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diff --git a/js/src/wasm/WasmModule.h b/js/src/wasm/WasmModule.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Copyright 2015 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_module_h
+#define wasm_module_h
+
+#include "js/WasmModule.h"
+#include "js/BuildId.h"
+
+#include "wasm/WasmCode.h"
+#include "wasm/WasmException.h"
+#include "wasm/WasmJS.h"
+#include "wasm/WasmSerialize.h"
+#include "wasm/WasmTable.h"
+
+namespace JS {
+class OptimizedEncodingListener;
+}
+
+namespace js {
+namespace wasm {
+
+struct CompileArgs;
+
+// In the context of wasm, the OptimizedEncodingListener specifically is
+// listening for the completion of tier-2.
+
+using Tier2Listener = RefPtr<JS::OptimizedEncodingListener>;
+
+// A struct containing the typed, imported values that are harvested from the
+// import object and passed to Module::instantiate(). This struct must be
+// stored in a (Persistent)Rooted, not in the heap due to its use of TraceRoot()
+// and complete lack of barriers.
+
+struct ImportValues {
+  JSObjectVector funcs;
+  WasmTableObjectVector tables;
+  WasmMemoryObject* memory;
+  WasmTagObjectVector tagObjs;
+  WasmGlobalObjectVector globalObjs;
+  ValVector globalValues;
+
+  ImportValues() : memory(nullptr) {}
+
+  void trace(JSTracer* trc) {
+    funcs.trace(trc);
+    tables.trace(trc);
+    if (memory) {
+      TraceRoot(trc, &memory, "import values memory");
+    }
+    tagObjs.trace(trc);
+    globalObjs.trace(trc);
+    globalValues.trace(trc);
+  }
+};
+
+// Module represents a compiled wasm module and primarily provides three
+// operations: instantiation, tiered compilation, serialization. A Module can be
+// instantiated any number of times to produce new Instance objects. A Module
+// can have a single tier-2 task initiated to augment a Module's code with a
+// higher tier. A Module can have its optimized code serialized at any point
+// where the LinkData is also available, which is primarily (1) at the end of
+// module generation, (2) at the end of tier-2 compilation.
+//
+// Fully linked-and-instantiated code (represented by SharedCode and its owned
+// ModuleSegment) can be shared between instances.
+
+class Module : public JS::WasmModule {
+  const SharedCode code_;
+  const ImportVector imports_;
+  const ExportVector exports_;
+  const DataSegmentVector dataSegments_;
+  const ElemSegmentVector elemSegments_;
+  const CustomSectionVector customSections_;
+
+  // This field is only meaningful when code_->metadata().debugEnabled.
+
+  const SharedBytes debugBytecode_;
+
+  // This field is set during tier-2 compilation and cleared on success or
+  // failure. These happen on different threads and are serialized by the
+  // control flow of helper tasks.
+
+  mutable Tier2Listener tier2Listener_;
+
+  // This flag is used for logging (and testing) purposes to indicate
+  // whether the module was deserialized (from a cache).
+
+  const bool loggingDeserialized_;
+
+  // This flag is only used for testing purposes and is cleared on success or
+  // failure. The field is racily polled from various threads.
+
+  mutable Atomic<bool> testingTier2Active_;
+
+  // Cached malloc allocation size for GC memory tracking.
+
+  size_t gcMallocBytesExcludingCode_;
+
+  bool instantiateFunctions(JSContext* cx,
+                            const JSObjectVector& funcImports) const;
+  bool instantiateMemory(JSContext* cx,
+                         MutableHandle<WasmMemoryObject*> memory) const;
+  bool instantiateTags(JSContext* cx, WasmTagObjectVector& tagObjs) const;
+  bool instantiateImportedTable(JSContext* cx, const TableDesc& td,
+                                Handle<WasmTableObject*> table,
+                                WasmTableObjectVector* tableObjs,
+                                SharedTableVector* tables) const;
+  bool instantiateLocalTable(JSContext* cx, const TableDesc& td,
+                             WasmTableObjectVector* tableObjs,
+                             SharedTableVector* tables) const;
+  bool instantiateTables(JSContext* cx,
+                         const WasmTableObjectVector& tableImports,
+                         MutableHandle<WasmTableObjectVector> tableObjs,
+                         SharedTableVector* tables) const;
+  bool instantiateGlobals(JSContext* cx, const ValVector& globalImportValues,
+                          WasmGlobalObjectVector& globalObjs) const;
+  bool initSegments(JSContext* cx, Handle<WasmInstanceObject*> instance,
+                    Handle<WasmMemoryObject*> memory) const;
+
+  class Tier2GeneratorTaskImpl;
+
+ public:
+  Module(const Code& code, ImportVector&& imports, ExportVector&& exports,
+         DataSegmentVector&& dataSegments, ElemSegmentVector&& elemSegments,
+         CustomSectionVector&& customSections,
+         const ShareableBytes* debugBytecode = nullptr,
+         bool loggingDeserialized = false)
+      : code_(&code),
+        imports_(std::move(imports)),
+        exports_(std::move(exports)),
+        dataSegments_(std::move(dataSegments)),
+        elemSegments_(std::move(elemSegments)),
+        customSections_(std::move(customSections)),
+        debugBytecode_(debugBytecode),
+        loggingDeserialized_(loggingDeserialized),
+        testingTier2Active_(false) {
+    initGCMallocBytesExcludingCode();
+  }
+  ~Module() override;
+
+  const Code& code() const { return *code_; }
+  const ModuleSegment& moduleSegment(Tier t) const { return code_->segment(t); }
+  const Metadata& metadata() const { return code_->metadata(); }
+  const MetadataTier& metadata(Tier t) const { return code_->metadata(t); }
+  const ImportVector& imports() const { return imports_; }
+  const ExportVector& exports() const { return exports_; }
+  const CustomSectionVector& customSections() const { return customSections_; }
+  const Bytes& debugBytecode() const { return debugBytecode_->bytes; }
+  uint32_t codeLength(Tier t) const { return code_->segment(t).length(); }
+
+  // Instantiate this module with the given imports:
+
+  bool instantiate(JSContext* cx, ImportValues& imports,
+                   HandleObject instanceProto,
+                   MutableHandle<WasmInstanceObject*> instanceObj) const;
+
+  // Tier-2 compilation may be initiated after the Module is constructed at
+  // most once. When tier-2 compilation completes, ModuleGenerator calls
+  // finishTier2() from a helper thread, passing tier-variant data which will
+  // be installed and made visible.
+
+  void startTier2(const CompileArgs& args, const ShareableBytes& bytecode,
+                  JS::OptimizedEncodingListener* listener);
+  bool finishTier2(const LinkData& linkData2, UniqueCodeTier code2) const;
+
+  void testingBlockOnTier2Complete() const;
+  bool testingTier2Active() const { return testingTier2Active_; }
+
+  // Code caching support.
+
+  [[nodiscard]] bool serialize(const LinkData& linkData, Bytes* bytes) const;
+  static RefPtr<Module> deserialize(const uint8_t* begin, size_t size);
+  bool loggingDeserialized() const { return loggingDeserialized_; }
+
+  // JS API and JS::WasmModule implementation:
+
+  JSObject* createObject(JSContext* cx) const override;
+  JSObject* createObjectForAsmJS(JSContext* cx) const override;
+
+  // about:memory reporting:
+
+  void addSizeOfMisc(MallocSizeOf mallocSizeOf, Metadata::SeenSet* seenMetadata,
+                     Code::SeenSet* seenCode, size_t* code, size_t* data) const;
+
+  // GC malloc memory tracking:
+
+  void initGCMallocBytesExcludingCode();
+  size_t gcMallocBytesExcludingCode() const {
+    return gcMallocBytesExcludingCode_;
+  }
+
+  // Generated code analysis support:
+
+  bool extractCode(JSContext* cx, Tier tier, MutableHandleValue vp) const;
+
+  WASM_DECLARE_FRIEND_SERIALIZE_ARGS(Module, const wasm::LinkData& linkData);
+};
+
+using MutableModule = RefPtr<Module>;
+using SharedModule = RefPtr<const Module>;
+
+// JS API implementations:
+
+[[nodiscard]] bool GetOptimizedEncodingBuildId(JS::BuildIdCharVector* buildId);
+
+}  // namespace wasm
+}  // namespace js
+
+#endif  // wasm_module_h