Shrink ObjC overhead (generated size and some runtime sizes)

NOTE: This is a binary breaking change as structure sizes have changed size
and/or order.

- Drop capturing field options, no other options were captured and other mobile
  targeted languages don't try to capture this sort information (saved 8
  bytes for every field defined (in static data and again in field descriptor
  instance size data).
- No longer generate/compile in the messages/enums in descriptor.proto. If
  developers need it, they should generate it and compile it in. Reduced the
  overhead of the core library.
- Compute the number of has_bits actually needs to avoid over reserving.
- Let the boolean single fields store via a has_bit to avoid storage, makes
  the common cases of the instance size smaller.
- Reorder some flags and down size the enums to contain the bits needed.
- Reorder the items in the structures to manually ensure they are are packed
  better (especially when generating 64bit code - 8 bytes for every field,
  16 bytes for every extension, instance sizes 8 bytes also).
- Split off the structure initialization so when the default is zero, the
  generated static storage doesn't need to reserve the space. This is batched
  at the message level, so all the fields for the message have to have zero
  defaults to get the saves. By definition all proto3 syntax  files fall into
  this case but it also saves space for the proto2 that use the standard
  defaults. (saves 8 bytes of static data for every field that had a zero
  default)
- Don't track the enums defined by a message. Nothing in the runtime needs it
  and it was just generation and runtime overhead. (saves 8 bytes per enum)
- Ensure EnumDescriptors are started up threadsafe in all cases.
- Split some of the Descriptor initialization into multiple methods so the
  generated code isn't padded with lots of zero/nil args.
- Change how oneof info is feed to the runtime enabling us to generate less
  static data (8 bytes saved per oneof for 64bit).
- Change how enum value informat is capture to pack the data and only decode
  it if it ends up being needed. Avoids padding issues causing bloat of 64bit,
  and removes the needs for extra pointers in addition to the data (just the
  data and one pointer now).

1 files changed, 18 insertions, 2 deletions

diff --git a/src/google/protobuf/compiler/objectivec/objectivec_field.h b/src/google/protobuf/compiler/objectivec/objectivec_field.h
index e8a20a72d..a3a4b1b6e 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_field.h
+++ b/src/google/protobuf/compiler/objectivec/objectivec_field.h
@@ -61,7 +61,6 @@ class FieldGenerator {
 
   // Called by GenerateFieldDescription, exposed for classes that need custom
   // generation.
-  virtual void GenerateFieldDescriptionTypeSpecific(io::Printer* printer) const;
 
   // Exposed for subclasses to extend, base does nothing.
   virtual void GenerateCFunctionDeclarations(io::Printer* printer) const;
@@ -71,9 +70,16 @@ class FieldGenerator {
   virtual void DetermineForwardDeclarations(set<string>* fwd_decls) const;
 
   // Used during generation, not intended to be extended by subclasses.
-  void GenerateFieldDescription(io::Printer* printer) const;
+  void GenerateFieldDescription(
+      io::Printer* printer, bool include_default) const;
   void GenerateFieldNumberConstant(io::Printer* printer) const;
 
+  // Exposed to get and set the has bits information.
+  virtual bool RuntimeUsesHasBit(void) const = 0;
+  void SetRuntimeHasBit(int has_index);
+  void SetNoHasBit(void);
+  virtual int ExtraRuntimeHasBitsNeeded(void) const;
+  virtual void SetExtraRuntimeHasBitsBase(int index_base);
   void SetOneofIndexBase(int index_base);
 
   string variable(const char* key) const {
@@ -109,6 +115,8 @@ class SingleFieldGenerator : public FieldGenerator {
 
   virtual void GeneratePropertyImplementation(io::Printer* printer) const;
 
+  virtual bool RuntimeUsesHasBit(void) const;
+
  protected:
   SingleFieldGenerator(const FieldDescriptor* descriptor,
                        const Options& options);
@@ -143,6 +151,8 @@ class RepeatedFieldGenerator : public ObjCObjFieldGenerator {
 
   virtual void GeneratePropertyImplementation(io::Printer* printer) const;
 
+  virtual bool RuntimeUsesHasBit(void) const;
+
  protected:
   RepeatedFieldGenerator(const FieldDescriptor* descriptor,
                          const Options& options);
@@ -162,8 +172,14 @@ class FieldGeneratorMap {
   const FieldGenerator& get(const FieldDescriptor* field) const;
   const FieldGenerator& get_extension(int index) const;
 
+  // Assigns the has bits and returns the number of bits needed.
+  int CalculateHasBits(void);
+
   void SetOneofIndexBase(int index_base);
 
+  // Check if any field of this message has a non zero default.
+  bool DoesAnyFieldHaveNonZeroDefault(void) const;
+
  private:
   const Descriptor* descriptor_;
   scoped_array<scoped_ptr<FieldGenerator> > field_generators_;