Eliminate 99% of allocated ExceptionHandler objects

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 40287)
+++ runtime/vm/object.cc	(working copy)
@@ -99,6 +99,7 @@
 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;
@@ -437,6 +438,7 @@
   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();
@@ -680,6 +682,21 @@
     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);
@@ -10991,7 +11008,7 @@
 
 
 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_;
 }
 
 
@@ -11078,7 +11095,7 @@
                                       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() :