From 9ae91d88b6166dfbbd82bd6ce2ef7341e3e725df Mon Sep 17 00:00:00 2001
From: Alex Kanunnikov <lifeart92@gmail.com>
Date: Wed, 6 Dec 2023 00:56:59 +0300
Subject: [PATCH] [perf] avoid double memory usage in append opcodes

---
 packages/@glimmer/debug/lib/opcode-metadata.ts | 14 ++------------
 packages/@glimmer/runtime/lib/opcodes.ts       |  5 +++--
 packages/@glimmer/util/index.ts                |  2 +-
 packages/@glimmer/util/lib/object-utils.ts     | 10 ----------
 4 files changed, 6 insertions(+), 25 deletions(-)

diff --git a/packages/@glimmer/debug/lib/opcode-metadata.ts b/packages/@glimmer/debug/lib/opcode-metadata.ts
index 29e5844bf9..c559bf57d3 100644
--- a/packages/@glimmer/debug/lib/opcode-metadata.ts
+++ b/packages/@glimmer/debug/lib/opcode-metadata.ts
@@ -5,16 +5,6 @@ import { MachineOp, Op } from '@glimmer/vm';
 
 import type { NormalizedMetadata } from './metadata';
 
-function fillNulls<T>(count: number): T[] {
-  let arr = new Array(count);
-
-  for (let i = 0; i < count; i++) {
-    arr[i] = null;
-  }
-
-  return arr;
-}
-
 export function opcodeMetadata(
   op: VmMachineOp | VmOp,
   isMachine: 0 | 1
@@ -24,8 +14,8 @@ export function opcodeMetadata(
   return value || null;
 }
 
-const METADATA: Nullable<NormalizedMetadata>[] = fillNulls(Op.Size);
-const MACHINE_METADATA: Nullable<NormalizedMetadata>[] = fillNulls(MachineOp.Size);
+const METADATA: Nullable<NormalizedMetadata>[] = new Array(Op.Size).fill(null);
+const MACHINE_METADATA: Nullable<NormalizedMetadata>[] = new Array(Op.Size).fill(null);
 MACHINE_METADATA[MachineOp.PushFrame] = {
   name: 'PushFrame',
   mnemonic: 'pushf',
diff --git a/packages/@glimmer/runtime/lib/opcodes.ts b/packages/@glimmer/runtime/lib/opcodes.ts
index 63bf3de582..3a9152e7e5 100644
--- a/packages/@glimmer/runtime/lib/opcodes.ts
+++ b/packages/@glimmer/runtime/lib/opcodes.ts
@@ -10,7 +10,7 @@ import type {
 import { debug, logOpcode, opcodeMetadata, recordStackSize } from '@glimmer/debug';
 import { LOCAL_DEBUG, LOCAL_SHOULD_LOG } from '@glimmer/local-debug-flags';
 import { valueForRef } from '@glimmer/reference';
-import { assert, fillNulls, LOCAL_LOGGER, unwrap } from '@glimmer/util';
+import { assert, LOCAL_LOGGER, unwrap } from '@glimmer/util';
 import { $fp, $pc, $ra, $sp, Op } from '@glimmer/vm';
 
 import type { LowLevelVM, VM } from './vm';
@@ -51,8 +51,9 @@ export type DebugState = {
   state: unknown;
 };
 
+const OPCODES_PLACEHOLDER = new Array(Op.Size).fill(null);
 export class AppendOpcodes {
-  private evaluateOpcode: Evaluate[] = fillNulls<Evaluate>(Op.Size).slice();
+  private evaluateOpcode: Evaluate[] = OPCODES_PLACEHOLDER.slice();
 
   add<Name extends VmOp>(name: Name, evaluate: Syscall): void;
   add<Name extends VmMachineOp>(name: Name, evaluate: MachineOpcode, kind: 'machine'): void;
diff --git a/packages/@glimmer/util/index.ts b/packages/@glimmer/util/index.ts
index 38c7af3b9c..df4c6eb773 100644
--- a/packages/@glimmer/util/index.ts
+++ b/packages/@glimmer/util/index.ts
@@ -11,7 +11,7 @@ export {
   isSerializationFirstNode,
   SERIALIZATION_FIRST_NODE_STRING,
 } from './lib/is-serialization-first-node';
-export { assign, entries, fillNulls, values } from './lib/object-utils';
+export { assign, entries, values } from './lib/object-utils';
 export * from './lib/platform-utils';
 export * from './lib/present';
 export {
diff --git a/packages/@glimmer/util/lib/object-utils.ts b/packages/@glimmer/util/lib/object-utils.ts
index 3a1bc08b12..dcf40d6150 100644
--- a/packages/@glimmer/util/lib/object-utils.ts
+++ b/packages/@glimmer/util/lib/object-utils.ts
@@ -1,15 +1,5 @@
 export let assign = Object.assign;
 
-export function fillNulls<T>(count: number): T[] {
-  let arr = new Array(count);
-
-  for (let i = 0; i < count; i++) {
-    arr[i] = null;
-  }
-
-  return arr;
-}
-
 export function values<T>(obj: { [s: string]: T }): T[] {
   return Object.values(obj);
 }