- Preallocate non-named ArgumentsDescriptors with a small amount of parameters.

runtime/vm/dart_entry.cc

Index: runtime/vm/dart_entry.cc
===================================================================
--- runtime/vm/dart_entry.cc	(revision 16642)
+++ runtime/vm/dart_entry.cc	(working copy)
@@ -13,6 +13,10 @@
 
 namespace dart {
 
+// A cache of VM heap allocated arguments descriptors.
+RawArray* ArgumentsDescriptor::cached_args_descriptors_[kCachedDescriptors];
+
+
 RawObject* DartEntry::InvokeDynamic(const Function& function,
                                     const Array& arguments) {
   const Array& arg_desc =
@@ -219,6 +223,9 @@
                                    const Array& optional_arguments_names) {
   const intptr_t num_named_args =
       optional_arguments_names.IsNull() ? 0 : optional_arguments_names.Length();
+  if (num_named_args == 0) {
+    return ArgumentsDescriptor::New(num_arguments);
+  }
   const intptr_t num_pos_args = num_arguments - num_named_args;
 
   // Build the arguments descriptor array, which consists of the total
@@ -268,6 +275,16 @@
 
 
 RawArray* ArgumentsDescriptor::New(intptr_t num_arguments) {
+  ASSERT(num_arguments >= 0);
+  if (num_arguments < kCachedDescriptors) {
+    return cached_args_descriptors_[num_arguments];
+  }
+  return NewNonCached(num_arguments);
+}
+
+
+RawArray* ArgumentsDescriptor::NewNonCached(intptr_t num_arguments,
+                                            bool canonicalize) {
   // Build the arguments descriptor array, which consists of the total
   // argument count; the positional argument count; and
   // a terminating null to simplify iterating in generated code.
@@ -285,12 +302,21 @@
   descriptor.SetAt((descriptor_len - 1), Object::Handle());
 
   // Share the immutable descriptor when possible by canonicalizing it.
-  descriptor.MakeImmutable();
-  descriptor ^= descriptor.Canonicalize();
+  if (canonicalize) {

[regis, 2013/01/05 01:05:29]

I suppose you do not canonicalize the cached descriptors so that a reference to
them is not stored twice. But why don't you make them immutable?

[Ivan Posva, 2013/01/07 18:27:12]

Making them immutable now. For this we need to make the ImmutableArray class
known to the VM isolate.

+    descriptor.MakeImmutable();
+    descriptor ^= descriptor.Canonicalize();
+  }
   return descriptor.raw();
 }
 
 
+void ArgumentsDescriptor::InitOnce() {
+  for (int i = 0; i < kCachedDescriptors; i++) {
+    cached_args_descriptors_[i] = ArgumentsDescriptor::NewNonCached(i, false);
+  }
+}
+
+
 RawObject* DartLibraryCalls::ExceptionCreate(const Library& lib,
                                              const String& class_name,
                                              const Array& arguments) {