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, 86 insertions, 54 deletions

diff --git a/src/google/protobuf/compiler/objectivec/objectivec_field.cc b/src/google/protobuf/compiler/objectivec/objectivec_field.cc
index 8697e225..7bb9837d 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_field.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_field.cc
@@ -28,6 +28,8 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include <iostream>
+
 #include <google/protobuf/compiler/objectivec/objectivec_field.h>
 #include <google/protobuf/compiler/objectivec/objectivec_helpers.h>
 #include <google/protobuf/compiler/objectivec/objectivec_enum_field.h>
@@ -75,7 +77,6 @@ void SetCommonFieldVariables(const FieldDescriptor* descriptor,
   (*variables)["field_number_name"] =
       classname + "_FieldNumber_" + capitalized_name;
   (*variables)["field_number"] = SimpleItoa(descriptor->number());
-  (*variables)["has_index"] = SimpleItoa(descriptor->index());
   (*variables)["field_type"] = GetCapitalizedType(descriptor);
   std::vector<string> field_flags;
   if (descriptor->is_repeated()) field_flags.push_back("GPBFieldRepeated");
@@ -99,18 +100,9 @@ void SetCommonFieldVariables(const FieldDescriptor* descriptor,
   (*variables)["dataTypeSpecific_name"] = "className";
   (*variables)["dataTypeSpecific_value"] = "NULL";
 
-  string field_options = descriptor->options().SerializeAsString();
-  // Must convert to a standard byte order for packing length into
-  // a cstring.
-  uint32 length = ghtonl(field_options.length());
-  if (length > 0) {
-    string bytes((const char*)&length, sizeof(length));
-    bytes.append(field_options);
-    string options_str = "\"" + CEscape(bytes) + "\"";
-    (*variables)["fieldoptions"] = "\"" + CEscape(bytes) + "\"";
-  } else {
-    (*variables)["fieldoptions"] = "";
-  }
+  (*variables)["storage_offset_value"] =
+      "(uint32_t)offsetof(" + classname + "__storage_, " + camel_case_name + ")";
+  (*variables)["storage_offset_comment"] = "";
 
   // Clear some common things so they can be set just when needed.
   (*variables)["storage_attribute"] = "";
@@ -190,52 +182,54 @@ void FieldGenerator::DetermineForwardDeclarations(
 }
 
 void FieldGenerator::GenerateFieldDescription(
-    io::Printer* printer) const {
-  printer->Print(
-      variables_,
-      "{\n"
-      "  .name = \"$name$\",\n"
-      "  .number = $field_number_name$,\n"
-      "  .hasIndex = $has_index$,\n"
-      "  .flags = $fieldflags$,\n"
-      "  .dataType = GPBDataType$field_type$,\n"
-      "  .offset = offsetof($classname$__storage_, $name$),\n"
-      "  .defaultValue.$default_name$ = $default$,\n");
-
-  // TODO(thomasvl): It might be useful to add a CPP wrapper to support
-  // compiling away the EnumDescriptors.  To do that, we'd need a #if here
-  // to control setting the descriptor vs. the validator, and above in
-  // SetCommonFieldVariables() we'd want to wrap how we add
-  // GPBFieldHasDefaultValue to the flags.
-
-  // "  .dataTypeSpecific.value* = [something],"
-  GenerateFieldDescriptionTypeSpecific(printer);
-
-  const string& field_options(variables_.find("fieldoptions")->second);
-  if (field_options.empty()) {
-    printer->Print("  .fieldOptions = NULL,\n");
+    io::Printer* printer, bool include_default) const {
+  // Printed in the same order as the structure decl.
+  if (include_default) {
+    printer->Print(
+        variables_,
+        "{\n"
+        "  .defaultValue.$default_name$ = $default$,\n"
+        "  .core.name = \"$name$\",\n"
+        "  .core.dataTypeSpecific.$dataTypeSpecific_name$ = $dataTypeSpecific_value$,\n"
+        "  .core.number = $field_number_name$,\n"
+        "  .core.hasIndex = $has_index$,\n"
+        "  .core.offset = $storage_offset_value$,$storage_offset_comment$\n"
+        "  .core.flags = $fieldflags$,\n"
+        "  .core.dataType = GPBDataType$field_type$,\n"
+        "},\n");
   } else {
-    // Can't use PrintRaw() here to get the #if/#else/#endif lines completely
-    // outdented because the need for indent captured on the previous
-    // printing of a \n and there is no way to get the current indent level
-    // to call the right number of Outdent()/Indents() to maintain state.
     printer->Print(
         variables_,
-        "#if GPBOBJC_INCLUDE_FIELD_OPTIONS\n"
-        "  .fieldOptions = $fieldoptions$,\n"
-        "#else\n"
-        "  .fieldOptions = NULL,\n"
-        "#endif  // GPBOBJC_INCLUDE_FIELD_OPTIONS\n");
+        "{\n"
+        "  .name = \"$name$\",\n"
+        "  .dataTypeSpecific.$dataTypeSpecific_name$ = $dataTypeSpecific_value$,\n"
+        "  .number = $field_number_name$,\n"
+        "  .hasIndex = $has_index$,\n"
+        "  .offset = $storage_offset_value$,$storage_offset_comment$\n"
+        "  .flags = $fieldflags$,\n"
+        "  .dataType = GPBDataType$field_type$,\n"
+        "},\n");
   }
+}
 
-  printer->Print("},\n");
+void FieldGenerator::SetRuntimeHasBit(int has_index) {
+  variables_["has_index"] = SimpleItoa(has_index);
 }
 
-void FieldGenerator::GenerateFieldDescriptionTypeSpecific(
-    io::Printer* printer) const {
-  printer->Print(
-      variables_,
-      "  .dataTypeSpecific.$dataTypeSpecific_name$ = $dataTypeSpecific_value$,\n");
+void FieldGenerator::SetNoHasBit(void) {
+  variables_["has_index"] = "GPBNoHasBit";
+}
+
+int FieldGenerator::ExtraRuntimeHasBitsNeeded(void) const {
+  return 0;
+}
+
+void FieldGenerator::SetExtraRuntimeHasBitsBase(int index_base) {
+  // NOTE: src/google/protobuf/compiler/plugin.cc makes use of cerr for some
+  // error cases, so it seems to be ok to use as a back door for errors.
+  cerr << "Error: should have overriden SetExtraRuntimeHasBitsBase()." << endl;
+  cerr.flush();
+  abort();
 }
 
 void FieldGenerator::SetOneofIndexBase(int index_base) {
@@ -302,6 +296,14 @@ bool SingleFieldGenerator::WantsHasProperty(void) const {
   return false;
 }
 
+bool SingleFieldGenerator::RuntimeUsesHasBit(void) const {
+  if (descriptor_->containing_oneof() != NULL) {
+    // The oneof tracks what is set instead.
+    return false;
+  }
+  return true;
+}
+
 ObjCObjFieldGenerator::ObjCObjFieldGenerator(const FieldDescriptor* descriptor,
                                              const Options& options)
     : SingleFieldGenerator(descriptor, options) {
@@ -347,8 +349,6 @@ void ObjCObjFieldGenerator::GeneratePropertyDeclaration(
 RepeatedFieldGenerator::RepeatedFieldGenerator(
     const FieldDescriptor* descriptor, const Options& options)
     : ObjCObjFieldGenerator(descriptor, options) {
-  // Repeated fields don't use the has index.
-  variables_["has_index"] = "GPBNoHasBit";
   // Default to no comment and let the cases needing it fill it in.
   variables_["array_comment"] = "";
 }
@@ -402,6 +402,10 @@ bool RepeatedFieldGenerator::WantsHasProperty(void) const {
   return false;
 }
 
+bool RepeatedFieldGenerator::RuntimeUsesHasBit(void) const {
+  return false;  // The array having anything is what is used.
+}
+
 FieldGeneratorMap::FieldGeneratorMap(const Descriptor* descriptor,
                                      const Options& options)
     : descriptor_(descriptor),
@@ -432,12 +436,40 @@ const FieldGenerator& FieldGeneratorMap::get_extension(int index) const {
   return *extension_generators_[index];
 }
 
+int FieldGeneratorMap::CalculateHasBits(void) {
+  int total_bits = 0;
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    if (field_generators_[i]->RuntimeUsesHasBit()) {
+      field_generators_[i]->SetRuntimeHasBit(total_bits);
+      ++total_bits;
+    } else {
+      field_generators_[i]->SetNoHasBit();
+    }
+    int extra_bits = field_generators_[i]->ExtraRuntimeHasBitsNeeded();
+    if (extra_bits) {
+      field_generators_[i]->SetExtraRuntimeHasBitsBase(total_bits);
+      total_bits += extra_bits;
+    }
+  }
+  return total_bits;
+}
+
 void FieldGeneratorMap::SetOneofIndexBase(int index_base) {
   for (int i = 0; i < descriptor_->field_count(); i++) {
     field_generators_[i]->SetOneofIndexBase(index_base);
   }
 }
 
+bool FieldGeneratorMap::DoesAnyFieldHaveNonZeroDefault(void) const {
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    if (HasNonZeroDefaultValue(descriptor_->field(i))) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 }  // namespace objectivec
 }  // namespace compiler
 }  // namespace protobuf