[dart2js] Cache globalThis

Feature-test for `self` and `globalThis`, and cache the result.

The cached access has smaller minified code size than either `self` or `globalThis`.

All older browsers that we have supported that don't have `globalThis`
do have `self`.

We prioritize `self` over `globalThis`. They are usually the same but it is possible that there are programs which run in an environment that has replaced `self`, for example, a test might do that. We don't want to break existing tests.

Bug: #59982
Change-Id: I11d19183d85a73e9552b66a2f49ac99be10c3c83
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/417912
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

@@ -2011,6 +2011,12 @@ class FragmentEmitter {
   ) {
     List<js.Property> globals = [];
 
+    globals.add(
+      js.Property(
+        js.string(CACHED_GLOBAL_THIS),
+        js.js(r'typeof self != "undefined" ? self : globalThis'),
+      ),
+    );
     if (fragmentsToLoad.isNotEmpty) {
       globals.addAll(
         emitEmbeddedGlobalsForDeferredLoading(

pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart

@@ -10,6 +10,7 @@ import 'package:js_runtime/synced/array_flags.dart' show ArrayFlags;
 
 import 'package:js_runtime/synced/embedded_names.dart'
     show
+        CACHED_GLOBAL_THIS,
         DEFERRED_INITIALIZED,
         DEFERRED_LIBRARY_PARTS,
         DEFERRED_PART_URIS,

pkg/compiler/lib/src/native/behavior.dart

@@ -654,6 +654,10 @@ class NativeBehavior {
       behavior.sideEffects.setTo(newEffects);
     }
 
+    void setUseGvn(bool useGvn) {
+      behavior.useGvn = useGvn;
+    }
+
     processSpecString(
       commonElements.dartTypes,
       reporter,
@@ -662,6 +666,7 @@ class NativeBehavior {
       validTags: validTags,
       lookupType: lookupType,
       setSideEffects: setSideEffects,
+      setUseGvn: setUseGvn,
       typesReturned: behavior.typesReturned,
       typesInstantiated: behavior.typesInstantiated,
       objectType: commonElements.objectType,
@@ -709,7 +714,7 @@ class NativeBehavior {
       lookupType,
       reporter,
       commonElements,
-      validTags: ['returns', 'creates'],
+      validTags: ['returns', 'creates', 'depends', 'effects', 'gvn'],
     );
     return behavior;
   }

pkg/compiler/lib/src/ssa/nodes.dart

@@ -2723,8 +2723,13 @@ class HForeignCode extends HForeign {
   bool typeEquals(other) => other is HForeignCode;
   @override
   bool dataEquals(HForeignCode other) {
-    return codeTemplate.source != null &&
-        codeTemplate.source == other.codeTemplate.source;
+    if (codeTemplate.source == null) {
+      return other.codeTemplate.source == null &&
+          // The ASTs will be equal if identical, and in some limited other
+          // cases, like a ModularExpression.
+          codeTemplate.ast == other.codeTemplate.ast;
+    }
+    return codeTemplate.source == other.codeTemplate.source;
   }
 
   @override

pkg/js_runtime/lib/synced/embedded_names.dart

@@ -183,6 +183,10 @@ const STARTUP_METRICS = 'sm';
 // TODO(51016): This might be moved to improve deferred loading.
 const RECORD_TYPE_TEST_COMBINATORS_PROPERTY = 'rttc';
 
+/// An embedded global that contains the value of `globalThis`.  Unlike many
+/// embedded globals, this one has many references, so we choose short name.
+const CACHED_GLOBAL_THIS = 'G';
+
 /// Names of fields of collected tear-off parameters object.
 ///
 /// Tear-off getters are created before the Dart classes are initialized, so a

sdk/lib/_internal/js_runtime/lib/js_helper.dart

@@ -6,6 +6,7 @@ library _js_helper;
 
 import 'dart:_js_embedded_names'
     show
+        CACHED_GLOBAL_THIS,
         CURRENT_SCRIPT,
         DEFERRED_LIBRARY_PARTS,
         DEFERRED_PART_URIS,
@@ -3953,8 +3954,17 @@ abstract class TrustedGetRuntimeType {}
 /// `pkg/_js_interop_checks/lib/src/js_util_optimizer.dart`.
 ///
 /// This should match the global context that non-static interop members use.
+@pragma('dart2js:prefer-inline')
+// Unlike `JS<T>(...)`, `JS_EMBEDDED_GLOBAL` is not generic. So we need to cast
+// the dynamic result to the desired type. We know the result is some kind of
+// non-null, non-Dart object.
+@pragma('dart2js:as:trust')
 Object get staticInteropGlobalContext =>
-    JS('creates:;returns:Object;depends:none;effects:none;gvn:true', 'self');
+    JS_EMBEDDED_GLOBAL(
+          'creates:;returns:JSObject;depends:none;effects:none;gvn:true',
+          CACHED_GLOBAL_THIS,
+        )
+        as Object;
 
 /// Return a fresh object literal.
 T createObjectLiteral<T>() => JS('PlainJavaScriptObject', '{}');

sdk/lib/_internal/js_runtime/lib/synced/embedded_names.dart

@@ -183,6 +183,10 @@ const STARTUP_METRICS = 'sm';
 // TODO(51016): This might be moved to improve deferred loading.
 const RECORD_TYPE_TEST_COMBINATORS_PROPERTY = 'rttc';
 
+/// An embedded global that contains the value of `globalThis`.  Unlike many
+/// embedded globals, this one has many references, so we choose short name.
+const CACHED_GLOBAL_THIS = 'G';
+
 /// Names of fields of collected tear-off parameters object.
 ///
 /// Tear-off getters are created before the Dart classes are initialized, so a