From c34c223122528f3d8073e6c770e130191db25aef Mon Sep 17 00:00:00 2001
From: Pawel Kozlowski <pkozlowski.opensource@gmail.com>
Date: Fri, 22 Mar 2019 14:29:45 +0100
Subject: [PATCH] fix(ivy): avoid type coercion in binding-related instruction
 asserts (#29470)

ivy's bindingUpdated instruction is using the assertNotEqual check to make
sure that NO_CHANGE value (of type Object) is not passed as a value to be
dirty-checked. In practice it means that any value passed as a binding
value would be compared to the NO_CHANGE object.

It turns out that the assertNotEqual is using == and given
that binding values are of different type and we always compare it to the
NO_CHANGE object we were doing lots of type coercion. It resulted in calls
to expensive types conversions and calls to Object.toString().

A profiler reported ~15% of the self time spent in the assertNotEqual
but it turns out that removing type coercion speeds up Material Chips with
input scenario much more (~40ms down to ~20ms).

This PR introduces new assert method `assertNotSame` that uses strict equality
check. The new assertion is used in binding instructions to compare to
NO_CHANGE object reference.

PR Close #29470
---
 packages/core/src/render3/bindings.ts | 6 +++---
 packages/core/src/util/assert.ts      | 6 ++++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/packages/core/src/render3/bindings.ts b/packages/core/src/render3/bindings.ts
index 400aec275e..0fe18bc2ee 100644
--- a/packages/core/src/render3/bindings.ts
+++ b/packages/core/src/render3/bindings.ts
@@ -7,7 +7,7 @@
  */
 
 import {devModeEqual} from '../change_detection/change_detection_util';
-import {assertDataInRange, assertLessThan, assertNotEqual} from '../util/assert';
+import {assertDataInRange, assertLessThan, assertNotSame} from '../util/assert';
 import {throwErrorIfNoChangesMode} from './errors';
 import {LView} from './interfaces/view';
 import {getCheckNoChangesMode} from './state';
@@ -27,13 +27,13 @@ export function updateBinding(lView: LView, bindingIndex: number, value: any): a
 export function getBinding(lView: LView, bindingIndex: number): any {
   ngDevMode && assertDataInRange(lView, bindingIndex);
   ngDevMode &&
-      assertNotEqual(lView[bindingIndex], NO_CHANGE, 'Stored value should never be NO_CHANGE.');
+      assertNotSame(lView[bindingIndex], NO_CHANGE, 'Stored value should never be NO_CHANGE.');
   return lView[bindingIndex];
 }
 
 /** Updates binding if changed, then returns whether it was updated. */
 export function bindingUpdated(lView: LView, bindingIndex: number, value: any): boolean {
-  ngDevMode && assertNotEqual(value, NO_CHANGE, 'Incoming value should never be NO_CHANGE.');
+  ngDevMode && assertNotSame(value, NO_CHANGE, 'Incoming value should never be NO_CHANGE.');
   ngDevMode &&
       assertLessThan(bindingIndex, lView.length, `Slot should have been initialized to NO_CHANGE`);
 
diff --git a/packages/core/src/util/assert.ts b/packages/core/src/util/assert.ts
index ea9ed55542..58b93ffb2f 100644
--- a/packages/core/src/util/assert.ts
+++ b/packages/core/src/util/assert.ts
@@ -34,6 +34,12 @@ export function assertSame<T>(actual: T, expected: T, msg: string) {
   }
 }
 
+export function assertNotSame<T>(actual: T, expected: T, msg: string) {
+  if (actual === expected) {
+    throwError(msg);
+  }
+}
+
 export function assertLessThan<T>(actual: T, expected: T, msg: string) {
   if (actual >= expected) {
     throwError(msg);