Minor cleanups in Code::Kind

In preparation for adding new NCI (and TP) code kinds.

- Free the unused bit in Code::flags.
- Be more precise about the flag field sizes (int32 instead of int).
- Add and refactor related static asserts.

Bug: v8:8888
Change-Id: Ice0d4df9de528de77dfb5c04279cfdc4b030efc9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2328788
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69213}

src/objects/code-inl.h

@@ -346,6 +346,7 @@ void Code::CopyRelocInfoToByteArray(ByteArray dest, const CodeDesc& desc) {
 int Code::CodeSize() const { return SizeFor(body_size()); }
 
 Code::Kind Code::kind() const {
+  STATIC_ASSERT(FIELD_SIZE(kFlagsOffset) == kInt32Size);
   return KindField::decode(ReadField<uint32_t>(kFlagsOffset));
 }
 
@@ -353,12 +354,13 @@ void Code::initialize_flags(Kind kind, bool has_unwinding_info,
                             bool is_turbofanned, int stack_slots,
                             bool is_off_heap_trampoline) {
   CHECK(0 <= stack_slots && stack_slots < StackSlotsField::kMax);
-  static_assert(Code::NUMBER_OF_KINDS <= KindField::kMax + 1, "field overflow");
+  DCHECK_NE(kind, NUMBER_OF_KINDS);
   uint32_t flags = HasUnwindingInfoField::encode(has_unwinding_info) |
                    KindField::encode(kind) |
                    IsTurbofannedField::encode(is_turbofanned) |
                    StackSlotsField::encode(stack_slots) |
                    IsOffHeapTrampoline::encode(is_off_heap_trampoline);
+  STATIC_ASSERT(FIELD_SIZE(kFlagsOffset) == kInt32Size);
   WriteField<uint32_t>(kFlagsOffset, flags);
   DCHECK_IMPLIES(stack_slots != 0, has_safepoint_info());
 }
@@ -607,6 +609,8 @@ bool Code::IsExecutable() {
 
 // This field has to have relaxed atomic accessors because it is accessed in the
 // concurrent marker.
+STATIC_ASSERT(FIELD_SIZE(CodeDataContainer::kKindSpecificFlagsOffset) ==
+              kInt32Size);
 RELAXED_INT32_ACCESSORS(CodeDataContainer, kind_specific_flags,
                         kKindSpecificFlagsOffset)
 ACCESSORS(CodeDataContainer, next_code_link, Object, kNextCodeLinkOffset)

src/objects/code.cc

@@ -242,10 +242,9 @@ const char* Code::Kind2String(Kind kind) {
 
 // Identify kind of code.
 const char* AbstractCode::Kind2String(Kind kind) {
-  if (kind < AbstractCode::INTERPRETED_FUNCTION)
-    return Code::Kind2String(static_cast<Code::Kind>(kind));
+  DCHECK_NE(kind, AbstractCode::NUMBER_OF_KINDS);
   if (kind == AbstractCode::INTERPRETED_FUNCTION) return "INTERPRETED_FUNCTION";
-  UNREACHABLE();
+  return Code::Kind2String(static_cast<Code::Kind>(kind));
 }
 
 bool Code::IsIsolateIndependent(Isolate* isolate) {

src/objects/code.h

@@ -28,6 +28,47 @@ namespace interpreter {
 class Register;
 }
 
+// CodeDataContainer is a container for all mutable fields associated with its
+// referencing {Code} object. Since {Code} objects reside on write-protected
+// pages within the heap, its header fields need to be immutable. There always
+// is a 1-to-1 relation between {Code} and {CodeDataContainer}, the referencing
+// field {Code::code_data_container} itself is immutable.
+class CodeDataContainer : public HeapObject {
+ public:
+  NEVER_READ_ONLY_SPACE
+  DECL_ACCESSORS(next_code_link, Object)
+  DECL_INT_ACCESSORS(kind_specific_flags)
+
+  // Clear uninitialized padding space. This ensures that the snapshot content
+  // is deterministic.
+  inline void clear_padding();
+
+  DECL_CAST(CodeDataContainer)
+
+  // Dispatched behavior.
+  DECL_PRINTER(CodeDataContainer)
+  DECL_VERIFIER(CodeDataContainer)
+
+// Layout description.
+#define CODE_DATA_FIELDS(V)                                 \
+  /* Weak pointer fields. */                                \
+  V(kPointerFieldsStrongEndOffset, 0)                       \
+  V(kNextCodeLinkOffset, kTaggedSize)                       \
+  V(kPointerFieldsWeakEndOffset, 0)                         \
+  /* Raw data fields. */                                    \
+  V(kKindSpecificFlagsOffset, kInt32Size)                   \
+  V(kUnalignedSize, OBJECT_POINTER_PADDING(kUnalignedSize)) \
+  /* Total size. */                                         \
+  V(kSize, 0)
+
+  DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize, CODE_DATA_FIELDS)
+#undef CODE_DATA_FIELDS
+
+  class BodyDescriptor;
+
+  OBJECT_CONSTRUCTORS(CodeDataContainer, HeapObject);
+};
+
 // Code describes objects with on-the-fly generated machine code.
 class Code : public HeapObject {
  public:
@@ -36,6 +77,10 @@ class Code : public HeapObject {
   // cache state, and arguments count.
   using Flags = uint32_t;
 
+// TODO(jgruber,rmcilroy): Rename OPTIMIZED_FUNCTION once we've fully
+// disambiguated Turboprop, Turbofan, and NCI code kinds.
+// TODO(jgruber): Rename STUB to DEOPT_ENTRIES_OR_FOR_TESTING, or split it into
+// DEOPT_ENTRIES and FOR_TESTING, or convert DEOPT_ENTRIES into a builtin.
 #define CODE_KIND_LIST(V)  \
   V(OPTIMIZED_FUNCTION)    \
   V(BYTECODE_HANDLER)      \
@@ -401,7 +446,7 @@ class Code : public HeapObject {
   /* Objects embedded into code is visited via reloc info. */             \
   V(kDataStart, 0)                                                        \
   V(kInstructionSizeOffset, kIntSize)                                     \
-  V(kFlagsOffset, kIntSize)                                               \
+  V(kFlagsOffset, kInt32Size)                                             \
   V(kSafepointTableOffsetOffset, kIntSize)                                \
   V(kHandlerTableOffsetOffset, kIntSize)                                  \
   V(kConstantPoolOffsetOffset,                                            \
@@ -450,17 +495,18 @@ class Code : public HeapObject {
   // Flags layout.  base::BitField<type, shift, size>.
 #define CODE_FLAGS_BIT_FIELDS(V, _)    \
   V(HasUnwindingInfoField, bool, 1, _) \
-  V(KindField, Kind, 5, _)             \
+  V(KindField, Kind, 4, _)             \
   V(IsTurbofannedField, bool, 1, _)    \
   V(StackSlotsField, int, 24, _)       \
   V(IsOffHeapTrampoline, bool, 1, _)
   DEFINE_BIT_FIELDS(CODE_FLAGS_BIT_FIELDS)
 #undef CODE_FLAGS_BIT_FIELDS
-  static_assert(NUMBER_OF_KINDS <= KindField::kMax, "Code::KindField size");
-  static_assert(IsOffHeapTrampoline::kLastUsedBit < 32,
-                "Code::flags field exhausted");
+  STATIC_ASSERT(NUMBER_OF_KINDS <= KindField::kMax);
+  STATIC_ASSERT(CODE_FLAGS_BIT_FIELDS_Ranges::kBitsCount == 31);
+  STATIC_ASSERT(CODE_FLAGS_BIT_FIELDS_Ranges::kBitsCount <=
+                FIELD_SIZE(kFlagsOffset) * kBitsPerByte);
 
-  // KindSpecificFlags layout (STUB, BUILTIN and OPTIMIZED_FUNCTION)
+  // KindSpecificFlags layout (STUB, BUILTIN, and OPTIMIZED_FUNCTION).
 #define CODE_KIND_SPECIFIC_FLAGS_BIT_FIELDS(V, _) \
   V(MarkedForDeoptimizationField, bool, 1, _)     \
   V(EmbeddedObjectsClearedField, bool, 1, _)      \
@@ -471,7 +517,10 @@ class Code : public HeapObject {
   V(DeoptCountField, int, 4, _)
   DEFINE_BIT_FIELDS(CODE_KIND_SPECIFIC_FLAGS_BIT_FIELDS)
 #undef CODE_KIND_SPECIFIC_FLAGS_BIT_FIELDS
-  static_assert(DeoptCountField::kLastUsedBit < 32, "KindSpecificFlags full");
+  STATIC_ASSERT(CODE_KIND_SPECIFIC_FLAGS_BIT_FIELDS_Ranges::kBitsCount == 10);
+  STATIC_ASSERT(CODE_KIND_SPECIFIC_FLAGS_BIT_FIELDS_Ranges::kBitsCount <=
+                FIELD_SIZE(CodeDataContainer::kKindSpecificFlagsOffset) *
+                    kBitsPerByte);
 
   // The {marked_for_deoptimization} field is accessed from generated code.
   static const int kMarkedForDeoptimizationBit =
@@ -504,47 +553,6 @@ class Code::OptimizedCodeIterator {
   DISALLOW_COPY_AND_ASSIGN(OptimizedCodeIterator);
 };
 
-// CodeDataContainer is a container for all mutable fields associated with its
-// referencing {Code} object. Since {Code} objects reside on write-protected
-// pages within the heap, its header fields need to be immutable. There always
-// is a 1-to-1 relation between {Code} and {CodeDataContainer}, the referencing
-// field {Code::code_data_container} itself is immutable.
-class CodeDataContainer : public HeapObject {
- public:
-  NEVER_READ_ONLY_SPACE
-  DECL_ACCESSORS(next_code_link, Object)
-  DECL_INT_ACCESSORS(kind_specific_flags)
-
-  // Clear uninitialized padding space. This ensures that the snapshot content
-  // is deterministic.
-  inline void clear_padding();
-
-  DECL_CAST(CodeDataContainer)
-
-  // Dispatched behavior.
-  DECL_PRINTER(CodeDataContainer)
-  DECL_VERIFIER(CodeDataContainer)
-
-// Layout description.
-#define CODE_DATA_FIELDS(V)                                 \
-  /* Weak pointer fields. */                                \
-  V(kPointerFieldsStrongEndOffset, 0)                       \
-  V(kNextCodeLinkOffset, kTaggedSize)                       \
-  V(kPointerFieldsWeakEndOffset, 0)                         \
-  /* Raw data fields. */                                    \
-  V(kKindSpecificFlagsOffset, kIntSize)                     \
-  V(kUnalignedSize, OBJECT_POINTER_PADDING(kUnalignedSize)) \
-  /* Total size. */                                         \
-  V(kSize, 0)
-
-  DEFINE_FIELD_OFFSET_CONSTANTS(HeapObject::kHeaderSize, CODE_DATA_FIELDS)
-#undef CODE_DATA_FIELDS
-
-  class BodyDescriptor;
-
-  OBJECT_CONSTRUCTORS(CodeDataContainer, HeapObject);
-};
-
 class AbstractCode : public HeapObject {
  public:
   NEVER_READ_ONLY_SPACE