Revert "Remove Code::active_instructions_."

This reverts commit 714027a81b.

Review URL: https://codereview.chromium.org/1821793002 .

runtime/vm/object.cc

@@ -13509,10 +13509,9 @@ bool Code::IsFunctionCode() const {
 void Code::DisableDartCode() const {
   DEBUG_ASSERT(IsMutatorOrAtSafepoint());
   ASSERT(IsFunctionCode());
-  ASSERT(!IsDisabled());
+  ASSERT(instructions() == active_instructions());
   const Code& new_code =
       Code::Handle(StubCode::FixCallersTarget_entry()->code());
-  ASSERT(new_code.instructions()->IsVMHeapObject());
   SetActiveInstructions(new_code.instructions());
 }
 
@@ -13520,10 +13519,9 @@ void Code::DisableDartCode() const {
 void Code::DisableStubCode() const {
   ASSERT(Thread::Current()->IsMutatorThread());
   ASSERT(IsAllocationStubCode());
-  ASSERT(!IsDisabled());
+  ASSERT(instructions() == active_instructions());
   const Code& new_code =
       Code::Handle(StubCode::FixAllocationStubTarget_entry()->code());
-  ASSERT(new_code.instructions()->IsVMHeapObject());
   SetActiveInstructions(new_code.instructions());
 }
 
@@ -13532,6 +13530,7 @@ void Code::SetActiveInstructions(RawInstructions* instructions) const {
   DEBUG_ASSERT(IsMutatorOrAtSafepoint() || !is_alive());
   // RawInstructions are never allocated in New space and hence a
   // store buffer update is not needed here.
+  StorePointer(&raw_ptr()->active_instructions_, instructions);
   StoreNonPointer(&raw_ptr()->entry_point_,
                   reinterpret_cast<uword>(instructions->ptr()) +
                   Instructions::HeaderSize());

runtime/vm/object.h

@@ -4324,7 +4324,9 @@ class DeoptInfo : public AllStatic {
 
 class Code : public Object {
  public:
-  uword active_entry_point() const { return raw_ptr()->entry_point_; }
+  RawInstructions* active_instructions() const {
+    return raw_ptr()->active_instructions_;
+  }
 
   RawInstructions* instructions() const { return raw_ptr()->instructions_; }
 
@@ -4606,11 +4608,12 @@ class Code : public Object {
   void Enable() const {
     if (!IsDisabled()) return;
     ASSERT(Thread::Current()->IsMutatorThread());
+    ASSERT(instructions() != active_instructions());
     SetActiveInstructions(instructions());
   }
 
   bool IsDisabled() const {
-    return active_entry_point() != EntryPoint();
+    return instructions() != active_instructions();
   }
 
  private:

runtime/vm/raw_object.cc

@@ -542,11 +542,8 @@ intptr_t RawCode::VisitCodePointers(RawCode* raw_obj,
 
   RawCode* obj = raw_obj->ptr();
   intptr_t length = Code::PtrOffBits::decode(obj->state_bits_);
-#if defined(TARGET_ARCH_IA32)
-  // On IA32 only we embed pointers to objects directly in the generated
-  // instructions. The variable porition of a Code object describes where to
-  // find those pointers for tracing.
   if (Code::AliveBit::decode(obj->state_bits_)) {
+    // Also visit all the embedded pointers in the corresponding instructions.
     uword entry_point = reinterpret_cast<uword>(obj->instructions_->ptr()) +
         Instructions::HeaderSize();
     for (intptr_t i = 0; i < length; i++) {
@@ -556,12 +553,6 @@ intptr_t RawCode::VisitCodePointers(RawCode* raw_obj,
     }
   }
   return Code::InstanceSize(length);
-#else
-  // On all other architectures, objects are referenced indirectly through
-  // either the ObjectPool or Thread.
-  ASSERT(length == 0);
-  return Code::InstanceSize(0);
-#endif
 }
 
 

runtime/vm/raw_object.h

@@ -1080,8 +1080,9 @@ class RawCode : public RawObject {
   uword entry_point_;
 
   RawObject** from() {
-    return reinterpret_cast<RawObject**>(&ptr()->instructions_);
+    return reinterpret_cast<RawObject**>(&ptr()->active_instructions_);
   }
+  RawInstructions* active_instructions_;
   RawInstructions* instructions_;
   RawObjectPool* object_pool_;
   // If owner_ is Function::null() the owner is a regular stub.