[wasm] Further reduce the size of WasmCode

Also, save dynamic allocations (plus their memory overhead).
This is realized by storing the relocation information, source position
table, and protected instruction information together in one "metadata"
byte array.
For each of the three components, we just store their size, such that
the accessors can return the respecitive {Vector} views as before.

This makes each WasmCode object 24 bytes smaller on 64-bit
architectures. It also saves a few more bytes per code object because
less padding is needed for the individual allocations, and each dynamic
allocation comes with some constant memory overhead.

Since the protected instructions will just be stored in a byte array
now, some APIs are refactored to just return that byte array directly
(instead of an array of {ProtectedInstructionData}). This also
simplifies serialization and deserialization, and will allow for
switching to a more compact representation in the future.

Drive-by: Add some more checks to {Vector::cast} to protect against
  undefined behaviour.

R=ahaas@chromium.org

Bug: v8:10254
Change-Id: I81ca847023841110e3e52cc402fcb0349325d7af
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2078545Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66596}

src/compiler/backend/code-generator.cc

@@ -432,10 +432,9 @@ OwnedVector<byte> CodeGenerator::GetSourcePositionTable() {
   return source_position_table_builder_.ToSourcePositionTableVector();
 }
 
-OwnedVector<trap_handler::ProtectedInstructionData>
-CodeGenerator::GetProtectedInstructions() {
-  return OwnedVector<trap_handler::ProtectedInstructionData>::Of(
-      protected_instructions_);
+OwnedVector<byte> CodeGenerator::GetProtectedInstructionsData() {
+  return OwnedVector<byte>::Of(
+      Vector<byte>::cast(VectorOf(protected_instructions_)));
 }
 
 MaybeHandle<Code> CodeGenerator::FinalizeCode() {

src/compiler/backend/code-generator.h

@@ -125,8 +125,7 @@ class V8_EXPORT_PRIVATE CodeGenerator final : public GapResolver::Assembler {
   MaybeHandle<Code> FinalizeCode();
 
   OwnedVector<byte> GetSourcePositionTable();
-  OwnedVector<trap_handler::ProtectedInstructionData>
-  GetProtectedInstructions();
+  OwnedVector<byte> GetProtectedInstructionsData();
 
   InstructionSequence* instructions() const { return instructions_; }
   FrameAccessState* frame_access_state() const { return frame_access_state_; }

src/compiler/pipeline.cc

@@ -2765,7 +2765,8 @@ wasm::WasmCompilationResult Pipeline::GenerateCodeForWasmNativeStub(
       static_cast<int>(code_generator->GetHandlerTableOffset()));
   result.instr_buffer = instruction_buffer->ReleaseBuffer();
   result.source_positions = code_generator->GetSourcePositionTable();
-  result.protected_instructions = code_generator->GetProtectedInstructions();
+  result.protected_instructions_data =
+      code_generator->GetProtectedInstructionsData();
   result.frame_slot_count = code_generator->frame()->GetTotalFrameSlotCount();
   result.tagged_parameter_slots = call_descriptor->GetTaggedParameterSlots();
   result.result_tier = wasm::ExecutionTier::kTurbofan;
@@ -2972,7 +2973,8 @@ void Pipeline::GenerateCodeForWasmFunction(
   result->frame_slot_count = code_generator->frame()->GetTotalFrameSlotCount();
   result->tagged_parameter_slots = call_descriptor->GetTaggedParameterSlots();
   result->source_positions = code_generator->GetSourcePositionTable();
-  result->protected_instructions = code_generator->GetProtectedInstructions();
+  result->protected_instructions_data =
+      code_generator->GetProtectedInstructionsData();
   result->result_tier = wasm::ExecutionTier::kTurbofan;
 
   if (data.info()->trace_turbo_json_enabled()) {

src/compiler/wasm-compiler.cc

@@ -6666,8 +6666,9 @@ wasm::WasmCode* CompileWasmCapiCallWrapper(wasm::WasmEngine* wasm_engine,
       WasmStubAssemblerOptions(), source_positions);
   std::unique_ptr<wasm::WasmCode> wasm_code = native_module->AddCode(
       wasm::kAnonymousFuncIndex, result.code_desc, result.frame_slot_count,
-      result.tagged_parameter_slots, std::move(result.protected_instructions),
-      std::move(result.source_positions), wasm::WasmCode::kWasmToCapiWrapper,
+      result.tagged_parameter_slots,
+      result.protected_instructions_data.as_vector(),
+      result.source_positions.as_vector(), wasm::WasmCode::kWasmToCapiWrapper,
       wasm::ExecutionTier::kNone);
   return native_module->PublishCode(std::move(wasm_code));
 }

src/utils/vector.h

@@ -9,6 +9,7 @@
 #include <cstring>
 #include <iterator>
 #include <memory>
+#include <type_traits>
 
 #include "src/common/checks.h"
 #include "src/common/globals.h"
@@ -116,6 +117,14 @@ class Vector {
 
   template <typename S>
   static constexpr Vector<T> cast(Vector<S> input) {
+    // Casting is potentially dangerous, so be really restrictive here. This
+    // might be lifted once we have use cases for that.
+    STATIC_ASSERT(std::is_pod<S>::value);
+    STATIC_ASSERT(std::is_pod<T>::value);
+#if V8_HAS_CXX14_CONSTEXPR
+    DCHECK_EQ(0, (input.length() * sizeof(S)) % sizeof(T));
+    DCHECK_EQ(0, reinterpret_cast<uintptr_t>(input.begin()) % alignof(T));
+#endif
     return Vector<T>(reinterpret_cast<T*>(input.begin()),
                      input.length() * sizeof(S) / sizeof(T));
   }

src/wasm/baseline/liftoff-compiler.cc

@@ -321,10 +321,9 @@ class LiftoffCompiler {
     return source_position_table_builder_.ToSourcePositionTableVector();
   }
 
-  OwnedVector<trap_handler::ProtectedInstructionData> GetProtectedInstructions()
-      const {
-    return OwnedVector<trap_handler::ProtectedInstructionData>::Of(
-        protected_instructions_);
+  OwnedVector<uint8_t> GetProtectedInstructionsData() const {
+    return OwnedVector<uint8_t>::Of(
+        Vector<const uint8_t>::cast(VectorOf(protected_instructions_)));
   }
 
   uint32_t GetTotalFrameSlotCount() const {
@@ -2796,7 +2795,7 @@ WasmCompilationResult ExecuteLiftoffCompilation(
   compiler->GetCode(&result.code_desc);
   result.instr_buffer = instruction_buffer->ReleaseBuffer();
   result.source_positions = compiler->GetSourcePositionTable();
-  result.protected_instructions = compiler->GetProtectedInstructions();
+  result.protected_instructions_data = compiler->GetProtectedInstructionsData();
   result.frame_slot_count = compiler->GetTotalFrameSlotCount();
   result.tagged_parameter_slots = call_descriptor->GetTaggedParameterSlots();
   result.func_index = func_index;

src/wasm/function-compiler.h

@@ -67,7 +67,7 @@ struct WasmCompilationResult {
   uint32_t frame_slot_count = 0;
   uint32_t tagged_parameter_slots = 0;
   OwnedVector<byte> source_positions;
-  OwnedVector<trap_handler::ProtectedInstructionData> protected_instructions;
+  OwnedVector<byte> protected_instructions_data;
   int func_index = kAnonymousFuncIndex;
   ExecutionTier requested_tier;
   ExecutionTier result_tier;

src/wasm/module-compiler.cc

@@ -2972,8 +2972,9 @@ WasmCode* CompileImportWrapper(
       wasm_engine, &env, kind, sig, source_positions);
   std::unique_ptr<WasmCode> wasm_code = native_module->AddCode(
       result.func_index, result.code_desc, result.frame_slot_count,
-      result.tagged_parameter_slots, std::move(result.protected_instructions),
-      std::move(result.source_positions), GetCodeKind(result),
+      result.tagged_parameter_slots,
+      result.protected_instructions_data.as_vector(),
+      result.source_positions.as_vector(), GetCodeKind(result),
       ExecutionTier::kNone);
   WasmCode* published_code = native_module->PublishCode(std::move(wasm_code));
   (*cache_scope)[key] = published_code;

src/wasm/wasm-code-manager.h

@@ -127,9 +127,12 @@ class V8_EXPORT_PRIVATE WasmCode final {
   Address instruction_start() const {
     return reinterpret_cast<Address>(instructions_.begin());
   }
-  Vector<const byte> reloc_info() const { return reloc_info_.as_vector(); }
+  Vector<const byte> reloc_info() const {
+    return {protected_instructions_data().end(),
+            static_cast<size_t>(reloc_info_size_)};
+  }
   Vector<const byte> source_positions() const {
-    return source_position_table_.as_vector();
+    return {reloc_info().end(), static_cast<size_t>(source_positions_size_)};
   }
 
   // TODO(clemensb): Make this return int.
@@ -160,9 +163,15 @@ class V8_EXPORT_PRIVATE WasmCode final {
            pc < reinterpret_cast<Address>(instructions_.end());
   }
 
-  Vector<trap_handler::ProtectedInstructionData> protected_instructions()
+  Vector<const uint8_t> protected_instructions_data() const {
+    return {meta_data_.get(),
+            static_cast<size_t>(protected_instructions_size_)};
+  }
+
+  Vector<const trap_handler::ProtectedInstructionData> protected_instructions()
       const {
-    return protected_instructions_.as_vector();
+    return Vector<const trap_handler::ProtectedInstructionData>::cast(
+        protected_instructions_data());
   }
 
   void Validate() const;
@@ -218,15 +227,17 @@ class V8_EXPORT_PRIVATE WasmCode final {
            int safepoint_table_offset, int handler_table_offset,
            int constant_pool_offset, int code_comments_offset,
            int unpadded_binary_size,
-           OwnedVector<trap_handler::ProtectedInstructionData>
-               protected_instructions,
-           OwnedVector<const byte> reloc_info,
-           OwnedVector<const byte> source_position_table, Kind kind,
+           Vector<const byte> protected_instructions_data,
+           Vector<const byte> reloc_info,
+           Vector<const byte> source_position_table, Kind kind,
            ExecutionTier tier)
       : instructions_(instructions),
-        reloc_info_(std::move(reloc_info)),
-        source_position_table_(std::move(source_position_table)),
         native_module_(native_module),
+        meta_data_(ConcatenateBytes(
+            {protected_instructions_data, reloc_info, source_position_table})),
+        reloc_info_size_(reloc_info.length()),
+        source_positions_size_(source_position_table.length()),
+        protected_instructions_size_(protected_instructions_data.length()),
         index_(index),
         kind_(kind),
         constant_pool_offset_(constant_pool_offset),
@@ -236,7 +247,6 @@ class V8_EXPORT_PRIVATE WasmCode final {
         handler_table_offset_(handler_table_offset),
         code_comments_offset_(code_comments_offset),
         unpadded_binary_size_(unpadded_binary_size),
-        protected_instructions_(std::move(protected_instructions)),
         tier_(tier) {
     DCHECK_LE(safepoint_table_offset, unpadded_binary_size);
     DCHECK_LE(handler_table_offset, unpadded_binary_size);
@@ -244,6 +254,9 @@ class V8_EXPORT_PRIVATE WasmCode final {
     DCHECK_LE(constant_pool_offset, unpadded_binary_size);
   }
 
+  std::unique_ptr<const byte[]> ConcatenateBytes(
+      std::initializer_list<Vector<const byte>>);
+
   // Code objects that have been registered with the global trap handler within
   // this process, will have a {trap_handler_index} associated with them.
   int trap_handler_index() const {
@@ -265,9 +278,16 @@ class V8_EXPORT_PRIVATE WasmCode final {
   V8_NOINLINE bool DecRefOnPotentiallyDeadCode();
 
   Vector<byte> instructions_;
-  OwnedVector<const byte> reloc_info_;
-  OwnedVector<const byte> source_position_table_;
   NativeModule* native_module_ = nullptr;
+  // {meta_data_} contains several byte vectors concatenated into one:
+  //  - protected instructions data of size {protected_instructions_size_}
+  //  - relocation info of size {reloc_info_size_}
+  //  - source positions of size {source_positions_size_}
+  // Note that the protected instructions come first to ensure alignment.
+  std::unique_ptr<const byte[]> meta_data_;
+  const int reloc_info_size_;
+  const int source_positions_size_;
+  const int protected_instructions_size_;
   int index_;
   Kind kind_;
   int constant_pool_offset_ = 0;
@@ -282,7 +302,6 @@ class V8_EXPORT_PRIVATE WasmCode final {
   int code_comments_offset_ = 0;
   int unpadded_binary_size_ = 0;
   int trap_handler_index_ = -1;
-  OwnedVector<trap_handler::ProtectedInstructionData> protected_instructions_;
   ExecutionTier tier_;
 
   // WasmCode is ref counted. Counters are held by:
@@ -304,7 +323,7 @@ class V8_EXPORT_PRIVATE WasmCode final {
 // often for rather small functions.
 // Increase the limit if needed, but first check if the size increase is
 // justified.
-STATIC_ASSERT(sizeof(WasmCode) <= 120);
+STATIC_ASSERT(sizeof(WasmCode) <= 96);
 
 WasmCode::Kind GetCodeKind(const WasmCompilationResult& result);
 
@@ -411,13 +430,11 @@ class V8_EXPORT_PRIVATE NativeModule final {
   // {AddCode} is thread safe w.r.t. other calls to {AddCode} or methods adding
   // code below, i.e. it can be called concurrently from background threads.
   // The returned code still needs to be published via {PublishCode}.
-  std::unique_ptr<WasmCode> AddCode(
-      int index, const CodeDesc& desc, int stack_slots,
-      int tagged_parameter_slots,
-      OwnedVector<trap_handler::ProtectedInstructionData>
-          protected_instructions,
-      OwnedVector<const byte> source_position_table, WasmCode::Kind kind,
-      ExecutionTier tier);
+  std::unique_ptr<WasmCode> AddCode(int index, const CodeDesc& desc,
+                                    int stack_slots, int tagged_parameter_slots,
+                                    Vector<const byte> protected_instructions,
+                                    Vector<const byte> source_position_table,
+                                    WasmCode::Kind kind, ExecutionTier tier);
 
   // {PublishCode} makes the code available to the system by entering it into
   // the code table and patching the jump table. It returns a raw pointer to the
@@ -431,11 +448,9 @@ class V8_EXPORT_PRIVATE NativeModule final {
       int tagged_parameter_slots, int safepoint_table_offset,
       int handler_table_offset, int constant_pool_offset,
       int code_comments_offset, int unpadded_binary_size,
-      OwnedVector<trap_handler::ProtectedInstructionData>
-          protected_instructions,
-      OwnedVector<const byte> reloc_info,
-      OwnedVector<const byte> source_position_table, WasmCode::Kind kind,
-      ExecutionTier tier);
+      Vector<const byte> protected_instructions_data,
+      Vector<const byte> reloc_info, Vector<const byte> source_position_table,
+      WasmCode::Kind kind, ExecutionTier tier);
 
   // Adds anonymous code for testing purposes.
   WasmCode* AddCodeForTesting(Handle<Code> code);
@@ -601,9 +616,8 @@ class V8_EXPORT_PRIVATE NativeModule final {
   std::unique_ptr<WasmCode> AddCodeWithCodeSpace(
       int index, const CodeDesc& desc, int stack_slots,
       int tagged_parameter_slots,
-      OwnedVector<trap_handler::ProtectedInstructionData>
-          protected_instructions,
-      OwnedVector<const byte> source_position_table, WasmCode::Kind kind,
+      Vector<const byte> protected_instructions_data,
+      Vector<const byte> source_position_table, WasmCode::Kind kind,
       ExecutionTier tier, Vector<uint8_t> code_space,
       const JumpTablesRef& jump_tables_ref);
 

src/wasm/wasm-debug.cc

@@ -900,8 +900,9 @@ void WasmDebugInfo::RedirectToInterpreter(Handle<WasmDebugInfo> debug_info,
         module->functions[func_index].sig);
     std::unique_ptr<wasm::WasmCode> wasm_code = native_module->AddCode(
         func_index, result.code_desc, result.frame_slot_count,
-        result.tagged_parameter_slots, std::move(result.protected_instructions),
-        std::move(result.source_positions), wasm::WasmCode::kInterpreterEntry,
+        result.tagged_parameter_slots,
+        result.protected_instructions_data.as_vector(),
+        result.source_positions.as_vector(), wasm::WasmCode::kInterpreterEntry,
         wasm::ExecutionTier::kInterpreter);
     native_module->PublishCode(std::move(wasm_code));
     DCHECK(native_module->IsRedirectedToInterpreter(func_index));

src/wasm/wasm-objects.cc

@@ -1460,8 +1460,9 @@ void WasmInstanceObject::ImportWasmJSFunctionIntoTable(
         isolate->wasm_engine(), &env, kind, sig, false);
     std::unique_ptr<wasm::WasmCode> wasm_code = native_module->AddCode(
         result.func_index, result.code_desc, result.frame_slot_count,
-        result.tagged_parameter_slots, std::move(result.protected_instructions),
-        std::move(result.source_positions), GetCodeKind(result),
+        result.tagged_parameter_slots,
+        result.protected_instructions_data.as_vector(),
+        result.source_positions.as_vector(), GetCodeKind(result),
         wasm::ExecutionTier::kNone);
     wasm::WasmCode* published_code =
         native_module->PublishCode(std::move(wasm_code));

src/wasm/wasm-serialization.cc

@@ -99,16 +99,17 @@ class Reader {
     return value;
   }
 
-  void ReadVector(Vector<byte> v) {
-    if (v.size() > 0) {
-      DCHECK_GE(current_size(), v.size());
-      memcpy(v.begin(), current_location(), v.size());
-      pos_ += v.size();
-    }
+  template <typename T>
+  Vector<const T> ReadVector(size_t size) {
+    DCHECK_GE(current_size(), size);
+    Vector<const byte> bytes{pos_, size * sizeof(T)};
+    pos_ += size * sizeof(T);
     if (FLAG_trace_wasm_serialization) {
-      StdoutStream{} << "read vector of " << v.size() << " elements"
+      StdoutStream{} << "read vector of " << size << " elements of size "
+                     << sizeof(T) << " (total size " << size * sizeof(T) << ")"
                      << std::endl;
     }
+    return Vector<const T>::cast(bytes);
   }
 
   void Skip(size_t size) { pos_ += size; }
@@ -304,8 +305,7 @@ size_t NativeModuleSerializer::MeasureCode(const WasmCode* code) const {
          code->kind() == WasmCode::kInterpreterEntry);
   return kCodeHeaderSize + code->instructions().size() +
          code->reloc_info().size() + code->source_positions().size() +
-         code->protected_instructions().size() *
-             sizeof(trap_handler::ProtectedInstructionData);
+         code->protected_instructions_data().size();
 }
 
 size_t NativeModuleSerializer::Measure() const {
@@ -343,7 +343,7 @@ void NativeModuleSerializer::WriteCode(const WasmCode* code, Writer* writer) {
   writer->Write(code->instructions().length());
   writer->Write(code->reloc_info().length());
   writer->Write(code->source_positions().length());
-  writer->Write(code->protected_instructions().length());
+  writer->Write(code->protected_instructions_data().length());
   writer->Write(code->kind());
   writer->Write(code->tier());
 
@@ -355,7 +355,7 @@ void NativeModuleSerializer::WriteCode(const WasmCode* code, Writer* writer) {
   // Write the reloc info, source positions, and protected code.
   writer->WriteVector(code->reloc_info());
   writer->WriteVector(code->source_positions());
-  writer->WriteVector(Vector<byte>::cast(code->protected_instructions()));
+  writer->WriteVector(code->protected_instructions_data());
 #if V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64 || V8_TARGET_ARCH_ARM || \
     V8_TARGET_ARCH_PPC || V8_TARGET_ARCH_PPC64 || V8_TARGET_ARCH_S390X
   // On platforms that don't support misaligned word stores, copy to an aligned
@@ -516,25 +516,17 @@ bool NativeModuleDeserializer::ReadCode(int fn_index, Reader* reader) {
   WasmCode::Kind kind = reader->Read<WasmCode::Kind>();
   ExecutionTier tier = reader->Read<ExecutionTier>();
 
-  Vector<const byte> code_buffer{reader->current_location(),
-                                 static_cast<size_t>(code_size)};
-  reader->Skip(code_size);
-
-  OwnedVector<byte> reloc_info = OwnedVector<byte>::New(reloc_size);
-  reader->ReadVector(reloc_info.as_vector());
-  OwnedVector<byte> source_pos = OwnedVector<byte>::New(source_position_size);
-  reader->ReadVector(source_pos.as_vector());
+  auto code_buffer = reader->ReadVector<byte>(code_size);
+  auto reloc_info = reader->ReadVector<byte>(reloc_size);
+  auto source_pos = reader->ReadVector<byte>(source_position_size);
   auto protected_instructions =
-      OwnedVector<trap_handler::ProtectedInstructionData>::New(
-          protected_instructions_size);
-  reader->ReadVector(Vector<byte>::cast(protected_instructions.as_vector()));
+      reader->ReadVector<byte>(protected_instructions_size);
 
   WasmCode* code = native_module_->AddDeserializedCode(
       fn_index, code_buffer, stack_slot_count, tagged_parameter_slots,
       safepoint_table_offset, handler_table_offset, constant_pool_offset,
-      code_comment_offset, unpadded_binary_size,
-      std::move(protected_instructions), std::move(reloc_info),
-      std::move(source_pos), kind, tier);
+      code_comment_offset, unpadded_binary_size, protected_instructions,
+      std::move(reloc_info), std::move(source_pos), kind, tier);
 
   // Relocate the code.
   int mask = RelocInfo::ModeMask(RelocInfo::WASM_CALL) |

test/cctest/wasm/test-run-wasm.cc

@@ -3753,9 +3753,9 @@ TEST(Liftoff_tier_up) {
     memcpy(buffer.get(), sub_code->instructions().begin(), sub_size);
     desc.buffer = buffer.get();
     desc.instr_size = static_cast<int>(sub_size);
-    std::unique_ptr<WasmCode> new_code = native_module->AddCode(
-        add.function_index(), desc, 0, 0, {}, OwnedVector<byte>(),
-        WasmCode::kFunction, ExecutionTier::kTurbofan);
+    std::unique_ptr<WasmCode> new_code =
+        native_module->AddCode(add.function_index(), desc, 0, 0, {}, {},
+                               WasmCode::kFunction, ExecutionTier::kTurbofan);
     native_module->PublishCode(std::move(new_code));
 
     // Second run should now execute {sub}.

test/cctest/wasm/wasm-run-utils.cc

@@ -144,8 +144,9 @@ uint32_t TestingModuleBuilder::AddFunction(const FunctionSig* sig,
         sig);
     std::unique_ptr<wasm::WasmCode> code = native_module_->AddCode(
         index, result.code_desc, result.frame_slot_count,
-        result.tagged_parameter_slots, std::move(result.protected_instructions),
-        std::move(result.source_positions), wasm::WasmCode::kInterpreterEntry,
+        result.tagged_parameter_slots,
+        result.protected_instructions_data.as_vector(),
+        result.source_positions.as_vector(), wasm::WasmCode::kInterpreterEntry,
         wasm::ExecutionTier::kInterpreter);
     native_module_->PublishCode(std::move(code));
   }