Implemented function that returns code age.

src/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 984 matching lines @@
   JSFunction* next_candidate;
   while (candidate != NULL) {
     next_candidate = GetNextCandidate(candidate);
     ClearNextCandidate(candidate, undefined);
 
     SharedFunctionInfo* shared = candidate->shared();
 
     Code* code = shared->code();
     MarkBit code_mark = Marking::MarkBitFrom(code);
     if (!code_mark.Get()) {
+      ASSERT(!FLAG_age_code || code->GetAge() >= Code::kSexagenarianCodeAge);

[Michael Starzinger, 2013/06/12 09:09:32]

I don't think this assert is entirely correct, if there are two closures
enqueued as flushing candidates then the first one will already have cleared the
SharedFunctionInfo, the second one already has cleared code. Sure, the
LazyRecompileStub should always be marked, but still, this assert seems mighty
weird and confuses more than it helps. Asserts should clarify the code an make
it safer, not make it harder to understand.

How about we move this assert outside the if, and rephrase is slightly to a more
general form ...

ASSERT(!FLAG_arg_code || !candidate->is_compiled() || code->GetAge() >= 3);

[Michael Starzinger, 2013/06/12 09:12:17]

Sorry, should have been ...

ASSERT(!FLAG_age_code || !candidate->is_compiled() ||
candidate->code()->GetAge() >= 3);

       if (FLAG_trace_code_flushing && shared->is_compiled()) {
         SmartArrayPointer<char> name = shared->DebugName()->ToCString();
         PrintF("[code-flushing clears: %s]\n", *name);
       }
       shared->set_code(lazy_compile);
       candidate->set_code(lazy_compile);
     } else {
       candidate->set_code(code);
     }
 
@@ skipping 21 matching lines @@
 
   SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
   SharedFunctionInfo* next_candidate;
   while (candidate != NULL) {
     next_candidate = GetNextCandidate(candidate);
     ClearNextCandidate(candidate);
 
     Code* code = candidate->code();
     MarkBit code_mark = Marking::MarkBitFrom(code);
     if (!code_mark.Get()) {
+      ASSERT(!FLAG_age_code || code->GetAge() >= Code::kSexagenarianCodeAge);

[danno, 2013/06/12 09:08:13]

Perhaps add a constant for Code::kOldCodeAge that is a copy of
Code::kSexagenarianCodeAge so that all usages are consistent and named?

[Michael Starzinger, 2013/06/12 09:09:32]

Likewise.

       if (FLAG_trace_code_flushing && candidate->is_compiled()) {
         SmartArrayPointer<char> name = candidate->DebugName()->ToCString();
         PrintF("[code-flushing clears: %s]\n", *name);
       }
       candidate->set_code(lazy_compile);
     }
 
     Object** code_slot =
         HeapObject::RawField(candidate, SharedFunctionInfo::kCodeOffset);
     isolate_->heap()->mark_compact_collector()->
@@ skipping 3209 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal