Eliminate 99% of allocated ExceptionHandler objects

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 81 matching lines @@
 #define RAW_NULL kHeapObjectTag
 Object* Object::null_object_ = NULL;
 Array* Object::null_array_ = NULL;
 String* Object::null_string_ = NULL;
 Instance* Object::null_instance_ = NULL;
 TypeArguments* Object::null_type_arguments_ = NULL;
 Array* Object::empty_array_ = NULL;
 Array* Object::zero_array_ = NULL;
 PcDescriptors* Object::empty_descriptors_ = NULL;
 LocalVarDescriptors* Object::empty_var_descriptors_ = NULL;
+ExceptionHandlers* Object::empty_exception_handlers_ = NULL;
 Instance* Object::sentinel_ = NULL;
 Instance* Object::transition_sentinel_ = NULL;
 Instance* Object::unknown_constant_ = NULL;
 Instance* Object::non_constant_ = NULL;
 Bool* Object::bool_true_ = NULL;
 Bool* Object::bool_false_ = NULL;
 Smi* Object::smi_illegal_cid_ = NULL;
 LanguageError* Object::snapshot_writer_error_ = NULL;
 LanguageError* Object::branch_offset_error_ = NULL;
 
@@ skipping 318 matching lines @@
   // Allocate the read only object handles here.
   null_object_ = Object::ReadOnlyHandle();
   null_array_ = Array::ReadOnlyHandle();
   null_string_ = String::ReadOnlyHandle();
   null_instance_ = Instance::ReadOnlyHandle();
   null_type_arguments_ = TypeArguments::ReadOnlyHandle();
   empty_array_ = Array::ReadOnlyHandle();
   zero_array_ = Array::ReadOnlyHandle();
   empty_descriptors_ = PcDescriptors::ReadOnlyHandle();
   empty_var_descriptors_ = LocalVarDescriptors::ReadOnlyHandle();
+  empty_exception_handlers_ = ExceptionHandlers::ReadOnlyHandle();
   sentinel_ = Instance::ReadOnlyHandle();
   transition_sentinel_ = Instance::ReadOnlyHandle();
   unknown_constant_ =  Instance::ReadOnlyHandle();
   non_constant_ =  Instance::ReadOnlyHandle();
   bool_true_ = Bool::ReadOnlyHandle();
   bool_false_ = Bool::ReadOnlyHandle();
   smi_illegal_cid_ = Smi::ReadOnlyHandle();
   snapshot_writer_error_ = LanguageError::ReadOnlyHandle();
   branch_offset_error_ = LanguageError::ReadOnlyHandle();
 
@@ skipping 223 matching lines @@
         heap->Allocate(LocalVarDescriptors::InstanceSize(0), Heap::kOld);
     InitializeObject(address,
                      kLocalVarDescriptorsCid,
                      LocalVarDescriptors::InstanceSize(0));
     LocalVarDescriptors::initializeHandle(
         empty_var_descriptors_,
         reinterpret_cast<RawLocalVarDescriptors*>(address + kHeapObjectTag));
     empty_var_descriptors_->raw_ptr()->num_entries_ = 0;
   }
 
+  // Allocate and initialize the canonical empty exception handler info object.
+  // The vast majority of all functions do not contain an exception handler
+  // and can share this cononical descriptor.

[srdjan, 2014/09/15 23:47:14]

s/cononical/cananical/ ;-)

[hausner, 2014/09/16 00:28:41]

Dro Chonoson mot dom Kontroboss, sosson of dor Strosso...

Done.

+  {
+    uword address =
+        heap->Allocate(ExceptionHandlers::InstanceSize(0), Heap::kOld);
+    InitializeObject(address,
+                     kExceptionHandlersCid,
+                     ExceptionHandlers::InstanceSize(0));
+    ExceptionHandlers::initializeHandle(
+        empty_exception_handlers_,
+        reinterpret_cast<RawExceptionHandlers*>(address + kHeapObjectTag));
+    empty_exception_handlers_->raw_ptr()->num_entries_ = 0;
+  }
+
   cls = Class::New<Instance>(kDynamicCid);
   cls.set_is_abstract();
   cls.set_num_type_arguments(0);
   cls.set_num_own_type_arguments(0);
   cls.set_is_type_finalized();
   cls.set_is_finalized();
   dynamic_class_ = cls.raw();
 
   cls = Class::New<Instance>(kVoidCid);
   cls.set_num_type_arguments(0);
@@ skipping 10290 matching lines @@
   }
   return result.raw();
 }
 
 
 intptr_t LocalVarDescriptors::Length() const {
   return raw_ptr()->num_entries_;
 }
 
 
 intptr_t ExceptionHandlers::Length() const {

[srdjan, 2014/09/15 23:47:15]

s/Length/num_entries/

[hausner, 2014/09/16 00:28:41]

Done.

(But what's the point of having accessors if they have to change when the
underlying implementation changes?)

-  return raw_ptr()->length_;
+  return raw_ptr()->num_entries_;
 }
 
 
 void ExceptionHandlers::SetHandlerInfo(intptr_t try_index,
                                        intptr_t outer_try_index,
                                        intptr_t handler_pc,
                                        bool needs_stacktrace,
                                        bool has_catch_all) const {
   ASSERT((try_index >= 0) && (try_index < Length()));
   RawExceptionHandlers::HandlerInfo* info = &raw_ptr()->data()[try_index];
@@ skipping 66 matching lines @@
            num_handlers);
   }
   ExceptionHandlers& result = ExceptionHandlers::Handle();
   {
     uword size = ExceptionHandlers::InstanceSize(num_handlers);
     RawObject* raw = Object::Allocate(ExceptionHandlers::kClassId,
                                       size,
                                       Heap::kOld);
     NoGCScope no_gc;
     result ^= raw;
-    result.raw_ptr()->length_ = num_handlers;
+    result.raw_ptr()->num_entries_ = num_handlers;
   }
   const Array& handled_types_data = (num_handlers == 0) ?
       Object::empty_array() :
       Array::Handle(Array::New(num_handlers));
   result.set_handled_types_data(handled_types_data);
   return result.raw();
 }
 
 
 const char* ExceptionHandlers::ToCString() const {
@@ skipping 9242 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart