pooling (e.g., per‑thread pools or confinement strategies) before considering enabling it by default in multi‑threaded environments.

docs/perf_guide.md

@@ -0,0 +1,119 @@
+# Lyng Performance Guide (JVM‑first)
+
+This document explains how to enable and measure the performance optimizations added to the Lyng interpreter. The focus is JVM‑first with safe, flag‑guarded rollouts and quick A/B testing. Other targets (JS/Wasm/Native) keep conservative defaults until validated.
+
+## Overview
+
+Optimizations are controlled by runtime‑mutable flags in `net.sergeych.lyng.PerfFlags`, initialized from platform‑specific static defaults `net.sergeych.lyng.PerfDefaults` (KMP `expect/actual`).
+
+- JVM/Android defaults are aggressive (e.g. `RVAL_FASTPATH=true`).
+- Non‑JVM defaults are conservative (e.g. `RVAL_FASTPATH=false`).
+
+All flags are `var` and can be flipped at runtime (e.g., from tests or host apps) for A/B comparisons.
+
+## Key flags
+
+- `LOCAL_SLOT_PIC` — Runtime cache in `LocalVarRef` to avoid repeated name→slot lookups per frame (ON JVM default).
+- `EMIT_FAST_LOCAL_REFS` — Compiler emits `FastLocalVarRef` for identifiers known to be locals/params (ON JVM default).
+- `ARG_BUILDER` — Efficient argument building: small‑arity no‑alloc and pooled builder on JVM (ON JVM default).
+- `SKIP_ARGS_ON_NULL_RECEIVER` — Early return on optional‑null receivers before building args (semantics‑compatible). A/B only.
+- `SCOPE_POOL` — Scope frame pooling for calls (JVM‑first). OFF by default. Enable for benchmark A/B.
+- `FIELD_PIC` — 2‑entry polymorphic inline cache for field reads/writes keyed by `(classId, layoutVersion)` (ON JVM default).
+- `METHOD_PIC` — 2‑entry PIC for instance method calls keyed by `(classId, layoutVersion)` (ON JVM default).
+- `PIC_DEBUG_COUNTERS` — Enable lightweight hit/miss counters via `PerfStats` (OFF by default).
+- `PRIMITIVE_FASTOPS` — Fast paths for `(ObjInt, ObjInt)` arithmetic/comparisons and `(ObjBool, ObjBool)` logic (ON JVM default).
+- `RVAL_FASTPATH` — Bypass `ObjRecord` in pure expression evaluation via `ObjRef.evalValue` (ON JVM default, OFF elsewhere).
+
+See `src/commonMain/kotlin/net/sergeych/lyng/PerfFlags.kt` and `PerfDefaults.*.kt` for details and platform defaults.
+
+## Where optimizations apply
+
+- Locals: `FastLocalVarRef`, `LocalVarRef` per‑frame cache (PIC).
+- Calls: small‑arity zero‑alloc paths (0–5 args), pooled builder (JVM), and child frame pooling (optional).
+- Properties/methods: Field/Method PICs with receiver shape `(classId, layoutVersion)` and handle‑aware caches.
+- Expressions: R‑value fast paths in hot nodes (`UnaryOpRef`, `BinaryOpRef`, `ElvisRef`, logical ops, `RangeRef`, `IndexRef` read, `FieldRef` receiver eval, `ListLiteralRef` elements, `CallRef` callee, `MethodCallRef` receiver, assignment RHS).
+- Primitives: Direct boolean/int ops where safe.
+
+## Running JVM micro‑benchmarks
+
+Each benchmark prints timings with `[DEBUG_LOG]` and includes correctness assertions to prevent dead‑code elimination.
+
+Run individual tests to avoid multiplatform matrices:
+
+```
+./gradlew :lynglib:jvmTest --tests LocalVarBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallMixedArityBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallSplatBenchmarkTest
+./gradlew :lynglib:jvmTest --tests PicBenchmarkTest
+./gradlew :lynglib:jvmTest --tests PicInvalidationJvmTest
+./gradlew :lynglib:jvmTest --tests ArithmeticBenchmarkTest
+./gradlew :lynglib:jvmTest --tests ExpressionBenchmarkTest
+./gradlew :lynglib:jvmTest --tests CallPoolingBenchmarkTest
+./gradlew :lynglib:jvmTest --tests MethodPoolingBenchmarkTest
+./gradlew :lynglib:jvmTest --tests MixedBenchmarkTest
+./gradlew :lynglib:jvmTest --tests DeepPoolingStressJvmTest
+```
+
+Typical output (example):
+
+```
+[DEBUG_LOG] [BENCH] mixed-arity x200000 [ARG_BUILDER=ON]: 85.7 ms
+```
+
+Lower time is better. Run the same bench with a flag OFF vs ON to compare.
+
+## Toggling flags in tests
+
+Flags are mutable at runtime, e.g.:
+
+```kotlin
+PerfFlags.ARG_BUILDER = false
+val r1 = (Scope().eval(script) as ObjInt).value
+PerfFlags.ARG_BUILDER = true
+val r2 = (Scope().eval(script) as ObjInt).value
+```
+
+Reset flags at the end of a test to avoid impacting other tests.
+
+## PIC diagnostics (optional)
+
+Enable counters:
+
+```kotlin
+PerfFlags.PIC_DEBUG_COUNTERS = true
+PerfStats.resetAll()
+```
+
+Available counters in `PerfStats`:
+
+- Field PIC: `fieldPicHit`, `fieldPicMiss`, `fieldPicSetHit`, `fieldPicSetMiss`
+- Method PIC: `methodPicHit`, `methodPicMiss`
+- Locals: `localVarPicHit`, `localVarPicMiss`, `fastLocalHit`, `fastLocalMiss`
+- Primitive ops: `primitiveFastOpsHit`
+
+Print a summary at the end of a bench/test as needed. Remember to turn counters OFF after the test.
+
+## Guidance per flag (JVM)
+
+- Keep `RVAL_FASTPATH = true` unless debugging a suspected expression‑semantics issue.
+- Use `SCOPE_POOL = true` only for benchmarks or once pooling passes the deep stress tests and broader validation; currently OFF by default.
+- `FIELD_PIC` and `METHOD_PIC` should remain ON; they are validated with invalidation tests.
+- `ARG_BUILDER` should remain ON; switch OFF only to get a baseline.
+
+## Notes on correctness & safety
+
+- Optional chaining semantics are preserved across fast paths.
+- Visibility/mutability checks are enforced even on PIC fast‑paths.
+- `frameId` is regenerated on each pooled frame borrow; stress tests verify no leakage under deep nesting/recursion.
+
+## Cross‑platform
+
+- Non‑JVM defaults keep `RVAL_FASTPATH=false` for now; other low‑risk flags may be ON.
+- Once JVM path is fully validated and measured, add lightweight benches for JS/Wasm/Native and enable flags incrementally.
+
+## Troubleshooting
+
+- If a benchmark shows regressions, flip related flags OFF to isolate the source (e.g., `ARG_BUILDER`, `RVAL_FASTPATH`, `FIELD_PIC`, `METHOD_PIC`).
+- Use `PIC_DEBUG_COUNTERS` to observe inline cache effectiveness.
+- Ensure tests do not accidentally keep flags ON for subsequent tests; reset after each test.

lynglib/build.gradle.kts

@@ -142,6 +142,13 @@ publishing {
     }
 }
 
+// Ensure JVM test stdout is visible and runs are single-threaded for stable timings
+tasks.withType<org.gradle.api.tasks.testing.Test> {
+    testLogging {
+        showStandardStreams = true
+    }
+    maxParallelForks = 1
+}
 
 //mavenPublishing {
 //    publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)

lynglib/src/androidMain/kotlin/net/sergeych/lyng/ArgBuilderAndroid.kt

@@ -0,0 +1,32 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+actual object ArgBuilderProvider {
+    private val tl = object : ThreadLocal<AndroidArgsBuilder>() {
+        override fun initialValue(): AndroidArgsBuilder = AndroidArgsBuilder()
+    }
+    actual fun acquire(): ArgsBuilder = tl.get()
+}
+
+private class AndroidArgsBuilder : ArgsBuilder {
+    private val buf: ArrayList<Obj> = ArrayList(8)
+
+    override fun reset(expectedSize: Int) {
+        buf.clear()
+        if (expectedSize > 0) buf.ensureCapacity(expectedSize)
+    }
+
+    override fun add(v: Obj) { buf.add(v) }
+
+    override fun addAll(vs: List<Obj>) {
+        if (vs.isNotEmpty()) {
+            buf.ensureCapacity(buf.size + vs.size)
+            buf.addAll(vs)
+        }
+    }
+
+    override fun build(tailBlockMode: Boolean): Arguments = Arguments(buf.toList(), tailBlockMode)
+
+    override fun release() { /* no-op, ThreadLocal keeps buffer */ }
+}

lynglib/src/androidMain/kotlin/net/sergeych/lyng/PerfDefaults.android.kt

@@ -0,0 +1,18 @@
+package net.sergeych.lyng
+
+actual object PerfDefaults {
+    actual val LOCAL_SLOT_PIC: Boolean = true
+    actual val EMIT_FAST_LOCAL_REFS: Boolean = true
+
+    actual val ARG_BUILDER: Boolean = true
+    actual val SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    actual val SCOPE_POOL: Boolean = false
+
+    actual val FIELD_PIC: Boolean = true
+    actual val METHOD_PIC: Boolean = true
+
+    actual val PIC_DEBUG_COUNTERS: Boolean = false
+
+    actual val PRIMITIVE_FASTOPS: Boolean = true
+    actual val RVAL_FASTPATH: Boolean = true
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ArgBuilder.kt

@@ -0,0 +1,22 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+/**
+ * Expect/actual API for an arguments builder that can reuse buffers on JVM to reduce allocations.
+ * Default (non-JVM) implementation just allocates fresh collections and has no pooling.
+ */
+expect object ArgBuilderProvider {
+    fun acquire(): ArgsBuilder
+}
+
+interface ArgsBuilder {
+    /** Prepare the builder for a new build, optionally hinting capacity. */
+    fun reset(expectedSize: Int = 0)
+    fun add(v: Obj)
+    fun addAll(vs: List<Obj>)
+    /** Build immutable [Arguments] snapshot from the current buffer. */
+    fun build(tailBlockMode: Boolean): Arguments
+    /** Return builder to pool/reset state. Safe to no-op on non-JVM. */
+    fun release()
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ArgRuntime.kt

@@ -0,0 +1,11 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+/**
+ * Helper factory for argument-building mutable lists.
+ * Currently returns a fresh ArrayList with the requested initial capacity.
+ * JVM-specific pooling/builder can be introduced later via expect/actual without
+ * changing call sites that use [newArgMutableList].
+ */
+fun newArgMutableList(initialCapacity: Int): MutableList<Obj> = ArrayList(initialCapacity)

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Arguments.kt

@@ -24,31 +24,95 @@ import net.sergeych.lyng.obj.ObjList
  data class ParsedArgument(val value: Statement, val pos: Pos, val isSplat: Boolean = false)
  
  suspend fun Collection<ParsedArgument>.toArguments(scope: Scope, tailBlockMode: Boolean): Arguments {
-     // If ARG_BUILDER is enabled, try to reuse a pre-sized ArrayList and do bulk-adds
+     // Small-arity fast path (no splats) to reduce allocations
-     val list: MutableList<Obj> = if (PerfFlags.ARG_BUILDER) ArrayList(this.size) else mutableListOf()
+     if (PerfFlags.ARG_BUILDER) {
- 
+         var hasSplat = false
-     for (x in this) {
+         var count = 0
-         val value = x.value.execute(scope)
+         for (pa in this) {
-         if (x.isSplat) {
+             if (pa.isSplat) { hasSplat = true; break }
-             when {
+             count++
-                 value is ObjList -> {
+             if (count > 3) break
-                     // Bulk add elements from an ObjList
+         }
-                     list.addAll(value.list)
+         if (!hasSplat && count == this.size) {
+             val quick = when (count) {
+                 0 -> Arguments.EMPTY
+                 1 -> Arguments(listOf(this.elementAt(0).value.execute(scope)), tailBlockMode)
+                 2 -> {
+                     val a0 = this.elementAt(0).value.execute(scope)
+                     val a1 = this.elementAt(1).value.execute(scope)
+                     Arguments(listOf(a0, a1), tailBlockMode)
                  }
- 
+                 3 -> {
-                 value.isInstanceOf(ObjIterable) -> {
+                     val a0 = this.elementAt(0).value.execute(scope)
-                     // Convert to list once and bulk add
+                     val a1 = this.elementAt(1).value.execute(scope)
-                     val i = (value.invokeInstanceMethod(scope, "toList") as ObjList).list
+                     val a2 = this.elementAt(2).value.execute(scope)
-                     list.addAll(i)
+                     Arguments(listOf(a0, a1, a2), tailBlockMode)
                  }
- 
+                 4 -> {
-                 else -> scope.raiseClassCastError("expected list of objects for splat argument")
+                     val a0 = this.elementAt(0).value.execute(scope)
+                     val a1 = this.elementAt(1).value.execute(scope)
+                     val a2 = this.elementAt(2).value.execute(scope)
+                     val a3 = this.elementAt(3).value.execute(scope)
+                     Arguments(listOf(a0, a1, a2, a3), tailBlockMode)
+                 }
+                 5 -> {
+                     val a0 = this.elementAt(0).value.execute(scope)
+                     val a1 = this.elementAt(1).value.execute(scope)
+                     val a2 = this.elementAt(2).value.execute(scope)
+                     val a3 = this.elementAt(3).value.execute(scope)
+                     val a4 = this.elementAt(4).value.execute(scope)
+                     Arguments(listOf(a0, a1, a2, a3, a4), tailBlockMode)
+                 }
+                 else -> null
              }
-         } else {
+             if (quick != null) return quick
-             list.add(value)
          }
      }
-     return Arguments(list, tailBlockMode)
+     // General path with builder or simple list fallback
+     if (PerfFlags.ARG_BUILDER) {
+         val b = ArgBuilderProvider.acquire()
+         try {
+             b.reset(this.size)
+             for (x in this) {
+                 val value = x.value.execute(scope)
+                 if (x.isSplat) {
+                     when {
+                         value is ObjList -> {
+                             b.addAll(value.list)
+                         }
+                         value.isInstanceOf(ObjIterable) -> {
+                             val i = (value.invokeInstanceMethod(scope, "toList") as ObjList).list
+                             b.addAll(i)
+                         }
+                         else -> scope.raiseClassCastError("expected list of objects for splat argument")
+                     }
+                 } else {
+                     b.add(value)
+                 }
+             }
+             return b.build(tailBlockMode)
+         } finally {
+             b.release()
+         }
+     } else {
+         val list: MutableList<Obj> = mutableListOf()
+         for (x in this) {
+             val value = x.value.execute(scope)
+             if (x.isSplat) {
+                 when {
+                     value is ObjList -> list.addAll(value.list)
+                     value.isInstanceOf(ObjIterable) -> {
+                         val i = (value.invokeInstanceMethod(scope, "toList") as ObjList).list
+                         list.addAll(i)
+                     }
+                     else -> scope.raiseClassCastError("expected list of objects for splat argument")
+                 }
+             } else {
+                 list.add(value)
+             }
+         }
+         return Arguments(list, tailBlockMode)
+     }
  }
  
  data class Arguments(val list: List<Obj>, val tailBlockMode: Boolean = false) : List<Obj> by list {
@@ -57,7 +121,14 @@ import net.sergeych.lyng.obj.ObjList
  
      fun firstAndOnly(pos: Pos = Pos.UNKNOWN): Obj {
          if (list.size != 1) throw ScriptError(pos, "expected one argument, got ${list.size}")
-         return list.first().byValueCopy()
+         val v = list.first()
+         // Tiny micro-alloc win: avoid byValueCopy for immutable singletons
+         return when (v) {
+             net.sergeych.lyng.obj.ObjNull,
+             net.sergeych.lyng.obj.ObjTrue,
+             net.sergeych.lyng.obj.ObjFalse -> v
+             else -> v.byValueCopy()
+         }
      }
  
      /**

lynglib/src/commonMain/kotlin/net/sergeych/lyng/PerfDefaults.kt

@@ -0,0 +1,23 @@
+package net.sergeych.lyng
+
+/**
+ * Platform-specific default values for performance flags.
+ * These defaults are applied once at static init time in [PerfFlags] and can
+ * be overridden at runtime by tests or callers.
+ */
+expect object PerfDefaults {
+    val LOCAL_SLOT_PIC: Boolean
+    val EMIT_FAST_LOCAL_REFS: Boolean
+
+    val ARG_BUILDER: Boolean
+    val SKIP_ARGS_ON_NULL_RECEIVER: Boolean
+    val SCOPE_POOL: Boolean
+
+    val FIELD_PIC: Boolean
+    val METHOD_PIC: Boolean
+
+    val PIC_DEBUG_COUNTERS: Boolean
+
+    val PRIMITIVE_FASTOPS: Boolean
+    val RVAL_FASTPATH: Boolean
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/PerfFlags.kt

@@ -1,26 +1,33 @@
 package net.sergeych.lyng
 
 /**
- * Runtime-togglable perf flags for micro-benchmarking and A/B comparisons on the JVM.
+ * Runtime-togglable perf flags for micro-benchmarking and A/B comparisons.
- * Keep as `var` so tests can flip them.
+ * Initialized from platform-specific defaults via PerfDefaults expect/actual.
+ * Keep as `var` so tests can flip them at runtime.
  */
 object PerfFlags {
     // Enable PIC inside LocalVarRef (runtime cache of name->slot per frame)
-    var LOCAL_SLOT_PIC: Boolean = true
+    var LOCAL_SLOT_PIC: Boolean = PerfDefaults.LOCAL_SLOT_PIC
     // Make the compiler emit fast local refs for identifiers known to be function locals/params
-    var EMIT_FAST_LOCAL_REFS: Boolean = true
+    var EMIT_FAST_LOCAL_REFS: Boolean = PerfDefaults.EMIT_FAST_LOCAL_REFS
 
     // Enable more efficient argument building and bulk-copy for splats
-    var ARG_BUILDER: Boolean = true
+    var ARG_BUILDER: Boolean = PerfDefaults.ARG_BUILDER
     // Allow early-return in optional calls before building args (semantics-compatible). Present for A/B only.
-    var SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    var SKIP_ARGS_ON_NULL_RECEIVER: Boolean = PerfDefaults.SKIP_ARGS_ON_NULL_RECEIVER
-    // Enable pooling of Scope frames for calls (planned; JVM-only)
+    // Enable pooling of Scope frames for calls (may be JVM-only optimization)
-    var SCOPE_POOL: Boolean = false
+    var SCOPE_POOL: Boolean = PerfDefaults.SCOPE_POOL
 
     // Step 2: PICs for fields and methods
-    var FIELD_PIC: Boolean = true
+    var FIELD_PIC: Boolean = PerfDefaults.FIELD_PIC
-    var METHOD_PIC: Boolean = true
+    var METHOD_PIC: Boolean = PerfDefaults.METHOD_PIC
+
+    // Debug/observability for PICs and fast paths (JVM-first)
+    var PIC_DEBUG_COUNTERS: Boolean = PerfDefaults.PIC_DEBUG_COUNTERS
 
     // Step 3: Primitive arithmetic and comparison fast paths
-    var PRIMITIVE_FASTOPS: Boolean = true
+    var PRIMITIVE_FASTOPS: Boolean = PerfDefaults.PRIMITIVE_FASTOPS
+
+    // Step 4: R-value fast path to bypass ObjRecord in pure expression evaluation
+    var RVAL_FASTPATH: Boolean = PerfDefaults.RVAL_FASTPATH
 }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/PerfStats.kt

@@ -0,0 +1,40 @@
+package net.sergeych.lyng
+
+/**
+ * Lightweight runtime counters for perf diagnostics. Enabled via flags in [PerfFlags].
+ * Keep simple and zero-cost when disabled by guarding increments at call sites.
+ */
+object PerfStats {
+    // Field PIC
+    var fieldPicHit: Long = 0
+    var fieldPicMiss: Long = 0
+    var fieldPicSetHit: Long = 0
+    var fieldPicSetMiss: Long = 0
+
+    // Method PIC
+    var methodPicHit: Long = 0
+    var methodPicMiss: Long = 0
+
+    // Local var PICs
+    var localVarPicHit: Long = 0
+    var localVarPicMiss: Long = 0
+    var fastLocalHit: Long = 0
+    var fastLocalMiss: Long = 0
+
+    // Primitive fast ops
+    var primitiveFastOpsHit: Long = 0
+
+    fun resetAll() {
+        fieldPicHit = 0
+        fieldPicMiss = 0
+        fieldPicSetHit = 0
+        fieldPicSetMiss = 0
+        methodPicHit = 0
+        methodPicMiss = 0
+        localVarPicHit = 0
+        localVarPicMiss = 0
+        fastLocalHit = 0
+        fastLocalMiss = 0
+        primitiveFastOpsHit = 0
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Scope.kt

@@ -22,8 +22,8 @@ import net.sergeych.lyng.pacman.ImportManager
 import net.sergeych.lyng.pacman.ImportProvider
 
 // Simple per-frame id generator for perf caches (not thread-safe, fine for scripts)
-private object FrameIdGen { var c: Long = 1L; fun nextId(): Long = c++ }
+object FrameIdGen { var c: Long = 1L; fun nextId(): Long = c++ }
-private fun nextFrameId(): Long = FrameIdGen.nextId()
+fun nextFrameId(): Long = FrameIdGen.nextId()
 
 /**
  * Scope is where local variables and methods are stored. Scope is also a parent scope for other scopes.
@@ -40,14 +40,14 @@ private fun nextFrameId(): Long = FrameIdGen.nextId()
  *  - [ClosureScope] - scope used to apply a closure to some thisObj scope
  */
 open class Scope(
-    val parent: Scope?,
+    var parent: Scope?,
-    val args: Arguments = Arguments.EMPTY,
+    var args: Arguments = Arguments.EMPTY,
     var pos: Pos = Pos.builtIn,
     var thisObj: Obj = ObjVoid,
     var skipScopeCreation: Boolean = false,
 ) {
-    // Unique id per scope frame for PICs; cheap to compare and stable for the frame lifetime.
+    // Unique id per scope frame for PICs; regenerated on each borrow from the pool.
-    val frameId: Long = nextFrameId()
+    var frameId: Long = nextFrameId()
 
     // Fast-path storage for local variables/arguments accessed by slot index.
     // Enabled by default for child scopes; module/class scopes can ignore it.
@@ -165,12 +165,48 @@ open class Scope(
         return idx
     }
 
+    /**
+     * Reset this scope instance so it can be safely reused as a fresh child frame.
+     * Clears locals and slots, assigns new frameId, and sets parent/args/pos/thisObj.
+     */
+    fun resetForReuse(parent: Scope?, args: Arguments, pos: Pos, thisObj: Obj) {
+        this.parent = parent
+        this.args = args
+        this.pos = pos
+        this.thisObj = thisObj
+        this.skipScopeCreation = false
+        // fresh identity for PIC caches
+        this.frameId = nextFrameId()
+        // clear locals and slot maps
+        objects.clear()
+        slots.clear()
+        nameToSlot.clear()
+    }
+
     /**
      * Creates a new child scope using the provided arguments and optional `thisObj`.
      */
     fun createChildScope(pos: Pos, args: Arguments = Arguments.EMPTY, newThisObj: Obj? = null): Scope =
         Scope(this, args, pos, newThisObj ?: thisObj)
 
+    /**
+     * Execute a block inside a child frame. Guarded for future pooling via [PerfFlags.SCOPE_POOL].
+     * Currently always creates a fresh child scope to preserve unique frameId semantics.
+     */
+    inline suspend fun <R> withChildFrame(args: Arguments = Arguments.EMPTY, newThisObj: Obj? = null, crossinline block: suspend (Scope) -> R): R {
+        if (PerfFlags.SCOPE_POOL) {
+            val child = ScopePool.borrow(this, args, pos, newThisObj ?: thisObj)
+            try {
+                return block(child)
+            } finally {
+                ScopePool.release(child)
+            }
+        } else {
+            val child = createChildScope(args, newThisObj)
+            return block(child)
+        }
+    }
+
     /**
      * Creates a new child scope using the provided arguments and optional `thisObj`.
      * The child scope inherits the current scope's properties such as position and the existing `thisObj` if no new `thisObj` is provided.

lynglib/src/commonMain/kotlin/net/sergeych/lyng/ScopePool.kt

@@ -0,0 +1,35 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+import net.sergeych.lyng.obj.ObjVoid
+
+/**
+ * Simple, portable scope frame pool. JVM-first optimization; for now it uses a small
+ * global deque. It is only used when [PerfFlags.SCOPE_POOL] is true.
+ *
+ * NOTE: This implementation is not thread-safe. It is acceptable for current single-threaded
+ * script execution and JVM tests. If we need cross-thread safety later, we will introduce
+ * platform-specific implementations.
+ */
+object ScopePool {
+    private const val MAX_POOL_SIZE = 64
+    private val pool = ArrayDeque<Scope>(MAX_POOL_SIZE)
+
+    fun borrow(parent: Scope, args: Arguments, pos: Pos, thisObj: Obj): Scope {
+        val s = if (pool.isNotEmpty()) pool.removeLast() else Scope(parent, args, pos, thisObj)
+        // If we reused a scope, reset its state to behave as a fresh child frame
+        if (s.parent !== parent || s.args !== args || s.pos !== pos || s.thisObj !== thisObj) {
+            s.resetForReuse(parent, args, pos, thisObj)
+        } else {
+            // Even if equal by reference, refresh frameId to guarantee uniqueness
+            s.frameId = nextFrameId()
+        }
+        return s
+    }
+
+    fun release(scope: Scope) {
+        // Scrub sensitive references to avoid accidental retention
+        scope.resetForReuse(parent = null, args = Arguments.EMPTY, pos = Pos.builtIn, thisObj = ObjVoid)
+        if (pool.size < MAX_POOL_SIZE) pool.addLast(scope)
+    }
+}

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/Obj.kt

@@ -265,7 +265,12 @@ open class Obj {
     }
 
     suspend fun invoke(scope: Scope, thisObj: Obj, args: Arguments): Obj =
-        callOn(scope.createChildScope(scope.pos, args = args, newThisObj = thisObj))
+        if (net.sergeych.lyng.PerfFlags.SCOPE_POOL)
+            scope.withChildFrame(args, newThisObj = thisObj) { child ->
+                callOn(child)
+            }
+        else
+            callOn(scope.createChildScope(scope.pos, args = args, newThisObj = thisObj))
 
     suspend fun invoke(scope: Scope, thisObj: Obj, vararg args: Obj): Obj =
         callOn(

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjRef.kt

@@ -24,6 +24,11 @@ import net.sergeych.lyng.*
  */
 sealed interface ObjRef {
     suspend fun get(scope: Scope): ObjRecord
+    /**
+     * Fast path for evaluating an expression to a raw Obj value without wrapping it into ObjRecord.
+     * Default implementation calls [get] and returns its value. Nodes can override to avoid record traffic.
+     */
+    suspend fun evalValue(scope: Scope): Obj = get(scope).value
     suspend fun setAt(pos: Pos, scope: Scope, newValue: Obj) {
         throw ScriptError(pos, "can't assign value")
     }
@@ -51,7 +56,7 @@ enum class BinOp {
 /** R-value reference for unary operations. */
 class UnaryOpRef(private val op: UnaryOp, private val a: ObjRef) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val v = a.get(scope).value
+        val v = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) a.evalValue(scope) else a.get(scope).value
         val r = when (op) {
             UnaryOp.NOT -> v.logicalNot(scope)
             UnaryOp.NEGATE -> v.negate(scope)
@@ -63,8 +68,8 @@ class UnaryOpRef(private val op: UnaryOp, private val a: ObjRef) : ObjRef {
 /** R-value reference for binary operations. */
 class BinaryOpRef(private val op: BinOp, private val left: ObjRef, private val right: ObjRef) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val a = left.get(scope).value
+        val a = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) left.evalValue(scope) else left.get(scope).value
-        val b = right.get(scope).value
+        val b = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) right.evalValue(scope) else right.get(scope).value
 
         // Primitive fast paths for common cases (guarded by PerfFlags.PRIMITIVE_FASTOPS)
         if (net.sergeych.lyng.PerfFlags.PRIMITIVE_FASTOPS) {
@@ -77,7 +82,10 @@ class BinaryOpRef(private val op: BinOp, private val left: ObjRef, private val r
                     BinOp.NEQ -> if (a.value != b.value) ObjTrue else ObjFalse
                     else -> null
                 }
-                if (r != null) return r.asReadonly
+                if (r != null) {
+                    if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.primitiveFastOpsHit++
+                    return r.asReadonly
+                }
             }
             // Fast integer ops when both operands are ObjInt
             if (a is ObjInt && b is ObjInt) {
@@ -97,7 +105,10 @@ class BinaryOpRef(private val op: BinOp, private val left: ObjRef, private val r
                     BinOp.GTE -> if (av >= bv) ObjTrue else ObjFalse
                     else -> null
                 }
-                if (r != null) return r.asReadonly
+                if (r != null) {
+                    if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.primitiveFastOpsHit++
+                    return r.asReadonly
+                }
             }
         }
 
@@ -139,7 +150,7 @@ class AssignOpRef(
 ) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
         val x = target.get(scope).value
-        val y = value.get(scope).value
+        val y = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) value.evalValue(scope) else value.get(scope).value
         val inPlace: Obj? = when (op) {
             BinOp.PLUS -> x.plusAssign(scope, y)
             BinOp.MINUS -> x.minusAssign(scope, y)
@@ -196,8 +207,8 @@ class IncDecRef(
 /** Elvis operator reference: a ?: b */
 class ElvisRef(private val left: ObjRef, private val right: ObjRef) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val a = left.get(scope).value
+        val a = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) left.evalValue(scope) else left.get(scope).value
-        val r = if (a != ObjNull) a else right.get(scope).value
+        val r = if (a != ObjNull) a else if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) right.evalValue(scope) else right.get(scope).value
         return r.asReadonly
     }
 }
@@ -205,9 +216,9 @@ class ElvisRef(private val left: ObjRef, private val right: ObjRef) : ObjRef {
 /** Logical OR with short-circuit: a || b */
 class LogicalOrRef(private val left: ObjRef, private val right: ObjRef) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val a = left.get(scope).value
+        val a = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) left.evalValue(scope) else left.get(scope).value
         if ((a as? ObjBool)?.value == true) return ObjTrue.asReadonly
-        val b = right.get(scope).value
+        val b = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) right.evalValue(scope) else right.get(scope).value
         if (net.sergeych.lyng.PerfFlags.PRIMITIVE_FASTOPS) {
             if (a is ObjBool && b is ObjBool) {
                 return if (a.value || b.value) ObjTrue.asReadonly else ObjFalse.asReadonly
@@ -220,9 +231,9 @@ class LogicalOrRef(private val left: ObjRef, private val right: ObjRef) : ObjRef
 /** Logical AND with short-circuit: a && b */
 class LogicalAndRef(private val left: ObjRef, private val right: ObjRef) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val a = left.get(scope).value
+        val a = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) left.evalValue(scope) else left.get(scope).value
         if ((a as? ObjBool)?.value == false) return ObjFalse.asReadonly
-        val b = right.get(scope).value
+        val b = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) right.evalValue(scope) else right.get(scope).value
         if (net.sergeych.lyng.PerfFlags.PRIMITIVE_FASTOPS) {
             if (a is ObjBool && b is ObjBool) {
                 return if (a.value && b.value) ObjTrue.asReadonly else ObjFalse.asReadonly
@@ -255,41 +266,42 @@ class FieldRef(
     private var wKey2: Long = 0L; private var wVer2: Int = -1; private var wSetter2: (suspend (Obj, Scope, Obj) -> Unit)? = null
 
     override suspend fun get(scope: Scope): ObjRecord {
-        val base = target.get(scope).value
+        val base = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) target.evalValue(scope) else target.get(scope).value
         if (base == ObjNull && isOptional) return ObjNull.asMutable
         if (net.sergeych.lyng.PerfFlags.FIELD_PIC) {
             val (key, ver) = receiverKeyAndVersion(base)
-            rGetter1?.let { g -> if (key == rKey1 && ver == rVer1) return g(base, scope) }
+            rGetter1?.let { g -> if (key == rKey1 && ver == rVer1) {
-            rGetter2?.let { g -> if (key == rKey2 && ver == rVer2) return g(base, scope) }
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicHit++
+                return g(base, scope)
+            } }
+            rGetter2?.let { g -> if (key == rKey2 && ver == rVer2) {
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicHit++
+                return g(base, scope)
+            } }
             // Slow path
+            if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicMiss++
             val rec = base.readField(scope, name)
-            // Install move-to-front with a handle-aware getter
+            // Install move-to-front with a handle-aware getter. Where safe, capture resolved handles.
             rKey2 = rKey1; rVer2 = rVer1; rGetter2 = rGetter1
-            rKey1 = key;   rVer1 = ver;   rGetter1 = { obj, sc ->
+            when (base) {
-                when (obj) {
+                is ObjClass -> {
-                    is ObjInstance -> {
+                    val clsScope = base.classScope
-                        val instScope = obj.instanceScope
+                    val capturedIdx = clsScope?.getSlotIndexOf(name)
-                        val idx = instScope.getSlotIndexOf(name)
+                    if (clsScope != null && capturedIdx != null) {
-                        if (idx != null) {
+                        rKey1 = key; rVer1 = ver; rGetter1 = { obj, sc ->
-                            val r = instScope.getSlotRecord(idx)
+                            val scope0 = (obj as ObjClass).classScope!!
-                            if (!r.visibility.isPublic)
+                            val r0 = scope0.getSlotRecord(capturedIdx)
+                            if (!r0.visibility.isPublic)
                                 sc.raiseError(ObjAccessException(sc, "can't access non-public field $name"))
-                            r
+                            r0
-                        } else obj.readField(sc, name)
+                        }
+                    } else {
+                        rKey1 = key; rVer1 = ver; rGetter1 = { obj, sc -> obj.readField(sc, name) }
                     }
-                    is ObjClass -> {
+                }
-                        val clsScope = obj.classScope
+                else -> {
-                        if (clsScope != null) {
+                    // For instances and other types, fall back to name-based lookup per access (slot index may differ per instance)
-                            val idx = clsScope.getSlotIndexOf(name)
+                    rKey1 = key; rVer1 = ver; rGetter1 = { obj, sc -> obj.readField(sc, name) }
-                            if (idx != null) {
-                                val r = clsScope.getSlotRecord(idx)
-                                if (!r.visibility.isPublic)
-                                    sc.raiseError(ObjAccessException(sc, "can't access non-public field $name"))
-                                r
-                            } else obj.readField(sc, name)
-                        } else obj.readField(sc, name)
-                    }
-                    else -> obj.readField(sc, name)
                 }
             }
             return rec
@@ -305,39 +317,38 @@ class FieldRef(
         }
         if (net.sergeych.lyng.PerfFlags.FIELD_PIC) {
             val (key, ver) = receiverKeyAndVersion(base)
-            wSetter1?.let { s -> if (key == wKey1 && ver == wVer1) return s(base, scope, newValue) }
+            wSetter1?.let { s -> if (key == wKey1 && ver == wVer1) {
-            wSetter2?.let { s -> if (key == wKey2 && ver == wVer2) return s(base, scope, newValue) }
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicSetHit++
+                return s(base, scope, newValue)
+            } }
+            wSetter2?.let { s -> if (key == wKey2 && ver == wVer2) {
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicSetHit++
+                return s(base, scope, newValue)
+            } }
             // Slow path
+            if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.fieldPicSetMiss++
             base.writeField(scope, name, newValue)
             // Install move-to-front with a handle-aware setter
             wKey2 = wKey1; wVer2 = wVer1; wSetter2 = wSetter1
-            wKey1 = key;   wVer1 = ver;   wSetter1 = { obj, sc, v ->
+            when (base) {
-                when (obj) {
+                is ObjClass -> {
-                    is ObjInstance -> {
+                    val clsScope = base.classScope
-                        val instScope = obj.instanceScope
+                    val capturedIdx = clsScope?.getSlotIndexOf(name)
-                        val idx = instScope.getSlotIndexOf(name)
+                    if (clsScope != null && capturedIdx != null) {
-                        if (idx != null) {
+                        wKey1 = key; wVer1 = ver; wSetter1 = { obj, sc, v ->
-                            val r = instScope.getSlotRecord(idx)
+                            val scope0 = (obj as ObjClass).classScope!!
-                            if (!r.visibility.isPublic)
+                            val r0 = scope0.getSlotRecord(capturedIdx)
-                                sc.raiseError(ObjAccessException(sc, "can't assign to non-public field $name"))
+                            if (!r0.isMutable)
-                            if (!r.isMutable)
                                 sc.raiseError(ObjIllegalAssignmentException(sc, "can't reassign val $name"))
-                            if (r.value.assign(sc, v) == null) r.value = v
+                            if (r0.value.assign(sc, v) == null) r0.value = v
-                        } else obj.writeField(sc, name, v)
+                        }
+                    } else {
+                        wKey1 = key; wVer1 = ver; wSetter1 = { obj, sc, v -> obj.writeField(sc, name, v) }
                     }
-                    is ObjClass -> {
+                }
-                        val clsScope = obj.classScope
+                else -> {
-                        if (clsScope != null) {
+                    // For instances and other types, fall back to generic write (instance slot indices may differ per instance)
-                            val idx = clsScope.getSlotIndexOf(name)
+                    wKey1 = key; wVer1 = ver; wSetter1 = { obj, sc, v -> obj.writeField(sc, name, v) }
-                            if (idx != null) {
-                                val r = clsScope.getSlotRecord(idx)
-                                if (!r.isMutable)
-                                    sc.raiseError(ObjIllegalAssignmentException(sc, "can't reassign val $name"))
-                                r.value = v
-                            } else obj.writeField(sc, name, v)
-                        } else obj.writeField(sc, name, v)
-                    }
-                    else -> obj.writeField(sc, name, v)
                 }
             }
             return
@@ -361,9 +372,9 @@ class IndexRef(
     private val isOptional: Boolean,
 ) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val base = target.get(scope).value
+        val base = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) target.evalValue(scope) else target.get(scope).value
         if (base == ObjNull && isOptional) return ObjNull.asMutable
-        val idx = index.get(scope).value
+        val idx = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) index.evalValue(scope) else index.get(scope).value
         return base.getAt(scope, idx).asMutable
     }
 
@@ -395,10 +406,16 @@ class CallRef(
     private val isOptionalInvoke: Boolean,
 ) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val callee = target.get(scope).value
+        val callee = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) target.evalValue(scope) else target.get(scope).value
         if (callee == ObjNull && isOptionalInvoke) return ObjNull.asReadonly
         val callArgs = args.toArguments(scope, tailBlock)
-        val result = callee.callOn(scope.createChildScope(scope.pos, callArgs))
+        val result: Obj = if (net.sergeych.lyng.PerfFlags.SCOPE_POOL) {
+            scope.withChildFrame(callArgs) { child ->
+                callee.callOn(child)
+            }
+        } else {
+            callee.callOn(scope.createChildScope(scope.pos, callArgs))
+        }
         return result.asReadonly
     }
 }
@@ -418,38 +435,54 @@ class MethodCallRef(
     private var mKey2: Long = 0L; private var mVer2: Int = -1; private var mInvoker2: (suspend (Obj, Scope, Arguments) -> Obj)? = null
 
     override suspend fun get(scope: Scope): ObjRecord {
-        val base = receiver.get(scope).value
+        val base = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) receiver.evalValue(scope) else receiver.get(scope).value
         if (base == ObjNull && isOptional) return ObjNull.asReadonly
         val callArgs = args.toArguments(scope, tailBlock)
         if (net.sergeych.lyng.PerfFlags.METHOD_PIC) {
             val (key, ver) = receiverKeyAndVersion(base)
-            mInvoker1?.let { inv -> if (key == mKey1 && ver == mVer1) return inv(base, scope, callArgs).asReadonly }
+            mInvoker1?.let { inv -> if (key == mKey1 && ver == mVer1) {
-            mInvoker2?.let { inv -> if (key == mKey2 && ver == mVer2) return inv(base, scope, callArgs).asReadonly }
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.methodPicHit++
+                return inv(base, scope, callArgs).asReadonly
+            } }
+            mInvoker2?.let { inv -> if (key == mKey2 && ver == mVer2) {
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.methodPicHit++
+                return inv(base, scope, callArgs).asReadonly
+            } }
             // Slow path
+            if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.methodPicMiss++
             val result = base.invokeInstanceMethod(scope, name, callArgs)
             // Install move-to-front with a handle-aware invoker
             mKey2 = mKey1; mVer2 = mVer1; mInvoker2 = mInvoker1
-            mKey1 = key;   mVer1 = ver;   mInvoker1 = { obj, sc, a ->
+            when (base) {
-                when (obj) {
+                is ObjInstance -> {
-                    is ObjInstance -> {
+                    // Prefer resolved class member to avoid per-call lookup on hit
-                        val instScope = obj.instanceScope
+                    val member = base.objClass.getInstanceMemberOrNull(name)
-                        val rec = instScope.get(name)
+                    if (member != null) {
-                        if (rec != null) {
+                        val visibility = member.visibility
-                            if (!rec.visibility.isPublic)
+                        val callable = member.value
+                        mKey1 = key; mVer1 = ver; mInvoker1 = { obj, sc, a ->
+                            val inst = obj as ObjInstance
+                            if (!visibility.isPublic)
                                 sc.raiseError(ObjAccessException(sc, "can't invoke non-public method $name"))
-                            rec.value.invoke(instScope, obj, a)
+                            callable.invoke(inst.instanceScope, inst, a)
-                        } else obj.invokeInstanceMethod(sc, name, a)
+                        }
+                    } else {
+                        // Fallback to name-based lookup per call (uncommon)
+                        mKey1 = key; mVer1 = ver; mInvoker1 = { obj, sc, a -> obj.invokeInstanceMethod(sc, name, a) }
                     }
-                    is ObjClass -> {
+                }
-                        val clsScope = obj.classScope
+                is ObjClass -> {
-                        if (clsScope != null) {
+                    val clsScope = base.classScope
-                            val rec = clsScope.get(name)
+                    val rec = clsScope?.get(name)
-                            if (rec != null) {
+                    if (rec != null) {
-                                rec.value.invoke(sc, obj, a)
+                        val callable = rec.value
-                            } else obj.invokeInstanceMethod(sc, name, a)
+                        mKey1 = key; mVer1 = ver; mInvoker1 = { obj, sc, a -> callable.invoke(sc, obj, a) }
-                        } else obj.invokeInstanceMethod(sc, name, a)
+                    } else {
+                        mKey1 = key; mVer1 = ver; mInvoker1 = { obj, sc, a -> obj.invokeInstanceMethod(sc, name, a) }
                     }
-                    else -> obj.invokeInstanceMethod(sc, name, a)
+                }
+                else -> {
+                    mKey1 = key; mVer1 = ver; mInvoker1 = { obj, sc, a -> obj.invokeInstanceMethod(sc, name, a) }
                 }
             }
             return result.asReadonly
@@ -486,11 +519,22 @@ class LocalVarRef(private val name: String, private val atPos: Pos) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
         scope.pos = atPos
         if (!PerfFlags.LOCAL_SLOT_PIC) {
-            scope.getSlotIndexOf(name)?.let { return scope.getSlotRecord(it) }
+            scope.getSlotIndexOf(name)?.let { 
+                if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.localVarPicHit++
+                return scope.getSlotRecord(it) 
+            }
+            if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.localVarPicMiss++
             return scope[name] ?: scope.raiseError("symbol not defined: '$name'")
         }
-        val slot = if (cachedFrameId == scope.frameId && cachedSlot >= 0 && cachedSlot < scope.slotCount()) cachedSlot else resolveSlot(scope)
+        val hit = (cachedFrameId == scope.frameId && cachedSlot >= 0 && cachedSlot < scope.slotCount())
-        if (slot >= 0) return scope.getSlotRecord(slot)
+        val slot = if (hit) cachedSlot else resolveSlot(scope)
+        if (slot >= 0) {
+            if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) {
+                if (hit) net.sergeych.lyng.PerfStats.localVarPicHit++ else net.sergeych.lyng.PerfStats.localVarPicMiss++
+            }
+            return scope.getSlotRecord(slot)
+        }
+        if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) net.sergeych.lyng.PerfStats.localVarPicMiss++
         return scope[name] ?: scope.raiseError("symbol not defined: '$name'")
     }
 
@@ -584,10 +628,13 @@ class FastLocalVarRef(
 
     override suspend fun get(scope: Scope): ObjRecord {
         scope.pos = atPos
-        val owner = if (isOwnerValidFor(scope)) cachedOwnerScope else null
+        val ownerValid = isOwnerValidFor(scope)
-        val slot = if (owner != null && cachedSlot >= 0) cachedSlot else resolveSlotInAncestry(scope)
+        val slot = if (ownerValid && cachedSlot >= 0) cachedSlot else resolveSlotInAncestry(scope)
         val actualOwner = cachedOwnerScope
         if (slot < 0 || actualOwner == null) scope.raiseError("local '$name' is not available in this scope")
+        if (net.sergeych.lyng.PerfFlags.PIC_DEBUG_COUNTERS) {
+            if (ownerValid) net.sergeych.lyng.PerfStats.fastLocalHit++ else net.sergeych.lyng.PerfStats.fastLocalMiss++
+        }
         return actualOwner.getSlotRecord(slot)
     }
 
@@ -609,10 +656,11 @@ class ListLiteralRef(private val entries: List<ListEntry>) : ObjRef {
         for (e in entries) {
             when (e) {
                 is ListEntry.Element -> {
-                    list += e.ref.get(scope).value
+                    val v = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) e.ref.evalValue(scope) else e.ref.get(scope).value
+                    list += v
                 }
                 is ListEntry.Spread -> {
-                    val elements = e.ref.get(scope).value
+                    val elements = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) e.ref.evalValue(scope) else e.ref.get(scope).value
                     when (elements) {
                         is ObjList -> list.addAll(elements.list)
                         else -> scope.raiseError("Spread element must be list")
@@ -633,8 +681,8 @@ class RangeRef(
     private val isEndInclusive: Boolean
 ) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val l = left?.get(scope)?.value ?: ObjNull
+        val l = left?.let { if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) it.evalValue(scope) else it.get(scope).value } ?: ObjNull
-        val r = right?.get(scope)?.value ?: ObjNull
+        val r = right?.let { if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) it.evalValue(scope) else it.get(scope).value } ?: ObjNull
         return ObjRange(l, r, isEndInclusive = isEndInclusive).asReadonly
     }
 }
@@ -646,7 +694,7 @@ class AssignRef(
     private val atPos: Pos,
 ) : ObjRef {
     override suspend fun get(scope: Scope): ObjRecord {
-        val v = value.get(scope).value
+        val v = if (net.sergeych.lyng.PerfFlags.RVAL_FASTPATH) value.evalValue(scope) else value.get(scope).value
         val rec = target.get(scope)
         if (!rec.isMutable) throw ScriptError(atPos, "cannot assign to immutable variable")
         if (rec.value.assign(scope, v) == null) {

lynglib/src/commonTest/kotlin/ScriptTest.kt

@@ -3332,7 +3332,7 @@ class ScriptTest {
     }
 
 
-//    @Test
+    ///@Test
     fun testMinimumOptimization() = runTest {
         for (i in 1..200) {
             bm {

lynglib/src/jsMain/kotlin/net/sergeych/lyng/ArgBuilderJs.kt

@@ -0,0 +1,20 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+actual object ArgBuilderProvider {
+    actual fun acquire(): ArgsBuilder = JsArgsBuilder()
+}
+
+private class JsArgsBuilder : ArgsBuilder {
+    private var buf: MutableList<Obj> = ArrayList()
+
+    override fun reset(expectedSize: Int) {
+        buf = ArrayList(expectedSize.coerceAtLeast(0))
+    }
+
+    override fun add(v: Obj) { buf.add(v) }
+    override fun addAll(vs: List<Obj>) { if (vs.isNotEmpty()) buf.addAll(vs) }
+    override fun build(tailBlockMode: Boolean): Arguments = Arguments(buf.toList(), tailBlockMode)
+    override fun release() { /* no-op */ }
+}

lynglib/src/jsMain/kotlin/net/sergeych/lyng/PerfDefaults.js.kt

@@ -0,0 +1,19 @@
+package net.sergeych.lyng
+
+actual object PerfDefaults {
+    actual val LOCAL_SLOT_PIC: Boolean = true
+    actual val EMIT_FAST_LOCAL_REFS: Boolean = true
+
+    actual val ARG_BUILDER: Boolean = true
+    actual val SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    actual val SCOPE_POOL: Boolean = false
+
+    actual val FIELD_PIC: Boolean = true
+    actual val METHOD_PIC: Boolean = true
+
+    actual val PIC_DEBUG_COUNTERS: Boolean = false
+
+    actual val PRIMITIVE_FASTOPS: Boolean = true
+    // Conservative default for non-JVM until validated
+    actual val RVAL_FASTPATH: Boolean = false
+}

lynglib/src/jvmMain/kotlin/net/sergeych/lyng/ArgBuilderJvm.kt

@@ -0,0 +1,36 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+actual object ArgBuilderProvider {
+    private val tl = object : ThreadLocal<JvmArgsBuilder>() {
+        override fun initialValue(): JvmArgsBuilder = JvmArgsBuilder()
+    }
+    actual fun acquire(): ArgsBuilder = tl.get()
+}
+
+private class JvmArgsBuilder : ArgsBuilder {
+    private val buf: ArrayList<Obj> = ArrayList(8)
+
+    override fun reset(expectedSize: Int) {
+        buf.clear()
+        if (expectedSize > 0) buf.ensureCapacity(expectedSize)
+    }
+
+    override fun add(v: Obj) {
+        buf.add(v)
+    }
+
+    override fun addAll(vs: List<Obj>) {
+        if (vs.isNotEmpty()) {
+            buf.ensureCapacity(buf.size + vs.size)
+            buf.addAll(vs)
+        }
+    }
+
+    override fun build(tailBlockMode: Boolean): Arguments = Arguments(buf.toList(), tailBlockMode)
+
+    override fun release() {
+        // ThreadLocal instance is reused automatically; nothing to do
+    }
+}

lynglib/src/jvmMain/kotlin/net/sergeych/lyng/PerfDefaults.jvm.kt

@@ -0,0 +1,18 @@
+package net.sergeych.lyng
+
+actual object PerfDefaults {
+    actual val LOCAL_SLOT_PIC: Boolean = true
+    actual val EMIT_FAST_LOCAL_REFS: Boolean = true
+
+    actual val ARG_BUILDER: Boolean = true
+    actual val SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    actual val SCOPE_POOL: Boolean = false
+
+    actual val FIELD_PIC: Boolean = true
+    actual val METHOD_PIC: Boolean = true
+
+    actual val PIC_DEBUG_COUNTERS: Boolean = false
+
+    actual val PRIMITIVE_FASTOPS: Boolean = true
+    actual val RVAL_FASTPATH: Boolean = true
+}

lynglib/src/jvmTest/kotlin/CallBenchmarkTest.kt

@@ -52,4 +52,49 @@ class CallBenchmarkTest {
         assertEquals(expected, r1)
         assertEquals(expected, r2)
     }
-}
+
+    @Test
+    fun benchmarkMixedArityCalls() = runBlocking {
+        val n = 200_000
+        val script = """
+            fun f0() { 1 }
+            fun f1(a) { a }
+            fun f2(a,b) { a + b }
+            fun f3(a,b,c) { a + b + c }
+            fun f4(a,b,c,d) { a + b + c + d }
+
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                s = s + f0()
+                s = s + f1(1)
+                s = s + f2(1, 1)
+                s = s + f3(1, 1, 1)
+                s = s + f4(1, 1, 1, 1)
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+
+        // Baseline
+        PerfFlags.ARG_BUILDER = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed-arity x$n [ARG_BUILDER=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // Optimized
+        PerfFlags.ARG_BUILDER = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed-arity x$n [ARG_BUILDER=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // Each loop: 1 + 1 + 2 + 3 + 4 = 11
+        val expected = 11L * n
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+    }
+}

lynglib/src/jvmTest/kotlin/CallMixedArityBenchmarkTest.kt

@@ -0,0 +1,57 @@
+/*
+ * JVM micro-benchmark for mixed-arity function calls and ARG_BUILDER.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class CallMixedArityBenchmarkTest {
+    @Test
+    fun benchmarkMixedArityCalls() = runBlocking {
+        val n = 200_000
+        val script = """
+            fun f0() { 1 }
+            fun f1(a) { a }
+            fun f2(a,b) { a + b }
+            fun f3(a,b,c) { a + b + c }
+            fun f4(a,b,c,d) { a + b + c + d }
+
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                s = s + f0()
+                s = s + f1(1)
+                s = s + f2(1, 1)
+                s = s + f3(1, 1, 1)
+                s = s + f4(1, 1, 1, 1)
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+
+        // Baseline
+        PerfFlags.ARG_BUILDER = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed-arity x$n [ARG_BUILDER=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // Optimized
+        PerfFlags.ARG_BUILDER = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed-arity x$n [ARG_BUILDER=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // Each loop: 1 + 1 + 2 + 3 + 4 = 11
+        val expected = 11L * n
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+    }
+}

lynglib/src/jvmTest/kotlin/CallPoolingBenchmarkTest.kt

@@ -0,0 +1,53 @@
+/*
+ * JVM micro-benchmark for Scope frame pooling impact on call-heavy code paths.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class CallPoolingBenchmarkTest {
+    @Test
+    fun benchmarkScopePoolingOnFunctionCalls() = runBlocking {
+        val n = 300_000
+        val script = """
+            fun inc1(a) { a + 1 }
+            fun inc2(a) { inc1(a) + 1 }
+            fun inc3(a) { inc2(a) + 1 }
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                s = inc3(s)
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+
+        // Baseline: pooling OFF
+        PerfFlags.SCOPE_POOL = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] call-pooling x$n [SCOPE_POOL=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // Optimized: pooling ON
+        PerfFlags.SCOPE_POOL = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] call-pooling x$n [SCOPE_POOL=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // Each inc3 performs 3 increments per loop
+        val expected = 3L * n
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+
+        // Reset flag to default (OFF) to avoid affecting other tests unintentionally
+        PerfFlags.SCOPE_POOL = false
+    }
+}

lynglib/src/jvmTest/kotlin/CallSplatBenchmarkTest.kt

@@ -0,0 +1,55 @@
+/*
+ * JVM micro-benchmark for calls with splat (spread) arguments.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class CallSplatBenchmarkTest {
+    @Test
+    fun benchmarkCallsWithSplatArgs() = runBlocking {
+        val n = 120_000
+        val script = """
+            fun sum4(a,b,c,d) { a + b + c + d }
+            val base = [1,1,1,1]
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                // two direct, one splat per iteration
+                s = s + sum4(1,1,1,1)
+                s = s + sum4(1,1,1,1)
+                s = s + sum4(base[0], base[1], base[2], base[3])
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+
+        // Baseline
+        PerfFlags.ARG_BUILDER = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] splat-calls x$n [ARG_BUILDER=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // Optimized
+        PerfFlags.ARG_BUILDER = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] splat-calls x$n [ARG_BUILDER=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // Each loop adds (4 + 4 + 4) = 12
+        val expected = 12L * n
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+
+        // Reset to default
+        PerfFlags.ARG_BUILDER = true
+    }
+}

lynglib/src/jvmTest/kotlin/DeepPoolingStressJvmTest.kt

@@ -0,0 +1,76 @@
+/*
+ * JVM stress tests for scope frame pooling (deep nesting and recursion).
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class DeepPoolingStressJvmTest {
+    @Test
+    fun deepNestedCalls_noLeak_and_correct_with_and_without_pooling() = runBlocking {
+        val depth = 200
+        val script = """
+            fun f0(x) { x + 1 }
+            fun f1(x) { f0(x) + 1 }
+            fun f2(x) { f1(x) + 1 }
+            fun f3(x) { f2(x) + 1 }
+            fun f4(x) { f3(x) + 1 }
+            fun f5(x) { f4(x) + 1 }
+
+            fun chain(x, d) {
+                var i = 0
+                var s = x
+                while (i < d) {
+                    // 5 nested calls per iteration
+                    s = f5(s)
+                    i = i + 1
+                }
+                s
+            }
+            chain(0, $depth)
+        """.trimIndent()
+
+        // Pool OFF
+        PerfFlags.SCOPE_POOL = false
+        val scope1 = Scope()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        // Pool ON
+        PerfFlags.SCOPE_POOL = true
+        val scope2 = Scope()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        // Each loop adds 6 (f0..f5 adds 6)
+        val expected = 6L * depth
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+        // Reset
+        PerfFlags.SCOPE_POOL = false
+    }
+
+    @Test
+    fun recursion_factorial_correct_with_and_without_pooling() = runBlocking {
+        val n = 10
+        val script = """
+            fun fact(x) {
+                if (x <= 1) 1 else x * fact(x - 1)
+            }
+            fact($n)
+        """.trimIndent()
+        // OFF
+        PerfFlags.SCOPE_POOL = false
+        val scope1 = Scope()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        // ON
+        PerfFlags.SCOPE_POOL = true
+        val scope2 = Scope()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        // 10! = 3628800
+        val expected = 3628800L
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+        PerfFlags.SCOPE_POOL = false
+    }
+}

lynglib/src/jvmTest/kotlin/ExpressionBenchmarkTest.kt

@@ -0,0 +1,61 @@
+/*
+ * JVM micro-benchmark for expression evaluation with RVAL_FASTPATH.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ExpressionBenchmarkTest {
+    @Test
+    fun benchmarkExpressionChains() = runBlocking {
+        val n = 350_000
+        val script = """
+            // arithmetic + elvis + logical chains
+            val maybe = null
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                // exercise elvis on a null
+                s = s + (maybe ?: 0)
+                // branch using booleans without coercion to int
+                if ((i % 3 == 0 && true) || false) { s = s + 1 } else { s = s + 2 }
+                // parity via arithmetic only (avoid adding booleans)
+                s = s + (i - (i / 2) * 2)
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+
+        // OFF
+        PerfFlags.RVAL_FASTPATH = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] expr-chain x$n [RVAL_FASTPATH=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // ON
+        PerfFlags.RVAL_FASTPATH = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] expr-chain x$n [RVAL_FASTPATH=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // correctness: compute expected with simple kotlin logic mirroring the loop
+        var s = 0L
+        var i = 0
+        while (i < n) {
+            if ((i % 3 == 0 && true) || false) s += 1 else s += 2
+            // parity via arithmetic only, matches script's single parity addition
+            s += i - (i / 2) * 2
+            i += 1
+        }
+        assertEquals(s, r1)
+        assertEquals(s, r2)
+    }
+}

lynglib/src/jvmTest/kotlin/MethodPoolingBenchmarkTest.kt

@@ -0,0 +1,50 @@
+/*
+ * JVM micro-benchmark for scope frame pooling on instance method calls.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class MethodPoolingBenchmarkTest {
+    @Test
+    fun benchmarkInstanceMethodCallsWithPooling() = runBlocking {
+        val n = 300_000
+        val script = """
+            class C() {
+                var x = 0
+                fun add1() { x = x + 1 }
+                fun get() { x }
+            }
+            val c = C()
+            var i = 0
+            while (i < $n) {
+                c.add1()
+                i = i + 1
+            }
+            c.get()
+        """.trimIndent()
+
+        // Pool OFF
+        PerfFlags.SCOPE_POOL = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] method-loop x$n [SCOPE_POOL=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // Pool ON
+        PerfFlags.SCOPE_POOL = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] method-loop x$n [SCOPE_POOL=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        assertEquals(n.toLong(), r1)
+        assertEquals(n.toLong(), r2)
+    }
+}

lynglib/src/jvmTest/kotlin/MixedBenchmarkTest.kt

@@ -0,0 +1,81 @@
+/*
+ * JVM mixed workload micro-benchmark to exercise multiple hot paths together.
+ */
+
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class MixedBenchmarkTest {
+    @Test
+    fun benchmarkMixedWorkloadRvalFastpath() = runBlocking {
+        // Keep iterations moderate to avoid CI timeouts
+        val n = 250_000
+        val script = """
+            class Acc() {
+                var x = 0
+                fun add(v) { x = x + v }
+                fun get() { x }
+            }
+            val acc = Acc()
+            val maybe = null
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                // exercise locals + primitive ops
+                s = s + i
+                // elvis on null
+                s = s + (maybe ?: 0)
+                // boolean logic (short-circuit + primitive fast path)
+                if ((i % 3 == 0 && true) || false) { s = s + 1 } else { s = s + 2 }
+                // instance field/method with PIC
+                acc.add(1)
+                // simple index with list building every 1024 steps (rare path)
+                if (i % 1024 == 0) {
+                    val lst = [0,1,2,3]
+                    s = s + lst[2]
+                }
+                i = i + 1
+            }
+            s + acc.get()
+        """.trimIndent()
+
+        // OFF
+        PerfFlags.RVAL_FASTPATH = false
+        val scope1 = Scope()
+        val t0 = System.nanoTime()
+        val r1 = (scope1.eval(script) as ObjInt).value
+        val t1 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed x$n [RVAL_FASTPATH=OFF]: ${(t1 - t0)/1_000_000.0} ms")
+
+        // ON
+        PerfFlags.RVAL_FASTPATH = true
+        val scope2 = Scope()
+        val t2 = System.nanoTime()
+        val r2 = (scope2.eval(script) as ObjInt).value
+        val t3 = System.nanoTime()
+        println("[DEBUG_LOG] [BENCH] mixed x$n [RVAL_FASTPATH=ON]: ${(t3 - t2)/1_000_000.0} ms")
+
+        // Compute expected value in Kotlin to ensure correctness
+        var s = 0L
+        var i = 0
+        var acc = 0L
+        while (i < n) {
+            s += i
+            s += 0 // (maybe ?: 0)
+            if ((i % 3 == 0 && true) || false) s += 1 else s += 2
+            acc += 1
+            if (i % 1024 == 0) s += 2
+            i += 1
+        }
+        val expected = s + acc
+        assertEquals(expected, r1)
+        assertEquals(expected, r2)
+
+        // Reset flag for other tests
+        PerfFlags.RVAL_FASTPATH = false
+    }
+}

lynglib/src/jvmTest/kotlin/PicBenchmarkTest.kt

@@ -45,6 +45,10 @@ class PicBenchmarkTest {
         val t3 = System.nanoTime()
         println("[DEBUG_LOG] [BENCH] Field PIC=ON: ${(t3 - t2) / 1_000_000.0} ms")
         assertEquals(iterations.toLong(), r2)
+        if (PerfFlags.PIC_DEBUG_COUNTERS) {
+            println("[DEBUG_LOG] [PIC] field get hit=${net.sergeych.lyng.PerfStats.fieldPicHit} miss=${net.sergeych.lyng.PerfStats.fieldPicMiss}")
+            println("[DEBUG_LOG] [PIC] field set hit=${net.sergeych.lyng.PerfStats.fieldPicSetHit} miss=${net.sergeych.lyng.PerfStats.fieldPicSetMiss}")
+        }
     }
 
     @Test

lynglib/src/jvmTest/kotlin/PicInvalidationJvmTest.kt

@@ -0,0 +1,105 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.PerfStats
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjClass
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class PicInvalidationJvmTest {
+    @Test
+    fun fieldPicInvalidatesOnClassLayoutChange() = runBlocking {
+        // Enable counters and PICs
+        PerfFlags.FIELD_PIC = true
+        PerfFlags.PIC_DEBUG_COUNTERS = true
+        PerfStats.resetAll()
+
+        val scope = Scope()
+        // Declare a class and warm up field access
+        val script = """
+            class C() {
+                var x = 0
+                fun getX() { x }
+            }
+            val c = C()
+            var i = 0
+            while (i < 1000) {
+                // warm read path
+                val t = c.x
+                i = i + 1
+            }
+            c.getX()
+        """.trimIndent()
+        val r1 = (scope.eval(script) as ObjInt).value
+        assertEquals(0L, r1)
+        val hitsBefore = PerfStats.fieldPicHit
+        val missesBefore = PerfStats.fieldPicMiss
+        assertTrue(hitsBefore >= 1, "Expected some PIC hits after warm-up")
+
+        // Mutate class layout from Kotlin side to bump layoutVersion and invalidate PIC
+        val cls = (scope["C"]!!.value as ObjClass)
+        cls.createClassField("yy", ObjInt(1), isMutable = false)
+
+        // Access the same field again; first access after version bump should miss PIC
+        val r2 = (scope.eval("c.x") as ObjInt).value
+        assertEquals(0L, r2)
+        val missesAfter = PerfStats.fieldPicMiss
+        assertTrue(missesAfter >= missesBefore + 1, "Expected PIC miss after class layout change")
+
+        // Optional summary when counters enabled
+        if (PerfFlags.PIC_DEBUG_COUNTERS) {
+            println("[DEBUG_LOG] [PIC] field get hit=${PerfStats.fieldPicHit} miss=${PerfStats.fieldPicMiss}")
+            println("[DEBUG_LOG] [PIC] field set hit=${PerfStats.fieldPicSetHit} miss=${PerfStats.fieldPicSetMiss}")
+        }
+
+        // Disable counters to avoid affecting other tests
+        PerfFlags.PIC_DEBUG_COUNTERS = false
+    }
+
+    @Test
+    fun methodPicInvalidatesOnClassLayoutChange() = runBlocking {
+        PerfFlags.METHOD_PIC = true
+        PerfFlags.PIC_DEBUG_COUNTERS = true
+        PerfStats.resetAll()
+
+        val scope = Scope()
+        val script = """
+            class D() {
+                var x = 0
+                fun inc() { x = x + 1 }
+                fun get() { x }
+            }
+            val d = D()
+            var i = 0
+            while (i < 1000) {
+                d.inc()
+                i = i + 1
+            }
+            d.get()
+        """.trimIndent()
+        val r1 = (scope.eval(script) as ObjInt).value
+        assertEquals(1000L, r1)
+        val mhBefore = PerfStats.methodPicHit
+        val mmBefore = PerfStats.methodPicMiss
+        assertTrue(mhBefore >= 1, "Expected method PIC hits after warm-up")
+
+        // Bump layout by adding a new class field
+        val cls = (scope["D"]!!.value as ObjClass)
+        cls.createClassField("zz", ObjInt(0), isMutable = false)
+
+        // Next invocation should miss and then re-fill
+        val r2 = (scope.eval("d.get()") as ObjInt).value
+        assertEquals(1000L, r2)
+        val mmAfter = PerfStats.methodPicMiss
+        assertTrue(mmAfter >= mmBefore + 1, "Expected method PIC miss after class layout change")
+
+        // Optional summary when counters enabled
+        if (PerfFlags.PIC_DEBUG_COUNTERS) {
+            println("[DEBUG_LOG] [PIC] method hit=${PerfStats.methodPicHit} miss=${PerfStats.methodPicMiss}")
+        }
+
+        PerfFlags.PIC_DEBUG_COUNTERS = false
+    }
+}

lynglib/src/jvmTest/kotlin/ScriptSubsetJvmTest.kt

@@ -0,0 +1,47 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import net.sergeych.lyng.obj.ObjList
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ScriptSubsetJvmTest {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+    private suspend fun evalList(code: String): List<Any?> = (Scope().eval(code) as ObjList).list.map { (it as? ObjInt)?.value ?: it }
+
+    @Test
+    fun binarySearchBasics_jvm_only() = runBlocking {
+        val code = """
+            val coll = [1,2,3,4,5]
+            coll.binarySearch(3)
+        """.trimIndent()
+        // OFF
+        PerfFlags.RVAL_FASTPATH = false
+        val rOff = evalInt(code)
+        // ON
+        PerfFlags.RVAL_FASTPATH = true
+        val rOn = evalInt(code)
+        assertEquals(2L, rOff)
+        assertEquals(2L, rOn)
+        PerfFlags.RVAL_FASTPATH = false
+    }
+
+    @Test
+    fun optionalChainingIndexField_jvm_only() = runBlocking {
+        val code = """
+            val a = null
+            val r1 = a?.x
+            val lst = [1,2,3]
+            val r2 = lst[1]
+            r2
+        """.trimIndent()
+        PerfFlags.RVAL_FASTPATH = false
+        val off = evalInt(code)
+        PerfFlags.RVAL_FASTPATH = true
+        val on = evalInt(code)
+        assertEquals(2L, off)
+        assertEquals(2L, on)
+        PerfFlags.RVAL_FASTPATH = false
+    }
+}

lynglib/src/jvmTest/kotlin/ScriptSubsetJvmTest_Additions3.kt

@@ -0,0 +1,140 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjBool
+import net.sergeych.lyng.obj.ObjInt
+import net.sergeych.lyng.obj.ObjList
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * JVM-only fast functional subset additions. Keep each test quick (< ~1s) and deterministic.
+ */
+class ScriptSubsetJvmTest_Additions3 {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+    private suspend fun evalBool(code: String): Boolean = (Scope().eval(code) as ObjBool).value
+    private suspend fun evalList(code: String): List<Any?> = (Scope().eval(code) as ObjList).list.map { (it as? ObjInt)?.value ?: it }
+
+    @Test
+    fun controlFlow_when_and_ifElse_jvm_only() = runBlocking {
+        val code = """
+            fun classify(x) {
+                when(x) {
+                    0 -> 100
+                    1 -> 200
+                    else -> 300
+                }
+            }
+            val a = classify(0)
+            val b = classify(1)
+            val c = classify(5)
+            if (true) 1 else 2
+            a + b + c
+        """.trimIndent()
+        val r = evalInt(code)
+        // 100 + 200 + 300 = 600
+        assertEquals(600L, r)
+    }
+
+    @Test
+    fun optionals_chain_field_index_method_jvm_only() = runBlocking {
+        val code = """
+            class Box() {
+                var xs = [10,20,30]
+                fun get(i) { xs[i] }
+            }
+            val maybe = null
+            val b = Box()
+            // optional on null yields null
+            val r1 = maybe?.xs
+            // optional on non-null: method and index
+            val r2 = b?.get(1)
+            r2
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(20L, r)
+    }
+
+    @Test
+    fun exceptions_try_catch_finally_jvm_only() = runBlocking {
+        val code = """
+            fun risky(x) { if (x == 0) throw "boom" else 7 }
+            var s = 0
+            try { s = risky(0) } catch (e) { s = 1 } finally { s = s + 2 }
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        // catch sets 1, finally adds 2 -> 3
+        assertEquals(3L, r)
+    }
+
+    @Test
+    fun classes_visibility_and_fields_jvm_only() = runBlocking {
+        val code = """
+            class C() {
+                var pub = 1
+                private var hidden = 9
+                fun getPub() { pub }
+                fun getHidden() { hidden }
+                fun setPub(v) { pub = v }
+            }
+            val c = C()
+            c.setPub(5)
+            c.getPub() + c.getHidden()
+        """.trimIndent()
+        val r = evalInt(code)
+        // 5 + 9
+        assertEquals(14L, r)
+    }
+
+    @Test
+    fun collections_insert_remove_and_maps_jvm_only() = runBlocking {
+        val code = """
+            val lst = []
+            lst.insertAt(0, 2)
+            lst.insertAt(0, 1)
+            lst.removeAt(1)
+            // now [1]
+            val a = 10
+            val b = 20
+            a + b + lst[0]
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(31L, r)
+    }
+
+    @Test
+    fun loops_for_and_while_basics_jvm_only() = runBlocking {
+        val n = 2000
+        val code = """
+            var s = 0
+            for (i in 0..$n) { s = s + 1 }
+            var j = 0
+            while (j < $n) { s = s + 1; j = j + 1 }
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        // for loop adds n+1, while adds n -> total 2n+1
+        assertEquals((2L*n + 1L), r)
+    }
+
+    @Test
+    fun pooling_edgecase_captures_and_exception_jvm_only() = runBlocking {
+        // Ensure pooling ON for this test, then restore default
+        val prev = PerfFlags.SCOPE_POOL
+        try {
+            PerfFlags.SCOPE_POOL = true
+            val code = """
+                fun outer(a) {
+                    fun inner(b) { if (b == 0) throw "err" else a + b }
+                    try { inner(0) } catch (e) { a + 2 }
+                }
+                outer(5)
+            """.trimIndent()
+            val r = evalInt(code)
+            assertEquals(7L, r)
+        } finally {
+            PerfFlags.SCOPE_POOL = prev
+        }
+    }
+}

lynglib/src/jvmTest/kotlin/ScriptSubsetJvmTest_Additions4.kt

@@ -0,0 +1,137 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import net.sergeych.lyng.obj.ObjList
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+/**
+ * More JVM-only fast functional tests migrated from ScriptTest to avoid MPP runs.
+ * Keep each test fast (<1s) and deterministic.
+ */
+class ScriptSubsetJvmTest_Additions4 {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+    private suspend fun evalList(code: String): List<Any?> = (Scope().eval(code) as ObjList).list.map { (it as? ObjInt)?.value ?: it }
+
+    @Test
+    fun mapsAndSetsBasics_jvm_only() = runBlocking {
+        // Validate simple list map behavior without relying on extra stdlib
+        val code = """
+            val src = [1,2,2,3,1]
+            // map over list
+            val doubled = src.map { it + 1 }
+            doubled.size()
+        """.trimIndent()
+        val r = evalInt(code)
+        // doubled size == original size (5)
+        assertEquals(5L, r)
+    }
+
+    @Test
+    fun optionalChainingDeep_jvm_only() = runBlocking {
+        val code = """
+            class A() { fun b() { null } }
+            val a = A()
+            val r1 = a?.b()?.c
+            val r2 = (a?.b()?.c ?: 7)
+            r2
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(7L, r)
+    }
+
+    @Test
+    fun whenExpressionBasics_jvm_only() = runBlocking {
+        val code = """
+            fun f(x) {
+                when(x) {
+                    0 -> 100
+                    1 -> 200
+                    else -> 300
+                }
+            }
+            f(0) + f(1) + f(2)
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(600L, r)
+    }
+
+    @Test
+    fun tryCatchFinallyWithReturn_jvm_only() = runBlocking {
+        val code = """
+            fun g(x) {
+                var t = 0
+                try {
+                    if (x < 0) throw("oops")
+                    t = x
+                } catch (e) {
+                    t = 5
+                } finally {
+                    t = t + 1
+                }
+                t
+            }
+            g(-1) + g(3)
+        """.trimIndent()
+        val r = evalInt(code)
+        // g(-1): catch sets 5, finally +1 => 6; g(3): t=3, finally +1 => 4; total 10
+        assertEquals(10L, r)
+    }
+
+    @Test
+    fun pooling_edge_case_closure_and_exception_jvm_only() = runBlocking {
+        val code = """
+            fun maker(base) { { base + 1 } }
+            val c = maker(41)
+            var r = 0
+            try {
+                r = c()
+                throw("fail")
+            } catch (e) {
+                r = r + 1
+            }
+            r
+        """.trimIndent()
+        // OFF
+        PerfFlags.SCOPE_POOL = false
+        val off = evalInt(code)
+        // ON
+        PerfFlags.SCOPE_POOL = true
+        val on = evalInt(code)
+        assertEquals(43L, off)
+        assertEquals(43L, on)
+        // reset
+        PerfFlags.SCOPE_POOL = false
+    }
+
+    @Test
+    fun forWhileNested_jvm_only() = runBlocking {
+        val code = """
+            var s = 0
+            for (i in 1..10) {
+                var j = 0
+                while (j < 3) {
+                    if (i % 2 == 0 && j == 1) { j = j + 1; continue }
+                    s = s + i + j
+                    j = j + 1
+                }
+            }
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        // Compute expected quickly in Kotlin mirror
+        var expected = 0L
+        for (i in 1..10) {
+            var j = 0
+            while (j < 3) {
+                if (i % 2 == 0 && j == 1) { j += 1; continue }
+                expected += i + j
+                j += 1
+            }
+        }
+        assertEquals(expected, r)
+        assertTrue(expected > 0)
+    }
+}

lynglib/src/jvmTest/kotlin/ScriptSubsetJvmTest_Additions5.kt

@@ -0,0 +1,81 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.PerfFlags
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+/**
+ * JVM-only fast functional tests to broaden coverage for pooling, classes, and control flow.
+ * Keep each test fast (<1s) and deterministic.
+ */
+class ScriptSubsetJvmTest_Additions5 {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+
+    @Test
+    fun classVisibility_public_vs_private_jvm_only() = runBlocking {
+        val code = """
+            class C() {
+                var pub = 3
+                private var prv = 5
+                fun getPrv() { prv }
+            }
+            val c = C()
+            c.pub + c.getPrv()
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(8L, r)
+    }
+
+    @Test
+    fun classVisibility_private_field_access_error_jvm_only() = runBlocking {
+        val code = """
+            class C() {
+                private var prv = 5
+            }
+            val c = C()
+            // attempt to access private field should fail
+            c.prv
+        """.trimIndent()
+        // We expect an exception; Scope.eval() will throw ExecutionError.
+        assertFailsWith<Throwable> { evalInt(code) }
+        // Ensure Unit return from the test body
+        Unit
+    }
+
+    @Test
+    fun inheritance_override_call_path_jvm_only() = runBlocking {
+        val code = """
+            // Simple two classes with same method name; no inheritance to avoid syntax dependencies
+            class A() { fun v() { 1 } }
+            class B() { fun v() { 2 } }
+            val a = A(); val b = B()
+            a.v() + b.v()
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(3L, r)
+    }
+
+    @Test
+    fun pooled_frames_closure_this_capture_jvm_only() = runBlocking {
+        val code = """
+            class Box() { var x = 40; fun inc() { x = x + 1 } fun get() { x } }
+            fun make(block) { block }
+            val b = Box()
+            val f = make { b.inc(); b.get() }
+            var r = 0
+            r = f()
+            r
+        """.trimIndent()
+        // OFF
+        PerfFlags.SCOPE_POOL = false
+        val off = evalInt(code)
+        // ON
+        PerfFlags.SCOPE_POOL = true
+        val on = evalInt(code)
+        assertEquals(41L, off)
+        assertEquals(41L, on)
+        PerfFlags.SCOPE_POOL = false
+    }
+}

lynglib/src/jvmTest/kotlin/ScriptSubsetJvmTest_additions.kt

@@ -0,0 +1,120 @@
+import kotlinx.coroutines.runBlocking
+import net.sergeych.lyng.Scope
+import net.sergeych.lyng.obj.ObjInt
+import net.sergeych.lyng.obj.ObjList
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Additional JVM-only fast functional tests migrated from ScriptTest to avoid MPP runs.
+ * Keep each test fast (<1s) and with clear assertions.
+ */
+class ScriptSubsetJvmTest_Additions {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+    private suspend fun evalList(code: String): List<Any?> = (Scope().eval(code) as ObjList).list.map { (it as? ObjInt)?.value ?: it }
+
+    @Test
+    fun rangesAndForLoop_jvm_only() = runBlocking {
+        val code = """
+            var s = 0
+            for (i in 1..100) s = s + i
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(5050L, r)
+    }
+
+    @Test
+    fun classFieldsAndMethods_jvm_only() = runBlocking {
+        val n = 20000
+        val code = """
+            class Counter() {
+                var x = 0
+                fun inc() { x = x + 1 }
+                fun get() { x }
+            }
+            val c = Counter()
+            var i = 0
+            while (i < $n) { c.inc(); i = i + 1 }
+            c.get()
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(n.toLong(), r)
+    }
+
+    @Test
+    fun elvisAndLogicalChains_jvm_only() = runBlocking {
+        val n = 10000
+        val code = """
+            val maybe = null
+            var s = 0
+            var i = 0
+            while (i < $n) {
+                s = s + (maybe ?: 0)
+                if ((i % 3 == 0 && true) || false) { s = s + 1 } else { s = s + 2 }
+                s = s + (i - (i / 2) * 2)
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        // Kotlin mirror for correctness
+        var s = 0L
+        var i = 0
+        while (i < n) {
+            if ((i % 3 == 0 && true) || false) s += 1 else s += 2
+            s += (i - (i / 2) * 2)
+            i += 1
+        }
+        assertEquals(s, r)
+    }
+
+    @Test
+    fun sortedInsertWithBinarySearch_jvm_only() = runBlocking {
+        val code = """
+            val src = [3,1,2]
+            val result = []
+            for (x in src) {
+                val i = result.binarySearch(x)
+                result.insertAt(if (i < 0) -i-1 else i, x)
+            }
+            result
+        """.trimIndent()
+        val r = evalList(code)
+        assertEquals(listOf(1L, 2L, 3L), r)
+    }
+}
+
+
+class ScriptSubsetJvmTest_Additions2 {
+    private suspend fun evalInt(code: String): Long = (Scope().eval(code) as ObjInt).value
+
+    @Test
+    fun optionalMethodCallWithElvis_jvm_only() = runBlocking {
+        val code = """
+            class C() { fun get() { 5 } }
+            val a = null
+            (a?.get() ?: 7)
+        """.trimIndent()
+        val r = evalInt(code)
+        assertEquals(7L, r)
+    }
+
+    @Test
+    fun continueAndBreakInWhile_jvm_only() = runBlocking {
+        val code = """
+            var s = 0
+            var i = 0
+            while (i <= 100) {
+                if (i > 50) break
+                if (i % 2 == 1) { i = i + 1; continue }
+                s = s + i
+                i = i + 1
+            }
+            s
+        """.trimIndent()
+        val r = evalInt(code)
+        // Sum of even numbers from 0 to 50 inclusive: 2 * (0+1+...+25) = 2 * 325 = 650
+        assertEquals(650L, r)
+    }
+}

lynglib/src/nativeMain/kotlin/net/sergeych/lyng/ArgBuilderNative.kt

@@ -0,0 +1,20 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+actual object ArgBuilderProvider {
+    actual fun acquire(): ArgsBuilder = NativeArgsBuilder()
+}
+
+private class NativeArgsBuilder : ArgsBuilder {
+    private var buf: MutableList<Obj> = ArrayList()
+
+    override fun reset(expectedSize: Int) {
+        buf = ArrayList(expectedSize.coerceAtLeast(0))
+    }
+
+    override fun add(v: Obj) { buf.add(v) }
+    override fun addAll(vs: List<Obj>) { if (vs.isNotEmpty()) buf.addAll(vs) }
+    override fun build(tailBlockMode: Boolean): Arguments = Arguments(buf.toList(), tailBlockMode)
+    override fun release() { /* no-op */ }
+}

lynglib/src/nativeMain/kotlin/net/sergeych/lyng/PerfDefaults.native.kt

@@ -0,0 +1,19 @@
+package net.sergeych.lyng
+
+actual object PerfDefaults {
+    actual val LOCAL_SLOT_PIC: Boolean = true
+    actual val EMIT_FAST_LOCAL_REFS: Boolean = true
+
+    actual val ARG_BUILDER: Boolean = true
+    actual val SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    actual val SCOPE_POOL: Boolean = false
+
+    actual val FIELD_PIC: Boolean = true
+    actual val METHOD_PIC: Boolean = true
+
+    actual val PIC_DEBUG_COUNTERS: Boolean = false
+
+    actual val PRIMITIVE_FASTOPS: Boolean = true
+    // Conservative default for non-JVM until validated
+    actual val RVAL_FASTPATH: Boolean = false
+}

lynglib/src/wasmJsMain/kotlin/net/sergeych/lyng/ArgBuilderWasm.kt

@@ -0,0 +1,20 @@
+package net.sergeych.lyng
+
+import net.sergeych.lyng.obj.Obj
+
+actual object ArgBuilderProvider {
+    actual fun acquire(): ArgsBuilder = WasmArgsBuilder()
+}
+
+private class WasmArgsBuilder : ArgsBuilder {
+    private var buf: MutableList<Obj> = ArrayList()
+
+    override fun reset(expectedSize: Int) {
+        buf = ArrayList(expectedSize.coerceAtLeast(0))
+    }
+
+    override fun add(v: Obj) { buf.add(v) }
+    override fun addAll(vs: List<Obj>) { if (vs.isNotEmpty()) buf.addAll(vs) }
+    override fun build(tailBlockMode: Boolean): Arguments = Arguments(buf.toList(), tailBlockMode)
+    override fun release() { /* no-op */ }
+}

lynglib/src/wasmJsMain/kotlin/net/sergeych/lyng/PerfDefaults.wasmJs.kt

@@ -0,0 +1,19 @@
+package net.sergeych.lyng
+
+actual object PerfDefaults {
+    actual val LOCAL_SLOT_PIC: Boolean = true
+    actual val EMIT_FAST_LOCAL_REFS: Boolean = true
+
+    actual val ARG_BUILDER: Boolean = true
+    actual val SKIP_ARGS_ON_NULL_RECEIVER: Boolean = true
+    actual val SCOPE_POOL: Boolean = false
+
+    actual val FIELD_PIC: Boolean = true
+    actual val METHOD_PIC: Boolean = true
+
+    actual val PIC_DEBUG_COUNTERS: Boolean = false
+
+    actual val PRIMITIVE_FASTOPS: Boolean = true
+    // Conservative default for non-JVM until validated
+    actual val RVAL_FASTPATH: Boolean = false
+}