From 97d070e0574d9688292eda89bd2026ff0f2ee2de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ole=20Andr=C3=A9=20Vadla=20Ravn=C3=A5s?=
 <oleavr@nowsecure.com>
Date: Fri, 11 Sep 2015 23:16:42 +0200
Subject: [PATCH] Improve TypedArray performance

Cherry-picked from Node.js:

commit acb6779c19abf248a4c6d5c3d3389805e7ee8b8d
Author: Fedor Indutny <fedor@indutny.com>
Date:   Thu Sep 10 12:26:50 2015 -0700

    deps: cherry-pick 6da51b4 from v8's upstream

    Original commit message:

        TypedArray accessor detection: consider entire prototype chain

        When looking up a special accessor for known TypedArray fields
        ("length", "byteLength", "byteOffset"), consider the entire
        prototype chain, not only the direct prototype.
        This allows subclasses of TypedArrays to benefit from fast
        specialized accesses.

        Review URL: https://codereview.chromium.org/1313493005

        Cr-Commit-Position: refs/heads/master@{#30678}

    Benchmark results:

       buffers/buffer-iterate.js size=16386 type=slow method=for n=1000:
       ./node: 71607 node: 8702.3 ............ 722.85%

    Improvement depends on the code, but generally brings us back to the
    performance that we had before the v8 update (if not making it
    faster).

    Fixes: https://github.com/nodejs/node/issues/2463
    PR-URL: https://github.com/nodejs/node/pull/2801
    Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
    Reviewed-By: Trevor Norris <trev.norris@gmail.com>
---
 src/accessors.cc                              | 41 +++++++++++++------
 .../regress/regress-typedarray-length.js      | 37 +++++++++++++++++
 2 files changed, 65 insertions(+), 13 deletions(-)

diff --git a/src/accessors.cc b/src/accessors.cc
index 9850cd388e4..e77dedbaeb8 100644
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -100,22 +100,37 @@ bool Accessors::IsJSArrayBufferViewFieldAccessor(Handle<Map> map,
   Isolate* isolate = name->GetIsolate();
 
   switch (map->instance_type()) {
-    case JS_TYPED_ARRAY_TYPE:
-      // %TypedArray%.prototype is non-configurable, and so are the following
-      // named properties on %TypedArray%.prototype, so we can directly inline
-      // the field-load for typed array maps that still use their
-      // %TypedArray%.prototype.
-      if (JSFunction::cast(map->GetConstructor())->prototype() !=
-          map->prototype()) {
+    case JS_TYPED_ARRAY_TYPE: {
+      if (!CheckForName(name, isolate->factory()->length_string(),
+                        JSTypedArray::kLengthOffset, object_offset) &&
+          !CheckForName(name, isolate->factory()->byte_length_string(),
+                        JSTypedArray::kByteLengthOffset, object_offset) &&
+          !CheckForName(name, isolate->factory()->byte_offset_string(),
+                        JSTypedArray::kByteOffsetOffset, object_offset)) {
         return false;
       }
-      return CheckForName(name, isolate->factory()->length_string(),
-                          JSTypedArray::kLengthOffset, object_offset) ||
-             CheckForName(name, isolate->factory()->byte_length_string(),
-                          JSTypedArray::kByteLengthOffset, object_offset) ||
-             CheckForName(name, isolate->factory()->byte_offset_string(),
-                          JSTypedArray::kByteOffsetOffset, object_offset);
 
+      if (map->is_dictionary_map()) return false;
+
+      // Check if the property is overridden on the instance.
+      DescriptorArray* descriptors = map->instance_descriptors();
+      int descriptor = descriptors->SearchWithCache(*name, *map);
+      if (descriptor != DescriptorArray::kNotFound) return false;
+
+      Handle<Object> proto = Handle<Object>(map->prototype(), isolate);
+      if (!proto->IsJSReceiver()) return false;
+
+      // Check if the property is defined in the prototype chain.
+      LookupIterator it(proto, name);
+      if (!it.IsFound()) return false;
+
+      Object* original_proto =
+          JSFunction::cast(map->GetConstructor())->prototype();
+
+      // Property is not configurable. It is enough to verify that
+      // the holder is the same.
+      return *it.GetHolder<Object>() == original_proto;
+    }
     case JS_DATA_VIEW_TYPE:
       return CheckForName(name, isolate->factory()->byte_length_string(),
                           JSDataView::kByteLengthOffset, object_offset) ||
diff --git a/test/mjsunit/regress/regress-typedarray-length.js b/test/mjsunit/regress/regress-typedarray-length.js
index cae55731f92..ee853647355 100644
--- a/test/mjsunit/regress/regress-typedarray-length.js
+++ b/test/mjsunit/regress/regress-typedarray-length.js
@@ -71,6 +71,43 @@ assertEquals(undefined, get(a));
   assertEquals(undefined, get(a));
 })();
 
+(function() {
+  "use strict";
+
+  class MyTypedArray extends Int32Array {
+    constructor(length) {
+      super(length);
+    }
+  }
+
+  a = new MyTypedArray(1024);
+
+  get = function(a) {
+    return a.length;
+  }
+
+  assertEquals(1024, get(a));
+  assertEquals(1024, get(a));
+  assertEquals(1024, get(a));
+  %OptimizeFunctionOnNextCall(get);
+  assertEquals(1024, get(a));
+})();
+
+(function() {
+  "use strict";
+  var a = new Uint8Array(4);
+  Object.defineProperty(a, "length", {get: function() { return "blah"; }});
+  get = function(a) {
+    return a.length;
+  }
+
+  assertEquals("blah", get(a));
+  assertEquals("blah", get(a));
+  assertEquals("blah", get(a));
+  %OptimizeFunctionOnNextCall(get);
+  assertEquals("blah", get(a));
+})();
+
 // Ensure we cannot delete length, byteOffset, byteLength.
 assertTrue(Int32Array.prototype.hasOwnProperty("length"));
 assertTrue(Int32Array.prototype.hasOwnProperty("byteOffset"));