Implement Fast Accessor Builder

test/cctest/test-api-fast-accessor-builder.cc

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// TODO(jochen): Remove this after the setting is turned on globally.
+#define V8_IMMINENT_DEPRECATION_WARNINGS

[jochen (gone - plz use gerrit), 2015/11/27 08:33:45]

yay :P

+
+#include <stdlib.h>
+
+#include "include/v8.h"
+
+#include "src/api.h"
+#include "test/cctest/cctest.h"
+
+namespace {
+
+static void NativePropertyAccessor(
+    const v8::FunctionCallbackInfo<v8::Value>& info) {
+  info.GetReturnValue().Set(v8_num(123));
+}
+
+}  // anonymous namespace
+
+
+// Build a simple "fast accessor" and verify that it is being called.
+TEST(FastAccessor) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+
+  v8::Local<v8::FunctionTemplate> foo = v8::FunctionTemplate::New(isolate);
+
+  // Native accessor, bar, returns 123.
+  foo->PrototypeTemplate()->SetAccessorProperty(
+      v8_str("bar"),
+      v8::FunctionTemplate::New(isolate, NativePropertyAccessor));
+
+  // Fast accessor, barf, returns 124.
+  auto fab = v8::experimental::FastAccessorBuilder::New(isolate);
+  fab->ReturnValue(fab->IntegerConstant(124));
+  foo->PrototypeTemplate()->SetAccessorProperty(
+      v8_str("barf"), v8::FunctionTemplate::NewWithFastHandler(
+                          isolate, NativePropertyAccessor, fab));
+
+  // Install foo on the global object.
+  CHECK(env->Global()
+            ->Set(env.local(), v8_str("foo"),
+                  foo->GetFunction(env.local()).ToLocalChecked())
+            .FromJust());
+
+  ExpectInt32("f = new foo(); f.bar", 123);
+  ExpectInt32("f = new foo(); f.barf", 123);
+  ExpectInt32("f = new foo(); f.barf", 123);
+  ExpectInt32("f = new foo(); f.barf", 123);
+  ExpectInt32("f = new foo(); f.barf", 124);

[Michael Starzinger, 2015/11/27 09:15:53]

This test seems to assume that it takes exactly four runs to trigger the "fast"
accessor. I don't know the exact details behind this, but this looks fragile.
Can this be made more robust?

[epertoso, 2015/11/27 10:04:56]

+mvstanton.

[mvstanton, 2015/11/27 10:21:17]

Good point. The code has the problem that it works accidentally. I read it and
wondered how in the heck are we ratcheting up the IC state chain? It's because
there is code/compilation caching going on for the same input strings. That's a
fragile assumption. I'd much prefer it to be written like:

CompileRun("function bar(f) { return f.barf; }");

and then

ExpectInt32("bar(new foo());", 123);  // PREMONOMORPHIC
ExpectInt32("bar(new foo());", 123);  // MONOMORPHIC
ExpectInt32("bar(new foo());", 124);  // MONOMORPHIC handler called.

That way it's clear that you are cycling the load through IC states.

And the comment shows why you expect it to take until the third call to get the
right answer.

Also...it really should be on the third call, not the 4th, right? I suspect it's
the 4th because of the implementation of the aforementioned code caching.

[Michael Starzinger, 2015/11/27 14:32:54]

SGTM. I am fine with wrapping it in a function and with the comments that
Michael suggested. Avoiding cycling through the IC states would probably be too
cumbersome.

[vogelheim, 2015/11/27 16:24:50]

Changed this (& below) to wrap the accessor, and to provide a WARMUP macro that
builds JS source to call the function N times. So there's still a secret
parameter N, but it's now only in one place. It also has a comment explaining
why it's there.

+}
+
+
+void AddInternalFieldAccessor(v8::Isolate* isolate,
+                              v8::Local<v8::Template> templ, const char* name,
+                              int field_no) {
+  auto builder = v8::experimental::FastAccessorBuilder::New(isolate);
+  builder->ReturnValue(
+      builder->GetInternalField(builder->GetCallTarget(), field_no));
+  templ->SetAccessorProperty(v8_str(name),
+                             v8::FunctionTemplate::NewWithFastHandler(
+                                 isolate, NativePropertyAccessor, builder));
+}
+
+
+// "Fast" accessor that accesses an internal field.
+TEST(FastAccessorWithInternalField) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+
+  v8::Local<v8::ObjectTemplate> foo = v8::ObjectTemplate::New(isolate);
+  foo->SetInternalFieldCount(3);
+  AddInternalFieldAccessor(isolate, foo, "field0", 0);
+  AddInternalFieldAccessor(isolate, foo, "field1", 1);
+  AddInternalFieldAccessor(isolate, foo, "field2", 2);
+
+  // Create an instance w/ 3 internal fields, put in a string, a Smi, nothing.
+  v8::Local<v8::Object> obj = foo->NewInstance(env.local()).ToLocalChecked();
+  obj->SetInternalField(0, v8_str("Hi there!"));
+  obj->SetInternalField(1, v8::Integer::New(isolate, 4321));
+  CHECK(env->Global()->Set(env.local(), v8_str("obj"), obj).FromJust());
+
+  // Ensure we go through accessors' fast paths, without checking anything.
+  CompileRun("obj.field0");
+  CompileRun("obj.field0");
+  CompileRun("obj.field0");
+  CompileRun("obj.field1");
+  CompileRun("obj.field1");
+  CompileRun("obj.field1");
+  CompileRun("obj.field2");
+  CompileRun("obj.field2");
+  CompileRun("obj.field2");
+
+  // Access fields.
+  ExpectString("obj.field0", "Hi there!");
+  ExpectInt32("obj.field1", 4321);
+  ExpectUndefined("obj.field2");
+}