1 files changed, 273 insertions, 0 deletions
diff --git a/js/src/vm/PromiseLookup.cpp b/js/src/vm/PromiseLookup.cpp
new file mode 100644
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+++ b/js/src/vm/PromiseLookup.cpp
@@ -0,0 +1,273 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "vm/PromiseLookup.h"
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+
+#include "jspubtd.h"  // JSProto_*
+
+#include "builtin/Promise.h"  // js::Promise_then, js::Promise_static_resolve, js::Promise_static_species
+#include "js/HeapAPI.h"  // js::gc::IsInsideNursery
+#include "js/Id.h"       // SYMBOL_TO_JSID
+#include "js/Value.h"    // JS::Value, JS::ObjectValue
+#include "util/Poison.h"  // js::AlwaysPoison, JS_RESET_VALUE_PATTERN, MemCheckKind
+#include "vm/GlobalObject.h"  // js::GlobalObject
+#include "vm/JSContext.h"     // JSContext
+#include "vm/JSFunction.h"    // JSFunction
+#include "vm/JSObject.h"      // JSObject
+#include "vm/NativeObject.h"  // js::NativeObject
+#include "vm/Runtime.h"       // js::WellKnownSymbols
+#include "vm/Shape.h"         // js::Shape
+
+#include "vm/JSObject-inl.h"  // js::IsFunctionObject, js::IsNativeFunction
+
+using JS::ObjectValue;
+using JS::Value;
+
+using js::NativeObject;
+
+JSFunction* js::PromiseLookup::getPromiseConstructor(JSContext* cx) {
+  JSObject* obj = cx->global()->maybeGetConstructor(JSProto_Promise);
+  return obj ? &obj->as<JSFunction>() : nullptr;
+}
+
+NativeObject* js::PromiseLookup::getPromisePrototype(JSContext* cx) {
+  JSObject* obj = cx->global()->maybeGetPrototype(JSProto_Promise);
+  return obj ? &obj->as<NativeObject>() : nullptr;
+}
+
+bool js::PromiseLookup::isDataPropertyNative(JSContext* cx, NativeObject* obj,
+                                             uint32_t slot, JSNative native) {
+  JSFunction* fun;
+  if (!IsFunctionObject(obj->getSlot(slot), &fun)) {
+    return false;
+  }
+  return fun->maybeNative() == native && fun->realm() == cx->realm();
+}
+
+bool js::PromiseLookup::isAccessorPropertyNative(JSContext* cx,
+                                                 NativeObject* holder,
+                                                 uint32_t getterSlot,
+                                                 JSNative native) {
+  JSObject* getter = holder->getGetter(getterSlot);
+  return getter && IsNativeFunction(getter, native) &&
+         getter->as<JSFunction>().realm() == cx->realm();
+}
+
+void js::PromiseLookup::initialize(JSContext* cx) {
+  MOZ_ASSERT(state_ == State::Uninitialized);
+
+  // Get the canonical Promise.prototype.
+  NativeObject* promiseProto = getPromisePrototype(cx);
+
+  // Check condition 1:
+  // Leave the cache uninitialized if the Promise class itself is not yet
+  // initialized.
+  if (!promiseProto) {
+    return;
+  }
+
+  // Get the canonical Promise constructor.
+  JSFunction* promiseCtor = getPromiseConstructor(cx);
+  MOZ_ASSERT(promiseCtor,
+             "The Promise constructor is initialized iff Promise.prototype is "
+             "initialized");
+
+  // Shortcut returns below means Promise[@@species] will never be
+  // optimizable, set to disabled now, and clear it later when we succeed.
+  state_ = State::Disabled;
+
+  // Check condition 2:
+  // Look up Promise.prototype.constructor and ensure it's a data property.
+  mozilla::Maybe<PropertyInfo> ctorProp =
+      promiseProto->lookup(cx, cx->names().constructor);
+  if (ctorProp.isNothing() || !ctorProp->isDataProperty()) {
+    return;
+  }
+
+  // Get the referred value, and ensure it holds the canonical Promise
+  // constructor.
+  JSFunction* ctorFun;
+  if (!IsFunctionObject(promiseProto->getSlot(ctorProp->slot()), &ctorFun)) {
+    return;
+  }
+  if (ctorFun != promiseCtor) {
+    return;
+  }
+
+  // Check condition 3:
+  // Look up Promise.prototype.then and ensure it's a data property.
+  mozilla::Maybe<PropertyInfo> thenProp =
+      promiseProto->lookup(cx, cx->names().then);
+  if (thenProp.isNothing() || !thenProp->isDataProperty()) {
+    return;
+  }
+
+  // Get the referred value, and ensure it holds the canonical "then"
+  // function.
+  if (!isDataPropertyNative(cx, promiseProto, thenProp->slot(), Promise_then)) {
+    return;
+  }
+
+  // Check condition 4:
+  // Look up the '@@species' value on Promise.
+  mozilla::Maybe<PropertyInfo> speciesProp = promiseCtor->lookup(
+      cx, PropertyKey::Symbol(cx->wellKnownSymbols().species));
+  if (speciesProp.isNothing() || !promiseCtor->hasGetter(*speciesProp)) {
+    return;
+  }
+
+  // Get the referred value, ensure it holds the canonical Promise[@@species]
+  // function.
+  uint32_t speciesGetterSlot = speciesProp->slot();
+  if (!isAccessorPropertyNative(cx, promiseCtor, speciesGetterSlot,
+                                Promise_static_species)) {
+    return;
+  }
+
+  // Check condition 5:
+  // Look up Promise.resolve and ensure it's a data property.
+  mozilla::Maybe<PropertyInfo> resolveProp =
+      promiseCtor->lookup(cx, cx->names().resolve);
+  if (resolveProp.isNothing() || !resolveProp->isDataProperty()) {
+    return;
+  }
+
+  // Get the referred value, and ensure it holds the canonical "resolve"
+  // function.
+  if (!isDataPropertyNative(cx, promiseCtor, resolveProp->slot(),
+                            Promise_static_resolve)) {
+    return;
+  }
+
+  // Store raw pointers below. This is okay to do here, because all objects
+  // are in the tenured heap.
+  MOZ_ASSERT(!gc::IsInsideNursery(promiseCtor->shape()));
+  MOZ_ASSERT(!gc::IsInsideNursery(promiseProto->shape()));
+
+  state_ = State::Initialized;
+  promiseConstructorShape_ = promiseCtor->shape();
+  promiseProtoShape_ = promiseProto->shape();
+  promiseSpeciesGetterSlot_ = speciesGetterSlot;
+  promiseResolveSlot_ = resolveProp->slot();
+  promiseProtoConstructorSlot_ = ctorProp->slot();
+  promiseProtoThenSlot_ = thenProp->slot();
+}
+
+void js::PromiseLookup::reset() {
+  AlwaysPoison(this, JS_RESET_VALUE_PATTERN, sizeof(*this),
+               MemCheckKind::MakeUndefined);
+  state_ = State::Uninitialized;
+}
+
+bool js::PromiseLookup::isPromiseStateStillSane(JSContext* cx) {
+  MOZ_ASSERT(state_ == State::Initialized);
+
+  NativeObject* promiseProto = getPromisePrototype(cx);
+  MOZ_ASSERT(promiseProto);
+
+  NativeObject* promiseCtor = getPromiseConstructor(cx);
+  MOZ_ASSERT(promiseCtor);
+
+  // Ensure that Promise.prototype still has the expected shape.
+  if (promiseProto->shape() != promiseProtoShape_) {
+    return false;
+  }
+
+  // Ensure that Promise still has the expected shape.
+  if (promiseCtor->shape() != promiseConstructorShape_) {
+    return false;
+  }
+
+  // Ensure that Promise.prototype.constructor is the canonical constructor.
+  if (promiseProto->getSlot(promiseProtoConstructorSlot_) !=
+      ObjectValue(*promiseCtor)) {
+    return false;
+  }
+
+  // Ensure that Promise.prototype.then is the canonical "then" function.
+  if (!isDataPropertyNative(cx, promiseProto, promiseProtoThenSlot_,
+                            Promise_then)) {
+    return false;
+  }
+
+  // Ensure the species getter contains the canonical @@species function.
+  if (!isAccessorPropertyNative(cx, promiseCtor, promiseSpeciesGetterSlot_,
+                                Promise_static_species)) {
+    return false;
+  }
+
+  // Ensure that Promise.resolve is the canonical "resolve" function.
+  if (!isDataPropertyNative(cx, promiseCtor, promiseResolveSlot_,
+                            Promise_static_resolve)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool js::PromiseLookup::ensureInitialized(JSContext* cx,
+                                          Reinitialize reinitialize) {
+  if (state_ == State::Uninitialized) {
+    // If the cache is not initialized, initialize it.
+    initialize(cx);
+  } else if (state_ == State::Initialized) {
+    if (reinitialize == Reinitialize::Allowed) {
+      if (!isPromiseStateStillSane(cx)) {
+        // If the promise state is no longer sane, reinitialize.
+        reset();
+        initialize(cx);
+      }
+    } else {
+      // When we're not allowed to reinitialize, the promise state must
+      // still be sane if the cache is already initialized.
+      MOZ_ASSERT(isPromiseStateStillSane(cx));
+    }
+  }
+
+  // If the cache is disabled or still uninitialized, don't bother trying to
+  // optimize.
+  if (state_ != State::Initialized) {
+    return false;
+  }
+
+  // By the time we get here, we should have a sane promise state.
+  MOZ_ASSERT(isPromiseStateStillSane(cx));
+
+  return true;
+}
+
+bool js::PromiseLookup::isDefaultPromiseState(JSContext* cx) {
+  // Promise and Promise.prototype are in their default states iff the
+  // lookup cache was successfully initialized.
+  return ensureInitialized(cx, Reinitialize::Allowed);
+}
+
+bool js::PromiseLookup::hasDefaultProtoAndNoShadowedProperties(
+    JSContext* cx, PromiseObject* promise) {
+  // Ensure |promise|'s prototype is the actual Promise.prototype.
+  if (promise->staticPrototype() != getPromisePrototype(cx)) {
+    return false;
+  }
+
+  // Ensure |promise| doesn't define any own properties. This serves as a
+  // quick check to make sure |promise| doesn't define an own "constructor"
+  // or "then" property which may shadow Promise.prototype.constructor or
+  // Promise.prototype.then.
+  return promise->empty();
+}
+
+bool js::PromiseLookup::isDefaultInstance(JSContext* cx, PromiseObject* promise,
+                                          Reinitialize reinitialize) {
+  // Promise and Promise.prototype must be in their default states.
+  if (!ensureInitialized(cx, reinitialize)) {
+    return false;
+  }
+
+  // The object uses the default properties from Promise.prototype.
+  return hasDefaultProtoAndNoShadowedProperties(cx, promise);
+}