commit d15d49b09dc7aef9edcc4cf6a0cb2b77a0db203f

Author: Nico Weber <thakis@chromium.org>

Date:   2022-07-29 20:07:40 -0400

    Make bitfields only as wide as necessary for enums

    clang now complains when a BitField for an enum is too wide.

    We could suppress this, but it seems kind of useful from an

    uninformed distance, so I made a few bitfields smaller instead.

    (For AddressingMode, since its size is target-dependent, I added

    an explicit underlying type to the enum instead, which suppresses

    the diag on a per-enum basis.)

    This is without any understanding of the code I'm touching.

    Especially the change in v8-internal.h feels a bit risky to me.

    Bug: chromium:1348574

    Change-Id: I73395de593045036b72dadf4e3147b5f7e13c958

    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3794708

    Commit-Queue: Nico Weber <thakis@chromium.org>

    Reviewed-by: Leszek Swirski <leszeks@chromium.org>

    Reviewed-by: Hannes Payer <hpayer@chromium.org>

    Auto-Submit: Nico Weber <thakis@chromium.org>

    Cr-Commit-Position: refs/heads/main@{#82109}

--- deps/v8/include/v8-internal.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/include/v8-internal.h

@@ -253,7 +253,7 @@ class Internals {

   static const int kNodeClassIdOffset = 1 * kApiSystemPointerSize;

   static const int kNodeFlagsOffset = 1 * kApiSystemPointerSize + 3;

-  static const int kNodeStateMask = 0x7;

+  static const int kNodeStateMask = 0x3;

   static const int kNodeStateIsWeakValue = 2;

   static const int kNodeStateIsPendingValue = 3;

--- deps/v8/src/ast/ast.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/ast/ast.h

@@ -998,7 +998,7 @@ class Literal final : public Expression {

   friend class AstNodeFactory;

   friend Zone;

-  using TypeField = Expression::NextBitField<Type, 4>;

+  using TypeField = Expression::NextBitField<Type, 3>;

   Literal(int smi, int position) : Expression(position, kLiteral), smi_(smi) {

     bit_field_ = TypeField::update(bit_field_, kSmi);

--- deps/v8/src/base/bit-field.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/base/bit-field.h

@@ -40,6 +40,11 @@ class BitField final {

   static constexpr U kNumValues = U{1} << kSize;

   // Value for the field with all bits set.

+  // If clang complains

+  // "constexpr variable 'kMax' must be initialized by a constant expression"

+  // on this line, then you're creating a BitField for an enum with more bits

+  // than needed for the enum values. Either reduce the BitField size,

+  // or give the enum an explicit underlying type.

   static constexpr T kMax = static_cast<T>(kNumValues - 1);

   template <class T2, int size2>

--- deps/v8/src/compiler/backend/instruction-codes.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/compiler/backend/instruction-codes.h

@@ -191,7 +191,7 @@ V8_EXPORT_PRIVATE std::ostream& operator<<(std::ostrea

   V(None)                       \

   TARGET_ADDRESSING_MODE_LIST(V)

-enum AddressingMode {

+enum AddressingMode : uint8_t {

 #define DECLARE_ADDRESSING_MODE(Name) kMode_##Name,

   ADDRESSING_MODE_LIST(DECLARE_ADDRESSING_MODE)

 #undef DECLARE_ADDRESSING_MODE

@@ -282,7 +282,7 @@ using LaneSizeField = base::BitField<int, 22, 8>;

 // LaneSizeField and AccessModeField are helper types to encode/decode a lane

 // size, an access mode, or both inside the overlapping MiscField.

 using LaneSizeField = base::BitField<int, 22, 8>;

-using AccessModeField = base::BitField<MemoryAccessMode, 30, 2>;

+using AccessModeField = base::BitField<MemoryAccessMode, 30, 1>;

 using MiscField = base::BitField<int, 22, 10>;

 }  // namespace compiler

--- deps/v8/src/compiler/backend/instruction.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/compiler/backend/instruction.h

@@ -584,8 +584,8 @@ class LocationOperand : public InstructionOperand {

   }

   STATIC_ASSERT(KindField::kSize == 3);

-  using LocationKindField = base::BitField64<LocationKind, 3, 2>;

-  using RepresentationField = base::BitField64<MachineRepresentation, 5, 8>;

+  using LocationKindField = base::BitField64<LocationKind, 3, 1>;

+  using RepresentationField = LocationKindField::Next<MachineRepresentation, 8>;

   using IndexField = base::BitField64<int32_t, 35, 29>;

 };

--- deps/v8/src/handles/global-handles.cc.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/handles/global-handles.cc

@@ -618,7 +618,7 @@ class GlobalHandles::Node final : public NodeBase<Glob

   // This stores three flags (independent, partially_dependent and

   // in_young_list) and a State.

-  using NodeState = base::BitField8<State, 0, 3>;

+  using NodeState = base::BitField8<State, 0, 2>;

   using IsInYoungList = NodeState::Next<bool, 1>;

   using NodeWeaknessType = IsInYoungList::Next<WeaknessType, 2>;

--- deps/v8/src/profiler/profile-generator.h.orig	2023-03-28 23:14:19 UTC

+++ deps/v8/src/profiler/profile-generator.h

@@ -224,7 +224,7 @@ class CodeEntry {

     return ref_count_;

   }

-  using TagField = base::BitField<CodeEventListener::LogEventsAndTags, 0, 8>;

+  using TagField = base::BitField<CodeEventListener::LogEventsAndTags, 0, 5>;

   using BuiltinField = base::BitField<Builtin, 8, 20>;

   static_assert(Builtins::kBuiltinCount <= BuiltinField::kNumValues,

                 "builtin_count exceeds size of bitfield");

--- deps/v8/src/wasm/wasm-code-manager.h.orig	2023-03-28 21:14:19 UTC

+++ deps/v8/src/wasm/wasm-code-manager.h

@@ -440,7 +440,7 @@ class V8_EXPORT_PRIVATE WasmCode final {

   int trap_handler_index_ = -1;

   // Bits encoded in {flags_}:

-  using KindField = base::BitField8<Kind, 0, 3>;

+  using KindField = base::BitField8<Kind, 0, 2>;

   using ExecutionTierField = KindField::Next<ExecutionTier, 2>;

   using ForDebuggingField = ExecutionTierField::Next<ForDebugging, 2>;