Remove redundant variable descriptors from optimized code.

runtime/vm/debugger.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/debugger.h"
 
 #include "include/dart_api.h"
 
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 442 matching lines @@
     } else {
       column_number_ = -1;
     }
   }
   return column_number_;
 }
 
 
 void ActivationFrame::GetVarDescriptors() {
   if (var_descriptors_.IsNull()) {
-    var_descriptors_ = code().var_descriptors();
+    if (code().is_optimized()) {
+      Compiler::EnsureUnoptimizedCode(Thread::Current(), function());
+    }
+    var_descriptors_ = code().is_optimized()
+        ? Code::Handle(function().unoptimized_code()).var_descriptors()
+        : code().var_descriptors();

[srdjan, 2015/04/15 16:25:45]

Could this be just :
var_descriptors = Code::Handle(function().unoptimized_code()).var_descriptors(),
no need to check if code is optimized. 

We could store var_descriptors into function instead of unoptimized-code, but
that would mean larger footprint (var_descriptors alive as long as function is).

[Florian Schneider, 2015/04/16 11:37:18]

Yes. I'll simplify it.

I think it is fine to have it on unoptimized code. And since they are only
needed for variable inspection, normal stack traces should not be affected
performance-wise.

     ASSERT(!var_descriptors_.IsNull());
   }
 }
 
 
 bool ActivationFrame::IsDebuggable() const {
   return Debugger::IsDebuggable(function());
 }
 
 
@@ skipping 173 matching lines @@
   }
   vars_initialized_ = true;
 }
 
 
 intptr_t ActivationFrame::NumLocalVariables() {
   GetDescIndices();
   return desc_indices_.length();
 }
 
-// TODO(hausner): Handle captured variables.
+
 RawObject* ActivationFrame::GetLocalVar(intptr_t slot_index) {
   if (deopt_frame_.IsNull()) {
     uword var_address = fp() + slot_index * kWordSize;
     return reinterpret_cast<RawObject*>(
         *reinterpret_cast<uword*>(var_address));
   } else {
     return deopt_frame_.At(deopt_frame_offset_ + slot_index);
   }
 }
 
@@ skipping 1968 matching lines @@
 }
 
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 }  // namespace dart