Bug 1840424 - Part 1: Cache the default time zone object. r=spidermonkey-reviewers,dminor

Add a global cache for the default time zone object. This avoids creating
new ICU time zone objects when using the default time zone in `Temporal`
code.

Differential Revision: https://phabricator.services.mozilla.com/D255270

Author: anba

js/src/builtin/intl/GlobalIntlData.cpp

@@ -90,6 +90,7 @@ bool js::intl::GlobalIntlData::ensureRuntimeDefaultTimeZone(JSContext* cx) {
 
     // Clear the cached default time zone.
     defaultTimeZone_ = nullptr;
+    defaultTimeZoneObject_ = nullptr;
 
     // Clear all cached DateTimeFormat instances when the time zone has changed.
     resetDateTimeFormat();
@@ -248,6 +249,30 @@ DateTimeFormatObject* js::intl::GlobalIntlData::getOrCreateDateTimeFormat(
   return &dtfObject->as<DateTimeFormatObject>();
 }
 
+temporal::TimeZoneObject* js::intl::GlobalIntlData::getOrCreateDefaultTimeZone(
+    JSContext* cx) {
+  // Ensure the runtime default time zone didn't change.
+  if (!ensureRuntimeDefaultTimeZone(cx)) {
+    return nullptr;
+  }
+
+  // If we didn't have a cache hit, compute the default time zone.
+  if (!defaultTimeZoneObject_) {
+    Rooted<JSLinearString*> identifier(cx, defaultTimeZone(cx));
+    if (!identifier) {
+      return nullptr;
+    }
+
+    auto* timeZone = temporal::CreateTimeZoneObject(cx, identifier, identifier);
+    if (!timeZone) {
+      return nullptr;
+    }
+    defaultTimeZoneObject_ = timeZone;
+  }
+
+  return &defaultTimeZoneObject_->as<temporal::TimeZoneObject>();
+}
+
 void js::intl::GlobalIntlData::trace(JSTracer* trc) {
   TraceNullableEdge(trc, &runtimeDefaultLocale_,
                     "GlobalIntlData::runtimeDefaultLocale_");
@@ -256,6 +281,8 @@ void js::intl::GlobalIntlData::trace(JSTracer* trc) {
   TraceNullableEdge(trc, &runtimeDefaultTimeZone_,
                     "GlobalIntlData::runtimeDefaultTimeZone_");
   TraceNullableEdge(trc, &defaultTimeZone_, "GlobalIntlData::defaultTimeZone_");
+  TraceNullableEdge(trc, &defaultTimeZoneObject_,
+                    "GlobalIntlData::defaultTimeZoneObject_");
 
   TraceNullableEdge(trc, &collatorLocale_, "GlobalIntlData::collatorLocale_");
   TraceNullableEdge(trc, &collator_, "GlobalIntlData::collator_");

js/src/builtin/intl/GlobalIntlData.h

@@ -18,6 +18,10 @@ namespace js {
 class CollatorObject;
 class DateTimeFormatObject;
 class NumberFormatObject;
+
+namespace temporal {
+class TimeZoneObject;
+}
 }  // namespace js
 
 namespace js::intl {
@@ -54,6 +58,11 @@ class GlobalIntlData {
    */
   GCPtr<JSLinearString*> defaultTimeZone_;
 
+  /**
+   * Cached temporal::TimeZoneObject for the default time zone.
+   */
+  GCPtr<JSObject*> defaultTimeZoneObject_;
+
   /**
    * Locale string passed to the last call to localeCompare String method. Not
    * necessarily the actual locale when the string can't be resolved to a
@@ -122,6 +131,12 @@ class GlobalIntlData {
    */
   JSLinearString* defaultTimeZone(JSContext* cx);
 
+  /**
+   * Get or create the time zone object for the host environment's current time
+   * zone.
+   */
+  temporal::TimeZoneObject* getOrCreateDefaultTimeZone(JSContext* cx);
+
   /**
    * Get or create the Intl.Collator instance for |locale|. The default locale
    * is used when |locale| is null.

js/src/builtin/temporal/TimeZone.cpp

@@ -98,7 +98,7 @@ static JSLinearString* FormatOffsetTimeZoneIdentifier(JSContext* cx,
   return NewStringCopyN<CanGC>(cx, result, std::size(result));
 }
 
-static TimeZoneObject* CreateTimeZoneObject(
+TimeZoneObject* js::temporal::CreateTimeZoneObject(
     JSContext* cx, Handle<JSLinearString*> identifier,
     Handle<JSLinearString*> primaryIdentifier) {
   // TODO: Implement a built-in time zone object cache.
@@ -318,12 +318,8 @@ JSLinearString* js::temporal::SystemTimeZoneIdentifier(JSContext* cx) {
  */
 bool js::temporal::SystemTimeZone(JSContext* cx,
                                   MutableHandle<TimeZoneValue> result) {
-  Rooted<JSLinearString*> identifier(cx, SystemTimeZoneIdentifier(cx));
-  if (!identifier) {
-    return false;
-  }
-
-  auto* timeZone = CreateTimeZoneObject(cx, identifier, identifier);
+  auto* timeZone =
+      cx->global()->globalIntlData().getOrCreateDefaultTimeZone(cx);
   if (!timeZone) {
     return false;
   }

js/src/builtin/temporal/TimeZone.h

@@ -261,6 +261,14 @@ class PossibleEpochNanoseconds final {
 struct ParsedTimeZone;
 enum class TemporalDisambiguation;
 
+/**
+ * Create a new |TimeZoneObject| whose identifier is |identifier| and whose
+ * primary identifier is |primaryIdentifier|.
+ */
+TimeZoneObject* CreateTimeZoneObject(
+    JSContext* cx, JS::Handle<JSLinearString*> identifier,
+    JS::Handle<JSLinearString*> primaryIdentifier);
+
 /**
  * SystemTimeZoneIdentifier ( )
  */