[interpreter] Add OSR nesting level to bytecode header.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 1ef9703be013bb7790d1c1f494bb60ad0ea52e53..55b47394e572d94f070742be8e120f102cdf3725 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -4517,6 +4517,10 @@ class BytecodeArray : public FixedArrayBase {
   inline int interrupt_budget() const;
   inline void set_interrupt_budget(int interrupt_budget);
 
+  // Accessors for OSR loop nesting level.
+  inline int osr_loop_nesting_level() const;
+  inline void set_osr_loop_nesting_level(int depth);
+
   // Accessors for the constant pool.
   DECL_ACCESSORS(constant_pool, FixedArray)
 
@@ -4556,7 +4560,10 @@ class BytecodeArray : public FixedArrayBase {
   static const int kFrameSizeOffset = kSourcePositionTableOffset + kPointerSize;
   static const int kParameterSizeOffset = kFrameSizeOffset + kIntSize;
   static const int kInterruptBudgetOffset = kParameterSizeOffset + kIntSize;
-  static const int kHeaderSize = kInterruptBudgetOffset + kIntSize;
+  // TODO(4764): The OSR nesting level is guaranteed to be in [0;6] bounds and
+  // could potentially be merged with another field (e.g. parameter_size).
+  static const int kOSRNestingLevelOffset = kInterruptBudgetOffset + kIntSize;
+  static const int kHeaderSize = kOSRNestingLevelOffset + kIntSize;
 
   // Maximal memory consumption for a single BytecodeArray.
   static const int kMaxSize = 512 * MB;
@@ -5358,10 +5365,6 @@ class Code: public HeapObject {
   static Handle<WeakCell> WeakCellFor(Handle<Code> code);
   WeakCell* CachedWeakCell();
 
-  // Max loop nesting marker used to postpose OSR. We don't take loop
-  // nesting that is deeper than 5 levels into account.
-  static const int kMaxLoopNestingMarker = 6;
-
   static const int kConstantPoolSize =
       FLAG_enable_embedded_constant_pool ? kIntSize : 0;
 
@@ -5465,7 +5468,6 @@ class Code: public HeapObject {
       kIsCrankshaftedBit + 1, 27> {};  // NOLINT
   class AllowOSRAtLoopNestingLevelField: public BitField<int,
       kIsCrankshaftedBit + 1 + 27, 4> {};  // NOLINT
-  STATIC_ASSERT(AllowOSRAtLoopNestingLevelField::kMax >= kMaxLoopNestingMarker);
 
   static const int kArgumentsBits = 16;
   static const int kMaxArguments = (1 << kArgumentsBits) - 1;
@@ -5537,6 +5539,12 @@ class AbstractCode : public HeapObject {
   DECLARE_CAST(AbstractCode)
   inline Code* GetCode();
   inline BytecodeArray* GetBytecodeArray();
+
+  // Max loop nesting marker used to postpose OSR. We don't take loop
+  // nesting that is deeper than 5 levels into account.
+  static const int kMaxLoopNestingMarker = 6;
+  STATIC_ASSERT(Code::AllowOSRAtLoopNestingLevelField::kMax >=
+                kMaxLoopNestingMarker);
 };
 
 // Dependent code is a singly linked list of fixed arrays. Each array contains