perf(ivy): avoid creating holey LView Arrays (#31839)

PR Close #31839

packages/core/src/render3/PERF_NOTES.md

@@ -22,6 +22,21 @@ Great reads:
 
  See benchmark [here](https://jsperf.com/mono-vs-megamorphic-property-access).
 
+## Packed vs. holey Array
+
+V8 represents arrays internally in a different way depending on:
+- type of elements in the array;
+- presence of holes (indexes that were never assigned).
+
+Generally speaking packed arrays (a set of continuous, initialized indexes) perform better as compared to arrays with holes. To assure that arrays are packed follow those guidelines:
+* create array literals with known values whenever possible (ex. `a = [0];` is better than `a = []; a.push[0];`;
+* don't use `Array` constructor with the size value (ex. `new Array(5)`) - this will create a `HOLEY_ELEMENTS` array (even if this array is filled in later on!);
+* don't delete elements from an array (ex. `delete a[0]`) - this will create a hole;
+* don't write past the array length as this will create holes;
+
+Great reads:
+- [Elements kinds in V8](https://v8.dev/blog/elements-kinds)
+
 ## Exporting top level variables
 
 Exporting top level variables should be avoided where possible where performance

packages/core/src/render3/instructions/shared.ts

@@ -642,11 +642,14 @@ export function createTView(
 }
 
 function createViewBlueprint(bindingStartIndex: number, initialViewLength: number): LView {
-  const blueprint = new (ngDevMode ? LViewBlueprint ! : Array)(initialViewLength)
+  const blueprint = ngDevMode ? new LViewBlueprint !() : [];
-                        .fill(null, 0, bindingStartIndex)
+
-                        .fill(NO_CHANGE, bindingStartIndex) as LView;
+  for (let i = 0; i < initialViewLength; i++) {
+    blueprint.push(i < bindingStartIndex ? null : NO_CHANGE);
+  }
   blueprint[BINDING_INDEX] = bindingStartIndex;
-  return blueprint;
+
+  return blueprint as LView;
 }
 
 export function createError(text: string, token: any) {
@@ -1562,7 +1565,7 @@ export function componentRefresh(hostLView: LView, adjustedElementIndex: number)
 function syncViewWithBlueprint(componentView: LView) {
   const componentTView = componentView[TVIEW];
   for (let i = componentView.length; i < componentTView.blueprint.length; i++) {
-    componentView[i] = componentTView.blueprint[i];
+    componentView.push(componentTView.blueprint[i]);
   }
 }