Extend assembler with ability to produce comments for the generated code.

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
diff --git a/runtime/vm/assembler_x64.cc b/runtime/vm/assembler_x64.cc
index b2c6614bccc291bc2134a57a246f992f0878f091..2d98b949e0e3d1a94698e54f93044c49bd64e703 100644
--- a/runtime/vm/assembler_x64.cc
+++ b/runtime/vm/assembler_x64.cc
@@ -14,6 +14,7 @@
 namespace dart {
 
 DEFINE_FLAG(bool, print_stop_message, true, "Print stop message.");
+DEFINE_FLAG(bool, code_comments, false, "Include comments into disassembly");
 
 
 void Assembler::InitializeMemoryWithBreakpoints(uword data, int length) {
@@ -1516,6 +1517,34 @@ void Assembler::EmitGenericShift(bool wide,
   EmitOperand(rm, Operand(operand));
 }
 
+
+void Assembler::Comment(const char* format, ...) {
+  if (FLAG_code_comments) {
+    char buffer[1024];
+
+    va_list args;
+    va_start(args, format);
+    OS::VSNPrint(buffer, sizeof(buffer), format, args);
+    va_end(args);
+
+    comments_.Add(new CodeComment(buffer_.GetPosition(),
+                                  String::Handle(String::New(buffer))));
+  }
+}
+
+
+CodeComments Assembler::GetComments() {
+  CodeComments comments = CodeComments::New(comments_.length());
+
+  for (int i = 0; i < comments_.length(); i++) {
+    comments.SetPCAt(i, comments_[i]->pc());
+    comments.SetCommentAt(i, comments_[i]->comment());
+  }
+
+  return comments;
+}
+
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64