Avoid class initializers to help ProGuard.

Class initializers prevent ProGuard from inlining any methods
because it thinks the class initializer may have side effects.
This is true for static methods, but instance methods can still
be inlined, because to have an instance you will have touched
the class and any class initializers would have run. But
ProGuard only starts inlining instance methods of classes with
class initializers from v4.11b6, and Android uses v4.4 now.

This change tries to avoid the class initializers as much as
possible, by delaying the initialization of the empty array and
some fields' saved defaults until when they're needed. However,
if the message hosts any extensions, they must be public static
final and therefore introducing the class initializer. In that
case we won't bother with lazy initialization.

Change-Id: I00d8296f6eb0023112b93ee135cdb28dbd52b0b8

1 files changed, 82 insertions, 10 deletions

diff --git a/src/google/protobuf/compiler/javanano/javanano_message.cc b/src/google/protobuf/compiler/javanano/javanano_message.cc
index f7ab62c..c09670a 100644
--- a/src/google/protobuf/compiler/javanano/javanano_message.cc
+++ b/src/google/protobuf/compiler/javanano/javanano_message.cc
@@ -155,14 +155,6 @@ void MessageGenerator::Generate(io::Printer* printer) {
       "    com.google.protobuf.nano.MessageNano {\n");
   }
   printer->Indent();
-  printer->Print(
-    "\n"
-    "public static final $classname$[] EMPTY_ARRAY = {};\n"
-    "\n"
-    "public $classname$() {\n"
-    "  clear();\n"
-    "}\n",
-    "classname", descriptor_->name());
 
   // Nested types and extensions
   for (int i = 0; i < descriptor_->extension_count(); i++) {
@@ -177,6 +169,42 @@ void MessageGenerator::Generate(io::Printer* printer) {
     MessageGenerator(descriptor_->nested_type(i), params_).Generate(printer);
   }
 
+  // Lazy initialization of otherwise static final fields can help prevent the
+  // class initializer from being generated. We want to prevent it because it
+  // stops ProGuard from inlining any methods in this class into call sites and
+  // therefore reducing the method count. However, extensions are best kept as
+  // public static final fields with initializers, so with their existence we
+  // won't bother with lazy initialization.
+  bool lazy_init = descriptor_->extension_count() == 0;
+
+  // Empty array
+  if (lazy_init) {
+    printer->Print(
+      "\n"
+      "private static volatile $classname$[] _emptyArray;\n"
+      "public static $classname$[] emptyArray() {\n"
+      "  // Lazily initializes the empty array\n"
+      "  if (_emptyArray == null) {\n"
+      "    synchronized (\n"
+      "        com.google.protobuf.nano.InternalNano.LAZY_INIT_LOCK) {\n"
+      "      if (_emptyArray == null) {\n"
+      "        _emptyArray = new $classname$[0];\n"
+      "      }\n"
+      "    }\n"
+      "  }\n"
+      "  return _emptyArray;\n"
+      "}\n",
+      "classname", descriptor_->name());
+  } else {
+    printer->Print(
+      "\n"
+      "private static final $classname$[] EMPTY_ARRAY = {};\n"
+      "public static $classname$[] emptyArray() {\n"
+      "  return EMPTY_ARRAY;\n"
+      "}\n",
+      "classname", descriptor_->name());
+  }
+
   // Integers for bit fields
   int totalInts = (field_generators_.total_bits() + 31) / 32;
   if (totalInts > 0) {
@@ -187,13 +215,57 @@ void MessageGenerator::Generate(io::Printer* printer) {
     }
   }
 
-  // Fields
+  // Fields and maybe their default values
   for (int i = 0; i < descriptor_->field_count(); i++) {
     printer->Print("\n");
     PrintFieldComment(printer, descriptor_->field(i));
-    field_generators_.get(descriptor_->field(i)).GenerateMembers(printer);
+    field_generators_.get(descriptor_->field(i)).GenerateMembers(
+        printer, lazy_init);
+  }
+
+  // Constructor, with lazy init code if needed
+  if (lazy_init && field_generators_.saved_defaults_needed()) {
+    printer->Print(
+      "\n"
+      "private static volatile boolean _classInitialized;\n"
+      "\n"
+      "public $classname$() {\n"
+      "  // Lazily initializes the field defaults\n"
+      "  if (!_classInitialized) {\n"
+      "    synchronized (\n"
+      "        com.google.protobuf.nano.InternalNano.LAZY_INIT_LOCK) {\n"
+      "      if (!_classInitialized) {\n",
+      "classname", descriptor_->name());
+    printer->Indent();
+    printer->Indent();
+    printer->Indent();
+    printer->Indent();
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateInitSavedDefaultCode(printer);
+    }
+    printer->Outdent();
+    printer->Outdent();
+    printer->Outdent();
+    printer->Outdent();
+    printer->Print(
+      "        _classInitialized = true;\n"
+      "      }\n"
+      "    }\n"
+      "  }\n"
+      "  clear();\n"
+      "}\n");
+  } else {
+    printer->Print(
+      "\n"
+      "public $classname$() {\n"
+      "  clear();\n"
+      "}\n",
+      "classname", descriptor_->name());
   }
 
+  // Other methods in this class
+
   GenerateClear(printer);
 
   if (params_.generate_equals()) {