Restore performance of accesses to JSGlobalProxy after r22802

src/arm64/stub-cache-arm64.cc

Index: src/arm64/stub-cache-arm64.cc
diff --git a/src/arm64/stub-cache-arm64.cc b/src/arm64/stub-cache-arm64.cc
index 1bd2ac8fed959bbf7fd1595992ae5a52955a8dd6..9c07c0a06ddab645619dc2e025c91aa012f92e78 100644
--- a/src/arm64/stub-cache-arm64.cc
+++ b/src/arm64/stub-cache-arm64.cc
@@ -691,8 +691,8 @@ Register PropertyHandlerCompiler::CheckPrototypes(
 
     prototype = handle(JSObject::cast(current_map->prototype()));
     if (current_map->is_dictionary_map() &&
-        !current_map->IsJSGlobalObjectMap() &&
-        !current_map->IsJSGlobalProxyMap()) {
+        !current_map->IsJSGlobalObjectMap()) {
+      DCHECK(!current_map->IsJSGlobalProxyMap());  // Proxy maps are fast.
       if (!name->IsUniqueName()) {
         DCHECK(name->IsString());
         name = factory()->InternalizeString(Handle<String>::cast(name));
@@ -724,6 +724,9 @@ Register PropertyHandlerCompiler::CheckPrototypes(
       // Check access rights to the global object.  This has to happen after
       // the map check so that we know that the object is actually a global
       // object.
+      // This allows us to install generated handlers for accesses to the
+      // global proxy (as opposed to using slow ICs). See corresponding code
+      // in LookupForRead().
       if (current_map->IsJSGlobalProxyMap()) {
         UseScratchRegisterScope temps(masm());
         __ CheckAccessGlobalProxy(reg, scratch2, temps.AcquireX(), miss);