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diff --git a/js/src/vm/JitActivation.h b/js/src/vm/JitActivation.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:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_JitActivation_h
+#define vm_JitActivation_h
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+#include "mozilla/Atomics.h"     // mozilla::Atomic, mozilla::Relaxed
+#include "mozilla/Maybe.h"       // mozilla::Maybe
+
+#include <stddef.h>  // size_t
+#include <stdint.h>  // uint8_t, uint32_t, uintptr_t
+
+#include "jstypes.h"  // JS_PUBLIC_API
+
+#include "jit/IonTypes.h"        // CHECK_OSIPOINT_REGISTERS
+#include "jit/JSJitFrameIter.h"  // js::jit::{JSJitFrameIter,RInstructionResults}
+#ifdef CHECK_OSIPOINT_REGISTERS
+#  include "jit/Registers.h"  // js::jit::RegisterDump
+#endif
+#include "jit/RematerializedFrame.h"  // js::jit::RematerializedFrame
+#include "js/GCVector.h"              // JS::GCVector
+#include "js/HashTable.h"             // js::HashMap
+#include "js/UniquePtr.h"             // js::UniquePtr
+#include "vm/Activation.h"            // js::Activation
+#include "wasm/WasmCodegenTypes.h"    // js::wasm::TrapData
+#include "wasm/WasmConstants.h"       // js::wasm::Trap
+#include "wasm/WasmFrame.h"           // js::wasm::Frame
+#include "wasm/WasmFrameIter.h"  // js::wasm::{ExitReason,RegisterState,WasmFrameIter}
+
+struct JS_PUBLIC_API JSContext;
+class JS_PUBLIC_API JSTracer;
+
+namespace js {
+
+namespace jit {
+
+class BailoutFrameInfo;
+
+// A JitActivation is used for frames running in Baseline or Ion.
+class JitActivation : public Activation {
+  // If Baseline, Ion or Wasm code is on the stack, and has called into C++,
+  // this will be aligned to an ExitFrame. The last bit indicates if it's a
+  // wasm frame (bit set to wasm::ExitOrJitEntryFPTag) or not
+  // (bit set to ~wasm::ExitOrJitEntryFPTag).
+  uint8_t* packedExitFP_;
+
+  // When hasWasmExitFP(), encodedWasmExitReason_ holds ExitReason.
+  uint32_t encodedWasmExitReason_;
+
+  JitActivation* prevJitActivation_;
+
+  // Rematerialized Ion frames which has info copied out of snapshots. Maps
+  // frame pointers (i.e. packedExitFP_) to a vector of rematerializations of
+  // all inline frames associated with that frame.
+  //
+  // This table is lazily initialized by calling getRematerializedFrame.
+  using RematerializedFrameVector =
+      JS::GCVector<js::UniquePtr<RematerializedFrame>>;
+  using RematerializedFrameTable =
+      js::HashMap<uint8_t*, RematerializedFrameVector>;
+  js::UniquePtr<RematerializedFrameTable> rematerializedFrames_;
+
+  // This vector is used to remember the outcome of the evaluation of recover
+  // instructions.
+  //
+  // RInstructionResults are appended into this vector when Snapshot values
+  // have to be read, or when the evaluation has to run before some mutating
+  // code.  Each RInstructionResults belongs to one frame which has to bailout
+  // as soon as we get back to it.
+  using IonRecoveryMap = Vector<RInstructionResults, 1>;
+  IonRecoveryMap ionRecovery_;
+
+  // If we are bailing out from Ion, then this field should be a non-null
+  // pointer which references the BailoutFrameInfo used to walk the inner
+  // frames. This field is used for all newly constructed JSJitFrameIters to
+  // read the innermost frame information from this bailout data instead of
+  // reading it from the stack.
+  BailoutFrameInfo* bailoutData_;
+
+  // When profiling is enabled, these fields will be updated to reflect the
+  // last pushed frame for this activation, and if that frame has been
+  // left for a call, the native code site of the call.
+  mozilla::Atomic<JitFrameLayout*, mozilla::Relaxed> lastProfilingFrame_;
+  mozilla::Atomic<void*, mozilla::Relaxed> lastProfilingCallSite_;
+  static_assert(sizeof(mozilla::Atomic<void*, mozilla::Relaxed>) ==
+                    sizeof(void*),
+                "Atomic should have same memory format as underlying type.");
+
+  // When wasm traps, the signal handler records some data for unwinding
+  // purposes. Wasm code can't trap reentrantly.
+  mozilla::Maybe<wasm::TrapData> wasmTrapData_;
+
+  void clearRematerializedFrames();
+
+#ifdef CHECK_OSIPOINT_REGISTERS
+ protected:
+  // Used to verify that live registers don't change between a VM call and
+  // the OsiPoint that follows it. Protected to silence Clang warning.
+  uint32_t checkRegs_ = 0;
+  RegisterDump regs_;
+#endif
+
+ public:
+  explicit JitActivation(JSContext* cx);
+  ~JitActivation();
+
+  bool isProfiling() const {
+    // All JitActivations can be profiled.
+    return true;
+  }
+
+  JitActivation* prevJitActivation() const { return prevJitActivation_; }
+  static size_t offsetOfPrevJitActivation() {
+    return offsetof(JitActivation, prevJitActivation_);
+  }
+
+  bool hasExitFP() const { return !!packedExitFP_; }
+  uint8_t* jsOrWasmExitFP() const {
+    if (hasWasmExitFP()) {
+      return wasm::Frame::untagExitFP(packedExitFP_);
+    }
+    return packedExitFP_;
+  }
+  static size_t offsetOfPackedExitFP() {
+    return offsetof(JitActivation, packedExitFP_);
+  }
+
+  bool hasJSExitFP() const { return !hasWasmExitFP(); }
+
+  uint8_t* jsExitFP() const {
+    MOZ_ASSERT(hasJSExitFP());
+    return packedExitFP_;
+  }
+  void setJSExitFP(uint8_t* fp) { packedExitFP_ = fp; }
+
+  uint8_t* packedExitFP() const { return packedExitFP_; }
+  void setPackedExitFP(uint8_t* fp) { packedExitFP_ = fp; }
+
+#ifdef CHECK_OSIPOINT_REGISTERS
+  void setCheckRegs(bool check) { checkRegs_ = check; }
+  static size_t offsetOfCheckRegs() {
+    return offsetof(JitActivation, checkRegs_);
+  }
+  static size_t offsetOfRegs() { return offsetof(JitActivation, regs_); }
+#endif
+
+  // Look up a rematerialized frame keyed by the fp, rematerializing the
+  // frame if one doesn't already exist. A frame can only be rematerialized
+  // if an IonFrameIterator pointing to the nearest uninlined frame can be
+  // provided, as values need to be read out of snapshots.
+  //
+  // The inlineDepth must be within bounds of the frame pointed to by iter.
+  RematerializedFrame* getRematerializedFrame(
+      JSContext* cx, const JSJitFrameIter& iter, size_t inlineDepth = 0,
+      MaybeReadFallback::FallbackConsequence consequence =
+          MaybeReadFallback::Fallback_Invalidate);
+
+  // Look up a rematerialized frame by the fp. If inlineDepth is out of
+  // bounds of what has been rematerialized, nullptr is returned.
+  RematerializedFrame* lookupRematerializedFrame(uint8_t* top,
+                                                 size_t inlineDepth = 0);
+
+  // Remove all rematerialized frames associated with the fp top from the
+  // Debugger.
+  void removeRematerializedFramesFromDebugger(JSContext* cx, uint8_t* top);
+
+  bool hasRematerializedFrame(uint8_t* top, size_t inlineDepth = 0) {
+    return !!lookupRematerializedFrame(top, inlineDepth);
+  }
+
+  // Remove a previous rematerialization by fp.
+  void removeRematerializedFrame(uint8_t* top);
+
+  void traceRematerializedFrames(JSTracer* trc);
+
+  // Register the results of on Ion frame recovery.
+  bool registerIonFrameRecovery(RInstructionResults&& results);
+
+  // Return the pointer to the Ion frame recovery, if it is already registered.
+  RInstructionResults* maybeIonFrameRecovery(JitFrameLayout* fp);
+
+  // If an Ion frame recovery exists for the |fp| frame exists, then remove it
+  // from the activation.
+  void removeIonFrameRecovery(JitFrameLayout* fp);
+
+  void traceIonRecovery(JSTracer* trc);
+
+  // Return the bailout information if it is registered.
+  const BailoutFrameInfo* bailoutData() const { return bailoutData_; }
+
+  // Register the bailout data when it is constructed.
+  void setBailoutData(BailoutFrameInfo* bailoutData);
+
+  // Unregister the bailout data when the frame is reconstructed.
+  void cleanBailoutData();
+
+  static size_t offsetOfLastProfilingFrame() {
+    return offsetof(JitActivation, lastProfilingFrame_);
+  }
+  JitFrameLayout* lastProfilingFrame() { return lastProfilingFrame_; }
+  void setLastProfilingFrame(JitFrameLayout* ptr) { lastProfilingFrame_ = ptr; }
+
+  static size_t offsetOfLastProfilingCallSite() {
+    return offsetof(JitActivation, lastProfilingCallSite_);
+  }
+  void* lastProfilingCallSite() { return lastProfilingCallSite_; }
+  void setLastProfilingCallSite(void* ptr) { lastProfilingCallSite_ = ptr; }
+
+  // WebAssembly specific attributes.
+  bool hasWasmExitFP() const { return wasm::Frame::isExitFP(packedExitFP_); }
+  wasm::Frame* wasmExitFP() const {
+    MOZ_ASSERT(hasWasmExitFP());
+    return reinterpret_cast<wasm::Frame*>(
+        wasm::Frame::untagExitFP(packedExitFP_));
+  }
+  wasm::Instance* wasmExitInstance() const {
+    return wasm::GetNearestEffectiveInstance(wasmExitFP());
+  }
+  void setWasmExitFP(const wasm::Frame* fp) {
+    if (fp) {
+      MOZ_ASSERT(!wasm::Frame::isExitFP(fp));
+      packedExitFP_ = wasm::Frame::addExitFPTag(fp);
+      MOZ_ASSERT(hasWasmExitFP());
+    } else {
+      packedExitFP_ = nullptr;
+    }
+  }
+  wasm::ExitReason wasmExitReason() const {
+    MOZ_ASSERT(hasWasmExitFP());
+    return wasm::ExitReason::Decode(encodedWasmExitReason_);
+  }
+  static size_t offsetOfEncodedWasmExitReason() {
+    return offsetof(JitActivation, encodedWasmExitReason_);
+  }
+
+  void startWasmTrap(wasm::Trap trap, uint32_t bytecodeOffset,
+                     const wasm::RegisterState& state);
+  void finishWasmTrap();
+  bool isWasmTrapping() const { return !!wasmTrapData_; }
+  const wasm::TrapData& wasmTrapData() { return *wasmTrapData_; }
+};
+
+// A filtering of the ActivationIterator to only stop at JitActivations.
+class JitActivationIterator : public ActivationIterator {
+  void settle() {
+    while (!done() && !activation_->isJit()) {
+      ActivationIterator::operator++();
+    }
+  }
+
+ public:
+  explicit JitActivationIterator(JSContext* cx) : ActivationIterator(cx) {
+    settle();
+  }
+
+  JitActivationIterator& operator++() {
+    ActivationIterator::operator++();
+    settle();
+    return *this;
+  }
+};
+
+}  // namespace jit
+
+}  // namespace js
+
+#endif  // vm_JitActivation_h