From fdb23b3a768cbc182a6de33f1815de6ca77d0f62 Mon Sep 17 00:00:00 2001
From: sergeych <real.sergeych@gmail.com>
Date: Mon, 16 Feb 2026 17:50:39 +0300
Subject: [PATCH] Reuse void slot for if statements

---
 .../sergeych/lyng/bytecode/BytecodeCompiler.kt  | 17 +++++++++++++----
 notes/fast_ops_optimizations_plan.md            |  6 +++---
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt
index 7920f0d..942dc52 100644
--- a/lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt
+++ b/lynglib/src/commonMain/kotlin/net/sergeych/lyng/bytecode/BytecodeCompiler.kt
@@ -86,6 +86,7 @@ class BytecodeCompiler(
     private val loopVarSlots = HashSet<Int>()
     private val loopStack = ArrayDeque<LoopContext>()
     private var currentPos: Pos? = null
+    private var cachedVoidSlot: Int? = null
 
     private data class LoopContext(
         val label: String?,
@@ -5623,6 +5624,17 @@ class BytecodeCompiler(
     private fun emitInlineBlock(stmt: BlockStatement, needResult: Boolean): CompiledValue? =
         emitInlineStatements(stmt.statements(), needResult)
 
+    private fun ensureVoidSlot(): Int {
+        val existing = cachedVoidSlot
+        if (existing != null) return existing
+        val slot = allocSlot()
+        val voidId = builder.addConst(BytecodeConst.ObjRef(ObjVoid))
+        builder.emit(Opcode.CONST_OBJ, voidId, slot)
+        updateSlotType(slot, SlotType.OBJ)
+        cachedVoidSlot = slot
+        return slot
+    }
+
     private fun shouldInlineBlock(stmt: BlockStatement): Boolean {
         return allowLocalSlots
     }
@@ -6449,10 +6461,7 @@ class BytecodeCompiler(
             restoreFlowTypeOverride(elseRestore)
         }
         builder.mark(endLabel)
-        val slot = allocSlot()
-        val voidId = builder.addConst(BytecodeConst.ObjRef(ObjVoid))
-        builder.emit(Opcode.CONST_OBJ, voidId, slot)
-        return CompiledValue(slot, SlotType.OBJ)
+        return CompiledValue(ensureVoidSlot(), SlotType.OBJ)
     }
 
     private fun updateSlotTypeByName(name: String, type: SlotType) {
diff --git a/notes/fast_ops_optimizations_plan.md b/notes/fast_ops_optimizations_plan.md
index def0503..01df7b9 100644
--- a/notes/fast_ops_optimizations_plan.md
+++ b/notes/fast_ops_optimizations_plan.md
@@ -13,9 +13,9 @@ Candidates (not started)
 3) Boolean conversion (done; do not revert without review)
    - Skip redundant OBJ_TO_BOOL in logical AND/OR when compiler already emits BOOL.
    - MixedCompareBenchmarkTest: 275 ms -> 249 ms.
-4) Range/loop hot path
-   - Keep range iteration in INT ops, avoid accidental boxing.
-   - Confirm loop-var slots avoid re-boxing in loop bodies.
+4) Range/loop hot path (done)
+   - Reuse a cached ObjVoid slot for if-statements in statement context (avoids per-iteration CONST_OBJ).
+   - MixedCompareBenchmarkTest: 249 ms -> 247 ms.
 5) String ops
    - Extend fast path for string comparisons in hot loops.
 6) Box/unbox audit