diff --git a/dom/svg/SVGAnimatedLength.h b/dom/svg/SVGAnimatedLength.h
index 01ee773cef28..580675c2f8cc 100644
--- a/dom/svg/SVGAnimatedLength.h
+++ b/dom/svg/SVGAnimatedLength.h
@@ -33,7 +33,7 @@ class SVGViewportElement;
 
 class UserSpaceMetrics {
  public:
-  virtual ~UserSpaceMetrics() {}
+  virtual ~UserSpaceMetrics() = default;
 
   virtual float GetEmLength() const = 0;
   virtual float GetExLength() const = 0;
diff --git a/dom/svg/SVGAnimatedLengthList.h b/dom/svg/SVGAnimatedLengthList.h
index 1454155ebd76..4cd5f4693cf5 100644
--- a/dom/svg/SVGAnimatedLengthList.h
+++ b/dom/svg/SVGAnimatedLengthList.h
@@ -42,7 +42,7 @@ class SVGAnimatedLengthList {
   friend class dom::DOMSVGLengthList;
 
  public:
-  SVGAnimatedLengthList() {}
+  SVGAnimatedLengthList() = default;
 
   /**
    * Because it's so important that mBaseVal and its DOMSVGLengthList wrapper
diff --git a/dom/svg/SVGAnimatedPathSegList.h b/dom/svg/SVGAnimatedPathSegList.h
index 3bd4e1d04fc9..0b369d5ceec1 100644
--- a/dom/svg/SVGAnimatedPathSegList.h
+++ b/dom/svg/SVGAnimatedPathSegList.h
@@ -44,7 +44,7 @@ class SVGAnimatedPathSegList final {
   friend class DOMSVGPathSegList;
 
  public:
-  SVGAnimatedPathSegList() {}
+  SVGAnimatedPathSegList() = default;
 
   /**
    * Because it's so important that mBaseVal and its DOMSVGPathSegList wrapper
diff --git a/dom/svg/SVGAnimatedPointList.h b/dom/svg/SVGAnimatedPointList.h
index cf7d67c339ab..157ecf3709be 100644
--- a/dom/svg/SVGAnimatedPointList.h
+++ b/dom/svg/SVGAnimatedPointList.h
@@ -43,7 +43,7 @@ class SVGAnimatedPointList {
   friend class DOMSVGPointList;
 
  public:
-  SVGAnimatedPointList() {}
+  SVGAnimatedPointList() = default;
 
   /**
    * Because it's so important that mBaseVal and its DOMSVGPointList wrapper
diff --git a/dom/svg/SVGComponentTransferFunctionElement.h b/dom/svg/SVGComponentTransferFunctionElement.h
index ae7fff6a2d25..cf3ed14cc444 100644
--- a/dom/svg/SVGComponentTransferFunctionElement.h
+++ b/dom/svg/SVGComponentTransferFunctionElement.h
@@ -34,7 +34,7 @@ class SVGComponentTransferFunctionElement
       already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
       : SVGComponentTransferFunctionElementBase(std::move(aNodeInfo)) {}
 
-  virtual ~SVGComponentTransferFunctionElement() {}
+  virtual ~SVGComponentTransferFunctionElement() = default;
 
  public:
   typedef gfx::ComponentTransferAttributes ComponentTransferAttributes;
diff --git a/dom/svg/SVGFilters.h b/dom/svg/SVGFilters.h
index 7960a9cbc2dd..f594e7b0bc2f 100644
--- a/dom/svg/SVGFilters.h
+++ b/dom/svg/SVGFilters.h
@@ -55,7 +55,7 @@ class SVGFE : public SVGFEBase {
 
   explicit SVGFE(already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
       : SVGFEBase(std::move(aNodeInfo)) {}
-  virtual ~SVGFE() {}
+  virtual ~SVGFE() = default;
 
  public:
   typedef mozilla::gfx::PrimitiveAttributes PrimitiveAttributes;
@@ -183,7 +183,7 @@ class SVGFELightingElement : public SVGFELightingElementBase {
       already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
       : SVGFELightingElementBase(std::move(aNodeInfo)) {}
 
-  virtual ~SVGFELightingElement() {}
+  virtual ~SVGFELightingElement() = default;
 
  public:
   // interfaces:
diff --git a/dom/svg/SVGIRect.h b/dom/svg/SVGIRect.h
index 01147f2e5b04..62055d5309e8 100644
--- a/dom/svg/SVGIRect.h
+++ b/dom/svg/SVGIRect.h
@@ -20,7 +20,7 @@ namespace dom {
 
 class SVGIRect : public nsISupports, public nsWrapperCache {
  public:
-  virtual ~SVGIRect() {}
+  virtual ~SVGIRect() = default;
 
   JSObject* WrapObject(JSContext* aCx,
                        JS::Handle<JSObject*> aGivenProto) override {
diff --git a/dom/svg/SVGIntegerPairSMILType.h b/dom/svg/SVGIntegerPairSMILType.h
index 4b15efa083a5..2a6708abcc26 100644
--- a/dom/svg/SVGIntegerPairSMILType.h
+++ b/dom/svg/SVGIntegerPairSMILType.h
@@ -41,7 +41,7 @@ class SVGIntegerPairSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGIntegerPairSMILType() {}
+  constexpr SVGIntegerPairSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGLengthList.h b/dom/svg/SVGLengthList.h
index dcd1d12f8f95..24c255ee06cc 100644
--- a/dom/svg/SVGLengthList.h
+++ b/dom/svg/SVGLengthList.h
@@ -39,8 +39,8 @@ class SVGLengthList {
   friend class SVGAnimatedLengthList;
 
  public:
-  SVGLengthList() {}
-  ~SVGLengthList() {}
+  SVGLengthList() = default;
+  ~SVGLengthList() = default;
 
   // Only methods that don't make/permit modification to this list are public.
   // Only our friend classes can access methods that may change us.
diff --git a/dom/svg/SVGLengthListSMILType.h b/dom/svg/SVGLengthListSMILType.h
index f4be976a9110..d1f1d8e19ca9 100644
--- a/dom/svg/SVGLengthListSMILType.h
+++ b/dom/svg/SVGLengthListSMILType.h
@@ -91,7 +91,7 @@ class SVGLengthListSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGLengthListSMILType() {}
+  constexpr SVGLengthListSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGMatrix.h b/dom/svg/SVGMatrix.h
index 85b8ac6f473a..23d8f794068f 100644
--- a/dom/svg/SVGMatrix.h
+++ b/dom/svg/SVGMatrix.h
@@ -63,7 +63,7 @@ class SVGMatrix final : public nsWrapperCache {
    * Ctors for SVGMatrix objects created independently of a DOMSVGTransform.
    */
   // Default ctor for gfxMatrix will produce identity mx
-  SVGMatrix() {}
+  SVGMatrix() = default;
 
   explicit SVGMatrix(const gfxMatrix& aMatrix) : mMatrix(aMatrix) {}
 
@@ -103,7 +103,7 @@ class SVGMatrix final : public nsWrapperCache {
   already_AddRefed<SVGMatrix> SkewY(float angle, ErrorResult& rv);
 
  private:
-  ~SVGMatrix() {}
+  ~SVGMatrix() = default;
 
   void SetMatrix(const gfxMatrix& aMatrix) {
     if (mTransform) {
diff --git a/dom/svg/SVGMotionSMILType.h b/dom/svg/SVGMotionSMILType.h
index 963b155e06f1..8cf0508128fb 100644
--- a/dom/svg/SVGMotionSMILType.h
+++ b/dom/svg/SVGMotionSMILType.h
@@ -71,7 +71,7 @@ class SVGMotionSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGMotionSMILType() {}
+  constexpr SVGMotionSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGNumberList.h b/dom/svg/SVGNumberList.h
index bc1642eb5166..9a37e7e8f919 100644
--- a/dom/svg/SVGNumberList.h
+++ b/dom/svg/SVGNumberList.h
@@ -37,8 +37,8 @@ class SVGNumberList {
   friend class SVGAnimatedNumberList;
 
  public:
-  SVGNumberList() {}
-  ~SVGNumberList() {}
+  SVGNumberList() = default;
+  ~SVGNumberList() = default;
 
   // Only methods that don't make/permit modification to this list are public.
   // Only our friend classes can access methods that may change us.
diff --git a/dom/svg/SVGNumberListSMILType.h b/dom/svg/SVGNumberListSMILType.h
index bdb88ecdf3d3..4353932390ff 100644
--- a/dom/svg/SVGNumberListSMILType.h
+++ b/dom/svg/SVGNumberListSMILType.h
@@ -45,7 +45,7 @@ class SVGNumberListSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGNumberListSMILType() {}
+  constexpr SVGNumberListSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGNumberPairSMILType.h b/dom/svg/SVGNumberPairSMILType.h
index 63140330f5a6..e5857de186b1 100644
--- a/dom/svg/SVGNumberPairSMILType.h
+++ b/dom/svg/SVGNumberPairSMILType.h
@@ -38,7 +38,7 @@ class SVGNumberPairSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGNumberPairSMILType() {}
+  constexpr SVGNumberPairSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGOrientSMILType.h b/dom/svg/SVGOrientSMILType.h
index 16bb7e15fa40..5e959f9392b3 100644
--- a/dom/svg/SVGOrientSMILType.h
+++ b/dom/svg/SVGOrientSMILType.h
@@ -58,7 +58,7 @@ class SVGOrientSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGOrientSMILType() {}
+  constexpr SVGOrientSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGPathData.h b/dom/svg/SVGPathData.h
index 593015870ba5..f59833343591 100644
--- a/dom/svg/SVGPathData.h
+++ b/dom/svg/SVGPathData.h
@@ -91,8 +91,8 @@ class SVGPathData {
  public:
   typedef const float* const_iterator;
 
-  SVGPathData() {}
-  ~SVGPathData() {}
+  SVGPathData() = default;
+  ~SVGPathData() = default;
 
   // Only methods that don't make/permit modification to this list are public.
   // Only our friend classes can access methods that may change us.
diff --git a/dom/svg/SVGPathSegListSMILType.h b/dom/svg/SVGPathSegListSMILType.h
index b5a08fe9dc4d..b712cd373f21 100644
--- a/dom/svg/SVGPathSegListSMILType.h
+++ b/dom/svg/SVGPathSegListSMILType.h
@@ -48,7 +48,7 @@ class SVGPathSegListSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGPathSegListSMILType() {}
+  constexpr SVGPathSegListSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGPathSegUtils.h b/dom/svg/SVGPathSegUtils.h
index 26654a8a34c9..53d05b04441f 100644
--- a/dom/svg/SVGPathSegUtils.h
+++ b/dom/svg/SVGPathSegUtils.h
@@ -73,7 +73,7 @@ struct SVGPathTraversalState {
  */
 class SVGPathSegUtils {
  private:
-  SVGPathSegUtils() {}  // private to prevent instances
+  SVGPathSegUtils() = default;  // private to prevent instances
 
  public:
   static void GetValueAsString(const float* aSeg, nsAString& aValue);
diff --git a/dom/svg/SVGPointList.h b/dom/svg/SVGPointList.h
index 78f7320642ed..7d12d64069de 100644
--- a/dom/svg/SVGPointList.h
+++ b/dom/svg/SVGPointList.h
@@ -37,8 +37,8 @@ class SVGPointList {
   friend class DOMSVGPoint;
 
  public:
-  SVGPointList() {}
-  ~SVGPointList() {}
+  SVGPointList() = default;
+  ~SVGPointList() = default;
 
   // Only methods that don't make/permit modification to this list are public.
   // Only our friend classes can access methods that may change us.
diff --git a/dom/svg/SVGPointListSMILType.h b/dom/svg/SVGPointListSMILType.h
index 8400ef8fd58d..88f79038cb72 100644
--- a/dom/svg/SVGPointListSMILType.h
+++ b/dom/svg/SVGPointListSMILType.h
@@ -45,7 +45,7 @@ class SVGPointListSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGPointListSMILType() {}
+  constexpr SVGPointListSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGRect.h b/dom/svg/SVGRect.h
index 934795e08a29..6474aefa3783 100644
--- a/dom/svg/SVGRect.h
+++ b/dom/svg/SVGRect.h
@@ -46,7 +46,7 @@ class SVGRect final : public SVGIRect {
   virtual nsIContent* GetParentObject() const override { return mParent; }
 
  protected:
-  ~SVGRect() {}
+  ~SVGRect() = default;
 
   nsCOMPtr<nsIContent> mParent;
   float mX, mY, mWidth, mHeight;
diff --git a/dom/svg/SVGSVGElement.h b/dom/svg/SVGSVGElement.h
index e4c471dc264d..550807b8e28d 100644
--- a/dom/svg/SVGSVGElement.h
+++ b/dom/svg/SVGSVGElement.h
@@ -65,7 +65,7 @@ class DOMSVGTranslatePoint final : public nsISVGPoint {
   RefPtr<SVGSVGElement> mElement;
 
  private:
-  ~DOMSVGTranslatePoint() {}
+  ~DOMSVGTranslatePoint() = default;
 };
 
 typedef SVGViewportElement SVGSVGElementBase;
diff --git a/dom/svg/SVGStringList.h b/dom/svg/SVGStringList.h
index e53c81a6c90d..2b9c604b9a70 100644
--- a/dom/svg/SVGStringList.h
+++ b/dom/svg/SVGStringList.h
@@ -22,7 +22,7 @@ class SVGStringList {
 
  public:
   SVGStringList() : mIsSet(false), mIsCommaSeparated(false) {}
-  ~SVGStringList() {}
+  ~SVGStringList() = default;
 
   void SetIsCommaSeparated(bool aIsCommaSeparated) {
     mIsCommaSeparated = aIsCommaSeparated;
diff --git a/dom/svg/SVGTests.h b/dom/svg/SVGTests.h
index 743e91622622..500af1c58fc0 100644
--- a/dom/svg/SVGTests.h
+++ b/dom/svg/SVGTests.h
@@ -105,7 +105,7 @@ class SVGTests : public nsISupports {
   }
 
  protected:
-  virtual ~SVGTests() {}
+  virtual ~SVGTests() = default;
 
  private:
   enum { FEATURES, EXTENSIONS, LANGUAGE };
diff --git a/dom/svg/SVGTransformList.h b/dom/svg/SVGTransformList.h
index 536056153b3a..adbb1cc8fc39 100644
--- a/dom/svg/SVGTransformList.h
+++ b/dom/svg/SVGTransformList.h
@@ -32,8 +32,8 @@ class SVGTransformList {
   friend class dom::DOMSVGTransform;
 
  public:
-  SVGTransformList() {}
-  ~SVGTransformList() {}
+  SVGTransformList() = default;
+  ~SVGTransformList() = default;
 
   // Only methods that don't make/permit modification to this list are public.
   // Only our friend classes can access methods that may change us.
diff --git a/dom/svg/SVGTransformListSMILType.h b/dom/svg/SVGTransformListSMILType.h
index 0b15b006966e..bc7833e04bf0 100644
--- a/dom/svg/SVGTransformListSMILType.h
+++ b/dom/svg/SVGTransformListSMILType.h
@@ -116,7 +116,7 @@ class SVGTransformListSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGTransformListSMILType() {}
+  constexpr SVGTransformListSMILType() = default;
 };
 
 }  // end namespace mozilla
diff --git a/dom/svg/SVGTransformableElement.h b/dom/svg/SVGTransformableElement.h
index 204e807ab8bf..2a3adce9a44f 100644
--- a/dom/svg/SVGTransformableElement.h
+++ b/dom/svg/SVGTransformableElement.h
@@ -27,7 +27,7 @@ class SVGTransformableElement : public SVGElement {
  public:
   explicit SVGTransformableElement(already_AddRefed<dom::NodeInfo>&& aNodeInfo)
       : SVGElement(std::move(aNodeInfo)) {}
-  virtual ~SVGTransformableElement() {}
+  virtual ~SVGTransformableElement() = default;
 
   virtual nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override = 0;
 
diff --git a/dom/svg/SVGViewBoxSMILType.h b/dom/svg/SVGViewBoxSMILType.h
index 996697aac62f..943831247fba 100644
--- a/dom/svg/SVGViewBoxSMILType.h
+++ b/dom/svg/SVGViewBoxSMILType.h
@@ -38,7 +38,7 @@ class SVGViewBoxSMILType : public SMILType {
 
  private:
   // Private constructor: prevent instances beyond my singleton.
-  constexpr SVGViewBoxSMILType() {}
+  constexpr SVGViewBoxSMILType() = default;
 };
 
 }  // namespace mozilla
diff --git a/dom/svg/SVGViewportElement.h b/dom/svg/SVGViewportElement.h
index c8b31b9c3c5a..b6c0fc8f5852 100644
--- a/dom/svg/SVGViewportElement.h
+++ b/dom/svg/SVGViewportElement.h
@@ -25,9 +25,9 @@ class nsSVGViewportFrame;
 
 namespace mozilla {
 class AutoPreserveAspectRatioOverride;
-class DOMSVGAnimatedPreserveAspectRatio;
 
 namespace dom {
+class DOMSVGAnimatedPreserveAspectRatio;
 class SVGAnimatedRect;
 class SVGViewElement;
 class SVGViewportElement;
diff --git a/gfx/thebes/gfxPlatform.cpp b/gfx/thebes/gfxPlatform.cpp
index 0a930430e820..0e4f91b1a2d8 100644
--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -923,6 +923,7 @@ void gfxPlatform::Init() {
 #else
 #  error "No gfxPlatform implementation available"
 #endif
+  gPlatform->PopulateScreenInfo();
   gPlatform->InitAcceleration();
   gPlatform->InitWebRenderConfig();
   // When using WebRender, we defer initialization of the D3D11 devices until
@@ -960,7 +961,6 @@ void gfxPlatform::Init() {
 
   InitLayersIPC();
 
-  gPlatform->PopulateScreenInfo();
   gPlatform->ComputeTileSize();
 
 #ifdef MOZ_ENABLE_FREETYPE
@@ -2511,7 +2511,7 @@ static bool CalculateWrQualifiedPrefValue() {
 }
 
 static FeatureState& WebRenderHardwareQualificationStatus(
-    bool aHasBattery, nsCString& aOutFailureId) {
+    const IntSize& aScreenSize, bool aHasBattery, nsCString& aOutFailureId) {
   FeatureState& featureWebRenderQualified =
       gfxConfig::GetFeature(Feature::WEBRENDER_QUALIFIED);
   featureWebRenderQualified.EnableByDefault();
@@ -2576,7 +2576,8 @@ static FeatureState& WebRenderHardwareQualificationStatus(
                 FeatureStatus::Blocked, "Device too old",
                 NS_LITERAL_CSTRING("FEATURE_FAILURE_DEVICE_TOO_OLD"));
           }
-        } else if (adapterVendorID == u"0x8086") {  // Intel
+        } else if (adapterVendorID == u"0x8086" ||
+                   adapterVendorID == u"mesa/i965") {  // Intel
           const uint16_t supportedDevices[] = {
               0x191d,  // HD Graphics P530
               0x192d,  // Iris Pro Graphics P555
@@ -2605,6 +2606,18 @@ static FeatureState& WebRenderHardwareQualificationStatus(
             featureWebRenderQualified.Disable(
                 FeatureStatus::Blocked, "Device too old",
                 NS_LITERAL_CSTRING("FEATURE_FAILURE_DEVICE_TOO_OLD"));
+          } else if (adapterVendorID == u"mesa/i965") {
+            const int32_t maxPixels = 3440 * 1440;  // UWQHD
+            int32_t pixels = aScreenSize.width * aScreenSize.height;
+            if (pixels > maxPixels) {
+              featureWebRenderQualified.Disable(
+                  FeatureStatus::Blocked, "Screen size too large",
+                  NS_LITERAL_CSTRING("FEATURE_FAILURE_SCREEN_SIZE_TOO_LARGE"));
+            } else if (pixels <= 0) {
+              featureWebRenderQualified.Disable(
+                  FeatureStatus::Blocked, "Screen size unknown",
+                  NS_LITERAL_CSTRING("FEATURE_FAILURE_SCREEN_SIZE_UNKNOWN"));
+            }
           }
 #endif
         } else {
@@ -2653,7 +2666,8 @@ void gfxPlatform::InitWebRenderConfig() {
 
   nsCString failureId;
   FeatureState& featureWebRenderQualified =
-      WebRenderHardwareQualificationStatus(HasBattery(), failureId);
+      WebRenderHardwareQualificationStatus(GetScreenSize(), HasBattery(),
+                                           failureId);
   FeatureState& featureWebRender = gfxConfig::GetFeature(Feature::WEBRENDER);
 
   featureWebRender.DisableByDefault(
@@ -2748,6 +2762,16 @@ void gfxPlatform::InitWebRenderConfig() {
           WebRenderDebugPrefChangeCallback, WR_DEBUG_PREF);
     }
   }
+#if defined(XP_LINUX) && !defined(MOZ_WIDGET_ANDROID)
+  else if (gfxConfig::IsEnabled(Feature::HW_COMPOSITING)) {
+    // Hardware compositing should be disabled by default if we aren't using
+    // WebRender. We had to check if it is enabled at all, because it may
+    // already have been forced disabled (e.g. safe mode, headless). It may
+    // still be forced on by the user, and if so, this should have no effect.
+    gfxConfig::Disable(Feature::HW_COMPOSITING, FeatureStatus::Blocked,
+                       "Acceleration blocked by platform");
+  }
+#endif
 
 #ifdef XP_WIN
   if (Preferences::GetBool("gfx.webrender.dcomp-win.enabled", false)) {
diff --git a/gfx/thebes/gfxPlatform.h b/gfx/thebes/gfxPlatform.h
index 34cf85857b72..896dff0452ff 100644
--- a/gfx/thebes/gfxPlatform.h
+++ b/gfx/thebes/gfxPlatform.h
@@ -736,7 +736,7 @@ class gfxPlatform : public mozilla::layers::MemoryPressureListener {
   gfxPlatform();
   virtual ~gfxPlatform();
 
-  virtual bool HasBattery() { return true; }
+  virtual bool HasBattery() { return false; }
 
   virtual void InitAcceleration();
   virtual void InitWebRenderConfig();
diff --git a/gfx/thebes/gfxPlatformGtk.cpp b/gfx/thebes/gfxPlatformGtk.cpp
index 144af010f76a..0a6ecc42342d 100644
--- a/gfx/thebes/gfxPlatformGtk.cpp
+++ b/gfx/thebes/gfxPlatformGtk.cpp
@@ -330,7 +330,7 @@ uint32_t gfxPlatformGtk::MaxGenericSubstitions() {
 }
 
 bool gfxPlatformGtk::AccelerateLayersByDefault() {
-  return gfxPrefs::WebRenderAll();
+  return true;
 }
 
 void gfxPlatformGtk::GetPlatformCMSOutputProfile(void*& mem, size_t& size) {
diff --git a/js/public/GCAPI.h b/js/public/GCAPI.h
index 2220909cbf98..41823ded73d4 100644
--- a/js/public/GCAPI.h
+++ b/js/public/GCAPI.h
@@ -307,6 +307,14 @@ typedef enum JSGCParamKey {
    */
   JSGC_MIN_NURSERY_BYTES = 31,
 
+  /*
+   * The minimum time to allow between triggering last ditch GCs in seconds.
+   *
+   * Default: 60 seconds
+   * Pref: None
+   */
+  JSGC_MIN_LAST_DITCH_GC_PERIOD = 32,
+
 } JSGCParamKey;
 
 /*
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 574d7a88a1ce..b10510e4e8d6 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -488,7 +488,8 @@ static bool MinorGC(JSContext* cx, unsigned argc, Value* vp) {
   _("allocationThreshold", JSGC_ALLOCATION_THRESHOLD, true)                  \
   _("minEmptyChunkCount", JSGC_MIN_EMPTY_CHUNK_COUNT, true)                  \
   _("maxEmptyChunkCount", JSGC_MAX_EMPTY_CHUNK_COUNT, true)                  \
-  _("compactingEnabled", JSGC_COMPACTING_ENABLED, true)
+  _("compactingEnabled", JSGC_COMPACTING_ENABLED, true)                      \
+  _("minLastDitchGCPeriod", JSGC_MIN_LAST_DITCH_GC_PERIOD, true)
 
 static const struct ParamInfo {
   const char* name;
diff --git a/js/src/frontend/BytecodeControlStructures.cpp b/js/src/frontend/BytecodeControlStructures.cpp
index eb1007251b7f..727a707fb762 100644
--- a/js/src/frontend/BytecodeControlStructures.cpp
+++ b/js/src/frontend/BytecodeControlStructures.cpp
@@ -41,7 +41,7 @@ LoopControl::LoopControl(BytecodeEmitter* bce, StatementKind loopKind)
 
   LoopControl* enclosingLoop = findNearest<LoopControl>(enclosing());
 
-  stackDepth_ = bce->stackDepth;
+  stackDepth_ = bce->bytecodeSection().stackDepth();
   loopDepth_ = enclosingLoop ? enclosingLoop->loopDepth_ + 1 : 1;
 
   int loopSlots;
@@ -81,7 +81,7 @@ bool LoopControl::emitContinueTarget(BytecodeEmitter* bce) {
 bool LoopControl::emitSpecialBreakForDone(BytecodeEmitter* bce) {
   // This doesn't pop stack values, nor handle any other controls.
   // Should be called on the toplevel of the loop.
-  MOZ_ASSERT(bce->stackDepth == stackDepth_);
+  MOZ_ASSERT(bce->bytecodeSection().stackDepth() == stackDepth_);
   MOZ_ASSERT(bce->innermostNestableControl == this);
 
   if (!bce->newSrcNote(SRC_BREAK)) {
@@ -109,7 +109,7 @@ bool LoopControl::emitLoopHead(BytecodeEmitter* bce,
     }
   }
 
-  head_ = {bce->offset()};
+  head_ = {bce->bytecodeSection().offset()};
   ptrdiff_t off;
   if (!bce->emitJumpTargetOp(JSOP_LOOPHEAD, &off)) {
     return false;
@@ -126,7 +126,7 @@ bool LoopControl::emitLoopEntry(BytecodeEmitter* bce,
     }
   }
 
-  JumpTarget entry = {bce->offset()};
+  JumpTarget entry = {bce->bytecodeSection().offset()};
   bce->patchJumpsToTarget(entryJump_, entry);
 
   MOZ_ASSERT(loopDepth_ > 0);
@@ -135,7 +135,8 @@ bool LoopControl::emitLoopEntry(BytecodeEmitter* bce,
   if (!bce->emitJumpTargetOp(JSOP_LOOPENTRY, &off)) {
     return false;
   }
-  SetLoopEntryDepthHintAndFlags(bce->code(off), loopDepth_, canIonOsr_);
+  SetLoopEntryDepthHintAndFlags(bce->bytecodeSection().code(off), loopDepth_,
+                                canIonOsr_);
 
   return true;
 }
diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index 0c2bab81ff09..af1e9316b6b9 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -91,6 +91,24 @@ static bool ParseNodeRequiresSpecialLineNumberNotes(ParseNode* pn) {
          kind == ParseNodeKind::Function;
 }
 
+BytecodeEmitter::BytecodeSection::BytecodeSection(JSContext* cx,
+                                                  uint32_t lineNum)
+    : code_(cx),
+      notes_(cx),
+      tryNoteList_(cx),
+      scopeNoteList_(cx),
+      resumeOffsetList_(cx),
+      currentLine_(lineNum) {}
+
+BytecodeEmitter::PerScriptData::PerScriptData(JSContext* cx)
+    : scopeList_(cx),
+      numberList_(cx),
+      atomIndices_(cx->frontendCollectionPool()) {}
+
+bool BytecodeEmitter::PerScriptData::init(JSContext* cx) {
+  return atomIndices_.acquire(cx);
+}
+
 BytecodeEmitter::BytecodeEmitter(
     BytecodeEmitter* parent, SharedContext* sc, HandleScript script,
     Handle<LazyScript*> lazyScript, uint32_t lineNum, EmitterMode emitterMode,
@@ -100,23 +118,17 @@ BytecodeEmitter::BytecodeEmitter(
       parent(parent),
       script(cx, script),
       lazyScript(cx, lazyScript),
-      code_(cx),
-      notes_(cx),
-      currentLine_(lineNum),
+      bytecodeSection_(cx, lineNum),
+      perScriptData_(cx),
       fieldInitializers_(fieldInitializers),
-      atomIndices(cx->frontendCollectionPool()),
       firstLine(lineNum),
-      numberList(cx),
-      scopeList(cx),
-      tryNoteList(cx),
-      scopeNoteList(cx),
-      resumeOffsetList(cx),
       emitterMode(emitterMode) {
   MOZ_ASSERT_IF(emitterMode == LazyFunction, lazyScript);
 
   if (sc->isFunctionBox()) {
     // Functions have IC entries for type monitoring |this| and arguments.
-    numICEntries = sc->asFunctionBox()->function()->nargs() + 1;
+    bytecodeSection().setNumICEntries(sc->asFunctionBox()->function()->nargs() +
+                                      1);
   }
 }
 
@@ -148,7 +160,7 @@ void BytecodeEmitter::initFromBodyPosition(TokenPos bodyPosition) {
   setFunctionBodyEndPos(bodyPosition.end);
 }
 
-bool BytecodeEmitter::init() { return atomIndices.acquire(cx); }
+bool BytecodeEmitter::init() { return perScriptData_.init(cx); }
 
 template <typename T>
 T* BytecodeEmitter::findInnermostNestableControl() const {
@@ -194,9 +206,7 @@ bool BytecodeEmitter::markStepBreakpoint() {
   // We track the location of the most recent separator for use in
   // markSimpleBreakpoint. Note that this means that the position must already
   // be set before markStepBreakpoint is called.
-  lastSeparatorOffet_ = code().length();
-  lastSeparatorLine_ = currentLine_;
-  lastSeparatorColumn_ = lastColumn_;
+  bytecodeSection().updateSeparatorPosition();
 
   return true;
 }
@@ -210,10 +220,7 @@ bool BytecodeEmitter::markSimpleBreakpoint() {
   // expression start, we need to skip marking it breakable in order to avoid
   // having two breakpoints with the same line/column position.
   // Note: This assumes that the position for the call has already been set.
-  bool isDuplicateLocation =
-      lastSeparatorLine_ == currentLine_ && lastSeparatorColumn_ == lastColumn_;
-
-  if (!isDuplicateLocation) {
+  if (!bytecodeSection().isDuplicateLocation()) {
     if (!newSrcNote(SRC_BREAKPOINT)) {
       return false;
     }
@@ -223,9 +230,9 @@ bool BytecodeEmitter::markSimpleBreakpoint() {
 }
 
 bool BytecodeEmitter::emitCheck(JSOp op, ptrdiff_t delta, ptrdiff_t* offset) {
-  *offset = code().length();
+  *offset = bytecodeSection().code().length();
 
-  if (!code().growByUninitialized(delta)) {
+  if (!bytecodeSection().code().growByUninitialized(delta)) {
     ReportOutOfMemory(cx);
     return false;
   }
@@ -233,30 +240,30 @@ bool BytecodeEmitter::emitCheck(JSOp op, ptrdiff_t delta, ptrdiff_t* offset) {
   // If op is JOF_TYPESET (see the type barriers comment in TypeInference.h),
   // reserve a type set to store its result.
   if (CodeSpec[op].format & JOF_TYPESET) {
-    if (typesetCount < JSScript::MaxBytecodeTypeSets) {
-      typesetCount++;
+    if (bytecodeSection().typesetCount() < JSScript::MaxBytecodeTypeSets) {
+      bytecodeSection().addTypesetCount();
     }
   }
 
   if (BytecodeOpHasIC(op)) {
-    numICEntries++;
+    bytecodeSection().addNumICEntries();
   }
 
   return true;
 }
 
-void BytecodeEmitter::updateDepth(ptrdiff_t target) {
+void BytecodeEmitter::BytecodeSection::updateDepth(ptrdiff_t target) {
   jsbytecode* pc = code(target);
 
   int nuses = StackUses(pc);
   int ndefs = StackDefs(pc);
 
-  stackDepth -= nuses;
-  MOZ_ASSERT(stackDepth >= 0);
-  stackDepth += ndefs;
+  stackDepth_ -= nuses;
+  MOZ_ASSERT(stackDepth_ >= 0);
+  stackDepth_ += ndefs;
 
-  if ((uint32_t)stackDepth > maxStackDepth) {
-    maxStackDepth = stackDepth;
+  if ((uint32_t)stackDepth_ > maxStackDepth_) {
+    maxStackDepth_ = stackDepth_;
   }
 }
 
@@ -280,9 +287,9 @@ bool BytecodeEmitter::emit1(JSOp op) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -294,10 +301,10 @@ bool BytecodeEmitter::emit2(JSOp op, uint8_t op1) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
   code[1] = jsbytecode(op1);
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -313,11 +320,11 @@ bool BytecodeEmitter::emit3(JSOp op, jsbytecode op1, jsbytecode op2) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
   code[1] = op1;
   code[2] = op2;
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -330,7 +337,7 @@ bool BytecodeEmitter::emitN(JSOp op, size_t extra, ptrdiff_t* offset) {
     return false;
   }
 
-  jsbytecode* code = this->code(off);
+  jsbytecode* code = bytecodeSection().code(off);
   code[0] = jsbytecode(op);
   /* The remaining |extra| bytes are set by the caller */
 
@@ -339,7 +346,7 @@ bool BytecodeEmitter::emitN(JSOp op, size_t extra, ptrdiff_t* offset) {
    * operand yet to be stored in the extra bytes after op.
    */
   if (CodeSpec[op].nuses >= 0) {
-    updateDepth(off);
+    bytecodeSection().updateDepth(off);
   }
 
   if (offset) {
@@ -351,7 +358,7 @@ bool BytecodeEmitter::emitN(JSOp op, size_t extra, ptrdiff_t* offset) {
 bool BytecodeEmitter::emitJumpTargetOp(JSOp op, ptrdiff_t* off) {
   MOZ_ASSERT(BytecodeIsJumpTarget(op));
 
-  size_t numEntries = numICEntries;
+  size_t numEntries = bytecodeSection().numICEntries();
   if (MOZ_UNLIKELY(numEntries > UINT32_MAX)) {
     reportError(nullptr, JSMSG_NEED_DIET, js_script_str);
     return false;
@@ -361,21 +368,22 @@ bool BytecodeEmitter::emitJumpTargetOp(JSOp op, ptrdiff_t* off) {
     return false;
   }
 
-  SET_ICINDEX(code(*off), numEntries);
+  SET_ICINDEX(bytecodeSection().code(*off), numEntries);
   return true;
 }
 
 bool BytecodeEmitter::emitJumpTarget(JumpTarget* target) {
-  ptrdiff_t off = offset();
+  ptrdiff_t off = bytecodeSection().offset();
 
   // Alias consecutive jump targets.
-  if (off == lastTarget.offset + ptrdiff_t(JSOP_JUMPTARGET_LENGTH)) {
-    target->offset = lastTarget.offset;
+  if (off == bytecodeSection().lastTargetOffset() +
+                 ptrdiff_t(JSOP_JUMPTARGET_LENGTH)) {
+    target->offset = bytecodeSection().lastTargetOffset();
     return true;
   }
 
   target->offset = off;
-  lastTarget.offset = off;
+  bytecodeSection().setLastTargetOffset(off);
 
   ptrdiff_t opOff;
   return emitJumpTargetOp(JSOP_JUMPTARGET, &opOff);
@@ -387,11 +395,11 @@ bool BytecodeEmitter::emitJumpNoFallthrough(JSOp op, JumpList* jump) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
   MOZ_ASSERT(-1 <= jump->offset && jump->offset < offset);
-  jump->push(this->code(0), offset);
-  updateDepth(offset);
+  jump->push(bytecodeSection().code(0), offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -425,11 +433,12 @@ bool BytecodeEmitter::emitBackwardJump(JSOp op, JumpTarget target,
 }
 
 void BytecodeEmitter::patchJumpsToTarget(JumpList jump, JumpTarget target) {
-  MOZ_ASSERT(-1 <= jump.offset && jump.offset <= offset());
-  MOZ_ASSERT(0 <= target.offset && target.offset <= offset());
-  MOZ_ASSERT_IF(jump.offset != -1 && target.offset + 4 <= offset(),
-                BytecodeIsJumpTarget(JSOp(*code(target.offset))));
-  jump.patchAll(code(0), target);
+  MOZ_ASSERT(-1 <= jump.offset && jump.offset <= bytecodeSection().offset());
+  MOZ_ASSERT(0 <= target.offset && target.offset <= bytecodeSection().offset());
+  MOZ_ASSERT_IF(
+      jump.offset != -1 && target.offset + 4 <= bytecodeSection().offset(),
+      BytecodeIsJumpTarget(JSOp(*bytecodeSection().code(target.offset))));
+  jump.patchAll(bytecodeSection().code(0), target);
 }
 
 bool BytecodeEmitter::emitJumpTargetAndPatch(JumpList jump) {
@@ -459,7 +468,7 @@ bool BytecodeEmitter::emitCall(JSOp op, uint16_t argc, ParseNode* pn) {
 }
 
 bool BytecodeEmitter::emitDupAt(unsigned slotFromTop) {
-  MOZ_ASSERT(slotFromTop < unsigned(stackDepth));
+  MOZ_ASSERT(slotFromTop < unsigned(bytecodeSection().stackDepth()));
 
   if (slotFromTop == 0) {
     return emit1(JSOP_DUP);
@@ -475,7 +484,7 @@ bool BytecodeEmitter::emitDupAt(unsigned slotFromTop) {
     return false;
   }
 
-  jsbytecode* pc = code(off);
+  jsbytecode* pc = bytecodeSection().code(off);
   SET_UINT24(pc, slotFromTop);
   return true;
 }
@@ -516,14 +525,14 @@ bool BytecodeEmitter::updateLineNumberNotes(uint32_t offset) {
 
   ErrorReporter* er = &parser->errorReporter();
   bool onThisLine;
-  if (!er->isOnThisLine(offset, currentLine(), &onThisLine)) {
+  if (!er->isOnThisLine(offset, bytecodeSection().currentLine(), &onThisLine)) {
     er->errorNoOffset(JSMSG_OUT_OF_MEMORY);
     return false;
   }
 
   if (!onThisLine) {
     unsigned line = er->lineAt(offset);
-    unsigned delta = line - currentLine();
+    unsigned delta = line - bytecodeSection().currentLine();
 
     /*
      * Encode any change in the current source line number by using
@@ -536,7 +545,7 @@ bool BytecodeEmitter::updateLineNumberNotes(uint32_t offset) {
      * unsigned delta_ wrap to a very large number, which triggers a
      * SRC_SETLINE.
      */
-    setCurrentLine(line);
+    bytecodeSection().setCurrentLine(line);
     if (delta >= LengthOfSetLine(line)) {
       if (!newSrcNote2(SRC_SETLINE, ptrdiff_t(line))) {
         return false;
@@ -549,7 +558,7 @@ bool BytecodeEmitter::updateLineNumberNotes(uint32_t offset) {
       } while (--delta != 0);
     }
 
-    updateSeparatorPosition();
+    bytecodeSection().updateSeparatorPositionIfPresent();
   }
   return true;
 }
@@ -566,7 +575,8 @@ bool BytecodeEmitter::updateSourceCoordNotes(uint32_t offset) {
   }
 
   uint32_t columnIndex = parser->errorReporter().columnAt(offset);
-  ptrdiff_t colspan = ptrdiff_t(columnIndex) - ptrdiff_t(lastColumn_);
+  ptrdiff_t colspan =
+      ptrdiff_t(columnIndex) - ptrdiff_t(bytecodeSection().lastColumn());
   if (colspan != 0) {
     // If the column span is so large that we can't store it, then just
     // discard this information. This can happen with minimized or otherwise
@@ -579,20 +589,12 @@ bool BytecodeEmitter::updateSourceCoordNotes(uint32_t offset) {
     if (!newSrcNote2(SRC_COLSPAN, SN_COLSPAN_TO_OFFSET(colspan))) {
       return false;
     }
-    lastColumn_ = columnIndex;
-    updateSeparatorPosition();
+    bytecodeSection().setLastColumn(columnIndex);
+    bytecodeSection().updateSeparatorPositionIfPresent();
   }
   return true;
 }
 
-/* Updates the last separator position, if present */
-void BytecodeEmitter::updateSeparatorPosition() {
-  if (!inPrologue() && lastSeparatorOffet_ == code().length()) {
-    lastSeparatorLine_ = currentLine_;
-    lastSeparatorColumn_ = lastColumn_;
-  }
-}
-
 Maybe<uint32_t> BytecodeEmitter::getOffsetForLoop(ParseNode* nextpn) {
   if (!nextpn) {
     return Nothing();
@@ -626,7 +628,7 @@ bool BytecodeEmitter::emitUint32Operand(JSOp op, uint32_t operand) {
   if (!emitN(op, 4, &off)) {
     return false;
   }
-  SET_UINT32(code(off), operand);
+  SET_UINT32(bytecodeSection().code(off), operand);
   return true;
 }
 
@@ -663,17 +665,18 @@ class NonLocalExitControl {
  public:
   NonLocalExitControl(BytecodeEmitter* bce, Kind kind)
       : bce_(bce),
-        savedScopeNoteIndex_(bce->scopeNoteList.length()),
-        savedDepth_(bce->stackDepth),
+        savedScopeNoteIndex_(bce->bytecodeSection().scopeNoteList().length()),
+        savedDepth_(bce->bytecodeSection().stackDepth()),
         openScopeNoteIndex_(bce->innermostEmitterScope()->noteIndex()),
         kind_(kind) {}
 
   ~NonLocalExitControl() {
-    for (uint32_t n = savedScopeNoteIndex_; n < bce_->scopeNoteList.length();
-         n++) {
-      bce_->scopeNoteList.recordEnd(n, bce_->offset());
+    for (uint32_t n = savedScopeNoteIndex_;
+         n < bce_->bytecodeSection().scopeNoteList().length(); n++) {
+      bce_->bytecodeSection().scopeNoteList().recordEnd(
+          n, bce_->bytecodeSection().offset());
     }
-    bce_->stackDepth = savedDepth_;
+    bce_->bytecodeSection().setStackDepth(savedDepth_);
   }
 
   MOZ_MUST_USE bool prepareForNonLocalJump(NestableControl* target);
@@ -695,11 +698,12 @@ bool NonLocalExitControl::leaveScope(EmitterScope* es) {
   if (es->enclosingInFrame()) {
     enclosingScopeIndex = es->enclosingInFrame()->index();
   }
-  if (!bce_->scopeNoteList.append(enclosingScopeIndex, bce_->offset(),
-                                  openScopeNoteIndex_)) {
+  if (!bce_->bytecodeSection().scopeNoteList().append(
+          enclosingScopeIndex, bce_->bytecodeSection().offset(),
+          openScopeNoteIndex_)) {
     return false;
   }
-  openScopeNoteIndex_ = bce_->scopeNoteList.length() - 1;
+  openScopeNoteIndex_ = bce_->bytecodeSection().scopeNoteList().length() - 1;
 
   return true;
 }
@@ -838,7 +842,7 @@ bool NonLocalExitControl::prepareForNonLocalJump(NestableControl* target) {
   }
 
   // Close FOR_OF_ITERCLOSE trynotes.
-  ptrdiff_t end = bce_->offset();
+  ptrdiff_t end = bce_->bytecodeSection().offset();
   for (ptrdiff_t start : forOfIterCloseScopeStarts) {
     if (!bce_->addTryNote(JSTRY_FOR_OF_ITERCLOSE, 0, start, end)) {
       return false;
@@ -884,10 +888,10 @@ bool BytecodeEmitter::emitIndex32(JSOp op, uint32_t index) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
   SET_UINT32_INDEX(code, index);
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -902,10 +906,10 @@ bool BytecodeEmitter::emitIndexOp(JSOp op, uint32_t index) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(op);
   SET_UINT32_INDEX(code, index);
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -940,24 +944,24 @@ bool BytecodeEmitter::emitAtomOp(uint32_t atomIndex, JSOp op) {
 
 bool BytecodeEmitter::emitInternedScopeOp(uint32_t index, JSOp op) {
   MOZ_ASSERT(JOF_OPTYPE(op) == JOF_SCOPE);
-  MOZ_ASSERT(index < scopeList.length());
+  MOZ_ASSERT(index < perScriptData().scopeList().length());
   return emitIndex32(op, index);
 }
 
 bool BytecodeEmitter::emitInternedObjectOp(uint32_t index, JSOp op) {
   MOZ_ASSERT(JOF_OPTYPE(op) == JOF_OBJECT);
-  MOZ_ASSERT(index < objectList.length);
+  MOZ_ASSERT(index < perScriptData().objectList().length);
   return emitIndex32(op, index);
 }
 
 bool BytecodeEmitter::emitObjectOp(ObjectBox* objbox, JSOp op) {
-  return emitInternedObjectOp(objectList.add(objbox), op);
+  return emitInternedObjectOp(perScriptData().objectList().add(objbox), op);
 }
 
 bool BytecodeEmitter::emitObjectPairOp(ObjectBox* objbox1, ObjectBox* objbox2,
                                        JSOp op) {
-  uint32_t index = objectList.add(objbox1);
-  objectList.add(objbox2);
+  uint32_t index = perScriptData().objectList().add(objbox1);
+  perScriptData().objectList().add(objbox2);
   return emitInternedObjectOp(index, op);
 }
 
@@ -974,7 +978,7 @@ bool BytecodeEmitter::emitLocalOp(JSOp op, uint32_t slot) {
     return false;
   }
 
-  SET_LOCALNO(code(off), slot);
+  SET_LOCALNO(bytecodeSection().code(off), slot);
   return true;
 }
 
@@ -985,7 +989,7 @@ bool BytecodeEmitter::emitArgOp(JSOp op, uint16_t slot) {
     return false;
   }
 
-  SET_ARGNO(code(off), slot);
+  SET_ARGNO(bytecodeSection().code(off), slot);
   return true;
 }
 
@@ -1000,7 +1004,7 @@ bool BytecodeEmitter::emitEnvCoordOp(JSOp op, EnvironmentCoordinate ec) {
     return false;
   }
 
-  jsbytecode* pc = code(off);
+  jsbytecode* pc = bytecodeSection().code(off);
   SET_ENVCOORD_HOPS(pc, ec.hops());
   pc += ENVCOORD_HOPS_LEN;
   SET_ENVCOORD_SLOT(pc, ec.slot());
@@ -1680,13 +1684,13 @@ bool BytecodeEmitter::emitNewInit() {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = JSOP_NEWINIT;
   code[1] = 0;
   code[2] = 0;
   code[3] = 0;
   code[4] = 0;
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -1716,7 +1720,7 @@ bool BytecodeEmitter::iteratorResultShape(unsigned* shape) {
     return false;
   }
 
-  *shape = objectList.add(objbox);
+  *shape = perScriptData().objectList().add(objbox);
 
   return true;
 }
@@ -2017,10 +2021,10 @@ bool BytecodeEmitter::emitDouble(double d) {
     return false;
   }
 
-  jsbytecode* code = this->code(offset);
+  jsbytecode* code = bytecodeSection().code(offset);
   code[0] = jsbytecode(JSOP_DOUBLE);
   SET_INLINE_VALUE(code, DoubleValue(d));
-  updateDepth(offset);
+  bytecodeSection().updateDepth(offset);
   return true;
 }
 
@@ -2047,13 +2051,13 @@ bool BytecodeEmitter::emitNumberOp(double dval) {
       if (!emitN(JSOP_UINT24, 3, &off)) {
         return false;
       }
-      SET_UINT24(code(off), u);
+      SET_UINT24(bytecodeSection().code(off), u);
     } else {
       ptrdiff_t off;
       if (!emitN(JSOP_INT32, 4, &off)) {
         return false;
       }
-      SET_INT32(code(off), ival);
+      SET_INT32(bytecodeSection().code(off), ival);
     }
     return true;
   }
@@ -2254,13 +2258,13 @@ bool BytecodeEmitter::allocateResumeIndex(ptrdiff_t offset,
       "resumeIndex * sizeof(uintptr_t) must fit in an int32. JIT code relies "
       "on this when loading resume entries from BaselineScript");
 
-  *resumeIndex = resumeOffsetList.length();
+  *resumeIndex = bytecodeSection().resumeOffsetList().length();
   if (*resumeIndex > MaxResumeIndex) {
     reportError(nullptr, JSMSG_TOO_MANY_RESUME_INDEXES);
     return false;
   }
 
-  return resumeOffsetList.append(offset);
+  return bytecodeSection().resumeOffsetList().append(offset);
 }
 
 bool BytecodeEmitter::allocateResumeIndexRange(mozilla::Span<ptrdiff_t> offsets,
@@ -2293,15 +2297,15 @@ bool BytecodeEmitter::emitYieldOp(JSOp op) {
   }
 
   if (op == JSOP_INITIALYIELD || op == JSOP_YIELD) {
-    numYields++;
+    bytecodeSection().addNumYields();
   }
 
   uint32_t resumeIndex;
-  if (!allocateResumeIndex(offset(), &resumeIndex)) {
+  if (!allocateResumeIndex(bytecodeSection().offset(), &resumeIndex)) {
     return false;
   }
 
-  SET_RESUMEINDEX(code(off), resumeIndex);
+  SET_RESUMEINDEX(bytecodeSection().code(off), resumeIndex);
 
   return emit1(JSOP_DEBUGAFTERYIELD);
 }
@@ -2569,7 +2573,7 @@ bool BytecodeEmitter::emitDestructuringLHSRef(ParseNode* target,
   }
 
 #ifdef DEBUG
-  int depth = stackDepth;
+  int depth = bytecodeSection().stackDepth();
 #endif
 
   switch (target->getKind()) {
@@ -2647,7 +2651,7 @@ bool BytecodeEmitter::emitDestructuringLHSRef(ParseNode* target,
       MOZ_CRASH("emitDestructuringLHSRef: bad lhs kind");
   }
 
-  MOZ_ASSERT(stackDepth == depth + int(*emitted));
+  MOZ_ASSERT(bytecodeSection().stackDepth() == depth + int(*emitted));
 
   return true;
 }
@@ -2810,7 +2814,7 @@ bool BytecodeEmitter::emitIteratorNext(
              "can run user-modifiable iteration code");
 
   //                [stack] ... NEXT ITER
-  MOZ_ASSERT(this->stackDepth >= 2);
+  MOZ_ASSERT(bytecodeSection().stackDepth() >= 2);
 
   if (!emitCall(JSOP_CALL, 0, callSourceCoordOffset)) {
     //              [stack] ... RESULT
@@ -2833,7 +2837,7 @@ bool BytecodeEmitter::emitIteratorNext(
 
 bool BytecodeEmitter::emitPushNotUndefinedOrNull() {
   //                [stack] V
-  MOZ_ASSERT(this->stackDepth > 0);
+  MOZ_ASSERT(bytecodeSection().stackDepth() > 0);
 
   if (!emit1(JSOP_DUP)) {
     //              [stack] V V
@@ -3081,7 +3085,7 @@ bool BytecodeEmitter::emitIteratorCloseInScope(
 template <typename InnerEmitter>
 bool BytecodeEmitter::wrapWithDestructuringTryNote(int32_t iterDepth,
                                                    InnerEmitter emitter) {
-  MOZ_ASSERT(this->stackDepth >= iterDepth);
+  MOZ_ASSERT(bytecodeSection().stackDepth() >= iterDepth);
 
   // Pad a nop at the beginning of the bytecode covered by the trynote so
   // that when unwinding environments, we may unwind to the scope
@@ -3092,11 +3096,11 @@ bool BytecodeEmitter::wrapWithDestructuringTryNote(int32_t iterDepth,
     return false;
   }
 
-  ptrdiff_t start = offset();
+  ptrdiff_t start = bytecodeSection().offset();
   if (!emitter(this)) {
     return false;
   }
-  ptrdiff_t end = offset();
+  ptrdiff_t end = bytecodeSection().offset();
   if (start != end) {
     return addTryNote(JSTRY_DESTRUCTURING, iterDepth, start, end);
   }
@@ -3202,7 +3206,7 @@ bool BytecodeEmitter::emitInitializer(ParseNode* initializer,
 bool BytecodeEmitter::emitDestructuringOpsArray(ListNode* pattern,
                                                 DestructuringFlavor flav) {
   MOZ_ASSERT(pattern->isKind(ParseNodeKind::ArrayExpr));
-  MOZ_ASSERT(this->stackDepth != 0);
+  MOZ_ASSERT(bytecodeSection().stackDepth() != 0);
 
   // Here's pseudo code for |let [a, b, , c=y, ...d] = x;|
   //
@@ -3326,7 +3330,7 @@ bool BytecodeEmitter::emitDestructuringOpsArray(ListNode* pattern,
   // JSTRY_DESTRUCTURING expects the iterator and the done value
   // to be the second to top and the top of the stack, respectively.
   // IteratorClose is called upon exception only if done is false.
-  int32_t tryNoteDepth = stackDepth;
+  int32_t tryNoteDepth = bytecodeSection().stackDepth();
 
   for (ParseNode* member : pattern->contents()) {
     bool isFirst = member == pattern->head();
@@ -3635,7 +3639,7 @@ bool BytecodeEmitter::emitDestructuringOpsObject(ListNode* pattern,
   MOZ_ASSERT(pattern->isKind(ParseNodeKind::ObjectExpr));
 
   //                [stack] ... RHS
-  MOZ_ASSERT(this->stackDepth > 0);
+  MOZ_ASSERT(bytecodeSection().stackDepth() > 0);
 
   if (!emit1(JSOP_CHECKOBJCOERCIBLE)) {
     //              [stack] ... RHS
@@ -3815,7 +3819,7 @@ bool BytecodeEmitter::emitDestructuringObjRestExclusionSet(ListNode* pattern) {
   MOZ_ASSERT(pattern->isKind(ParseNodeKind::ObjectExpr));
   MOZ_ASSERT(pattern->last()->isKind(ParseNodeKind::Spread));
 
-  ptrdiff_t offset = this->offset();
+  ptrdiff_t offset = bytecodeSection().offset();
   if (!emitNewInit()) {
     return false;
   }
@@ -4690,11 +4694,11 @@ MOZ_MUST_USE bool BytecodeEmitter::emitGoSub(JumpList* jump) {
   }
 
   uint32_t resumeIndex;
-  if (!allocateResumeIndex(offset(), &resumeIndex)) {
+  if (!allocateResumeIndex(bytecodeSection().offset(), &resumeIndex)) {
     return false;
   }
 
-  SET_RESUMEINDEX(code(off), resumeIndex);
+  SET_RESUMEINDEX(bytecodeSection().code(off), resumeIndex);
   return true;
 }
 
@@ -4899,7 +4903,7 @@ bool BytecodeEmitter::emitWith(BinaryNode* withNode) {
 }
 
 bool BytecodeEmitter::emitCopyDataProperties(CopyOption option) {
-  DebugOnly<int32_t> depth = this->stackDepth;
+  DebugOnly<int32_t> depth = bytecodeSection().stackDepth();
 
   uint32_t argc;
   if (option == CopyOption::Filtered) {
@@ -4954,15 +4958,15 @@ bool BytecodeEmitter::emitCopyDataProperties(CopyOption option) {
     return false;
   }
 
-  MOZ_ASSERT(depth - int(argc) == this->stackDepth);
+  MOZ_ASSERT(depth - int(argc) == bytecodeSection().stackDepth());
   return true;
 }
 
 bool BytecodeEmitter::emitBigIntOp(BigInt* bigint) {
-  if (!numberList.append(BigIntValue(bigint))) {
+  if (!perScriptData().numberList().append(BigIntValue(bigint))) {
     return false;
   }
-  return emitIndex32(JSOP_BIGINT, numberList.length() - 1);
+  return emitIndex32(JSOP_BIGINT, perScriptData().numberList().length() - 1);
 }
 
 bool BytecodeEmitter::emitIterator() {
@@ -5145,11 +5149,11 @@ bool BytecodeEmitter::emitSpread(bool allowSelfHosted) {
   // when we reach this point on the loop backedge (if spreading produces at
   // least one value), we've additionally pushed a RESULT iteration value.
   // Increment manually to reflect this.
-  this->stackDepth++;
+  bytecodeSection().setStackDepth(bytecodeSection().stackDepth() + 1);
 
   {
 #ifdef DEBUG
-    auto loopDepth = this->stackDepth;
+    auto loopDepth = bytecodeSection().stackDepth();
 #endif
 
     // Emit code to assign result.value to the iteration variable.
@@ -5162,7 +5166,7 @@ bool BytecodeEmitter::emitSpread(bool allowSelfHosted) {
       return false;
     }
 
-    MOZ_ASSERT(this->stackDepth == loopDepth - 1);
+    MOZ_ASSERT(bytecodeSection().stackDepth() == loopDepth - 1);
 
     // Spread operations can't contain |continue|, so don't bother setting loop
     // and enclosing "update" offsets, as we do with for-loops.
@@ -5199,7 +5203,7 @@ bool BytecodeEmitter::emitSpread(bool allowSelfHosted) {
       return false;
     }
 
-    MOZ_ASSERT(this->stackDepth == loopDepth);
+    MOZ_ASSERT(bytecodeSection().stackDepth() == loopDepth);
   }
 
   // Let Ion know where the closing jump of this loop is.
@@ -5212,8 +5216,8 @@ bool BytecodeEmitter::emitSpread(bool allowSelfHosted) {
   MOZ_ASSERT(loopInfo.breaks.offset == -1);
   MOZ_ASSERT(loopInfo.continues.offset == -1);
 
-  if (!addTryNote(JSTRY_FOR_OF, stackDepth, loopInfo.headOffset(),
-                  loopInfo.breakTargetOffset())) {
+  if (!addTryNote(JSTRY_FOR_OF, bytecodeSection().stackDepth(),
+                  loopInfo.headOffset(), loopInfo.breakTargetOffset())) {
     return false;
   }
 
@@ -5234,7 +5238,7 @@ bool BytecodeEmitter::emitInitializeForInOrOfTarget(TernaryNode* forHead) {
   MOZ_ASSERT(forHead->isKind(ParseNodeKind::ForIn) ||
              forHead->isKind(ParseNodeKind::ForOf));
 
-  MOZ_ASSERT(this->stackDepth >= 1,
+  MOZ_ASSERT(bytecodeSection().stackDepth() >= 1,
              "must have a per-iteration value for initializing");
 
   ParseNode* target = forHead->kid1();
@@ -5282,14 +5286,14 @@ bool BytecodeEmitter::emitInitializeForInOrOfTarget(TernaryNode* forHead) {
       // iteration value *before* initializing.  Thus the initializing
       // value may be buried under a bind-specific value on the stack.
       // Swap it to the top of the stack.
-      MOZ_ASSERT(stackDepth >= 2);
+      MOZ_ASSERT(bytecodeSection().stackDepth() >= 2);
       if (!emit1(JSOP_SWAP)) {
         return false;
       }
     } else {
       // In cases of emitting a frame slot or environment slot,
       // nothing needs be done.
-      MOZ_ASSERT(stackDepth >= 1);
+      MOZ_ASSERT(bytecodeSection().stackDepth() >= 1);
     }
     if (!noe.emitAssignment()) {
       return false;
@@ -5967,7 +5971,7 @@ bool BytecodeEmitter::emitReturn(UnaryNode* returnNode) {
    * In this case we mutate JSOP_RETURN into JSOP_SETRVAL and add an
    * extra JSOP_RETRVAL after the fixups.
    */
-  ptrdiff_t top = offset();
+  ptrdiff_t top = bytecodeSection().offset();
 
   bool needsFinalYield =
       sc->isFunctionBox() && sc->asFunctionBox()->needsFinalYield();
@@ -6028,12 +6032,13 @@ bool BytecodeEmitter::emitReturn(UnaryNode* returnNode) {
       return false;
     }
   } else if (isDerivedClassConstructor) {
-    MOZ_ASSERT(code()[top] == JSOP_SETRVAL);
+    MOZ_ASSERT(bytecodeSection().code()[top] == JSOP_SETRVAL);
     if (!emit1(JSOP_RETRVAL)) {
       return false;
     }
-  } else if (top + static_cast<ptrdiff_t>(JSOP_RETURN_LENGTH) != offset()) {
-    code()[top] = JSOP_SETRVAL;
+  } else if (top + static_cast<ptrdiff_t>(JSOP_RETURN_LENGTH) !=
+             bytecodeSection().offset()) {
+    bytecodeSection().code()[top] = JSOP_SETRVAL;
     if (!emit1(JSOP_RETRVAL)) {
       return false;
     }
@@ -6213,7 +6218,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
   }
 
   int32_t savedDepthTemp;
-  int32_t startDepth = stackDepth;
+  int32_t startDepth = bytecodeSection().stackDepth();
   MOZ_ASSERT(startDepth >= 3);
 
   TryEmitter tryCatch(this, TryEmitter::Kind::TryCatchFinally,
@@ -6245,7 +6250,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  MOZ_ASSERT(this->stackDepth == startDepth);
+  MOZ_ASSERT(bytecodeSection().stackDepth() == startDepth);
 
   // Step 7.a.vi.
   // Step 7.b.ii.7.
@@ -6278,7 +6283,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  MOZ_ASSERT(stackDepth == startDepth);
+  MOZ_ASSERT(bytecodeSection().stackDepth() == startDepth);
 
   if (!emit1(JSOP_EXCEPTION)) {
     //              [stack] NEXT ITER RESULT EXCEPTION
@@ -6297,7 +6302,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  savedDepthTemp = stackDepth;
+  savedDepthTemp = bytecodeSection().stackDepth();
   InternalIfEmitter ifThrowMethodIsNotDefined(this);
   if (!emitPushNotUndefinedOrNull()) {
     //              [stack] NEXT ITER RESULT EXCEPTION ITER THROW
@@ -6348,7 +6353,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     //              [stack] NEXT ITER RESULT
     return false;
   }
-  MOZ_ASSERT(this->stackDepth == startDepth);
+  MOZ_ASSERT(bytecodeSection().stackDepth() == startDepth);
 
   JumpList checkResult;
   // Note that there is no GOSUB to the finally block here. If the iterator has
@@ -6359,7 +6364,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  stackDepth = savedDepthTemp;
+  bytecodeSection().setStackDepth(savedDepthTemp);
   if (!ifThrowMethodIsNotDefined.emitElse()) {
     //              [stack] NEXT ITER RESULT EXCEPTION ITER THROW
     return false;
@@ -6384,12 +6389,12 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  stackDepth = savedDepthTemp;
+  bytecodeSection().setStackDepth(savedDepthTemp);
   if (!ifThrowMethodIsNotDefined.emitEnd()) {
     return false;
   }
 
-  stackDepth = startDepth;
+  bytecodeSection().setStackDepth(startDepth);
   if (!tryCatch.emitFinally()) {
     return false;
   }
@@ -6516,7 +6521,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     //              [stack] NEXT ITER OLDRESULT FTYPE FVALUE
     return false;
   }
-  savedDepthTemp = this->stackDepth;
+  savedDepthTemp = bytecodeSection().stackDepth();
   if (!ifReturnDone.emitElse()) {
     //              [stack] NEXT ITER OLDRESULT FTYPE FVALUE RESULT
     return false;
@@ -6538,7 +6543,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
       return false;
     }
   }
-  this->stackDepth = savedDepthTemp;
+  bytecodeSection().setStackDepth(savedDepthTemp);
   if (!ifReturnDone.emitEnd()) {
     return false;
   }
@@ -6613,7 +6618,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     //              [stack] NEXT ITER RESULT
     return false;
   }
-  MOZ_ASSERT(this->stackDepth == startDepth);
+  MOZ_ASSERT(bytecodeSection().stackDepth() == startDepth);
 
   // Steps 7.a.iv-v.
   // Steps 7.b.ii.5-6.
@@ -6658,7 +6663,7 @@ bool BytecodeEmitter::emitYieldStar(ParseNode* iter) {
     return false;
   }
 
-  MOZ_ASSERT(this->stackDepth == startDepth - 2);
+  MOZ_ASSERT(bytecodeSection().stackDepth() == startDepth - 2);
 
   return true;
 }
@@ -6707,7 +6712,7 @@ bool BytecodeEmitter::emitExpressionStatement(UnaryNode* exprStmt) {
     if (innermostNestableControl &&
         innermostNestableControl->is<LabelControl>() &&
         innermostNestableControl->as<LabelControl>().startOffset() >=
-            offset()) {
+            bytecodeSection().offset()) {
       useful = true;
     }
   }
@@ -8182,8 +8187,8 @@ bool BytecodeEmitter::replaceNewInitWithNewObject(JSObject* obj,
       JSOP_NEWINIT_LENGTH == JSOP_NEWOBJECT_LENGTH,
       "newinit and newobject must have equal length to edit in-place");
 
-  uint32_t index = objectList.add(objbox);
-  jsbytecode* code = this->code(offset);
+  uint32_t index = perScriptData().objectList().add(objbox);
+  jsbytecode* code = bytecodeSection().code(offset);
 
   MOZ_ASSERT(code[0] == JSOP_NEWINIT);
   code[0] = JSOP_NEWOBJECT;
@@ -9233,7 +9238,8 @@ bool BytecodeEmitter::emitTree(
       break;
 
     case ParseNodeKind::RegExpExpr:
-      if (!emitRegExp(objectList.add(pn->as<RegExpLiteral>().objbox()))) {
+      if (!emitRegExp(perScriptData().objectList().add(
+              pn->as<RegExpLiteral>().objbox()))) {
         return false;
       }
       break;
@@ -9334,11 +9340,13 @@ static bool AllocSrcNote(JSContext* cx, SrcNotesVector& notes,
 bool BytecodeEmitter::addTryNote(JSTryNoteKind kind, uint32_t stackDepth,
                                  size_t start, size_t end) {
   MOZ_ASSERT(!inPrologue());
-  return tryNoteList.append(kind, stackDepth, start, end);
+  return bytecodeSection().tryNoteList().append(kind, stackDepth, start, end);
 }
 
 bool BytecodeEmitter::newSrcNote(SrcNoteType type, unsigned* indexp) {
-  SrcNotesVector& notes = this->notes();
+  // Prologue shouldn't have source notes.
+  MOZ_ASSERT(!inPrologue());
+  SrcNotesVector& notes = bytecodeSection().notes();
   unsigned index;
   if (!AllocSrcNote(cx, notes, &index)) {
     return false;
@@ -9348,9 +9356,9 @@ bool BytecodeEmitter::newSrcNote(SrcNoteType type, unsigned* indexp) {
    * Compute delta from the last annotated bytecode's offset.  If it's too
    * big to fit in sn, allocate one or more xdelta notes and reset sn.
    */
-  ptrdiff_t offset = this->offset();
-  ptrdiff_t delta = offset - lastNoteOffset();
-  lastNoteOffset_ = offset;
+  ptrdiff_t offset = bytecodeSection().offset();
+  ptrdiff_t delta = offset - bytecodeSection().lastNoteOffset();
+  bytecodeSection().setLastNoteOffset(offset);
   if (delta >= SN_DELTA_LIMIT) {
     do {
       ptrdiff_t xdelta = Min(delta, SN_XDELTA_MASK);
@@ -9420,7 +9428,7 @@ bool BytecodeEmitter::setSrcNoteOffset(unsigned index, unsigned which,
     return false;
   }
 
-  SrcNotesVector& notes = this->notes();
+  SrcNotesVector& notes = bytecodeSection().notes();
 
   /* Find the offset numbered which (i.e., skip exactly which offsets). */
   jssrcnote* sn = &notes[index];
@@ -9458,10 +9466,10 @@ bool BytecodeEmitter::setSrcNoteOffset(unsigned index, unsigned which,
 }
 
 void BytecodeEmitter::copySrcNotes(jssrcnote* destination, uint32_t nsrcnotes) {
-  unsigned count = notes_.length();
+  unsigned count = bytecodeSection().notes().length();
   // nsrcnotes includes SN_MAKE_TERMINATOR in addition to the srcnotes.
   MOZ_ASSERT(nsrcnotes == count + 1);
-  PodCopy(destination, notes_.begin(), count);
+  PodCopy(destination, bytecodeSection().notes().begin(), count);
   SN_MAKE_TERMINATOR(&destination[count]);
 }
 
diff --git a/js/src/frontend/BytecodeEmitter.h b/js/src/frontend/BytecodeEmitter.h
index 7d4c9e93d2f9..83cd4a7fb6dd 100644
--- a/js/src/frontend/BytecodeEmitter.h
+++ b/js/src/frontend/BytecodeEmitter.h
@@ -124,29 +124,249 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
   Rooted<LazyScript*> lazyScript;
 
  private:
-  BytecodeVector code_;  /* bytecode */
-  SrcNotesVector notes_; /* source notes, see below */
+  // Bytecode and all data directly associated with specific opcode/index inside
+  // bytecode is stored in this class.
+  class BytecodeSection {
+   public:
+    BytecodeSection(JSContext* cx, uint32_t lineNum);
 
-  // Code offset for last source note
-  ptrdiff_t lastNoteOffset_ = 0;
+    // ---- Bytecode ----
 
-  // Line number for srcnotes.
-  //
-  // WARNING: If this becomes out of sync with already-emitted srcnotes,
-  // we can get undefined behavior.
-  uint32_t currentLine_ = 0;
+    BytecodeVector& code() { return code_; }
+    const BytecodeVector& code() const { return code_; }
 
-  // Zero-based column index on currentLine of last SRC_COLSPAN-annotated
-  // opcode.
-  //
-  // WARNING: If this becomes out of sync with already-emitted srcnotes,
-  // we can get undefined behavior.
-  uint32_t lastColumn_ = 0;
+    jsbytecode* code(ptrdiff_t offset) { return code_.begin() + offset; }
+    ptrdiff_t offset() const { return code_.end() - code_.begin(); }
 
-  uint32_t lastSeparatorOffet_ = 0;
-  uint32_t lastSeparatorLine_ = 0;
-  uint32_t lastSeparatorColumn_ = 0;
+    // ---- Source notes ----
 
+    SrcNotesVector& notes() { return notes_; }
+    const SrcNotesVector& notes() const { return notes_; }
+
+    ptrdiff_t lastNoteOffset() const { return lastNoteOffset_; }
+    void setLastNoteOffset(ptrdiff_t offset) { lastNoteOffset_ = offset; }
+
+    // ---- Jump ----
+
+    ptrdiff_t lastTargetOffset() const { return lastTarget_.offset; }
+    void setLastTargetOffset(ptrdiff_t offset) { lastTarget_.offset = offset; }
+
+    // Check if the last emitted opcode is a jump target.
+    bool lastOpcodeIsJumpTarget() const {
+      return offset() - lastTarget_.offset == ptrdiff_t(JSOP_JUMPTARGET_LENGTH);
+    }
+
+    // JumpTarget should not be part of the emitted statement, as they can be
+    // aliased by multiple statements. If we included the jump target as part of
+    // the statement we might have issues where the enclosing statement might
+    // not contain all the opcodes of the enclosed statements.
+    ptrdiff_t lastNonJumpTargetOffset() const {
+      return lastOpcodeIsJumpTarget() ? lastTarget_.offset : offset();
+    }
+
+    // ---- Stack ----
+
+    int32_t stackDepth() const { return stackDepth_; }
+    void setStackDepth(int32_t depth) { stackDepth_ = depth; }
+
+    uint32_t maxStackDepth() const { return maxStackDepth_; }
+
+    void updateDepth(ptrdiff_t target);
+
+    // ---- Try notes ----
+
+    CGTryNoteList& tryNoteList() { return tryNoteList_; };
+    const CGTryNoteList& tryNoteList() const { return tryNoteList_; };
+
+    // ---- Scope ----
+
+    CGScopeNoteList& scopeNoteList() { return scopeNoteList_; };
+    const CGScopeNoteList& scopeNoteList() const { return scopeNoteList_; };
+
+    // ---- Generator ----
+
+    CGResumeOffsetList& resumeOffsetList() { return resumeOffsetList_; }
+    const CGResumeOffsetList& resumeOffsetList() const {
+      return resumeOffsetList_;
+    }
+
+    uint32_t numYields() const { return numYields_; }
+    void addNumYields() { numYields_++; }
+
+    // ---- Line and column ----
+
+    uint32_t currentLine() const { return currentLine_; }
+    uint32_t lastColumn() const { return lastColumn_; }
+    void setCurrentLine(uint32_t line) {
+      currentLine_ = line;
+      lastColumn_ = 0;
+    }
+    void setLastColumn(uint32_t column) { lastColumn_ = column; }
+
+    void updateSeparatorPosition() {
+      lastSeparatorOffet_ = code().length();
+      lastSeparatorLine_ = currentLine_;
+      lastSeparatorColumn_ = lastColumn_;
+    }
+
+    void updateSeparatorPositionIfPresent() {
+      if (lastSeparatorOffet_ == code().length()) {
+        lastSeparatorLine_ = currentLine_;
+        lastSeparatorColumn_ = lastColumn_;
+      }
+    }
+
+    bool isDuplicateLocation() const {
+      return lastSeparatorLine_ == currentLine_ &&
+             lastSeparatorColumn_ == lastColumn_;
+    }
+
+    // ---- JIT ----
+
+    size_t numICEntries() const { return numICEntries_; }
+    void addNumICEntries() { numICEntries_++; }
+    void setNumICEntries(size_t entries) { numICEntries_ = entries; }
+
+    uint16_t typesetCount() const { return typesetCount_; }
+    void addTypesetCount() { typesetCount_++; }
+
+   private:
+    // ---- Bytecode ----
+
+    // Bytecode.
+    BytecodeVector code_;
+
+    // ---- Source notes ----
+
+    // Source notes
+    SrcNotesVector notes_;
+
+    // Code offset for last source note
+    ptrdiff_t lastNoteOffset_ = 0;
+
+    // ---- Jump ----
+
+    // Last jump target emitted.
+    JumpTarget lastTarget_ = {-1 - ptrdiff_t(JSOP_JUMPTARGET_LENGTH)};
+
+    // ---- Stack ----
+
+    // Maximum number of expression stack slots so far.
+    uint32_t maxStackDepth_ = 0;
+
+    // Current stack depth in script frame.
+    int32_t stackDepth_ = 0;
+
+    // ---- Try notes ----
+
+    // List of emitted try notes.
+    CGTryNoteList tryNoteList_;
+
+    // ---- Scope ----
+
+    // List of emitted block scope notes.
+    CGScopeNoteList scopeNoteList_;
+
+    // ---- Generator ----
+
+    // Certain ops (yield, await, gosub) have an entry in the script's
+    // resumeOffsets list. This can be used to map from the op's resumeIndex to
+    // the bytecode offset of the next pc. This indirection makes it easy to
+    // resume in the JIT (because BaselineScript stores a resumeIndex => native
+    // code array).
+    CGResumeOffsetList resumeOffsetList_;
+
+    // Number of yield instructions emitted. Does not include JSOP_AWAIT.
+    uint32_t numYields_ = 0;
+
+    // ---- Line and column ----
+
+    // Line number for srcnotes.
+    //
+    // WARNING: If this becomes out of sync with already-emitted srcnotes,
+    // we can get undefined behavior.
+    uint32_t currentLine_;
+
+    // Zero-based column index on currentLine_ of last SRC_COLSPAN-annotated
+    // opcode.
+    //
+    // WARNING: If this becomes out of sync with already-emitted srcnotes,
+    // we can get undefined behavior.
+    uint32_t lastColumn_ = 0;
+
+    // The offset, line and column numbers of the last opcode for the
+    // breakpoint for step execution.
+    uint32_t lastSeparatorOffet_ = 0;
+    uint32_t lastSeparatorLine_ = 0;
+    uint32_t lastSeparatorColumn_ = 0;
+
+    // ---- JIT ----
+
+    // Number of JOF_IC opcodes emitted.
+    size_t numICEntries_ = 0;
+
+    // Number of JOF_TYPESET opcodes generated.
+    uint16_t typesetCount_ = 0;
+  };
+
+  BytecodeSection bytecodeSection_;
+
+ public:
+  BytecodeSection& bytecodeSection() { return bytecodeSection_; }
+  const BytecodeSection& bytecodeSection() const { return bytecodeSection_; }
+
+ private:
+  // Data that is not directly associated with specific opcode/index inside
+  // bytecode, but referred from bytecode is stored in this class.
+  class PerScriptData {
+   public:
+    explicit PerScriptData(JSContext* cx);
+
+    MOZ_MUST_USE bool init(JSContext* cx);
+
+    // ---- Scope ----
+
+    CGScopeList& scopeList() { return scopeList_; }
+    const CGScopeList& scopeList() const { return scopeList_; }
+
+    // ---- Literals ----
+
+    CGNumberList& numberList() { return numberList_; }
+    const CGNumberList& numberList() const { return numberList_; }
+
+    CGObjectList& objectList() { return objectList_; }
+    const CGObjectList& objectList() const { return objectList_; }
+
+    PooledMapPtr<AtomIndexMap>& atomIndices() { return atomIndices_; }
+    const PooledMapPtr<AtomIndexMap>& atomIndices() const {
+      return atomIndices_;
+    }
+
+   private:
+    // ---- Scope ----
+
+    // List of emitted scopes.
+    CGScopeList scopeList_;
+
+    // ---- Literals ----
+
+    // List of double and bigint values used by script.
+    CGNumberList numberList_;
+
+    // List of emitted objects.
+    CGObjectList objectList_;
+
+    // Map from atom to index.
+    PooledMapPtr<AtomIndexMap> atomIndices_;
+  };
+
+  PerScriptData perScriptData_;
+
+ public:
+  PerScriptData& perScriptData() { return perScriptData_; }
+  const PerScriptData& perScriptData() const { return perScriptData_; }
+
+ private:
   // switchToMain sets this to the bytecode offset of the main section.
   mozilla::Maybe<uint32_t> mainOffset_ = {};
 
@@ -154,22 +374,14 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
   const FieldInitializers fieldInitializers_;
 
  public:
-  // Last jump target emitted.
-  JumpTarget lastTarget = {-1 - ptrdiff_t(JSOP_JUMPTARGET_LENGTH)};
-
   // Private storage for parser wrapper. DO NOT REFERENCE INTERNALLY. May not be
   // initialized. Use |parser| instead.
   mozilla::Maybe<EitherParser> ep_ = {};
   BCEParserHandle* parser = nullptr;
 
-  PooledMapPtr<AtomIndexMap> atomIndices; /* literals indexed for mapping */
   unsigned firstLine = 0; /* first line, for JSScript::initFromEmitter */
 
   uint32_t maxFixedSlots = 0; /* maximum number of fixed frame slots so far */
-  uint32_t maxStackDepth =
-      0; /* maximum number of expression stack slots so far */
-
-  int32_t stackDepth = 0; /* current stack depth in script frame */
 
   uint32_t bodyScopeIndex =
       UINT32_MAX; /* index into scopeList of the body scope */
@@ -195,28 +407,6 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
     return innermostEmitterScope_;
   }
 
-  CGNumberList numberList;       /* double and bigint values used by script */
-  CGObjectList objectList;       /* list of emitted objects */
-  CGScopeList scopeList;         /* list of emitted scopes */
-  CGTryNoteList tryNoteList;     /* list of emitted try notes */
-  CGScopeNoteList scopeNoteList; /* list of emitted block scope notes */
-
-  // Certain ops (yield, await, gosub) have an entry in the script's
-  // resumeOffsets list. This can be used to map from the op's resumeIndex to
-  // the bytecode offset of the next pc. This indirection makes it easy to
-  // resume in the JIT (because BaselineScript stores a resumeIndex => native
-  // code array).
-  CGResumeOffsetList resumeOffsetList;
-
-  // Number of JOF_IC opcodes emitted.
-  size_t numICEntries = 0;
-
-  // Number of yield instructions emitted. Does not include JSOP_AWAIT.
-  uint32_t numYields = 0;
-
-  // Number of JOF_TYPESET opcodes generated.
-  uint16_t typesetCount = 0;
-
   // Script contains singleton initializer JSOP_OBJECT.
   bool hasSingletons = false;
 
@@ -360,24 +550,26 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
     varEmitterScope = emitterScope;
   }
 
-  Scope* outermostScope() const { return scopeList.vector[0]; }
+  Scope* outermostScope() const {
+    return perScriptData().scopeList().vector[0];
+  }
   Scope* innermostScope() const;
   Scope* bodyScope() const {
-    MOZ_ASSERT(bodyScopeIndex < scopeList.length());
-    return scopeList.vector[bodyScopeIndex];
+    MOZ_ASSERT(bodyScopeIndex < perScriptData().scopeList().length());
+    return perScriptData().scopeList().vector[bodyScopeIndex];
   }
 
   MOZ_ALWAYS_INLINE
   MOZ_MUST_USE bool makeAtomIndex(JSAtom* atom, uint32_t* indexp) {
-    MOZ_ASSERT(atomIndices);
-    AtomIndexMap::AddPtr p = atomIndices->lookupForAdd(atom);
+    MOZ_ASSERT(perScriptData().atomIndices());
+    AtomIndexMap::AddPtr p = perScriptData().atomIndices()->lookupForAdd(atom);
     if (p) {
       *indexp = p->value();
       return true;
     }
 
-    uint32_t index = atomIndices->count();
-    if (!atomIndices->add(p, atom, index)) {
+    uint32_t index = perScriptData().atomIndices()->count();
+    if (!perScriptData().atomIndices()->add(p, atom, index)) {
       ReportOutOfMemory(cx);
       return false;
     }
@@ -400,45 +592,13 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
 
   void tellDebuggerAboutCompiledScript(JSContext* cx);
 
-  BytecodeVector& code() { return code_; }
-  const BytecodeVector& code() const { return code_; }
-
-  jsbytecode* code(ptrdiff_t offset) { return code_.begin() + offset; }
-  ptrdiff_t offset() const { return code_.end() - code_.begin(); }
-
   uint32_t mainOffset() const { return *mainOffset_; }
 
   bool inPrologue() const { return mainOffset_.isNothing(); }
 
   void switchToMain() {
     MOZ_ASSERT(inPrologue());
-    mainOffset_.emplace(code_.length());
-  }
-
-  SrcNotesVector& notes() {
-    // Prologue shouldn't have source notes.
-    MOZ_ASSERT(!inPrologue());
-    return notes_;
-  }
-  ptrdiff_t lastNoteOffset() const { return lastNoteOffset_; }
-  unsigned currentLine() const { return currentLine_; }
-
-  void setCurrentLine(uint32_t line) {
-    currentLine_ = line;
-    lastColumn_ = 0;
-  }
-
-  // Check if the last emitted opcode is a jump target.
-  bool lastOpcodeIsJumpTarget() const {
-    return offset() - lastTarget.offset == ptrdiff_t(JSOP_JUMPTARGET_LENGTH);
-  }
-
-  // JumpTarget should not be part of the emitted statement, as they can be
-  // aliased by multiple statements. If we included the jump target as part of
-  // the statement we might have issues where the enclosing statement might
-  // not contain all the opcodes of the enclosed statements.
-  ptrdiff_t lastNonJumpTargetOffset() const {
-    return lastOpcodeIsJumpTarget() ? lastTarget.offset : offset();
+    mainOffset_.emplace(bytecodeSection().code().length());
   }
 
   void setFunctionBodyEndPos(uint32_t pos) {
@@ -509,12 +669,10 @@ struct MOZ_STACK_CLASS BytecodeEmitter {
   MOZ_MUST_USE bool emitFunctionScript(FunctionNode* funNode,
                                        TopLevelFunction isTopLevel);
 
-  void updateDepth(ptrdiff_t target);
   MOZ_MUST_USE bool markStepBreakpoint();
   MOZ_MUST_USE bool markSimpleBreakpoint();
   MOZ_MUST_USE bool updateLineNumberNotes(uint32_t offset);
   MOZ_MUST_USE bool updateSourceCoordNotes(uint32_t offset);
-  void updateSeparatorPosition();
 
   JSOp strictifySetNameOp(JSOp op);
 
diff --git a/js/src/frontend/CForEmitter.cpp b/js/src/frontend/CForEmitter.cpp
index e2be22fa3a86..fc6dce61297b 100644
--- a/js/src/frontend/CForEmitter.cpp
+++ b/js/src/frontend/CForEmitter.cpp
@@ -75,7 +75,7 @@ bool CForEmitter::emitBody(Cond cond, const Maybe<uint32_t>& bodyPos) {
     return false;
   }
 
-  biasedTop_ = bce_->offset();
+  biasedTop_ = bce_->bytecodeSection().offset();
 
   if (cond_ == Cond::Present) {
     // Goto the loop condition, which branches back to iterate.
@@ -163,11 +163,11 @@ bool CForEmitter::emitCond(const Maybe<uint32_t>& forPos,
     // Restore the absolute line number for source note readers.
     if (endPos) {
       uint32_t lineNum = bce_->parser->errorReporter().lineAt(*endPos);
-      if (bce_->currentLine() != lineNum) {
+      if (bce_->bytecodeSection().currentLine() != lineNum) {
         if (!bce_->newSrcNote2(SRC_SETLINE, ptrdiff_t(lineNum))) {
           return false;
         }
-        bce_->setCurrentLine(lineNum);
+        bce_->bytecodeSection().setCurrentLine(lineNum);
       }
     }
   }
@@ -176,7 +176,7 @@ bool CForEmitter::emitCond(const Maybe<uint32_t>& forPos,
     tdzCache_.reset();
   }
 
-  condOffset_ = bce_->offset();
+  condOffset_ = bce_->bytecodeSection().offset();
 
   if (cond_ == Cond::Present) {
     if (!loopInfo_->emitLoopEntry(bce_, condPos)) {
@@ -228,7 +228,8 @@ bool CForEmitter::emitEnd() {
     return false;
   }
 
-  if (!bce_->addTryNote(JSTRY_LOOP, bce_->stackDepth, loopInfo_->headOffset(),
+  if (!bce_->addTryNote(JSTRY_LOOP, bce_->bytecodeSection().stackDepth(),
+                        loopInfo_->headOffset(),
                         loopInfo_->breakTargetOffset())) {
     return false;
   }
diff --git a/js/src/frontend/DoWhileEmitter.cpp b/js/src/frontend/DoWhileEmitter.cpp
index 3a57036cf8c0..35d86b312f4d 100644
--- a/js/src/frontend/DoWhileEmitter.cpp
+++ b/js/src/frontend/DoWhileEmitter.cpp
@@ -75,7 +75,8 @@ bool DoWhileEmitter::emitEnd() {
     return false;
   }
 
-  if (!bce_->addTryNote(JSTRY_LOOP, bce_->stackDepth, loopInfo_->headOffset(),
+  if (!bce_->addTryNote(JSTRY_LOOP, bce_->bytecodeSection().stackDepth(),
+                        loopInfo_->headOffset(),
                         loopInfo_->breakTargetOffset())) {
     return false;
   }
diff --git a/js/src/frontend/EmitterScope.cpp b/js/src/frontend/EmitterScope.cpp
index 7c31ab46438e..6f0bf4bb0ea4 100644
--- a/js/src/frontend/EmitterScope.cpp
+++ b/js/src/frontend/EmitterScope.cpp
@@ -342,8 +342,8 @@ bool EmitterScope::internScope(BytecodeEmitter* bce, ScopeCreator createScope) {
     return false;
   }
   hasEnvironment_ = scope->hasEnvironment();
-  scopeIndex_ = bce->scopeList.length();
-  return bce->scopeList.append(scope);
+  scopeIndex_ = bce->perScriptData().scopeList().length();
+  return bce->perScriptData().scopeList().append(scope);
 }
 
 template <typename ScopeCreator>
@@ -351,18 +351,18 @@ bool EmitterScope::internBodyScope(BytecodeEmitter* bce,
                                    ScopeCreator createScope) {
   MOZ_ASSERT(bce->bodyScopeIndex == UINT32_MAX,
              "There can be only one body scope");
-  bce->bodyScopeIndex = bce->scopeList.length();
+  bce->bodyScopeIndex = bce->perScriptData().scopeList().length();
   return internScope(bce, createScope);
 }
 
 bool EmitterScope::appendScopeNote(BytecodeEmitter* bce) {
   MOZ_ASSERT(ScopeKindIsInBody(scope(bce)->kind()) && enclosingInFrame(),
              "Scope notes are not needed for body-level scopes.");
-  noteIndex_ = bce->scopeNoteList.length();
-  return bce->scopeNoteList.append(index(), bce->offset(),
-                                   enclosingInFrame()
-                                       ? enclosingInFrame()->noteIndex()
-                                       : ScopeNote::NoScopeNoteIndex);
+  noteIndex_ = bce->bytecodeSection().scopeNoteList().length();
+  return bce->bytecodeSection().scopeNoteList().append(
+      index(), bce->bytecodeSection().offset(),
+      enclosingInFrame() ? enclosingInFrame()->noteIndex()
+                         : ScopeNote::NoScopeNoteIndex);
 }
 
 bool EmitterScope::deadZoneFrameSlotRange(BytecodeEmitter* bce,
@@ -1057,9 +1057,10 @@ bool EmitterScope::leave(BytecodeEmitter* bce, bool nonLocal) {
     if (ScopeKindIsInBody(kind)) {
       // The extra function var scope is never popped once it's pushed,
       // so its scope note extends until the end of any possible code.
-      uint32_t offset =
-          kind == ScopeKind::FunctionBodyVar ? UINT32_MAX : bce->offset();
-      bce->scopeNoteList.recordEnd(noteIndex_, offset);
+      uint32_t offset = kind == ScopeKind::FunctionBodyVar
+                            ? UINT32_MAX
+                            : bce->bytecodeSection().offset();
+      bce->bytecodeSection().scopeNoteList().recordEnd(noteIndex_, offset);
     }
   }
 
@@ -1067,7 +1068,7 @@ bool EmitterScope::leave(BytecodeEmitter* bce, bool nonLocal) {
 }
 
 Scope* EmitterScope::scope(const BytecodeEmitter* bce) const {
-  return bce->scopeList.vector[index()];
+  return bce->perScriptData().scopeList().vector[index()];
 }
 
 NameLocation EmitterScope::lookup(BytecodeEmitter* bce, JSAtom* name) {
diff --git a/js/src/frontend/ExpressionStatementEmitter.cpp b/js/src/frontend/ExpressionStatementEmitter.cpp
index ef70db1beccf..c786f3486091 100644
--- a/js/src/frontend/ExpressionStatementEmitter.cpp
+++ b/js/src/frontend/ExpressionStatementEmitter.cpp
@@ -29,7 +29,7 @@ bool ExpressionStatementEmitter::prepareForExpr(
   }
 
 #ifdef DEBUG
-  depth_ = bce_->stackDepth;
+  depth_ = bce_->bytecodeSection().stackDepth();
   state_ = State::Expr;
 #endif
   return true;
@@ -37,7 +37,7 @@ bool ExpressionStatementEmitter::prepareForExpr(
 
 bool ExpressionStatementEmitter::emitEnd() {
   MOZ_ASSERT(state_ == State::Expr);
-  MOZ_ASSERT(bce_->stackDepth == depth_ + 1);
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_ + 1);
 
   //                [stack] VAL
 
diff --git a/js/src/frontend/ForInEmitter.cpp b/js/src/frontend/ForInEmitter.cpp
index 9ca13747b9a3..627fa668b5b5 100644
--- a/js/src/frontend/ForInEmitter.cpp
+++ b/js/src/frontend/ForInEmitter.cpp
@@ -94,7 +94,7 @@ bool ForInEmitter::emitInitialize() {
   }
 
 #ifdef DEBUG
-  loopDepth_ = bce_->stackDepth;
+  loopDepth_ = bce_->bytecodeSection().stackDepth();
 #endif
   MOZ_ASSERT(loopDepth_ >= 2);
 
@@ -112,7 +112,7 @@ bool ForInEmitter::emitInitialize() {
 bool ForInEmitter::emitBody() {
   MOZ_ASSERT(state_ == State::Initialize);
 
-  MOZ_ASSERT(bce_->stackDepth == loopDepth_,
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == loopDepth_,
              "iterator and iterval must be left on the stack");
 
 #ifdef DEBUG
@@ -124,7 +124,7 @@ bool ForInEmitter::emitBody() {
 bool ForInEmitter::emitEnd(const Maybe<uint32_t>& forPos) {
   MOZ_ASSERT(state_ == State::Body);
 
-  loopInfo_->setContinueTarget(bce_->offset());
+  loopInfo_->setContinueTarget(bce_->bytecodeSection().offset());
 
   if (forPos) {
     // Make sure this code is attributed to the "for".
@@ -171,8 +171,9 @@ bool ForInEmitter::emitEnd(const Maybe<uint32_t>& forPos) {
     return false;
   }
 
-  if (!bce_->addTryNote(JSTRY_FOR_IN, bce_->stackDepth, loopInfo_->headOffset(),
-                        bce_->offset())) {
+  if (!bce_->addTryNote(JSTRY_FOR_IN, bce_->bytecodeSection().stackDepth(),
+                        loopInfo_->headOffset(),
+                        bce_->bytecodeSection().offset())) {
     return false;
   }
 
diff --git a/js/src/frontend/ForOfEmitter.cpp b/js/src/frontend/ForOfEmitter.cpp
index 3efabeed38d6..dac23f9e5ba7 100644
--- a/js/src/frontend/ForOfEmitter.cpp
+++ b/js/src/frontend/ForOfEmitter.cpp
@@ -58,7 +58,7 @@ bool ForOfEmitter::emitInitialize(const Maybe<uint32_t>& forPos) {
     }
   }
 
-  int32_t iterDepth = bce_->stackDepth;
+  int32_t iterDepth = bce_->bytecodeSection().stackDepth();
 
   // For-of loops have the iterator next method, the iterator itself, and
   // the result.value on the stack.
@@ -111,7 +111,7 @@ bool ForOfEmitter::emitInitialize(const Maybe<uint32_t>& forPos) {
   }
 
 #ifdef DEBUG
-  loopDepth_ = bce_->stackDepth;
+  loopDepth_ = bce_->bytecodeSection().stackDepth();
 #endif
 
   // Make sure this code is attributed to the "for".
@@ -195,7 +195,7 @@ bool ForOfEmitter::emitInitialize(const Maybe<uint32_t>& forPos) {
 bool ForOfEmitter::emitBody() {
   MOZ_ASSERT(state_ == State::Initialize);
 
-  MOZ_ASSERT(bce_->stackDepth == loopDepth_,
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == loopDepth_,
              "the stack must be balanced around the initializing "
              "operation");
 
@@ -218,14 +218,14 @@ bool ForOfEmitter::emitBody() {
 bool ForOfEmitter::emitEnd(const Maybe<uint32_t>& iteratedPos) {
   MOZ_ASSERT(state_ == State::Body);
 
-  MOZ_ASSERT(bce_->stackDepth == loopDepth_,
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == loopDepth_,
              "the stack must be balanced around the for-of body");
 
   if (!loopInfo_->emitEndCodeNeedingIteratorClose(bce_)) {
     return false;
   }
 
-  loopInfo_->setContinueTarget(bce_->offset());
+  loopInfo_->setContinueTarget(bce_->bytecodeSection().offset());
 
   // We use the iterated value's position to attribute JSOP_LOOPENTRY,
   // which corresponds to the iteration protocol.
@@ -244,7 +244,7 @@ bool ForOfEmitter::emitEnd(const Maybe<uint32_t>& iteratedPos) {
     return false;
   }
 
-  MOZ_ASSERT(bce_->stackDepth == loopDepth_);
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == loopDepth_);
 
   // Let Ion know where the closing jump of this loop is.
   if (!bce_->setSrcNoteOffset(noteIndex_, SrcNote::ForOf::BackJumpOffset,
@@ -256,7 +256,8 @@ bool ForOfEmitter::emitEnd(const Maybe<uint32_t>& iteratedPos) {
     return false;
   }
 
-  if (!bce_->addTryNote(JSTRY_FOR_OF, bce_->stackDepth, loopInfo_->headOffset(),
+  if (!bce_->addTryNote(JSTRY_FOR_OF, bce_->bytecodeSection().stackDepth(),
+                        loopInfo_->headOffset(),
                         loopInfo_->breakTargetOffset())) {
     return false;
   }
diff --git a/js/src/frontend/ForOfLoopControl.cpp b/js/src/frontend/ForOfLoopControl.cpp
index f8cb520ea1bd..473242e8d875 100644
--- a/js/src/frontend/ForOfLoopControl.cpp
+++ b/js/src/frontend/ForOfLoopControl.cpp
@@ -30,7 +30,7 @@ bool ForOfLoopControl::emitBeginCodeNeedingIteratorClose(BytecodeEmitter* bce) {
   }
 
   MOZ_ASSERT(numYieldsAtBeginCodeNeedingIterClose_ == UINT32_MAX);
-  numYieldsAtBeginCodeNeedingIterClose_ = bce->numYields;
+  numYieldsAtBeginCodeNeedingIterClose_ = bce->bytecodeSection().numYields();
 
   return true;
 }
@@ -45,7 +45,7 @@ bool ForOfLoopControl::emitEndCodeNeedingIteratorClose(BytecodeEmitter* bce) {
     //              [stack] ITER ... EXCEPTION
     return false;
   }
-  unsigned slotFromTop = bce->stackDepth - iterDepth_;
+  unsigned slotFromTop = bce->bytecodeSection().stackDepth() - iterDepth_;
   if (!bce->emitDupAt(slotFromTop)) {
     //              [stack] ITER ... EXCEPTION ITER
     return false;
@@ -69,7 +69,8 @@ bool ForOfLoopControl::emitEndCodeNeedingIteratorClose(BytecodeEmitter* bce) {
     return false;
   }
 
-  MOZ_ASSERT(slotFromTop == unsigned(bce->stackDepth - iterDepth_));
+  MOZ_ASSERT(slotFromTop ==
+             unsigned(bce->bytecodeSection().stackDepth() - iterDepth_));
   if (!bce->emitDupAt(slotFromTop)) {
     //              [stack] ITER ... EXCEPTION ITER
     return false;
@@ -92,7 +93,7 @@ bool ForOfLoopControl::emitEndCodeNeedingIteratorClose(BytecodeEmitter* bce) {
   // If any yields were emitted, then this for-of loop is inside a star
   // generator and must handle the case of Generator.return. Like in
   // yield*, it is handled with a finally block.
-  uint32_t numYieldsEmitted = bce->numYields;
+  uint32_t numYieldsEmitted = bce->bytecodeSection().numYields();
   if (numYieldsEmitted > numYieldsAtBeginCodeNeedingIterClose_) {
     if (!tryCatch_->emitFinally()) {
       return false;
@@ -135,12 +136,12 @@ bool ForOfLoopControl::emitEndCodeNeedingIteratorClose(BytecodeEmitter* bce) {
 bool ForOfLoopControl::emitIteratorCloseInInnermostScopeWithTryNote(
     BytecodeEmitter* bce,
     CompletionKind completionKind /* = CompletionKind::Normal */) {
-  ptrdiff_t start = bce->offset();
+  ptrdiff_t start = bce->bytecodeSection().offset();
   if (!emitIteratorCloseInScope(bce, *bce->innermostEmitterScope(),
                                 completionKind)) {
     return false;
   }
-  ptrdiff_t end = bce->offset();
+  ptrdiff_t end = bce->bytecodeSection().offset();
   return bce->addTryNote(JSTRY_FOR_OF_ITERCLOSE, 0, start, end);
 }
 
@@ -193,7 +194,7 @@ bool ForOfLoopControl::emitPrepareForNonLocalJumpFromScope(
     return false;
   }
 
-  *tryNoteStart = bce->offset();
+  *tryNoteStart = bce->bytecodeSection().offset();
   if (!emitIteratorCloseInScope(bce, currentScope, CompletionKind::Normal)) {
     //              [stack] UNDEF
     return false;
diff --git a/js/src/frontend/FunctionEmitter.cpp b/js/src/frontend/FunctionEmitter.cpp
index 0aefbdb94854..ec1f69486cf4 100644
--- a/js/src/frontend/FunctionEmitter.cpp
+++ b/js/src/frontend/FunctionEmitter.cpp
@@ -220,7 +220,7 @@ bool FunctionEmitter::emitAsmJSModule() {
 
 bool FunctionEmitter::emitFunction() {
   // Make the function object a literal in the outer script's pool.
-  unsigned index = bce_->objectList.add(funbox_);
+  unsigned index = bce_->perScriptData().objectList().add(funbox_);
 
   //                [stack]
 
diff --git a/js/src/frontend/IfEmitter.cpp b/js/src/frontend/IfEmitter.cpp
index 6925ba96cf40..f9b9f7f656dd 100644
--- a/js/src/frontend/IfEmitter.cpp
+++ b/js/src/frontend/IfEmitter.cpp
@@ -41,10 +41,10 @@ bool BranchEmitterBase::emitThenInternal(SrcNoteType type) {
   // To restore stack depth in else part, save depth of the then part.
 #ifdef DEBUG
   // If DEBUG, this is also necessary to calculate |pushed_|.
-  thenDepth_ = bce_->stackDepth;
+  thenDepth_ = bce_->bytecodeSection().stackDepth();
 #else
   if (type == SRC_COND || type == SRC_IF_ELSE) {
-    thenDepth_ = bce_->stackDepth;
+    thenDepth_ = bce_->bytecodeSection().stackDepth();
   }
 #endif
 
@@ -59,10 +59,10 @@ bool BranchEmitterBase::emitThenInternal(SrcNoteType type) {
 void BranchEmitterBase::calculateOrCheckPushed() {
 #ifdef DEBUG
   if (!calculatedPushed_) {
-    pushed_ = bce_->stackDepth - thenDepth_;
+    pushed_ = bce_->bytecodeSection().stackDepth() - thenDepth_;
     calculatedPushed_ = true;
   } else {
-    MOZ_ASSERT(pushed_ == bce_->stackDepth - thenDepth_);
+    MOZ_ASSERT(pushed_ == bce_->bytecodeSection().stackDepth() - thenDepth_);
   }
 #endif
 }
@@ -92,7 +92,7 @@ bool BranchEmitterBase::emitElseInternal() {
   jumpAroundThen_ = JumpList();
 
   // Restore stack depth of the then part.
-  bce_->stackDepth = thenDepth_;
+  bce_->bytecodeSection().setStackDepth(thenDepth_);
 
   // Enclose else-branch with TDZCheckCache.
   if (kind_ == Kind::MayContainLexicalAccessInBranch) {
diff --git a/js/src/frontend/LabelEmitter.cpp b/js/src/frontend/LabelEmitter.cpp
index 79a62da171c1..30d863d6e974 100644
--- a/js/src/frontend/LabelEmitter.cpp
+++ b/js/src/frontend/LabelEmitter.cpp
@@ -27,7 +27,7 @@ bool LabelEmitter::emitLabel(JSAtom* name) {
     return false;
   }
 
-  controlInfo_.emplace(bce_, name, bce_->offset());
+  controlInfo_.emplace(bce_, name, bce_->bytecodeSection().offset());
 
 #ifdef DEBUG
   state_ = State::Label;
@@ -39,8 +39,8 @@ bool LabelEmitter::emitEnd() {
   MOZ_ASSERT(state_ == State::Label);
 
   // Patch the JSOP_LABEL offset.
-  jsbytecode* labelpc = bce_->code(top_);
-  int32_t offset = bce_->lastNonJumpTargetOffset() - top_;
+  jsbytecode* labelpc = bce_->bytecodeSection().code(top_);
+  int32_t offset = bce_->bytecodeSection().lastNonJumpTargetOffset() - top_;
   MOZ_ASSERT(*labelpc == JSOP_LABEL);
   SET_CODE_OFFSET(labelpc, offset);
 
diff --git a/js/src/frontend/ObjectEmitter.cpp b/js/src/frontend/ObjectEmitter.cpp
index b19483eb1639..df42cee8767c 100644
--- a/js/src/frontend/ObjectEmitter.cpp
+++ b/js/src/frontend/ObjectEmitter.cpp
@@ -412,7 +412,7 @@ bool ObjectEmitter::emitObject(size_t propertyCount) {
   // Emit code for {p:a, '%q':b, 2:c} that is equivalent to constructing
   // a new object and defining (in source order) each property on the object
   // (or mutating the object's [[Prototype]], in the case of __proto__).
-  top_ = bce_->offset();
+  top_ = bce_->bytecodeSection().offset();
   if (!bce_->emitNewInit()) {
     //              [stack] OBJ
     return false;
diff --git a/js/src/frontend/SwitchEmitter.cpp b/js/src/frontend/SwitchEmitter.cpp
index 9e62613b8491..58d17e7c1932 100644
--- a/js/src/frontend/SwitchEmitter.cpp
+++ b/js/src/frontend/SwitchEmitter.cpp
@@ -151,7 +151,7 @@ bool SwitchEmitter::emitCond() {
 
   // After entering the scope if necessary, push the switch control.
   controlInfo_.emplace(bce_, StatementKind::Switch);
-  top_ = bce_->offset();
+  top_ = bce_->bytecodeSection().offset();
 
   if (!caseOffsets_.resize(caseCount_)) {
     ReportOutOfMemory(bce_->cx);
@@ -164,7 +164,7 @@ bool SwitchEmitter::emitCond() {
     return false;
   }
 
-  MOZ_ASSERT(top_ == bce_->offset());
+  MOZ_ASSERT(top_ == bce_->bytecodeSection().offset());
   if (!bce_->emitN(JSOP_CONDSWITCH, 0)) {
     return false;
   }
@@ -181,7 +181,7 @@ bool SwitchEmitter::emitTable(const TableGenerator& tableGen) {
 
   // After entering the scope if necessary, push the switch control.
   controlInfo_.emplace(bce_, StatementKind::Switch);
-  top_ = bce_->offset();
+  top_ = bce_->bytecodeSection().offset();
 
   // The note has one offset that tells total switch code length.
   if (!bce_->newSrcNote2(SRC_TABLESWITCH, 0, &noteIndex_)) {
@@ -193,14 +193,14 @@ bool SwitchEmitter::emitTable(const TableGenerator& tableGen) {
     return false;
   }
 
-  MOZ_ASSERT(top_ == bce_->offset());
+  MOZ_ASSERT(top_ == bce_->bytecodeSection().offset());
   if (!bce_->emitN(JSOP_TABLESWITCH,
                    JSOP_TABLESWITCH_LENGTH - sizeof(jsbytecode))) {
     return false;
   }
 
   // Skip default offset.
-  jsbytecode* pc = bce_->code(top_ + JUMP_OFFSET_LEN);
+  jsbytecode* pc = bce_->bytecodeSection().code(top_ + JUMP_OFFSET_LEN);
 
   // Fill in switch bounds, which we know fit in 16-bit offsets.
   SET_JUMP_OFFSET(pc, tableGen.low());
@@ -223,9 +223,9 @@ bool SwitchEmitter::emitCaseOrDefaultJump(uint32_t caseIndex, bool isDefault) {
   if (caseIndex > 0) {
     // Link the last JSOP_CASE's SRC_NEXTCASE to current JSOP_CASE for the
     // benefit of IonBuilder.
-    if (!bce_->setSrcNoteOffset(caseNoteIndex_,
-                                SrcNote::NextCase::NextCaseOffset,
-                                bce_->offset() - lastCaseOffset_)) {
+    if (!bce_->setSrcNoteOffset(
+            caseNoteIndex_, SrcNote::NextCase::NextCaseOffset,
+            bce_->bytecodeSection().offset() - lastCaseOffset_)) {
       return false;
     }
   }
@@ -243,11 +243,12 @@ bool SwitchEmitter::emitCaseOrDefaultJump(uint32_t caseIndex, bool isDefault) {
 
   if (caseIndex == 0) {
     // Switch note's second offset is to first JSOP_CASE.
-    unsigned noteCount = bce_->notes().length();
+    unsigned noteCount = bce_->bytecodeSection().notes().length();
     if (!bce_->setSrcNoteOffset(noteIndex_, 1, lastCaseOffset_ - top_)) {
       return false;
     }
-    unsigned noteCountDelta = bce_->notes().length() - noteCount;
+    unsigned noteCountDelta =
+        bce_->bytecodeSection().notes().length() - noteCount;
     if (noteCountDelta != 0) {
       caseNoteIndex_ += noteCountDelta;
     }
@@ -398,7 +399,7 @@ bool SwitchEmitter::emitEnd() {
                              defaultJumpTargetOffset_);
   } else {
     // Fill in the default jump target.
-    pc = bce_->code(top_);
+    pc = bce_->bytecodeSection().code(top_);
     SET_JUMP_OFFSET(pc, defaultJumpTargetOffset_.offset - top_);
     pc += JUMP_OFFSET_LEN;
   }
@@ -408,8 +409,9 @@ bool SwitchEmitter::emitEnd() {
   static_assert(unsigned(SrcNote::TableSwitch::EndOffset) ==
                     unsigned(SrcNote::CondSwitch::EndOffset),
                 "{TableSwitch,CondSwitch}::EndOffset should be same");
-  if (!bce_->setSrcNoteOffset(noteIndex_, SrcNote::TableSwitch::EndOffset,
-                              bce_->lastNonJumpTargetOffset() - top_)) {
+  if (!bce_->setSrcNoteOffset(
+          noteIndex_, SrcNote::TableSwitch::EndOffset,
+          bce_->bytecodeSection().lastNonJumpTargetOffset() - top_)) {
     return false;
   }
 
diff --git a/js/src/frontend/TryEmitter.cpp b/js/src/frontend/TryEmitter.cpp
index 2de77536e139..d194c14810ca 100644
--- a/js/src/frontend/TryEmitter.cpp
+++ b/js/src/frontend/TryEmitter.cpp
@@ -53,7 +53,7 @@ bool TryEmitter::emitTry() {
   // For that we store in a try note associated with the catch or
   // finally block the stack depth upon the try entry. The interpreter
   // uses this depth to properly unwind the stack and the scope chain.
-  depth_ = bce_->stackDepth;
+  depth_ = bce_->bytecodeSection().stackDepth();
 
   // Record the try location, then emit the try block.
   if (!bce_->newSrcNote(SRC_TRY, &noteIndex_)) {
@@ -62,7 +62,7 @@ bool TryEmitter::emitTry() {
   if (!bce_->emit1(JSOP_TRY)) {
     return false;
   }
-  tryStart_ = bce_->offset();
+  tryStart_ = bce_->bytecodeSection().offset();
 
 #ifdef DEBUG
   state_ = State::Try;
@@ -72,7 +72,7 @@ bool TryEmitter::emitTry() {
 
 bool TryEmitter::emitTryEnd() {
   MOZ_ASSERT(state_ == State::Try);
-  MOZ_ASSERT(depth_ == bce_->stackDepth);
+  MOZ_ASSERT(depth_ == bce_->bytecodeSection().stackDepth());
 
   // GOSUB to finally, if present.
   if (hasFinally() && controlInfo_) {
@@ -82,8 +82,9 @@ bool TryEmitter::emitTryEnd() {
   }
 
   // Source note points to the jump at the end of the try block.
-  if (!bce_->setSrcNoteOffset(noteIndex_, SrcNote::Try::EndOfTryJumpOffset,
-                              bce_->offset() - tryStart_ + JSOP_TRY_LENGTH)) {
+  if (!bce_->setSrcNoteOffset(
+          noteIndex_, SrcNote::Try::EndOfTryJumpOffset,
+          bce_->bytecodeSection().offset() - tryStart_ + JSOP_TRY_LENGTH)) {
     return false;
   }
 
@@ -105,7 +106,7 @@ bool TryEmitter::emitCatch() {
     return false;
   }
 
-  MOZ_ASSERT(bce_->stackDepth == depth_);
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
 
   if (controlKind_ == ControlKind::Syntactic) {
     // Clear the frame's return value that might have been set by the
@@ -138,7 +139,7 @@ bool TryEmitter::emitCatchEnd() {
     if (!bce_->emitGoSub(&controlInfo_->gosubs)) {
       return false;
     }
-    MOZ_ASSERT(bce_->stackDepth == depth_);
+    MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
 
     // Jump over the finally block.
     if (!bce_->emitJump(JSOP_GOTO, &catchAndFinallyJump_)) {
@@ -177,7 +178,7 @@ bool TryEmitter::emitFinally(
     }
   }
 
-  MOZ_ASSERT(bce_->stackDepth == depth_);
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
 
   if (!bce_->emitJumpTarget(&finallyStart_)) {
     return false;
@@ -253,7 +254,7 @@ bool TryEmitter::emitEnd() {
     }
   }
 
-  MOZ_ASSERT(bce_->stackDepth == depth_);
+  MOZ_ASSERT(bce_->bytecodeSection().stackDepth() == depth_);
 
   // ReconstructPCStack needs a NOP here to mark the end of the last
   // catch block.
diff --git a/js/src/frontend/WhileEmitter.cpp b/js/src/frontend/WhileEmitter.cpp
index c73ef4a5da57..f76d4010641b 100644
--- a/js/src/frontend/WhileEmitter.cpp
+++ b/js/src/frontend/WhileEmitter.cpp
@@ -100,7 +100,8 @@ bool WhileEmitter::emitEnd() {
     return false;
   }
 
-  if (!bce_->addTryNote(JSTRY_LOOP, bce_->stackDepth, loopInfo_->headOffset(),
+  if (!bce_->addTryNote(JSTRY_LOOP, bce_->bytecodeSection().stackDepth(),
+                        loopInfo_->headOffset(),
                         loopInfo_->breakTargetOffset())) {
     return false;
   }
diff --git a/js/src/gc/Allocator.cpp b/js/src/gc/Allocator.cpp
index 684a42b48b2d..b51270037235 100644
--- a/js/src/gc/Allocator.cpp
+++ b/js/src/gc/Allocator.cpp
@@ -7,6 +7,7 @@
 #include "gc/Allocator.h"
 
 #include "mozilla/DebugOnly.h"
+#include "mozilla/TimeStamp.h"
 
 #include "gc/GCInternals.h"
 #include "gc/GCTrace.h"
@@ -22,6 +23,9 @@
 #include "gc/PrivateIterators-inl.h"
 #include "vm/JSObject-inl.h"
 
+using mozilla::TimeDuration;
+using mozilla::TimeStamp;
+
 using namespace js;
 using namespace gc;
 
@@ -268,19 +272,16 @@ T* GCRuntime::tryNewTenuredThing(JSContext* cx, AllocKind kind,
     // chunks available it may also allocate new memory directly.
     t = reinterpret_cast<T*>(refillFreeListFromAnyThread(cx, kind));
 
-    if (MOZ_UNLIKELY(!t && allowGC)) {
-      if (!cx->helperThread()) {
-        // We have no memory available for a new chunk; perform an
-        // all-compartments, non-incremental, shrinking GC and wait for
-        // sweeping to finish.
-        JS::PrepareForFullGC(cx);
-        cx->runtime()->gc.gc(GC_SHRINK, JS::GCReason::LAST_DITCH);
-        cx->runtime()->gc.waitBackgroundSweepOrAllocEnd();
-
+    if (MOZ_UNLIKELY(!t)) {
+      if (allowGC) {
+        cx->runtime()->gc.attemptLastDitchGC(cx);
         t = tryNewTenuredThing<T, NoGC>(cx, kind, thingSize);
       }
       if (!t) {
-        ReportOutOfMemory(cx);
+        if (allowGC) {
+          ReportOutOfMemory(cx);
+        }
+        return nullptr;
       }
     }
   }
@@ -294,6 +295,28 @@ T* GCRuntime::tryNewTenuredThing(JSContext* cx, AllocKind kind,
   return t;
 }
 
+void GCRuntime::attemptLastDitchGC(JSContext* cx) {
+  // Either there was no memory available for a new chunk or the heap hit its
+  // size limit. Try to perform an all-compartments, non-incremental, shrinking
+  // GC and wait for it to finish.
+
+  if (cx->helperThread()) {
+    return;
+  }
+
+  if (!lastLastDitchTime.IsNull() &&
+      TimeStamp::Now() - lastLastDitchTime <= tunables.minLastDitchGCPeriod()) {
+    return;
+  }
+
+  JS::PrepareForFullGC(cx);
+  gc(GC_SHRINK, JS::GCReason::LAST_DITCH);
+  waitBackgroundAllocEnd();
+  waitBackgroundFreeEnd();
+
+  lastLastDitchTime = mozilla::TimeStamp::Now();
+}
+
 template <AllowGC allowGC>
 bool GCRuntime::checkAllocatorState(JSContext* cx, AllocKind kind) {
   if (allowGC) {
diff --git a/js/src/gc/GC.cpp b/js/src/gc/GC.cpp
index 6a0229377fce..ae17d38ce577 100644
--- a/js/src/gc/GC.cpp
+++ b/js/src/gc/GC.cpp
@@ -364,6 +364,9 @@ static const float PretenureThreshold = 0.6f;
 /* JSGC_PRETENURE_GROUP_THRESHOLD */
 static const float PretenureGroupThreshold = 3000;
 
+/* JSGC_MIN_LAST_DITCH_GC_PERIOD */
+static const TimeDuration MinLastDitchGCPeriod = TimeDuration::FromSeconds(60);
+
 }  // namespace TuningDefaults
 }  // namespace gc
 }  // namespace js
@@ -1521,6 +1524,9 @@ bool GCSchedulingTunables::setParameter(JSGCParamKey key, uint32_t value,
       }
       pretenureGroupThreshold_ = value;
       break;
+    case JSGC_MIN_LAST_DITCH_GC_PERIOD:
+      minLastDitchGCPeriod_ = TimeDuration::FromSeconds(value);
+      break;
     default:
       MOZ_CRASH("Unknown GC parameter.");
   }
@@ -1613,7 +1619,8 @@ GCSchedulingTunables::GCSchedulingTunables()
       nurseryFreeThresholdForIdleCollectionFraction_(
           TuningDefaults::NurseryFreeThresholdForIdleCollectionFraction),
       pretenureThreshold_(TuningDefaults::PretenureThreshold),
-      pretenureGroupThreshold_(TuningDefaults::PretenureGroupThreshold) {}
+      pretenureGroupThreshold_(TuningDefaults::PretenureGroupThreshold),
+      minLastDitchGCPeriod_(TuningDefaults::MinLastDitchGCPeriod) {}
 
 void GCRuntime::resetParameter(JSGCParamKey key, AutoLockGC& lock) {
   switch (key) {
@@ -1708,6 +1715,9 @@ void GCSchedulingTunables::resetParameter(JSGCParamKey key,
     case JSGC_PRETENURE_GROUP_THRESHOLD:
       pretenureGroupThreshold_ = TuningDefaults::PretenureGroupThreshold;
       break;
+    case JSGC_MIN_LAST_DITCH_GC_PERIOD:
+      minLastDitchGCPeriod_ = TuningDefaults::MinLastDitchGCPeriod;
+      break;
     default:
       MOZ_CRASH("Unknown GC parameter.");
   }
@@ -1783,6 +1793,8 @@ uint32_t GCRuntime::getParameter(JSGCParamKey key, const AutoLockGC& lock) {
       return uint32_t(tunables.pretenureThreshold() * 100);
     case JSGC_PRETENURE_GROUP_THRESHOLD:
       return tunables.pretenureGroupThreshold();
+    case JSGC_MIN_LAST_DITCH_GC_PERIOD:
+      return tunables.minLastDitchGCPeriod().ToSeconds();
     default:
       MOZ_CRASH("Unknown parameter key");
   }
diff --git a/js/src/gc/GCRuntime.h b/js/src/gc/GCRuntime.h
index 924a6002f06c..0811336803b2 100644
--- a/js/src/gc/GCRuntime.h
+++ b/js/src/gc/GCRuntime.h
@@ -310,8 +310,7 @@ class GCRuntime {
   bool isForegroundSweeping() const { return state() == State::Sweep; }
   bool isBackgroundSweeping() { return sweepTask.isRunning(); }
   void waitBackgroundSweepEnd();
-  void waitBackgroundSweepOrAllocEnd() {
-    waitBackgroundSweepEnd();
+  void waitBackgroundAllocEnd() {
     allocTask.cancelAndWait();
   }
   void waitBackgroundFreeEnd();
@@ -535,6 +534,7 @@ class GCRuntime {
                                                    AllocKind thingKind);
   static TenuredCell* refillFreeListFromHelperThread(JSContext* cx,
                                                      AllocKind thingKind);
+  void attemptLastDitchGC(JSContext* cx);
 
   /*
    * Return the list of chunks that can be released outside the GC lock.
@@ -1045,6 +1045,8 @@ class GCRuntime {
     minorGC(reason, gcstats::PhaseKind::EVICT_NURSERY);
   }
 
+  mozilla::TimeStamp lastLastDitchTime;
+
   friend class MarkingValidator;
   friend class AutoEnterIteration;
 };
diff --git a/js/src/gc/Scheduling.h b/js/src/gc/Scheduling.h
index 35a005353be3..a2e7eb8299c9 100644
--- a/js/src/gc/Scheduling.h
+++ b/js/src/gc/Scheduling.h
@@ -456,6 +456,14 @@ class GCSchedulingTunables {
    */
   UnprotectedData<uint32_t> pretenureGroupThreshold_;
 
+  /*
+   * JSGC_MIN_LAST_DITCH_GC_PERIOD
+   *
+   * Last ditch GC is skipped if allocation failure occurs less than this many
+   * seconds from the previous one.
+   */
+  MainThreadData<mozilla::TimeDuration> minLastDitchGCPeriod_;
+
  public:
   GCSchedulingTunables();
 
@@ -502,6 +510,10 @@ class GCSchedulingTunables {
   float pretenureThreshold() const { return pretenureThreshold_; }
   uint32_t pretenureGroupThreshold() const { return pretenureGroupThreshold_; }
 
+  mozilla::TimeDuration minLastDitchGCPeriod() const {
+    return minLastDitchGCPeriod_;
+  }
+
   MOZ_MUST_USE bool setParameter(JSGCParamKey key, uint32_t value,
                                  const AutoLockGC& lock);
   void resetParameter(JSGCParamKey key, const AutoLockGC& lock);
diff --git a/js/src/gc/Verifier.cpp b/js/src/gc/Verifier.cpp
index fd8f6eed2302..0d54c6e8f8f2 100644
--- a/js/src/gc/Verifier.cpp
+++ b/js/src/gc/Verifier.cpp
@@ -789,8 +789,14 @@ bool js::gc::CheckWeakMapEntryMarking(const WeakMapBase* map, Cell* key,
   }
 
   CellColor keyColor = GetCellColor(key);
-  CellColor valueColor =
-      valueZone->isGCMarking() ? GetCellColor(value) : CellColor::Black;
+
+  // Values belonging to other runtimes or in uncollected zones are treated as
+  // black.
+  CellColor valueColor = CellColor::Black;
+  if (value->runtimeFromAnyThread() == zone->runtimeFromAnyThread() &&
+      valueZone->isGCMarking()) {
+    valueColor = GetCellColor(value);
+  }
 
   if (valueColor < Min(mapColor, keyColor)) {
     fprintf(stderr, "WeakMap value is less marked than map and key\n");
diff --git a/js/src/jit-test/tests/gc/bug-1505622.js b/js/src/jit-test/tests/gc/bug-1505622.js
new file mode 100644
index 000000000000..c6eb07a59a19
--- /dev/null
+++ b/js/src/jit-test/tests/gc/bug-1505622.js
@@ -0,0 +1,45 @@
+// Test that we don't repeatedly trigger last-ditch GCs.
+
+function allocUntilFail() {
+    gc();
+    let initGCNumber = gcparam("gcNumber");
+    let error;
+    try {
+        let a = [];
+        while (true) {
+            a.push(Symbol()); // Symbols are tenured.
+        }
+    } catch(err) {
+        error = err;
+    }
+    let finalGCNumber = gcparam("gcNumber");
+    gc();
+    assertEq(error, "out of memory");
+    return finalGCNumber - initGCNumber;
+}
+
+// Turn of any zeal which will disrupt GC number checks.
+gczeal(0);
+
+// Set a small heap limit.
+gcparam("maxBytes", 1024 * 1024);
+
+// Set the time limit for skipping last ditch GCs to 5 seconds.
+gcparam("minLastDitchGCPeriod", 5);
+assertEq(gcparam("minLastDitchGCPeriod"), 5);
+
+// Allocate up to the heap limit. This triggers a last ditch GC.
+let gcCount = allocUntilFail();
+assertEq(gcCount, 1)
+
+// Allocate up to the limit again. The second time we fail without
+// triggering a GC.
+gcCount = allocUntilFail();
+assertEq(gcCount, 0)
+
+// Wait for time limit to expire.
+sleep(6);
+
+// Check we trigger a GC again.
+gcCount = allocUntilFail();
+assertEq(gcCount, 1)
diff --git a/js/src/jit-test/tests/gc/bug-1543014.js b/js/src/jit-test/tests/gc/bug-1543014.js
new file mode 100644
index 000000000000..9f91ad35260c
--- /dev/null
+++ b/js/src/jit-test/tests/gc/bug-1543014.js
@@ -0,0 +1,11 @@
+// |jit-test| skip-if: helperThreadCount() === 0
+gczeal(0);
+evalInWorker(`
+  var sym4 = Symbol.match;
+  function basicSweeping() {};
+  var wm1 = new WeakMap();
+  wm1.set(basicSweeping, sym4);
+  startgc(100000, 'shrinking');
+`);
+gczeal(2);
+var d1 = newGlobal({});
diff --git a/js/src/tests/lib/progressbar.py b/js/src/tests/lib/progressbar.py
index 2ba90c4930fe..5faa2e19fefa 100644
--- a/js/src/tests/lib/progressbar.py
+++ b/js/src/tests/lib/progressbar.py
@@ -39,6 +39,8 @@ class ProgressBar(object):
         self.limit_digits = int(math.ceil(math.log10(self.limit)))
         # datetime: The start time.
         self.t0 = datetime.now()
+        # datetime: Optional, the last time update() ran.
+        self.last_update_time = None
 
         # Compute the width of the counters and build the format string.
         self.counters_width = 1  # [
@@ -79,7 +81,8 @@ class ProgressBar(object):
         sys.stdout.write(bar + '|')
 
         # Update the bar.
-        dt = datetime.now() - self.t0
+        now = datetime.now()
+        dt = now - self.t0
         dt = dt.seconds + dt.microseconds * 1e-6
         sys.stdout.write('{:6.1f}s'.format(dt))
         Terminal.clear_right()
@@ -87,9 +90,13 @@ class ProgressBar(object):
         # Force redisplay, since we didn't write a \n.
         sys.stdout.flush()
 
+        self.last_update_time = now
+
     def poke(self):
         if not self.prior:
             return
+        if datetime.now() - self.last_update_time < self.update_granularity():
+            return
         self.update(*self.prior)
 
     def finish(self, complete=True):
diff --git a/js/src/vm/CompilationAndEvaluation.cpp b/js/src/vm/CompilationAndEvaluation.cpp
index 80bb89d76df1..d4ca5c02a03b 100644
--- a/js/src/vm/CompilationAndEvaluation.cpp
+++ b/js/src/vm/CompilationAndEvaluation.cpp
@@ -508,9 +508,10 @@ JS_PUBLIC_API bool JS::CloneAndExecuteScript(JSContext* cx,
   return ExecuteScript(cx, envChain, script, rval.address());
 }
 
+template <typename Unit>
 static bool Evaluate(JSContext* cx, ScopeKind scopeKind, HandleObject env,
                      const ReadOnlyCompileOptions& optionsArg,
-                     SourceText<char16_t>& srcBuf, MutableHandleValue rval) {
+                     SourceText<Unit>& srcBuf, MutableHandleValue rval) {
   CompileOptions options(cx, optionsArg);
   MOZ_ASSERT(!cx->zone()->isAtomsZone());
   AssertHeapIsIdle();
@@ -548,14 +549,8 @@ static bool Evaluate(JSContext* cx, HandleObjectVector envChain,
 extern JS_PUBLIC_API bool JS::EvaluateUtf8(
     JSContext* cx, const ReadOnlyCompileOptions& options, const char* bytes,
     size_t length, MutableHandle<Value> rval) {
-  auto chars = UniqueTwoByteChars(
-      UTF8CharsToNewTwoByteCharsZ(cx, UTF8Chars(bytes, length), &length).get());
-  if (!chars) {
-    return false;
-  }
-
-  SourceText<char16_t> srcBuf;
-  if (!srcBuf.init(cx, std::move(chars), length)) {
+  SourceText<Utf8Unit> srcBuf;
+  if (!srcBuf.init(cx, bytes, length, SourceOwnership::Borrowed)) {
     return false;
   }
 
@@ -594,7 +589,19 @@ JS_PUBLIC_API bool JS::EvaluateUtf8Path(
   CompileOptions options(cx, optionsArg);
   options.setFileAndLine(filename, 1);
 
-  return EvaluateUtf8(cx, options,
-                      reinterpret_cast<const char*>(buffer.begin()),
-                      buffer.length(), rval);
+  auto contents = reinterpret_cast<const char*>(buffer.begin());
+  size_t length = buffer.length();
+  auto chars = UniqueTwoByteChars(
+      UTF8CharsToNewTwoByteCharsZ(cx, UTF8Chars(contents, length), &length)
+          .get());
+  if (!chars) {
+    return false;
+  }
+
+  SourceText<char16_t> srcBuf;
+  if (!srcBuf.init(cx, std::move(chars), length)) {
+    return false;
+  }
+
+  return Evaluate(cx, options, srcBuf, rval);
 }
diff --git a/js/src/vm/JSScript.cpp b/js/src/vm/JSScript.cpp
index 6c02540e09a7..18a74af6a27c 100644
--- a/js/src/vm/JSScript.cpp
+++ b/js/src/vm/JSScript.cpp
@@ -3238,12 +3238,12 @@ PrivateScriptData* PrivateScriptData::new_(JSContext* cx, uint32_t nscopes,
 
 /* static */ bool PrivateScriptData::InitFromEmitter(
     JSContext* cx, js::HandleScript script, frontend::BytecodeEmitter* bce) {
-  uint32_t nscopes = bce->scopeList.length();
-  uint32_t nconsts = bce->numberList.length();
-  uint32_t nobjects = bce->objectList.length;
-  uint32_t ntrynotes = bce->tryNoteList.length();
-  uint32_t nscopenotes = bce->scopeNoteList.length();
-  uint32_t nresumeoffsets = bce->resumeOffsetList.length();
+  uint32_t nscopes = bce->perScriptData().scopeList().length();
+  uint32_t nconsts = bce->perScriptData().numberList().length();
+  uint32_t nobjects = bce->perScriptData().objectList().length;
+  uint32_t ntrynotes = bce->bytecodeSection().tryNoteList().length();
+  uint32_t nscopenotes = bce->bytecodeSection().scopeNoteList().length();
+  uint32_t nresumeoffsets = bce->bytecodeSection().resumeOffsetList().length();
 
   // Create and initialize PrivateScriptData
   if (!JSScript::createPrivateScriptData(cx, script, nscopes, nconsts, nobjects,
@@ -3254,22 +3254,22 @@ PrivateScriptData* PrivateScriptData::new_(JSContext* cx, uint32_t nscopes,
 
   js::PrivateScriptData* data = script->data_;
   if (nscopes) {
-    bce->scopeList.finish(data->scopes());
+    bce->perScriptData().scopeList().finish(data->scopes());
   }
   if (nconsts) {
-    bce->numberList.finish(data->consts());
+    bce->perScriptData().numberList().finish(data->consts());
   }
   if (nobjects) {
-    bce->objectList.finish(data->objects());
+    bce->perScriptData().objectList().finish(data->objects());
   }
   if (ntrynotes) {
-    bce->tryNoteList.finish(data->tryNotes());
+    bce->bytecodeSection().tryNoteList().finish(data->tryNotes());
   }
   if (nscopenotes) {
-    bce->scopeNoteList.finish(data->scopeNotes());
+    bce->bytecodeSection().scopeNoteList().finish(data->scopeNotes());
   }
   if (nresumeoffsets) {
-    bce->resumeOffsetList.finish(data->resumeOffsets());
+    bce->bytecodeSection().resumeOffsetList().finish(data->resumeOffsets());
   }
 
   return true;
@@ -3565,11 +3565,12 @@ bool JSScript::fullyInitFromEmitter(JSContext* cx, HandleScript script,
       mozilla::MakeScopeExit([&] { script->freeScriptData(); });
 
   /* The counts of indexed things must be checked during code generation. */
-  MOZ_ASSERT(bce->atomIndices->count() <= INDEX_LIMIT);
-  MOZ_ASSERT(bce->objectList.length <= INDEX_LIMIT);
+  MOZ_ASSERT(bce->perScriptData().atomIndices()->count() <= INDEX_LIMIT);
+  MOZ_ASSERT(bce->perScriptData().objectList().length <= INDEX_LIMIT);
 
   uint64_t nslots =
-      bce->maxFixedSlots + static_cast<uint64_t>(bce->maxStackDepth);
+      bce->maxFixedSlots +
+      static_cast<uint64_t>(bce->bytecodeSection().maxStackDepth());
   if (nslots > UINT32_MAX) {
     bce->reportError(nullptr, JSMSG_NEED_DIET, js_script_str);
     return false;
@@ -3581,7 +3582,7 @@ bool JSScript::fullyInitFromEmitter(JSContext* cx, HandleScript script,
   script->nfixed_ = bce->maxFixedSlots;
   script->nslots_ = nslots;
   script->bodyScopeIndex_ = bce->bodyScopeIndex;
-  script->numBytecodeTypeSets_ = bce->typesetCount;
+  script->numBytecodeTypeSets_ = bce->bytecodeSection().typesetCount();
 
   // Initialize script flags from BytecodeEmitter
   script->setFlag(ImmutableFlags::Strict, bce->sc->strict());
@@ -3628,7 +3629,7 @@ bool JSScript::fullyInitFromEmitter(JSContext* cx, HandleScript script,
   // Part of the parse result – the scope containing each inner function – must
   // be stored in the inner function itself. Do this now that compilation is
   // complete and can no longer fail.
-  bce->objectList.finishInnerFunctions();
+  bce->perScriptData().objectList().finishInnerFunctions();
 
 #ifdef JS_STRUCTURED_SPEW
   // We want this to happen after line number initialization to allow filtering
@@ -4522,12 +4523,12 @@ bool JSScript::hasBreakpointsAt(jsbytecode* pc) {
 
 /* static */ bool SharedScriptData::InitFromEmitter(
     JSContext* cx, js::HandleScript script, frontend::BytecodeEmitter* bce) {
-  uint32_t natoms = bce->atomIndices->count();
-  uint32_t codeLength = bce->code().length();
+  uint32_t natoms = bce->perScriptData().atomIndices()->count();
+  uint32_t codeLength = bce->bytecodeSection().code().length();
 
   // The + 1 is to account for the final SN_MAKE_TERMINATOR that is appended
   // when the notes are copied to their final destination by copySrcNotes.
-  uint32_t noteLength = bce->notes().length() + 1;
+  uint32_t noteLength = bce->bytecodeSection().notes().length() + 1;
 
   // Create and initialize SharedScriptData
   if (!script->createSharedScriptData(cx, codeLength, noteLength, natoms)) {
@@ -4537,9 +4538,9 @@ bool JSScript::hasBreakpointsAt(jsbytecode* pc) {
   js::SharedScriptData* data = script->scriptData_;
 
   // Initialize trailing arrays
-  std::copy_n(bce->code().begin(), codeLength, data->code());
+  std::copy_n(bce->bytecodeSection().code().begin(), codeLength, data->code());
   bce->copySrcNotes(data->notes(), noteLength);
-  InitAtomMap(*bce->atomIndices, data->atoms());
+  InitAtomMap(*bce->perScriptData().atomIndices(), data->atoms());
 
   return true;
 }
diff --git a/widget/GfxInfoX11.cpp b/widget/GfxInfoX11.cpp
index beb720660d40..13777676add5 100644
--- a/widget/GfxInfoX11.cpp
+++ b/widget/GfxInfoX11.cpp
@@ -307,6 +307,34 @@ const nsTArray<GfxDriverInfo> &GfxInfo::GetGfxDriverInfo() {
         GfxDriverInfo::allDevices, GfxDriverInfo::allFeatures,
         nsIGfxInfo::FEATURE_BLOCKED_DRIVER_VERSION, DRIVER_LESS_THAN,
         V(13, 15, 100, 1), "FEATURE_FAILURE_OLD_FGLRX", "fglrx 13.15.100.1");
+
+    ////////////////////////////////////
+    // FEATURE_WEBRENDER
+
+    // Mesa baseline (chosen arbitrarily as that which ships with
+    // Ubuntu 18.04 LTS).
+    APPEND_TO_DRIVER_BLOCKLIST(
+        OperatingSystem::Linux,
+        (nsAString &)GfxDriverInfo::GetDeviceVendor(VendorMesaAll),
+        GfxDriverInfo::allDevices, nsIGfxInfo::FEATURE_WEBRENDER,
+        nsIGfxInfo::FEATURE_BLOCKED_DRIVER_VERSION, DRIVER_LESS_THAN,
+        V(18, 2, 8, 0), "FEATURE_FAILURE_WEBRENDER_OLD_MESA", "Mesa 18.2.8.0");
+
+    // Disable on all NVIDIA devices for now.
+    APPEND_TO_DRIVER_BLOCKLIST(
+        OperatingSystem::Linux,
+        (nsAString &)GfxDriverInfo::GetDeviceVendor(VendorNVIDIA),
+        GfxDriverInfo::allDevices, nsIGfxInfo::FEATURE_WEBRENDER,
+        nsIGfxInfo::FEATURE_BLOCKED_DEVICE, DRIVER_COMPARISON_IGNORED,
+        V(0, 0, 0, 0), "FEATURE_FAILURE_WEBRENDER_NO_LINUX_NVIDIA", "");
+
+    // Disable on all ATI devices for now.
+    APPEND_TO_DRIVER_BLOCKLIST(
+        OperatingSystem::Linux,
+        (nsAString &)GfxDriverInfo::GetDeviceVendor(VendorATI),
+        GfxDriverInfo::allDevices, nsIGfxInfo::FEATURE_WEBRENDER,
+        nsIGfxInfo::FEATURE_BLOCKED_DEVICE, DRIVER_COMPARISON_IGNORED,
+        V(0, 0, 0, 0), "FEATURE_FAILURE_WEBRENDER_NO_LINUX_ATI", "");
   }
   return *sDriverInfo;
 }
diff --git a/widget/windows/GfxInfo.cpp b/widget/windows/GfxInfo.cpp
index fe91244fbacb..e5213b20a7f1 100644
--- a/widget/windows/GfxInfo.cpp
+++ b/widget/windows/GfxInfo.cpp
@@ -1602,9 +1602,9 @@ const nsTArray<GfxDriverInfo>& GfxInfo::GetGfxDriverInfo() {
     ////////////////////////////////////
     // FEATURE_WEBRENDER
 
-    // We are blocking all non-Nvidia cards in gfxPlatform.cpp where we check
-    // for the WEBRENDER_QUALIFIED feature. However we also want to block some
-    // specific Nvidia cards for being too low-powered, so we do that here.
+    // We are blocking most hardware explicitly in gfxPlatform.cpp where we
+    // check for the WEBRENDER_QUALIFIED feature. However we also want to block
+    // some specific Nvidia cards for being too low-powered, so we do that here.
     APPEND_TO_DRIVER_BLOCKLIST2(
         OperatingSystem::Windows10,
         (nsAString&)GfxDriverInfo::GetDeviceVendor(VendorNVIDIA),