1 files changed, 162 insertions, 0 deletions
diff --git a/js/src/gc/ObjectKind-inl.h b/js/src/gc/ObjectKind-inl.h
new file mode 100644
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+++ b/js/src/gc/ObjectKind-inl.h
@@ -0,0 +1,162 @@
+/* -*- 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/. */
+
+/*
+ * GC-internal helper functions for getting the AllocKind used to allocate a
+ * JSObject and related information.
+ */
+
+#ifndef gc_ObjectKind_inl_h
+#define gc_ObjectKind_inl_h
+
+#include "util/Memory.h"
+#include "vm/NativeObject.h"
+
+namespace js {
+namespace gc {
+
+/* Capacity for slotsToThingKind */
+const size_t SLOTS_TO_THING_KIND_LIMIT = 17;
+extern const AllocKind slotsToThingKind[];
+extern const uint32_t slotsToAllocKindBytes[];
+
+/* Get the best kind to use when making an object with the given slot count. */
+static inline AllocKind GetGCObjectKind(size_t numSlots) {
+  if (numSlots >= SLOTS_TO_THING_KIND_LIMIT) {
+    return AllocKind::OBJECT16;
+  }
+  return slotsToThingKind[numSlots];
+}
+
+static inline AllocKind GetGCObjectKind(const JSClass* clasp) {
+  MOZ_ASSERT(!clasp->isProxyObject(),
+             "Proxies should use GetProxyGCObjectKind");
+  MOZ_ASSERT(!clasp->isJSFunction());
+
+  uint32_t nslots = JSCLASS_RESERVED_SLOTS(clasp);
+  return GetGCObjectKind(nslots);
+}
+
+static constexpr bool CanUseFixedElementsForArray(size_t numElements) {
+  if (numElements > NativeObject::MAX_DENSE_ELEMENTS_COUNT) {
+    return false;
+  }
+  size_t numSlots = numElements + ObjectElements::VALUES_PER_HEADER;
+  return numSlots < SLOTS_TO_THING_KIND_LIMIT;
+}
+
+/* As for GetGCObjectKind, but for dense array allocation. */
+static inline AllocKind GetGCArrayKind(size_t numElements) {
+  /*
+   * Dense arrays can use their fixed slots to hold their elements array
+   * (less two Values worth of ObjectElements header), but if more than the
+   * maximum number of fixed slots is needed then the fixed slots will be
+   * unused.
+   */
+  static_assert(ObjectElements::VALUES_PER_HEADER == 2);
+  if (!CanUseFixedElementsForArray(numElements)) {
+    return AllocKind::OBJECT2;
+  }
+  return slotsToThingKind[numElements + ObjectElements::VALUES_PER_HEADER];
+}
+
+static inline AllocKind GetGCObjectFixedSlotsKind(size_t numFixedSlots) {
+  MOZ_ASSERT(numFixedSlots < SLOTS_TO_THING_KIND_LIMIT);
+  return slotsToThingKind[numFixedSlots];
+}
+
+// Get the best kind to use when allocating an object that needs a specific
+// number of bytes.
+static inline AllocKind GetGCObjectKindForBytes(size_t nbytes) {
+  MOZ_ASSERT(nbytes <= JSObject::MAX_BYTE_SIZE);
+
+  if (nbytes <= sizeof(NativeObject)) {
+    return AllocKind::OBJECT0;
+  }
+  nbytes -= sizeof(NativeObject);
+
+  size_t dataSlots = AlignBytes(nbytes, sizeof(Value)) / sizeof(Value);
+  MOZ_ASSERT(nbytes <= dataSlots * sizeof(Value));
+  return GetGCObjectKind(dataSlots);
+}
+
+/* Get the number of fixed slots and initial capacity associated with a kind. */
+static constexpr inline size_t GetGCKindSlots(AllocKind thingKind) {
+  // Using a switch in hopes that thingKind will usually be a compile-time
+  // constant.
+  switch (thingKind) {
+    case AllocKind::OBJECT0:
+    case AllocKind::OBJECT0_BACKGROUND:
+      return 0;
+    case AllocKind::OBJECT2:
+    case AllocKind::OBJECT2_BACKGROUND:
+      return 2;
+    case AllocKind::FUNCTION:
+    case AllocKind::OBJECT4:
+    case AllocKind::OBJECT4_BACKGROUND:
+      return 4;
+    case AllocKind::FUNCTION_EXTENDED:
+      return 7;
+    case AllocKind::OBJECT8:
+    case AllocKind::OBJECT8_BACKGROUND:
+      return 8;
+    case AllocKind::OBJECT12:
+    case AllocKind::OBJECT12_BACKGROUND:
+      return 12;
+    case AllocKind::OBJECT16:
+    case AllocKind::OBJECT16_BACKGROUND:
+      return 16;
+    default:
+      MOZ_CRASH("Bad object alloc kind");
+  }
+}
+
+static inline size_t GetGCKindBytes(AllocKind thingKind) {
+  return sizeof(JSObject_Slots0) + GetGCKindSlots(thingKind) * sizeof(Value);
+}
+
+static inline bool CanUseBackgroundAllocKind(const JSClass* clasp) {
+  return !clasp->hasFinalize() || (clasp->flags & JSCLASS_BACKGROUND_FINALIZE);
+}
+
+static inline bool CanChangeToBackgroundAllocKind(AllocKind kind,
+                                                  const JSClass* clasp) {
+  // If a foreground alloc kind is specified but the class has no finalizer or a
+  // finalizer that is safe to call on a different thread, we can change the
+  // alloc kind to one which is finalized on a background thread.
+  //
+  // For example, AllocKind::OBJECT0 calls the finalizer on the main thread, and
+  // AllocKind::OBJECT0_BACKGROUND calls the finalizer on the a helper thread.
+
+  MOZ_ASSERT(IsObjectAllocKind(kind));
+
+  if (IsBackgroundFinalized(kind)) {
+    return false;  // This kind is already a background finalized kind.
+  }
+
+  return CanUseBackgroundAllocKind(clasp);
+}
+
+static inline AllocKind ForegroundToBackgroundAllocKind(AllocKind fgKind) {
+  MOZ_ASSERT(IsObjectAllocKind(fgKind));
+  MOZ_ASSERT(IsForegroundFinalized(fgKind));
+
+  // For objects, each background alloc kind is defined just after the
+  // corresponding foreground alloc kind so we can convert between them by
+  // incrementing or decrementing as appropriate.
+  AllocKind bgKind = AllocKind(size_t(fgKind) + 1);
+
+  MOZ_ASSERT(IsObjectAllocKind(bgKind));
+  MOZ_ASSERT(IsBackgroundFinalized(bgKind));
+  MOZ_ASSERT(GetGCKindSlots(bgKind) == GetGCKindSlots(fgKind));
+
+  return bgKind;
+}
+
+}  // namespace gc
+}  // namespace js
+
+#endif  // gc_ObjectKind_inl_h