Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 689 insertions, 0 deletions

diff --git a/xpcom/ds/nsTArray-inl.h b/xpcom/ds/nsTArray-inl.h
new file mode 100644
index 0000000000..3d9ff1d410
--- /dev/null
+++ b/xpcom/ds/nsTArray-inl.h
@@ -0,0 +1,689 @@
+/* -*- 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 nsTArray_h__
+#  error "Don't include this file directly"
+#endif
+
+// NOTE: We don't use MOZ_COUNT_CTOR/MOZ_COUNT_DTOR to perform leak checking of
+// nsTArray_base objects intentionally for the following reasons:
+// * The leak logging isn't as useful as other types of logging, as
+//   nsTArray_base is frequently relocated without invoking a constructor, such
+//   as when stored within another nsTArray. This means that
+//   XPCOM_MEM_LOG_CLASSES cannot be used to identify specific leaks of nsTArray
+//   objects.
+// * The nsTArray type is layout compatible with the ThinVec crate with the
+//   correct flags, and ThinVec does not currently perform leak logging.
+//   This means that if a large number of arrays are transferred between Rust
+//   and C++ code using ThinVec, for example within another ThinVec, they
+//   will not be logged correctly and might appear as e.g. negative leaks.
+// * Leaks which have been found thanks to the leak logging added by this
+//   type have often not been significant, and/or have needed to be
+//   circumvented using some other mechanism. Most leaks found with this type
+//   in them also include other types which will continue to be tracked.
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc, RelocationStrategy>::nsTArray_base() : mHdr(EmptyHdr()) {}
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc, RelocationStrategy>::~nsTArray_base() {
+  if (!HasEmptyHeader() && !UsesAutoArrayBuffer()) {
+    Alloc::Free(mHdr);
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc, RelocationStrategy>::nsTArray_base(const nsTArray_base&)
+    : mHdr(EmptyHdr()) {
+  // Actual copying happens through nsTArray_CopyEnabler, we just need to do the
+  // initialization of mHdr.
+}
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc, RelocationStrategy>&
+nsTArray_base<Alloc, RelocationStrategy>::operator=(const nsTArray_base&) {
+  // Actual copying happens through nsTArray_CopyEnabler, so do nothing here (do
+  // not copy mHdr).
+  return *this;
+}
+
+template <class Alloc, class RelocationStrategy>
+const nsTArrayHeader*
+nsTArray_base<Alloc, RelocationStrategy>::GetAutoArrayBufferUnsafe(
+    size_t aElemAlign) const {
+  // Assuming |this| points to an nsAutoArray, we want to get a pointer to
+  // mAutoBuf.  So just cast |this| to nsAutoArray* and read &mAutoBuf!
+
+  const void* autoBuf =
+      &reinterpret_cast<const AutoTArray<nsTArray<uint32_t>, 1>*>(this)
+           ->mAutoBuf;
+
+  // If we're on a 32-bit system and aElemAlign is 8, we need to adjust our
+  // pointer to take into account the extra alignment in the auto array.
+
+  static_assert(
+      sizeof(void*) != 4 || (MOZ_ALIGNOF(mozilla::AlignedElem<8>) == 8 &&
+                             sizeof(AutoTArray<mozilla::AlignedElem<8>, 1>) ==
+                                 sizeof(void*) + sizeof(nsTArrayHeader) + 4 +
+                                     sizeof(mozilla::AlignedElem<8>)),
+      "auto array padding wasn't what we expected");
+
+  // We don't support alignments greater than 8 bytes.
+  MOZ_ASSERT(aElemAlign <= 4 || aElemAlign == 8, "unsupported alignment.");
+  if (sizeof(void*) == 4 && aElemAlign == 8) {
+    autoBuf = reinterpret_cast<const char*>(autoBuf) + 4;
+  }
+
+  return reinterpret_cast<const Header*>(autoBuf);
+}
+
+template <class Alloc, class RelocationStrategy>
+bool nsTArray_base<Alloc, RelocationStrategy>::UsesAutoArrayBuffer() const {
+  if (!mHdr->mIsAutoArray) {
+    return false;
+  }
+
+  // This is nuts.  If we were sane, we'd pass aElemAlign as a parameter to
+  // this function.  Unfortunately this function is called in nsTArray_base's
+  // destructor, at which point we don't know value_type's alignment.
+  //
+  // We'll fall on our face and return true when we should say false if
+  //
+  //   * we're not using our auto buffer,
+  //   * aElemAlign == 4, and
+  //   * mHdr == GetAutoArrayBuffer(8).
+  //
+  // This could happen if |*this| lives on the heap and malloc allocated our
+  // buffer on the heap adjacent to |*this|.
+  //
+  // However, we can show that this can't happen.  If |this| is an auto array
+  // (as we ensured at the beginning of the method), GetAutoArrayBuffer(8)
+  // always points to memory owned by |*this|, because (as we assert below)
+  //
+  //   * GetAutoArrayBuffer(8) is at most 4 bytes past GetAutoArrayBuffer(4),
+  //     and
+  //   * sizeof(nsTArrayHeader) > 4.
+  //
+  // Since AutoTArray always contains an nsTArrayHeader,
+  // GetAutoArrayBuffer(8) will always point inside the auto array object,
+  // even if it doesn't point at the beginning of the header.
+  //
+  // Note that this means that we can't store elements with alignment 16 in an
+  // nsTArray, because GetAutoArrayBuffer(16) could lie outside the memory
+  // owned by this AutoTArray.  We statically assert that value_type's
+  // alignment is 8 bytes or less in AutoTArray.
+
+  static_assert(sizeof(nsTArrayHeader) > 4, "see comment above");
+
+#ifdef DEBUG
+  ptrdiff_t diff = reinterpret_cast<const char*>(GetAutoArrayBuffer(8)) -
+                   reinterpret_cast<const char*>(GetAutoArrayBuffer(4));
+  MOZ_ASSERT(diff >= 0 && diff <= 4,
+             "GetAutoArrayBuffer doesn't do what we expect.");
+#endif
+
+  return mHdr == GetAutoArrayBuffer(4) || mHdr == GetAutoArrayBuffer(8);
+}
+
+// defined in nsTArray.cpp
+bool IsTwiceTheRequiredBytesRepresentableAsUint32(size_t aCapacity,
+                                                  size_t aElemSize);
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+typename ActualAlloc::ResultTypeProxy
+nsTArray_base<Alloc, RelocationStrategy>::ExtendCapacity(size_type aLength,
+                                                         size_type aCount,
+                                                         size_type aElemSize) {
+  mozilla::CheckedInt<size_type> newLength = aLength;
+  newLength += aCount;
+
+  if (!newLength.isValid()) {
+    return ActualAlloc::FailureResult();
+  }
+
+  return this->EnsureCapacity<ActualAlloc>(newLength.value(), aElemSize);
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+typename ActualAlloc::ResultTypeProxy
+nsTArray_base<Alloc, RelocationStrategy>::EnsureCapacityImpl(
+    size_type aCapacity, size_type aElemSize) {
+  MOZ_ASSERT(aCapacity > mHdr->mCapacity,
+             "Should have been checked by caller (EnsureCapacity)");
+
+  // If the requested memory allocation exceeds size_type(-1)/2, then
+  // our doubling algorithm may not be able to allocate it.
+  // Additionally, if it exceeds uint32_t(-1) then we couldn't fit in the
+  // Header::mCapacity member. Just bail out in cases like that.  We don't want
+  // to be allocating 2 GB+ arrays anyway.
+  if (!IsTwiceTheRequiredBytesRepresentableAsUint32(aCapacity, aElemSize)) {
+    ActualAlloc::SizeTooBig((size_t)aCapacity * aElemSize);
+    return ActualAlloc::FailureResult();
+  }
+
+  size_t reqSize = sizeof(Header) + aCapacity * aElemSize;
+
+  if (HasEmptyHeader()) {
+    // Malloc() new data
+    Header* header = static_cast<Header*>(ActualAlloc::Malloc(reqSize));
+    if (!header) {
+      return ActualAlloc::FailureResult();
+    }
+    header->mLength = 0;
+    header->mCapacity = aCapacity;
+    header->mIsAutoArray = 0;
+    mHdr = header;
+
+    return ActualAlloc::SuccessResult();
+  }
+
+  // We increase our capacity so that the allocated buffer grows exponentially,
+  // which gives us amortized O(1) appending. Below the threshold, we use
+  // powers-of-two. Above the threshold, we grow by at least 1.125, rounding up
+  // to the nearest MiB.
+  const size_t slowGrowthThreshold = 8 * 1024 * 1024;
+
+  size_t bytesToAlloc;
+  if (reqSize >= slowGrowthThreshold) {
+    size_t currSize = sizeof(Header) + Capacity() * aElemSize;
+    size_t minNewSize = currSize + (currSize >> 3);  // multiply by 1.125
+    bytesToAlloc = reqSize > minNewSize ? reqSize : minNewSize;
+
+    // Round up to the next multiple of MiB.
+    const size_t MiB = 1 << 20;
+    bytesToAlloc = MiB * ((bytesToAlloc + MiB - 1) / MiB);
+  } else {
+    // Round up to the next power of two.
+    bytesToAlloc = mozilla::RoundUpPow2(reqSize);
+  }
+
+  Header* header;
+  if (UsesAutoArrayBuffer() || !RelocationStrategy::allowRealloc) {
+    // Malloc() and copy
+    header = static_cast<Header*>(ActualAlloc::Malloc(bytesToAlloc));
+    if (!header) {
+      return ActualAlloc::FailureResult();
+    }
+
+    RelocationStrategy::RelocateNonOverlappingRegionWithHeader(
+        header, mHdr, Length(), aElemSize);
+
+    if (!UsesAutoArrayBuffer()) {
+      ActualAlloc::Free(mHdr);
+    }
+  } else {
+    // Realloc() existing data
+    header = static_cast<Header*>(ActualAlloc::Realloc(mHdr, bytesToAlloc));
+    if (!header) {
+      return ActualAlloc::FailureResult();
+    }
+  }
+
+  // How many elements can we fit in bytesToAlloc?
+  size_t newCapacity = (bytesToAlloc - sizeof(Header)) / aElemSize;
+  MOZ_ASSERT(newCapacity >= aCapacity, "Didn't enlarge the array enough!");
+  header->mCapacity = newCapacity;
+
+  mHdr = header;
+
+  return ActualAlloc::SuccessResult();
+}
+
+// We don't need use Alloc template parameter specified here because failure to
+// shrink the capacity will leave the array unchanged.
+template <class Alloc, class RelocationStrategy>
+void nsTArray_base<Alloc, RelocationStrategy>::ShrinkCapacity(
+    size_type aElemSize, size_t aElemAlign) {
+  if (HasEmptyHeader() || UsesAutoArrayBuffer()) {
+    return;
+  }
+
+  if (mHdr->mLength >= mHdr->mCapacity) {  // should never be greater than...
+    return;
+  }
+
+  size_type length = Length();
+
+  if (IsAutoArray() && GetAutoArrayBuffer(aElemAlign)->mCapacity >= length) {
+    Header* header = GetAutoArrayBuffer(aElemAlign);
+
+    // Move the data, but don't copy the header to avoid overwriting mCapacity.
+    header->mLength = length;
+    RelocationStrategy::RelocateNonOverlappingRegion(header + 1, mHdr + 1,
+                                                     length, aElemSize);
+
+    nsTArrayFallibleAllocator::Free(mHdr);
+    mHdr = header;
+    return;
+  }
+
+  if (length == 0) {
+    MOZ_ASSERT(!IsAutoArray(), "autoarray should have fit 0 elements");
+    nsTArrayFallibleAllocator::Free(mHdr);
+    mHdr = EmptyHdr();
+    return;
+  }
+
+  size_type newSize = sizeof(Header) + length * aElemSize;
+
+  Header* newHeader;
+  if (!RelocationStrategy::allowRealloc) {
+    // Malloc() and copy.
+    newHeader =
+        static_cast<Header*>(nsTArrayFallibleAllocator::Malloc(newSize));
+    if (!newHeader) {
+      return;
+    }
+
+    RelocationStrategy::RelocateNonOverlappingRegionWithHeader(
+        newHeader, mHdr, Length(), aElemSize);
+
+    nsTArrayFallibleAllocator::Free(mHdr);
+  } else {
+    // Realloc() existing data.
+    newHeader =
+        static_cast<Header*>(nsTArrayFallibleAllocator::Realloc(mHdr, newSize));
+    if (!newHeader) {
+      return;
+    }
+  }
+
+  mHdr = newHeader;
+  mHdr->mCapacity = length;
+}
+
+template <class Alloc, class RelocationStrategy>
+void nsTArray_base<Alloc, RelocationStrategy>::ShrinkCapacityToZero(
+    size_type aElemSize, size_t aElemAlign) {
+  MOZ_ASSERT(mHdr->mLength == 0);
+
+  if (HasEmptyHeader() || UsesAutoArrayBuffer()) {
+    return;
+  }
+
+  const bool isAutoArray = IsAutoArray();
+
+  nsTArrayFallibleAllocator::Free(mHdr);
+
+  if (isAutoArray) {
+    mHdr = GetAutoArrayBufferUnsafe(aElemAlign);
+    mHdr->mLength = 0;
+  } else {
+    mHdr = EmptyHdr();
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+void nsTArray_base<Alloc, RelocationStrategy>::ShiftData(index_type aStart,
+                                                         size_type aOldLen,
+                                                         size_type aNewLen,
+                                                         size_type aElemSize,
+                                                         size_t aElemAlign) {
+  if (aOldLen == aNewLen) {
+    return;
+  }
+
+  // Determine how many elements need to be shifted
+  size_type num = mHdr->mLength - (aStart + aOldLen);
+
+  // Compute the resulting length of the array
+  mHdr->mLength += aNewLen - aOldLen;
+  if (mHdr->mLength == 0) {
+    ShrinkCapacityToZero(aElemSize, aElemAlign);
+  } else {
+    // Maybe nothing needs to be shifted
+    if (num == 0) {
+      return;
+    }
+    // Perform shift (change units to bytes first)
+    aStart *= aElemSize;
+    aNewLen *= aElemSize;
+    aOldLen *= aElemSize;
+    char* baseAddr = reinterpret_cast<char*>(mHdr + 1) + aStart;
+    RelocationStrategy::RelocateOverlappingRegion(
+        baseAddr + aNewLen, baseAddr + aOldLen, num, aElemSize);
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+void nsTArray_base<Alloc, RelocationStrategy>::SwapFromEnd(index_type aStart,
+                                                           size_type aCount,
+                                                           size_type aElemSize,
+                                                           size_t aElemAlign) {
+  // This method is part of the implementation of
+  // nsTArray::SwapRemoveElement{s,}At. For more information, read the
+  // documentation on that method.
+  if (aCount == 0) {
+    return;
+  }
+
+  // We are going to be removing aCount elements. Update our length to point to
+  // the new end of the array.
+  size_type oldLength = mHdr->mLength;
+  mHdr->mLength -= aCount;
+
+  if (mHdr->mLength == 0) {
+    // If we have no elements remaining in the array, we can free our buffer.
+    ShrinkCapacityToZero(aElemSize, aElemAlign);
+    return;
+  }
+
+  // Determine how many elements we need to move from the end of the array into
+  // the now-removed section. This will either be the number of elements which
+  // were removed (if there are more elements in the tail of the array), or the
+  // entire tail of the array, whichever is smaller.
+  size_type relocCount = std::min(aCount, mHdr->mLength - aStart);
+  if (relocCount == 0) {
+    return;
+  }
+
+  // Move the elements which are now stranded after the end of the array back
+  // into the now-vacated memory.
+  index_type sourceBytes = (oldLength - relocCount) * aElemSize;
+  index_type destBytes = aStart * aElemSize;
+
+  // Perform the final copy. This is guaranteed to be a non-overlapping copy
+  // as our source contains only still-valid entries, and the destination
+  // contains only invalid entries which need to be overwritten.
+  MOZ_ASSERT(sourceBytes >= destBytes,
+             "The source should be after the destination.");
+  MOZ_ASSERT(sourceBytes - destBytes >= relocCount * aElemSize,
+             "The range should be nonoverlapping");
+
+  char* baseAddr = reinterpret_cast<char*>(mHdr + 1);
+  RelocationStrategy::RelocateNonOverlappingRegion(
+      baseAddr + destBytes, baseAddr + sourceBytes, relocCount, aElemSize);
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+typename ActualAlloc::ResultTypeProxy
+nsTArray_base<Alloc, RelocationStrategy>::InsertSlotsAt(index_type aIndex,
+                                                        size_type aCount,
+                                                        size_type aElemSize,
+                                                        size_t aElemAlign) {
+  if (MOZ_UNLIKELY(aIndex > Length())) {
+    mozilla::detail::InvalidArrayIndex_CRASH(aIndex, Length());
+  }
+
+  if (!ActualAlloc::Successful(
+          this->ExtendCapacity<ActualAlloc>(Length(), aCount, aElemSize))) {
+    return ActualAlloc::FailureResult();
+  }
+
+  // Move the existing elements as needed.  Note that this will
+  // change our mLength, so no need to call IncrementLength.
+  ShiftData<ActualAlloc>(aIndex, 0, aCount, aElemSize, aElemAlign);
+
+  return ActualAlloc::SuccessResult();
+}
+
+// nsTArray_base::IsAutoArrayRestorer is an RAII class which takes
+// |nsTArray_base &array| in its constructor.  When it's destructed, it ensures
+// that
+//
+//   * array.mIsAutoArray has the same value as it did when we started, and
+//   * if array has an auto buffer and mHdr would otherwise point to
+//     sEmptyTArrayHeader, array.mHdr points to array's auto buffer.
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc, RelocationStrategy>::IsAutoArrayRestorer::
+    IsAutoArrayRestorer(nsTArray_base<Alloc, RelocationStrategy>& aArray,
+                        size_t aElemAlign)
+    : mArray(aArray), mElemAlign(aElemAlign), mIsAuto(aArray.IsAutoArray()) {}
+
+template <class Alloc, class RelocationStrategy>
+nsTArray_base<Alloc,
+              RelocationStrategy>::IsAutoArrayRestorer::~IsAutoArrayRestorer() {
+  // Careful: We don't want to set mIsAutoArray = 1 on sEmptyTArrayHeader.
+  if (mIsAuto && mArray.HasEmptyHeader()) {
+    // Call GetAutoArrayBufferUnsafe() because GetAutoArrayBuffer() asserts
+    // that mHdr->mIsAutoArray is true, which surely isn't the case here.
+    mArray.mHdr = mArray.GetAutoArrayBufferUnsafe(mElemAlign);
+    mArray.mHdr->mLength = 0;
+  } else if (!mArray.HasEmptyHeader()) {
+    mArray.mHdr->mIsAutoArray = mIsAuto;
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc, class Allocator>
+typename ActualAlloc::ResultTypeProxy
+nsTArray_base<Alloc, RelocationStrategy>::SwapArrayElements(
+    nsTArray_base<Allocator, RelocationStrategy>& aOther, size_type aElemSize,
+    size_t aElemAlign) {
+  // EnsureNotUsingAutoArrayBuffer will set mHdr = sEmptyTArrayHeader even if we
+  // have an auto buffer.  We need to point mHdr back to our auto buffer before
+  // we return, otherwise we'll forget that we have an auto buffer at all!
+  // IsAutoArrayRestorer takes care of this for us.
+
+  IsAutoArrayRestorer ourAutoRestorer(*this, aElemAlign);
+  typename nsTArray_base<Allocator, RelocationStrategy>::IsAutoArrayRestorer
+      otherAutoRestorer(aOther, aElemAlign);
+
+  // If neither array uses an auto buffer which is big enough to store the
+  // other array's elements, then ensure that both arrays use malloc'ed storage
+  // and swap their mHdr pointers.
+  if ((!UsesAutoArrayBuffer() || Capacity() < aOther.Length()) &&
+      (!aOther.UsesAutoArrayBuffer() || aOther.Capacity() < Length())) {
+    if (!EnsureNotUsingAutoArrayBuffer<ActualAlloc>(aElemSize) ||
+        !aOther.template EnsureNotUsingAutoArrayBuffer<ActualAlloc>(
+            aElemSize)) {
+      return ActualAlloc::FailureResult();
+    }
+
+    Header* temp = mHdr;
+    mHdr = aOther.mHdr;
+    aOther.mHdr = temp;
+
+    return ActualAlloc::SuccessResult();
+  }
+
+  // Swap the two arrays by copying, since at least one is using an auto
+  // buffer which is large enough to hold all of the aOther's elements.  We'll
+  // copy the shorter array into temporary storage.
+  //
+  // (We could do better than this in some circumstances.  Suppose we're
+  // swapping arrays X and Y.  X has space for 2 elements in its auto buffer,
+  // but currently has length 4, so it's using malloc'ed storage.  Y has length
+  // 2.  When we swap X and Y, we don't need to use a temporary buffer; we can
+  // write Y straight into X's auto buffer, write X's malloc'ed buffer on top
+  // of Y, and then switch X to using its auto buffer.)
+
+  if (!ActualAlloc::Successful(
+          EnsureCapacity<ActualAlloc>(aOther.Length(), aElemSize)) ||
+      !Allocator::Successful(
+          aOther.template EnsureCapacity<Allocator>(Length(), aElemSize))) {
+    return ActualAlloc::FailureResult();
+  }
+
+  // The EnsureCapacity calls above shouldn't have caused *both* arrays to
+  // switch from their auto buffers to malloc'ed space.
+  MOZ_ASSERT(UsesAutoArrayBuffer() || aOther.UsesAutoArrayBuffer(),
+             "One of the arrays should be using its auto buffer.");
+
+  size_type smallerLength = XPCOM_MIN(Length(), aOther.Length());
+  size_type largerLength = XPCOM_MAX(Length(), aOther.Length());
+  void* smallerElements;
+  void* largerElements;
+  if (Length() <= aOther.Length()) {
+    smallerElements = Hdr() + 1;
+    largerElements = aOther.Hdr() + 1;
+  } else {
+    smallerElements = aOther.Hdr() + 1;
+    largerElements = Hdr() + 1;
+  }
+
+  // Allocate temporary storage for the smaller of the two arrays.  We want to
+  // allocate this space on the stack, if it's not too large.  Sounds like a
+  // job for AutoTArray!  (One of the two arrays we're swapping is using an
+  // auto buffer, so we're likely not allocating a lot of space here.  But one
+  // could, in theory, allocate a huge AutoTArray on the heap.)
+  AutoTArray<uint8_t, 64 * sizeof(void*)> temp;
+  if (!ActualAlloc::Successful(temp.template EnsureCapacity<ActualAlloc>(
+          smallerLength * aElemSize, sizeof(uint8_t)))) {
+    return ActualAlloc::FailureResult();
+  }
+
+  RelocationStrategy::RelocateNonOverlappingRegion(
+      temp.Elements(), smallerElements, smallerLength, aElemSize);
+  RelocationStrategy::RelocateNonOverlappingRegion(
+      smallerElements, largerElements, largerLength, aElemSize);
+  RelocationStrategy::RelocateNonOverlappingRegion(
+      largerElements, temp.Elements(), smallerLength, aElemSize);
+
+  // Swap the arrays' lengths.
+  MOZ_ASSERT((aOther.Length() == 0 || !HasEmptyHeader()) &&
+                 (Length() == 0 || !aOther.HasEmptyHeader()),
+             "Don't set sEmptyTArrayHeader's length.");
+  size_type tempLength = Length();
+
+  // Avoid writing to EmptyHdr, since it can trigger false
+  // positives with TSan.
+  if (!HasEmptyHeader()) {
+    mHdr->mLength = aOther.Length();
+  }
+  if (!aOther.HasEmptyHeader()) {
+    aOther.mHdr->mLength = tempLength;
+  }
+
+  return ActualAlloc::SuccessResult();
+}
+
+template <class Alloc, class RelocationStrategy>
+template <class Allocator>
+void nsTArray_base<Alloc, RelocationStrategy>::MoveInit(
+    nsTArray_base<Allocator, RelocationStrategy>& aOther, size_type aElemSize,
+    size_t aElemAlign) {
+  // This method is similar to SwapArrayElements, but specialized for the case
+  // where the target array is empty with no allocated heap storage. It is
+  // provided and used to simplify template instantiation and enable better code
+  // generation.
+
+  MOZ_ASSERT(Length() == 0);
+  MOZ_ASSERT(Capacity() == 0 || (IsAutoArray() && UsesAutoArrayBuffer()));
+
+  // EnsureNotUsingAutoArrayBuffer will set mHdr = sEmptyTArrayHeader even if we
+  // have an auto buffer.  We need to point mHdr back to our auto buffer before
+  // we return, otherwise we'll forget that we have an auto buffer at all!
+  // IsAutoArrayRestorer takes care of this for us.
+
+  IsAutoArrayRestorer ourAutoRestorer(*this, aElemAlign);
+  typename nsTArray_base<Allocator, RelocationStrategy>::IsAutoArrayRestorer
+      otherAutoRestorer(aOther, aElemAlign);
+
+  // If neither array uses an auto buffer which is big enough to store the
+  // other array's elements, then ensure that both arrays use malloc'ed storage
+  // and swap their mHdr pointers.
+  if ((!IsAutoArray() || Capacity() < aOther.Length()) &&
+      !aOther.UsesAutoArrayBuffer()) {
+    mHdr = aOther.mHdr;
+
+    aOther.mHdr = EmptyHdr();
+
+    return;
+  }
+
+  // Move the data by copying, since at least one has an auto
+  // buffer which is large enough to hold all of the aOther's elements.
+
+  EnsureCapacity<nsTArrayInfallibleAllocator>(aOther.Length(), aElemSize);
+
+  // The EnsureCapacity calls above shouldn't have caused *both* arrays to
+  // switch from their auto buffers to malloc'ed space.
+  MOZ_ASSERT(UsesAutoArrayBuffer() || aOther.UsesAutoArrayBuffer(),
+             "One of the arrays should be using its auto buffer.");
+
+  RelocationStrategy::RelocateNonOverlappingRegion(Hdr() + 1, aOther.Hdr() + 1,
+                                                   aOther.Length(), aElemSize);
+
+  // Swap the arrays' lengths.
+  MOZ_ASSERT((aOther.Length() == 0 || !HasEmptyHeader()) &&
+                 (Length() == 0 || !aOther.HasEmptyHeader()),
+             "Don't set sEmptyTArrayHeader's length.");
+
+  // Avoid writing to EmptyHdr, since it can trigger false
+  // positives with TSan.
+  if (!HasEmptyHeader()) {
+    mHdr->mLength = aOther.Length();
+  }
+  if (!aOther.HasEmptyHeader()) {
+    aOther.mHdr->mLength = 0;
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+template <class Allocator>
+void nsTArray_base<Alloc, RelocationStrategy>::MoveConstructNonAutoArray(
+    nsTArray_base<Allocator, RelocationStrategy>& aOther, size_type aElemSize,
+    size_t aElemAlign) {
+  // We know that we are not an (Copyable)AutoTArray and we know that we are
+  // empty, so don't use SwapArrayElements which doesn't know either of these
+  // facts and is very complex.
+
+  if (aOther.IsEmpty()) {
+    return;
+  }
+
+  // aOther might be an (Copyable)AutoTArray though, and it might use its inline
+  // buffer.
+  const bool otherUsesAutoArrayBuffer = aOther.UsesAutoArrayBuffer();
+  if (otherUsesAutoArrayBuffer) {
+    // Use nsTArrayInfallibleAllocator regardless of Alloc because this is
+    // called from a move constructor, which cannot report an error to the
+    // caller.
+    aOther.template EnsureNotUsingAutoArrayBuffer<nsTArrayInfallibleAllocator>(
+        aElemSize);
+  }
+
+  const bool otherIsAuto = otherUsesAutoArrayBuffer || aOther.IsAutoArray();
+  mHdr = aOther.mHdr;
+  // We might write to mHdr, so ensure it's not the static empty header. aOther
+  // shouldn't have been empty if we get here anyway.
+  MOZ_ASSERT(!HasEmptyHeader());
+
+  if (otherIsAuto) {
+    mHdr->mIsAutoArray = false;
+    aOther.mHdr = aOther.GetAutoArrayBufferUnsafe(aElemAlign);
+    aOther.mHdr->mLength = 0;
+  } else {
+    aOther.mHdr = aOther.EmptyHdr();
+  }
+}
+
+template <class Alloc, class RelocationStrategy>
+template <typename ActualAlloc>
+bool nsTArray_base<Alloc, RelocationStrategy>::EnsureNotUsingAutoArrayBuffer(
+    size_type aElemSize) {
+  if (UsesAutoArrayBuffer()) {
+    // If you call this on a 0-length array, we'll set that array's mHdr to
+    // sEmptyTArrayHeader, in flagrant violation of the AutoTArray invariants.
+    // It's up to you to set it back!  (If you don't, the AutoTArray will
+    // forget that it has an auto buffer.)
+    if (Length() == 0) {
+      mHdr = EmptyHdr();
+      return true;
+    }
+
+    size_type size = sizeof(Header) + Length() * aElemSize;
+
+    Header* header = static_cast<Header*>(ActualAlloc::Malloc(size));
+    if (!header) {
+      return false;
+    }
+
+    RelocationStrategy::RelocateNonOverlappingRegionWithHeader(
+        header, mHdr, Length(), aElemSize);
+    header->mCapacity = Length();
+    mHdr = header;
+  }
+
+  return true;
+}