Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 273 insertions, 0 deletions

diff --git a/js/public/TraceKind.h b/js/public/TraceKind.h
new file mode 100644
index 0000000000..268db56957
--- /dev/null
+++ b/js/public/TraceKind.h
@@ -0,0 +1,273 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef js_TraceKind_h
+#define js_TraceKind_h
+
+#include "mozilla/UniquePtr.h"
+
+#include "js/TypeDecls.h"
+
+// Forward declarations of all the types a TraceKind can denote.
+class JSLinearString;
+
+namespace js {
+class BaseScript;
+class BaseShape;
+class GetterSetter;
+class PropMap;
+class RegExpShared;
+class Shape;
+class Scope;
+namespace jit {
+class JitCode;
+}  // namespace jit
+}  // namespace js
+
+namespace JS {
+
+// When tracing a thing, the GC needs to know about the layout of the object it
+// is looking at. There are a fixed number of different layouts that the GC
+// knows about. The "trace kind" is a static map which tells which layout a GC
+// thing has.
+//
+// Although this map is public, the details are completely hidden. Not all of
+// the matching C++ types are exposed, and those that are, are opaque.
+//
+// See Value::gcKind() and JSTraceCallback in Tracer.h for more details.
+enum class TraceKind {
+  // These trace kinds have a publicly exposed, although opaque, C++ type.
+  // Note: The order here is determined by our Value packing. Other users
+  //       should sort alphabetically, for consistency.
+  // Note: Nursery allocatable kinds go first. See js::gc::NurseryTraceKinds.
+  Object = 0x00,
+  BigInt = 0x01,
+  String = 0x02,
+  Symbol = 0x03,
+
+  // Shape details are exposed through JS_TraceShapeCycleCollectorChildren.
+  Shape = 0x04,
+
+  BaseShape = 0x05,
+
+  // The kind associated with a nullptr.
+  Null = 0x06,
+
+  // The following kinds do not have an exposed C++ idiom.
+  JitCode,
+  Script,
+  Scope,
+  RegExpShared,
+  GetterSetter,
+  PropMap,
+};
+
+// GCCellPtr packs the trace kind into the low bits of the pointer for common
+// kinds.
+const static uintptr_t OutOfLineTraceKindMask = 0x07;
+static_assert(uintptr_t(JS::TraceKind::Null) < OutOfLineTraceKindMask,
+              "GCCellPtr requires an inline representation for nullptr");
+
+// When this header is imported inside SpiderMonkey, the class definitions are
+// available and we can query those definitions to find the correct kind
+// directly from the class hierarchy.
+template <typename T>
+struct MapTypeToTraceKind {
+  static const JS::TraceKind kind = T::TraceKind;
+};
+
+// When this header is used outside SpiderMonkey, the class definitions are not
+// available, so the following table containing all public GC types is used.
+//
+// canBeGray: GC can mark things of this kind gray. The cycle collector
+//            traverses gray GC things when looking for cycles.
+// inCCGraph: Things of this kind are represented as nodes in the CC graph. This
+//            also means they can be used as a keys in WeakMap.
+
+// clang-format off
+#define JS_FOR_EACH_TRACEKIND(D)                                 \
+  /* name         type              canBeGray       inCCGraph */ \
+  D(BaseShape,    js::BaseShape,    true,           false)       \
+  D(JitCode,      js::jit::JitCode, true,           false)       \
+  D(Scope,        js::Scope,        true,           true)        \
+  D(Object,       JSObject,         true,           true)        \
+  D(Script,       js::BaseScript,   true,           true)        \
+  D(Shape,        js::Shape,        true,           false)       \
+  D(String,       JSString,         false,          false)       \
+  D(Symbol,       JS::Symbol,       false,          false)       \
+  D(BigInt,       JS::BigInt,       false,          false)       \
+  D(RegExpShared, js::RegExpShared, true,           true)        \
+  D(GetterSetter, js::GetterSetter, true,           true)        \
+  D(PropMap,      js::PropMap,      false,          false)
+// clang-format on
+
+// Returns true if the JS::TraceKind is represented as a node in cycle collector
+// graph.
+inline constexpr bool IsCCTraceKind(JS::TraceKind aKind) {
+  switch (aKind) {
+#define JS_EXPAND_DEF(name, _1, _2, inCCGraph) \
+  case JS::TraceKind::name:                    \
+    return inCCGraph;
+    JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
+#undef JS_EXPAND_DEF
+    default:
+      return false;
+  }
+}
+
+// Helper for SFINAE to ensure certain methods are only used on appropriate base
+// types. This avoids common footguns such as `Cell::is<JSFunction>()` which
+// match any type of JSObject.
+template <typename T>
+struct IsBaseTraceType : std::false_type {};
+
+#define JS_EXPAND_DEF(_, type, _1, _2) \
+  template <>                          \
+  struct IsBaseTraceType<type> : std::true_type {};
+JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
+#undef JS_EXPAND_DEF
+
+template <typename T>
+inline constexpr bool IsBaseTraceType_v = IsBaseTraceType<T>::value;
+
+// Map from all public types to their trace kind.
+#define JS_EXPAND_DEF(name, type, _, _1)                   \
+  template <>                                              \
+  struct MapTypeToTraceKind<type> {                        \
+    static const JS::TraceKind kind = JS::TraceKind::name; \
+  };
+JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
+#undef JS_EXPAND_DEF
+
+template <>
+struct MapTypeToTraceKind<JSLinearString> {
+  static const JS::TraceKind kind = JS::TraceKind::String;
+};
+template <>
+struct MapTypeToTraceKind<JSFunction> {
+  static const JS::TraceKind kind = JS::TraceKind::Object;
+};
+template <>
+struct MapTypeToTraceKind<JSScript> {
+  static const JS::TraceKind kind = JS::TraceKind::Script;
+};
+
+// RootKind is closely related to TraceKind. Whereas TraceKind's indices are
+// laid out for convenient embedding as a pointer tag, the indicies of RootKind
+// are designed for use as array keys via EnumeratedArray.
+enum class RootKind : int8_t {
+// These map 1:1 with trace kinds.
+#define EXPAND_ROOT_KIND(name, _0, _1, _2) name,
+  JS_FOR_EACH_TRACEKIND(EXPAND_ROOT_KIND)
+#undef EXPAND_ROOT_KIND
+
+  // These tagged pointers are special-cased for performance.
+  Id,
+  Value,
+
+  // Everything else.
+  Traceable,
+
+  Limit
+};
+
+// Most RootKind correspond directly to a trace kind.
+template <TraceKind traceKind>
+struct MapTraceKindToRootKind {};
+#define JS_EXPAND_DEF(name, _0, _1, _2)                  \
+  template <>                                            \
+  struct MapTraceKindToRootKind<JS::TraceKind::name> {   \
+    static const JS::RootKind kind = JS::RootKind::name; \
+  };
+JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF)
+#undef JS_EXPAND_DEF
+
+// Specify the RootKind for all types. Value and jsid map to special cases;
+// Cell pointer types we can derive directly from the TraceKind; everything else
+// should go in the Traceable list and use GCPolicy<T>::trace for tracing.
+template <typename T>
+struct MapTypeToRootKind {
+  static const JS::RootKind kind = JS::RootKind::Traceable;
+};
+template <typename T>
+struct MapTypeToRootKind<T*> {
+  static const JS::RootKind kind =
+      JS::MapTraceKindToRootKind<JS::MapTypeToTraceKind<T>::kind>::kind;
+};
+template <>
+struct MapTypeToRootKind<JS::Realm*> {
+  // Not a pointer to a GC cell. Use GCPolicy.
+  static const JS::RootKind kind = JS::RootKind::Traceable;
+};
+template <typename T>
+struct MapTypeToRootKind<mozilla::UniquePtr<T>> {
+  static const JS::RootKind kind = JS::MapTypeToRootKind<T>::kind;
+};
+template <>
+struct MapTypeToRootKind<JS::Value> {
+  static const JS::RootKind kind = JS::RootKind::Value;
+};
+template <>
+struct MapTypeToRootKind<jsid> {
+  static const JS::RootKind kind = JS::RootKind::Id;
+};
+
+// Fortunately, few places in the system need to deal with fully abstract
+// cells. In those places that do, we generally want to move to a layout
+// templated function as soon as possible. This template wraps the upcast
+// for that dispatch.
+//
+// Given a call:
+//
+//    DispatchTraceKindTyped(f, thing, traceKind, ... args)
+//
+// Downcast the |void *thing| to the specific type designated by |traceKind|,
+// and pass it to the functor |f| along with |... args|, forwarded. Pass the
+// type designated by |traceKind| as the functor's template argument. The
+// |thing| parameter is optional; without it, we simply pass through |... args|.
+template <typename F, typename... Args>
+auto DispatchTraceKindTyped(F f, JS::TraceKind traceKind, Args&&... args) {
+  switch (traceKind) {
+#define JS_EXPAND_DEF(name, type, _, _1) \
+  case JS::TraceKind::name:              \
+    return f.template operator()<type>(std::forward<Args>(args)...);
+    JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
+#undef JS_EXPAND_DEF
+    default:
+      MOZ_CRASH("Invalid trace kind in DispatchTraceKindTyped.");
+  }
+}
+
+// Given a GC thing specified by pointer and trace kind, calls the functor |f|
+// with a template argument of the actual type of the pointer and returns the
+// result.
+template <typename F>
+auto MapGCThingTyped(void* thing, JS::TraceKind traceKind, F&& f) {
+  switch (traceKind) {
+#define JS_EXPAND_DEF(name, type, _, _1) \
+  case JS::TraceKind::name:              \
+    return f(static_cast<type*>(thing));
+    JS_FOR_EACH_TRACEKIND(JS_EXPAND_DEF);
+#undef JS_EXPAND_DEF
+    default:
+      MOZ_CRASH("Invalid trace kind in MapGCThingTyped.");
+  }
+}
+
+// Given a GC thing specified by pointer and trace kind, calls the functor |f|
+// with a template argument of the actual type of the pointer and ignores the
+// result.
+template <typename F>
+void ApplyGCThingTyped(void* thing, JS::TraceKind traceKind, F&& f) {
+  // This function doesn't do anything but is supplied for symmetry with other
+  // MapGCThingTyped/ApplyGCThingTyped implementations that have to wrap the
+  // functor to return a dummy value that is ignored.
+  MapGCThingTyped(thing, traceKind, std::move(f));
+}
+
+}  // namespace JS
+
+#endif  // js_TraceKind_h