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#509: M1348772 M1364345 (push and splice)

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This commit is contained in:
Cameron Kaiser 2018-07-08 08:37:12 -07:00
parent 80c343933f
commit c7075f4527
12 changed files with 339 additions and 91 deletions
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19
js/src/gc/Barrier.cpp
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@ -38,18 +38,25 @@ FOR_EACH_GC_POINTER_TYPE(INSTANTIATE_ALL_VALID_TYPES)
bool
HeapSlot::preconditionForSet(NativeObject* owner, Kind kind, uint32_t slot)
{
return kind == Slot
? &owner->getSlotRef(slot) == this
: &owner->getDenseElement(slot) == (const Value*)this;
if (kind == Slot)
return &owner->getSlotRef(slot) == this;
uint32_t numShifted = owner->getElementsHeader()->numShiftedElements();
MOZ_ASSERT(slot >= numShifted);
return &owner->getDenseElement(slot - numShifted) == (const Value*)this;
}
bool
HeapSlot::preconditionForWriteBarrierPost(NativeObject* obj, Kind kind, uint32_t slot,
Value target) const
{
return kind == Slot
? obj->getSlotAddressUnchecked(slot)->get() == target
: static_cast<HeapSlot*>(obj->getDenseElements() + slot)->get() == target;
if (kind == Slot) {
return (obj->getSlotAddressUnchecked(slot)->get() == target);
} else {
uint32_t numShifted = obj->getElementsHeader()->numShiftedElements();
MOZ_ASSERT(slot >= numShifted);
return (static_cast<HeapSlot*>(obj->getDenseElements() + (slot - numShifted))->get() == target);
}
}
bool

47
js/src/gc/Marking.cpp
View File

@ -1543,7 +1543,10 @@ GCMarker::saveValueRanges()
HeapSlot* vp = obj->getDenseElementsAllowCopyOnWrite();
if (arr->end == vp + obj->getDenseInitializedLength()) {
MOZ_ASSERT(arr->start >= vp);
arr->index = arr->start - vp;
// Add the number of shifted elements here (and subtract in
// restoreValueArray) to ensure shift() calls on the array
// are handled correctly.
arr->index = obj->unshiftedIndex(arr->start - vp);
arr->kind = HeapSlot::Element;
} else {
HeapSlot* vp = obj->fixedSlots();
@ -1582,6 +1585,11 @@ GCMarker::restoreValueArray(JSObject* objArg, void** vpp, void** endp)
return false;
uint32_t initlen = obj->getDenseInitializedLength();
// Account for shifted elements.
uint32_t numShifted = obj->getElementsHeader()->numShiftedElements();
start = (numShifted < start) ? start - numShifted : 0;
HeapSlot* vp = obj->getDenseElementsAllowCopyOnWrite();
if (start < initlen) {
*vpp = vp + start;
@ -1992,8 +2000,11 @@ js::gc::StoreBuffer::SlotsEdge::trace(TenuringTracer& mover) const
if (kind() == ElementKind) {
int32_t initLen = obj->getDenseInitializedLength();
int32_t clampedStart = Min(start_, initLen);
int32_t clampedEnd = Min(start_ + count_, initLen);
int32_t numShifted = obj->getElementsHeader()->numShiftedElements();
int32_t clampedStart = Min(Max(0, start_ - numShifted), initLen);
int32_t clampedEnd = Min(Max(0, start_ + count_ - numShifted), initLen);
MOZ_ASSERT(clampedStart >= 0);
MOZ_ASSERT(clampedStart <= clampedEnd);
mover.traceSlots(static_cast<HeapSlot*>(obj->getDenseElements() + clampedStart)
->unsafeUnbarrieredForTracing(), clampedEnd - clampedStart);
} else {
@ -2249,30 +2260,35 @@ js::TenuringTracer::moveElementsToTenured(NativeObject* dst, NativeObject* src,
if (src->hasEmptyElements() || src->denseElementsAreCopyOnWrite())
return 0;
Zone* zone = src->zone();
ObjectElements* srcHeader = src->getElementsHeader();
ObjectElements* dstHeader;
void* srcAllocatedHeader = src->getUnshiftedElementsHeader();
/* TODO Bug 874151: Prefer to put element data inline if we have space. */
if (!nursery().isInside(srcHeader)) {
if (!nursery().isInside(srcAllocatedHeader)) {
MOZ_ASSERT(src->elements_ == dst->elements_);
nursery().removeMallocedBuffer(srcHeader);
nursery().removeMallocedBuffer(srcAllocatedHeader);
return 0;
}
size_t nslots = ObjectElements::VALUES_PER_HEADER + srcHeader->capacity;
ObjectElements* srcHeader = src->getElementsHeader();
// Shifted elements are copied too.
uint32_t numShifted = srcHeader->numShiftedElements();
size_t nslots = srcHeader->numAllocatedElements();
/* Unlike other objects, Arrays can have fixed elements. */
if (src->is<ArrayObject>() && nslots <= GetGCKindSlots(dstKind)) {
dst->as<ArrayObject>().setFixedElements();
dstHeader = dst->as<ArrayObject>().getElementsHeader();
js_memcpy(dstHeader, srcHeader, nslots * sizeof(HeapSlot));
nursery().setElementsForwardingPointer(srcHeader, dstHeader, nslots);
js_memcpy(dst->getElementsHeader(), srcAllocatedHeader, nslots * sizeof(HeapSlot));
dst->elements_ += numShifted;
nursery().setElementsForwardingPointer(srcHeader, dst->getElementsHeader(),
srcHeader->capacity);
return nslots * sizeof(HeapSlot);
}
MOZ_ASSERT(nslots >= 2);
Zone* zone = src->zone();
ObjectElements* dstHeader;
{
AutoEnterOOMUnsafeRegion oomUnsafe;
dstHeader = reinterpret_cast<ObjectElements*>(zone->pod_malloc<HeapSlot>(nslots));
@ -2280,9 +2296,10 @@ js::TenuringTracer::moveElementsToTenured(NativeObject* dst, NativeObject* src,
oomUnsafe.crash("Failed to allocate elements while tenuring.");
}
js_memcpy(dstHeader, srcHeader, nslots * sizeof(HeapSlot));
nursery().setElementsForwardingPointer(srcHeader, dstHeader, nslots);
dst->elements_ = dstHeader->elements();
js_memcpy(dstHeader, srcAllocatedHeader, nslots * sizeof(HeapSlot));
dst->elements_ = dstHeader->elements() + numShifted;
nursery().setElementsForwardingPointer(srcHeader, dst->getElementsHeader(),
srcHeader->capacity);
return nslots * sizeof(HeapSlot);
}

4
js/src/gc/Nursery.cpp
View File

@ -359,11 +359,11 @@ Nursery::setSlotsForwardingPointer(HeapSlot* oldSlots, HeapSlot* newSlots, uint3
void
Nursery::setElementsForwardingPointer(ObjectElements* oldHeader, ObjectElements* newHeader,
uint32_t nelems)
uint32_t capacity)
{
// Only use a direct forwarding pointer if there is enough space for one.
setForwardingPointer(oldHeader->elements(), newHeader->elements(),
nelems > ObjectElements::VALUES_PER_HEADER);
capacity > 0);
}
#ifdef DEBUG

2
js/src/gc/Nursery.h
View File

@ -374,7 +374,7 @@ class Nursery
void setSlotsForwardingPointer(HeapSlot* oldSlots, HeapSlot* newSlots, uint32_t nslots);
void setElementsForwardingPointer(ObjectElements* oldHeader, ObjectElements* newHeader,
uint32_t nelems);
uint32_t capacity);
/* Free malloced pointers owned by freed things in the nursery. */
void freeMallocedBuffers();

32
js/src/jit/CodeGenerator.cpp
View File

@ -7899,7 +7899,26 @@ CodeGenerator::emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, R
Address elementFlags(elementsTemp, ObjectElements::offsetOfFlags());
Imm32 bit(ObjectElements::NONWRITABLE_ARRAY_LENGTH);
masm.branchTest32(Assembler::NonZero, elementFlags, bit, ool->entry());
}
if (mir->mode() == MArrayPopShift::Shift) {
// Don't save the elementsTemp register.
LiveRegisterSet temps;
temps.add(elementsTemp);
saveVolatile(temps);
masm.setupUnalignedABICall(elementsTemp);
masm.passABIArg(obj);
masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, js::ArrayShiftMoveElements));
restoreVolatile(temps);
if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
// Reload elementsTemp as ArrayShiftMoveElements may have moved it.
masm.loadPtr(Address(obj, NativeObject::offsetOfElements()), elementsTemp);
}
}
if (mir->unboxedType() == JSVAL_TYPE_MAGIC) {
// Now adjust length and initializedLength.
masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfLength()));
masm.store32(lengthTemp, Address(elementsTemp, ObjectElements::offsetOfInitializedLength()));
@ -7910,19 +7929,6 @@ CodeGenerator::emitArrayPopShift(LInstruction* lir, const MArrayPopShift* mir, R
masm.add32(Imm32(-1), Address(obj, UnboxedArrayObject::offsetOfCapacityIndexAndInitializedLength()));
}
if (mir->mode() == MArrayPopShift::Shift) {
// Don't save the temp registers.
LiveRegisterSet temps;
temps.add(elementsTemp);
temps.add(lengthTemp);
saveVolatile(temps);
masm.setupUnalignedABICall(lengthTemp);
masm.passABIArg(obj);
masm.callWithABI(JS_FUNC_TO_DATA_PTR(void*, js::ArrayShiftMoveElements));
restoreVolatile(temps);
}
masm.bind(&done);
masm.bind(ool->rejoin());
}

39
js/src/jsarray.cpp
View File

@ -768,6 +768,11 @@ js::ArraySetLength(JSContext* cx, Handle<ArrayObject*> arr, HandleId id,
header->initializedLength = Min(header->initializedLength, newLen);
if (attrs & JSPROP_READONLY) {
if (header->numShiftedElements() > 0) {
arr->unshiftElements();
header = arr->getElementsHeader();
}
header->setNonwritableArrayLength();
// When an array's length becomes non-writable, writes to indexes
@ -2101,18 +2106,16 @@ ShiftMoveBoxedOrUnboxedDenseElements(JSObject* obj)
{
MOZ_ASSERT(HasBoxedOrUnboxedDenseElements<Type>(obj));
/*
* At this point the length and initialized length have already been
* decremented and the result fetched, so just shift the array elements
* themselves.
*/
size_t initlen = GetBoxedOrUnboxedInitializedLength<Type>(obj);
MOZ_ASSERT(initlen > 0);
if (Type == JSVAL_TYPE_MAGIC) {
obj->as<NativeObject>().moveDenseElementsNoPreBarrier(0, 1, initlen);
if (!obj->as<NativeObject>().tryShiftDenseElements(1))
obj->as<NativeObject>().moveDenseElementsNoPreBarrier(0, 1, initlen - 1);
} else {
uint8_t* data = obj->as<UnboxedArrayObject>().elements();
size_t elementSize = UnboxedTypeSize(Type);
memmove(data, data + elementSize, initlen * elementSize);
memmove(data, data + elementSize, (initlen - 1) * elementSize);
}
return DenseElementResult::Success;
@ -2151,6 +2154,11 @@ ArrayShiftDenseKernel(JSContext* cx, HandleObject obj, MutableHandleValue rval)
if (rval.isMagic(JS_ELEMENTS_HOLE))
rval.setUndefined();
if (Type == JSVAL_TYPE_MAGIC) {
if (obj->as<NativeObject>().tryShiftDenseElements(1))
return DenseElementResult::Success;
}
DenseElementResult result = MoveBoxedOrUnboxedDenseElements<Type>(cx, obj, 0, 1, initlen - 1);
MOZ_ASSERT(result != DenseElementResult::Incomplete);
if (result == DenseElementResult::Failure)
@ -2445,12 +2453,17 @@ js::array_splice_impl(JSContext* cx, unsigned argc, Value* vp, bool returnValueI
if (CanOptimizeForDenseStorage(obj, 0, len, cx)) {
/* Steps 12(a)-(b). */
DenseElementResult result =
MoveAnyBoxedOrUnboxedDenseElements(cx, obj, targetIndex, sourceIndex,
len - sourceIndex);
MOZ_ASSERT(result != DenseElementResult::Incomplete);
if (result == DenseElementResult::Failure)
return false;
if (targetIndex != 0 ||
!obj->is<NativeObject>() ||
!obj->as<NativeObject>().tryShiftDenseElements(sourceIndex))
{
DenseElementResult result =
MoveAnyBoxedOrUnboxedDenseElements(cx, obj, targetIndex, sourceIndex,
len - sourceIndex);
MOZ_ASSERT(result != DenseElementResult::Incomplete);
if (result == DenseElementResult::Failure)
return false;
}
/* Steps 12(c)-(d). */
SetAnyBoxedOrUnboxedInitializedLength(cx, obj, finalLength);

6
js/src/jsgc.cpp
View File

@ -2128,8 +2128,10 @@ RelocateCell(Zone* zone, TenuredCell* src, AllocKind thingKind, size_t thingSize
NativeObject* dstNative = &dstObj->as<NativeObject>();
// Fixup the pointer to inline object elements if necessary.
if (srcNative->hasFixedElements())
dstNative->setFixedElements();
if (srcNative->hasFixedElements()) {
uint32_t numShifted = srcNative->getElementsHeader()->numShiftedElements();
dstNative->setFixedElements(numShifted);
}
// For copy-on-write objects that own their elements, fix up the
// owner pointer to point to the relocated object.

10
js/src/jsobj.cpp
View File

@ -536,6 +536,8 @@ js::SetIntegrityLevel(JSContext* cx, HandleObject obj, IntegrityLevel level)
if (level == IntegrityLevel::Frozen && obj->is<ArrayObject>()) {
if (!obj->as<ArrayObject>().maybeCopyElementsForWrite(cx))
return false;
if (nobj->getElementsHeader()->numShiftedElements() > 0)
nobj->unshiftElements();
obj->as<ArrayObject>().getElementsHeader()->setNonwritableArrayLength();
}
} else {
@ -3653,8 +3655,10 @@ JSObject::addSizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf, JS::ClassIn
if (is<NativeObject>() && as<NativeObject>().hasDynamicElements()) {
js::ObjectElements* elements = as<NativeObject>().getElementsHeader();
if (!elements->isCopyOnWrite() || elements->ownerObject() == this)
info->objectsMallocHeapElementsNonAsmJS += mallocSizeOf(elements);
if (!elements->isCopyOnWrite() || elements->ownerObject() == this) {
void* allocatedElements = as<NativeObject>().getUnshiftedElementsHeader();
info->objectsMallocHeapElementsNonAsmJS += mallocSizeOf(allocatedElements);
}
}
// Other things may be measured in the future if DMD indicates it is worthwhile.
@ -3722,7 +3726,7 @@ JSObject::sizeOfIncludingThisInNursery() const
if (native.hasDynamicElements()) {
js::ObjectElements& elements = *native.getElementsHeader();
if (!elements.isCopyOnWrite() || elements.ownerObject() == this)
size += elements.capacity * sizeof(HeapSlot);
size += (elements.capacity + elements.numShiftedElements()) * sizeof(HeapSlot);
}
if (is<ArgumentsObject>())

3
js/src/jsobjinlines.h
View File

@ -96,10 +96,11 @@ JSObject::finalize(js::FreeOp* fop)
// Don't free the elements until object finalization finishes,
// so that other objects can access these elements while they
// are themselves finalized.
MOZ_ASSERT(elements->numShiftedElements() == 0);
fop->freeLater(elements);
}
} else {
fop->free_(elements);
fop->free_(nobj->getUnshiftedElementsHeader());
}
}

33
js/src/vm/NativeObject-inl.h
View File

@ -130,12 +130,13 @@ NativeObject::ensureDenseInitializedLengthNoPackedCheck(ExclusiveContext* cx, ui
uint32_t& initlen = getElementsHeader()->initializedLength;
if (initlen < index + extra) {
uint32_t numShifted = getElementsHeader()->numShiftedElements();
size_t offset = initlen;
for (HeapSlot* sp = elements_ + initlen;
sp != elements_ + (index + extra);
sp++, offset++)
{
sp->init(this, HeapSlot::Element, offset, MagicValue(JS_ELEMENTS_HOLE));
sp->init(this, HeapSlot::Element, offset + numShifted, MagicValue(JS_ELEMENTS_HOLE));
}
initlen = index + extra;
}
@ -286,6 +287,36 @@ NativeObject::setSlotWithType(ExclusiveContext* cx, Shape* shape,
AddTypePropertyId(cx, this, shape->propid(), value);
}
inline bool
NativeObject::tryShiftDenseElements(uint32_t count)
{
ObjectElements* header = getElementsHeader();
if (header->initializedLength == count ||
count > ObjectElements::MaxShiftedElements ||
header->isCopyOnWrite() ||
// header->isFrozen() || // NYI
header->hasNonwritableArrayLength())
{
return false;
}
MOZ_ASSERT(count > 0);
MOZ_ASSERT(count < header->initializedLength);
if (MOZ_UNLIKELY(header->numShiftedElements() + count > ObjectElements::MaxShiftedElements)) {
unshiftElements();
header = getElementsHeader();
}
prepareElementRangeForOverwrite(0, count);
header->addShiftedElements(count);
elements_ += count;
ObjectElements* newHeader = getElementsHeader();
memmove(newHeader, header, sizeof(ObjectElements));
return true;
}
/* Make an object with pregenerated shape from a NEWOBJECT bytecode. */
static inline PlainObject*
CopyInitializerObject(JSContext* cx, HandlePlainObject baseobj, NewObjectKind newKind = GenericObject)

114
js/src/vm/NativeObject.cpp
View File

@ -8,6 +8,7 @@
#include "mozilla/ArrayUtils.h"
#include "mozilla/Casting.h"
#include "mozilla/CheckedInt.h"
#include "jswatchpoint.h"
@ -27,6 +28,7 @@ using namespace js;
using JS::GenericNaN;
using mozilla::ArrayLength;
using mozilla::CheckedInt;
using mozilla::DebugOnly;
using mozilla::PodCopy;
using mozilla::RoundUpPow2;
@ -343,7 +345,7 @@ NativeObject::setLastPropertyMakeNonNative(Shape* shape)
MOZ_ASSERT(shape->numFixedSlots() == 0);
if (hasDynamicElements())
js_free(getElementsHeader());
js_free(getUnshiftedElementsHeader());
if (hasDynamicSlots()) {
js_free(slots_);
slots_ = nullptr;
@ -757,6 +759,49 @@ NativeObject::goodElementsAllocationAmount(ExclusiveContext* cx, uint32_t reqCap
return true;
}
void
NativeObject::unshiftElements()
{
ObjectElements* header = getElementsHeader();
uint32_t numShifted = header->numShiftedElements();
MOZ_ASSERT(numShifted > 0);
uint32_t initLength = header->initializedLength;
ObjectElements* newHeader = static_cast<ObjectElements*>(getUnshiftedElementsHeader());
memmove(newHeader, header, sizeof(ObjectElements));
newHeader->clearShiftedElements();
newHeader->capacity += numShifted;
elements_ = newHeader->elements();
// To move the elements, temporarily update initializedLength to include
// both shifted and unshifted elements.
newHeader->initializedLength += numShifted;
// Move the elements. Initialize to |undefined| to ensure pre-barriers
// don't see garbage.
for (size_t i = 0; i < numShifted; i++)
initDenseElement(i, UndefinedValue());
moveDenseElements(0, numShifted, initLength);
// Restore the initialized length. We use setDenseInitializedLength to
// make sure prepareElementRangeForOverwrite is called on the shifted
// elements.
setDenseInitializedLength(initLength);
}
void
NativeObject::maybeUnshiftElements()
{
ObjectElements* header = getElementsHeader();
MOZ_ASSERT(header->numShiftedElements() > 0);
// Unshift if less than a third of the allocated space is in use.
if (header->capacity < header->numAllocatedElements() / 3)
unshiftElements();
}
bool
NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
{
@ -765,6 +810,26 @@ NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
if (denseElementsAreCopyOnWrite())
MOZ_CRASH();
// If there are shifted elements, consider unshifting them first. If we
// don't unshift here, the code below will include the shifted elements in
// the resize.
uint32_t numShifted = getElementsHeader()->numShiftedElements();
if (numShifted > 0) {
maybeUnshiftElements();
if (getDenseCapacity() >= reqCapacity)
return true;
numShifted = getElementsHeader()->numShiftedElements();
// Ensure |reqCapacity + numShifted| below won't overflow by forcing an
// unshift in that case.
CheckedInt<uint32_t> checkedReqCapacity(reqCapacity);
checkedReqCapacity += numShifted;
if (MOZ_UNLIKELY(!checkedReqCapacity.isValid())) {
unshiftElements();
numShifted = 0;
}
}
uint32_t oldCapacity = getDenseCapacity();
MOZ_ASSERT(oldCapacity < reqCapacity);
@ -775,13 +840,17 @@ NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
// Preserve the |capacity <= length| invariant for arrays with
// non-writable length. See also js::ArraySetLength which initially
// enforces this requirement.
newAllocated = reqCapacity + ObjectElements::VALUES_PER_HEADER;
newAllocated = reqCapacity + numShifted + ObjectElements::VALUES_PER_HEADER;
} else {
if (!goodElementsAllocationAmount(cx, reqCapacity, getElementsHeader()->length, &newAllocated))
if (!goodElementsAllocationAmount(cx, reqCapacity + numShifted,
getElementsHeader()->length,
&newAllocated))
{
return false;
}
}
uint32_t newCapacity = newAllocated - ObjectElements::VALUES_PER_HEADER;
uint32_t newCapacity = newAllocated - ObjectElements::VALUES_PER_HEADER - numShifted;
MOZ_ASSERT(newCapacity > oldCapacity && newCapacity >= reqCapacity);
// If newCapacity exceeds MAX_DENSE_ELEMENTS_COUNT, the array should become
@ -790,11 +859,11 @@ NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
uint32_t initlen = getDenseInitializedLength();
HeapSlot* oldHeaderSlots = reinterpret_cast<HeapSlot*>(getElementsHeader());
HeapSlot* oldHeaderSlots = reinterpret_cast<HeapSlot*>(getUnshiftedElementsHeader());
HeapSlot* newHeaderSlots;
if (hasDynamicElements()) {
MOZ_ASSERT(oldCapacity <= MAX_DENSE_ELEMENTS_COUNT);
uint32_t oldAllocated = oldCapacity + ObjectElements::VALUES_PER_HEADER;
uint32_t oldAllocated = oldCapacity + ObjectElements::VALUES_PER_HEADER + numShifted;
newHeaderSlots = ReallocateObjectBuffer<HeapSlot>(cx, this, oldHeaderSlots, oldAllocated, newAllocated);
if (!newHeaderSlots)
@ -803,12 +872,13 @@ NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
newHeaderSlots = AllocateObjectBuffer<HeapSlot>(cx, this, newAllocated);
if (!newHeaderSlots)
return false; // Leave elements at its old size.
PodCopy(newHeaderSlots, oldHeaderSlots, ObjectElements::VALUES_PER_HEADER + initlen);
PodCopy(newHeaderSlots, oldHeaderSlots,
ObjectElements::VALUES_PER_HEADER + initlen + numShifted);
}
ObjectElements* newheader = reinterpret_cast<ObjectElements*>(newHeaderSlots);
newheader->capacity = newCapacity;
elements_ = newheader->elements();
elements_ = newheader->elements() + numShifted;
getElementsHeader()->capacity = newCapacity;
Debug_SetSlotRangeToCrashOnTouch(elements_ + initlen, newCapacity - initlen);
@ -818,9 +888,6 @@ NativeObject::growElements(ExclusiveContext* cx, uint32_t reqCapacity)
void
NativeObject::shrinkElements(ExclusiveContext* cx, uint32_t reqCapacity)
{
uint32_t oldCapacity = getDenseCapacity();
MOZ_ASSERT(reqCapacity < oldCapacity);
MOZ_ASSERT(canHaveNonEmptyElements());
if (denseElementsAreCopyOnWrite())
MOZ_CRASH();
@ -828,18 +895,29 @@ NativeObject::shrinkElements(ExclusiveContext* cx, uint32_t reqCapacity)
if (!hasDynamicElements())
return;
// If we have shifted elements, consider unshifting them.
uint32_t numShifted = getElementsHeader()->numShiftedElements();
if (numShifted > 0) {
maybeUnshiftElements();
numShifted = getElementsHeader()->numShiftedElements();
}
uint32_t oldCapacity = getDenseCapacity();
MOZ_ASSERT(reqCapacity < oldCapacity);
uint32_t newAllocated = 0;
MOZ_ALWAYS_TRUE(goodElementsAllocationAmount(cx, reqCapacity, 0, &newAllocated));
MOZ_ALWAYS_TRUE(goodElementsAllocationAmount(cx, reqCapacity + numShifted, 0, &newAllocated));
MOZ_ASSERT(oldCapacity <= MAX_DENSE_ELEMENTS_COUNT);
uint32_t oldAllocated = oldCapacity + ObjectElements::VALUES_PER_HEADER;
uint32_t oldAllocated = oldCapacity + ObjectElements::VALUES_PER_HEADER + numShifted;
if (newAllocated == oldAllocated)
return; // Leave elements at its old size.
MOZ_ASSERT(newAllocated > ObjectElements::VALUES_PER_HEADER);
uint32_t newCapacity = newAllocated - ObjectElements::VALUES_PER_HEADER;
uint32_t newCapacity = newAllocated - ObjectElements::VALUES_PER_HEADER - numShifted;
MOZ_ASSERT(newCapacity <= MAX_DENSE_ELEMENTS_COUNT);
HeapSlot* oldHeaderSlots = reinterpret_cast<HeapSlot*>(getElementsHeader());
HeapSlot* oldHeaderSlots = reinterpret_cast<HeapSlot*>(getUnshiftedElementsHeader());
HeapSlot* newHeaderSlots = ReallocateObjectBuffer<HeapSlot>(cx, this, oldHeaderSlots,
oldAllocated, newAllocated);
if (!newHeaderSlots) {
@ -848,8 +926,8 @@ NativeObject::shrinkElements(ExclusiveContext* cx, uint32_t reqCapacity)
}
ObjectElements* newheader = reinterpret_cast<ObjectElements*>(newHeaderSlots);
newheader->capacity = newCapacity;
elements_ = newheader->elements();
elements_ = newheader->elements() + numShifted;
getElementsHeader()->capacity = newCapacity;
}
/* static */ bool

121
js/src/vm/NativeObject.h
View File

@ -156,11 +156,28 @@ ArraySetLength(JSContext* cx, Handle<ArrayObject*> obj, HandleId id,
* Elements do not track property creation order, so enumerating the elements
* of an object does not necessarily visit indexes in the order they were
* created.
*
* Shifted elements
* ----------------
* It's pretty common to use an array as a queue, like this:
*
* while (arr.length > 0)
* foo(arr.shift());
*
* To ensure we don't get quadratic behavior on this, elements can be 'shifted'
* in memory. tryShiftDenseElements does this by incrementing elements_ to point
* to the next element and moving the ObjectElements header in memory (so it's
* stored where the shifted Value used to be).
*
* Shifted elements can be unshifted when we grow the array, when the array is
* frozen (for simplicity, shifted elements are not supported on objects that
* are frozen, have copy-on-write elements, or on arrays with non-writable
* length).
*/
class ObjectElements
{
public:
enum Flags {
enum Flags: uint16_t {
// Integers written to these elements must be converted to doubles.
CONVERT_DOUBLE_ELEMENTS = 0x1,
@ -180,9 +197,22 @@ class ObjectElements
// For TypedArrays only: this TypedArray's storage is mapping shared
// memory. This is a static property of the TypedArray, set when it
// is created and never changed.
SHARED_MEMORY = 0x8
SHARED_MEMORY = 0x8,
// These elements are set to integrity level "frozen".
// Not currently implemented.
FROZEN = 0x10,
};
// The flags word stores both the flags and the number of shifted elements.
// Allow shifting 2047 elements before unshifting.
static const size_t NumShiftedElementsBits = 11;
static const size_t MaxShiftedElements = (1 << NumShiftedElementsBits) - 1;
static const size_t NumShiftedElementsShift = 32 - NumShiftedElementsBits;
static const size_t FlagsMask = (1 << NumShiftedElementsShift) - 1;
static_assert(MaxShiftedElements == 2047,
"MaxShiftedElements should match the comment");
private:
friend class ::JSObject;
friend class ArrayObject;
@ -195,7 +225,9 @@ class ObjectElements
ArraySetLength(JSContext* cx, Handle<ArrayObject*> obj, HandleId id,
unsigned attrs, HandleValue value, ObjectOpResult& result);
/* See Flags enum above. */
// The NumShiftedElementsBits high bits of this are used to store the
// number of shifted elements, the other bits are available for the flags.
// See Flags enum above.
uint32_t flags;
/*
@ -238,6 +270,21 @@ class ObjectElements
flags &= ~COPY_ON_WRITE;
}
void addShiftedElements(uint32_t count) {
MOZ_ASSERT(count < capacity);
MOZ_ASSERT(count < initializedLength);
MOZ_ASSERT(!(flags & (NONWRITABLE_ARRAY_LENGTH | FROZEN | COPY_ON_WRITE)));
uint32_t numShifted = numShiftedElements() + count;
MOZ_ASSERT(numShifted <= MaxShiftedElements);
flags = (numShifted << NumShiftedElementsShift) | (flags & FlagsMask);
capacity -= count;
initializedLength -= count;
}
void clearShiftedElements() {
flags &= FlagsMask;
MOZ_ASSERT(numShiftedElements() == 0);
}
public:
MOZ_CONSTEXPR ObjectElements(uint32_t capacity, uint32_t length)
: flags(0), initializedLength(0), capacity(capacity), length(length)
@ -257,7 +304,7 @@ class ObjectElements
const HeapSlot* elements() const {
return reinterpret_cast<const HeapSlot*>(uintptr_t(this) + sizeof(ObjectElements));
}
static ObjectElements * fromElements(HeapSlot* elems) {
static ObjectElements* fromElements(HeapSlot* elems) {
return reinterpret_cast<ObjectElements*>(uintptr_t(elems) - sizeof(ObjectElements));
}
@ -286,6 +333,17 @@ class ObjectElements
static bool ConvertElementsToDoubles(JSContext* cx, uintptr_t elements);
static bool MakeElementsCopyOnWrite(ExclusiveContext* cx, NativeObject* obj);
uint32_t numShiftedElements() const {
uint32_t numShifted = flags >> NumShiftedElementsShift;
MOZ_ASSERT_IF(numShifted > 0,
!(flags & (NONWRITABLE_ARRAY_LENGTH | FROZEN | COPY_ON_WRITE)));
return numShifted;
}
uint32_t numAllocatedElements() const {
return VALUES_PER_HEADER + capacity + numShiftedElements();
}
// This is enough slots to store an object of this class. See the static
// assertion below.
static const size_t VALUES_PER_HEADER = 2;
@ -943,10 +1001,26 @@ class NativeObject : public JSObject
"uint32_t (and sometimes int32_t ,too)");
}
ObjectElements * getElementsHeader() const {
ObjectElements* getElementsHeader() const {
return ObjectElements::fromElements(elements_);
}
// Returns a pointer to the first element, including shifted elements.
inline HeapSlot* unshiftedElements() const {
return elements_ - getElementsHeader()->numShiftedElements();
}
// Like getElementsHeader, but returns a pointer to the unshifted header.
// This is mainly useful for free()ing dynamic elements: the pointer
// returned here is the one we got from malloc.
void* getUnshiftedElementsHeader() const {
return ObjectElements::fromElements(unshiftedElements());
}
uint32_t unshiftedIndex(uint32_t index) const {
return index + getElementsHeader()->numShiftedElements();
}
/* Accessors for elements. */
bool ensureElements(ExclusiveContext* cx, uint32_t capacity) {
MOZ_ASSERT(!denseElementsAreCopyOnWrite());
@ -955,6 +1029,15 @@ class NativeObject : public JSObject
return true;
}
// Try to shift |count| dense elements, see the "Shifted elements" comment.
inline bool tryShiftDenseElements(uint32_t count);
// Unshift all shifted elements so that numShiftedElements is 0.
void unshiftElements();
// If this object has many shifted elements, unshift them.
void maybeUnshiftElements();
static bool goodElementsAllocationAmount(ExclusiveContext* cx, uint32_t reqAllocated,
uint32_t length, uint32_t* goodAmount);
bool growElements(ExclusiveContext* cx, uint32_t newcap);
@ -985,7 +1068,8 @@ class NativeObject : public JSObject
if (v.isObject() && IsInsideNursery(&v.toObject())) {
JS::shadow::Runtime* shadowRuntime = shadowRuntimeFromMainThread();
shadowRuntime->gcStoreBufferPtr()->putSlot(this, HeapSlot::Element,
start + i, count - i);
unshiftedIndex(start + i),
count - i);
return;
}
}
@ -1004,13 +1088,13 @@ class NativeObject : public JSObject
void setDenseElement(uint32_t index, const Value& val) {
MOZ_ASSERT(index < getDenseInitializedLength());
MOZ_ASSERT(!denseElementsAreCopyOnWrite());
elements_[index].set(this, HeapSlot::Element, index, val);
elements_[index].set(this, HeapSlot::Element, unshiftedIndex(index), val);
}
void initDenseElement(uint32_t index, const Value& val) {
MOZ_ASSERT(index < getDenseInitializedLength());
MOZ_ASSERT(!denseElementsAreCopyOnWrite());
elements_[index].init(this, HeapSlot::Element, index, val);
elements_[index].init(this, HeapSlot::Element, unshiftedIndex(index), val);
}
void setDenseElementMaybeConvertDouble(uint32_t index, const Value& val) {
@ -1034,8 +1118,12 @@ class NativeObject : public JSObject
MOZ_ASSERT(dstStart + count <= getDenseCapacity());
MOZ_ASSERT(!denseElementsAreCopyOnWrite());
if (JS::shadow::Zone::asShadowZone(zone())->needsIncrementalBarrier()) {
for (uint32_t i = 0; i < count; ++i)
elements_[dstStart + i].set(this, HeapSlot::Element, dstStart + i, src[i]);
uint32_t numShifted = getElementsHeader()->numShiftedElements();
for (uint32_t i = 0; i < count; ++i) {
elements_[dstStart + i].set(this, HeapSlot::Element,
dstStart + i + numShifted,
src[i]);
}
} else {
memcpy(&elements_[dstStart], src, count * sizeof(HeapSlot));
elementsRangeWriteBarrierPost(dstStart, count);
@ -1067,16 +1155,17 @@ class NativeObject : public JSObject
* the array before and after the move.
*/
if (JS::shadow::Zone::asShadowZone(zone())->needsIncrementalBarrier()) {
uint32_t numShifted = getElementsHeader()->numShiftedElements();
if (dstStart < srcStart) {
HeapSlot* dst = elements_ + dstStart;
HeapSlot* src = elements_ + srcStart;
for (uint32_t i = 0; i < count; i++, dst++, src++)
dst->set(this, HeapSlot::Element, dst - elements_, *src);
dst->set(this, HeapSlot::Element, dst - elements_ + numShifted, *src);
} else {
HeapSlot* dst = elements_ + dstStart + count - 1;
HeapSlot* src = elements_ + srcStart + count - 1;
for (uint32_t i = 0; i < count; i++, dst--, src--)
dst->set(this, HeapSlot::Element, dst - elements_, *src);
dst->set(this, HeapSlot::Element, dst - elements_ + numShifted, *src);
}
} else {
memmove(elements_ + dstStart, elements_ + srcStart, count * sizeof(HeapSlot));
@ -1161,9 +1250,9 @@ class NativeObject : public JSObject
bool canHaveNonEmptyElements();
#endif
void setFixedElements() {
void setFixedElements(uint32_t numShifted = 0) {
MOZ_ASSERT(canHaveNonEmptyElements());
elements_ = fixedElements();
elements_ = fixedElements() + numShifted;
}
inline bool hasDynamicElements() const {
@ -1174,11 +1263,11 @@ class NativeObject : public JSObject
* immediately afterwards. Such cases cannot occur for dense arrays
* (which have at least two fixed slots) and can only result in a leak.
*/
return !hasEmptyElements() && elements_ != fixedElements();
return !hasEmptyElements() && !hasFixedElements();
}
inline bool hasFixedElements() const {
return elements_ == fixedElements();
return unshiftedElements() == fixedElements();
}
inline bool hasEmptyElements() const {