VM: Add infrastructure to support deferred generation of unoptimized code.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
===================================================================
--- runtime/vm/compiler.cc	(revision 44707)
+++ runtime/vm/compiler.cc	(working copy)
@@ -973,6 +973,7 @@
     TIMERSCOPE(isolate, time_compilation);
     Timer per_compile_timer(FLAG_trace_compiler, "Compilation time");
     per_compile_timer.Start();
+
     ParsedFunction* parsed_function = new(zone) ParsedFunction(
         thread, Function::ZoneHandle(zone, function.raw()));
     if (FLAG_trace_compiler) {
@@ -1052,6 +1053,33 @@
 }
 
 
+void Compiler::EnsureUnoptimizedCode(Thread* thread,
+                                     const Function& function) {
+  if (function.unoptimized_code() != Object::null()) {
+    return;
+  }
+  Code& original_code = Code::ZoneHandle();

[srdjan, 2015/04/02 17:43:40]

pass thread->zone() to it.

[Florian Schneider, 2015/04/07 09:07:57]

Done.

+  if (function.HasCode()) {
+    original_code = function.CurrentCode();
+  }
+  CompilationPipeline* pipeline =
+      CompilationPipeline::New(thread->zone(), function);
+  const Error& error = Error::Handle(
+      CompileFunctionHelper(pipeline, function, false, Isolate::kNoDeoptId));
+  if (!error.IsNull()) {
+    Exceptions::PropagateError(error);
+  }
+  if (!original_code.IsNull() &&

[Ivan Posva, 2015/04/02 17:14:00]

This logic here is really hard to follow. Please explain what the intent is here
in a comment.

[Florian Schneider, 2015/04/07 09:07:57]

Done.

+      (original_code.raw() != function.CurrentCode())) {
+    function.AttachCode(original_code);
+  }
+  ASSERT(function.unoptimized_code() != Object::null());
+  if (FLAG_trace_compiler) {
+    ISL_Print("Ensure unoptimized code for %s\n", function.ToCString());
+  }
+}
+
+
 RawError* Compiler::CompileOptimizedFunction(Thread* thread,
                                              const Function& function,
                                              intptr_t osr_id) {