Add m-esr52 at 52.6.0

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diff --git a/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h b/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h
new file mode 100644
index 000000000..74fa60b12
--- /dev/null
+++ b/js/src/jit/shared/IonAssemblerBufferWithConstantPools.h
@@ -0,0 +1,1145 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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 jit_shared_IonAssemblerBufferWithConstantPools_h
+#define jit_shared_IonAssemblerBufferWithConstantPools_h
+
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/SizePrintfMacros.h"
+
+#include <algorithm>
+
+#include "jit/JitSpewer.h"
+#include "jit/shared/IonAssemblerBuffer.h"
+
+// This code extends the AssemblerBuffer to support the pooling of values loaded
+// using program-counter relative addressing modes. This is necessary with the
+// ARM instruction set because it has a fixed instruction size that can not
+// encode all values as immediate arguments in instructions. Pooling the values
+// allows the values to be placed in large chunks which minimizes the number of
+// forced branches around them in the code. This is used for loading floating
+// point constants, for loading 32 bit constants on the ARMv6, for absolute
+// branch targets, and in future will be needed for large branches on the ARMv6.
+//
+// For simplicity of the implementation, the constant pools are always placed
+// after the loads referencing them. When a new constant pool load is added to
+// the assembler buffer, a corresponding pool entry is added to the current
+// pending pool. The finishPool() method copies the current pending pool entries
+// into the assembler buffer at the current offset and patches the pending
+// constant pool load instructions.
+//
+// Before inserting instructions or pool entries, it is necessary to determine
+// if doing so would place a pending pool entry out of reach of an instruction,
+// and if so then the pool must firstly be dumped. With the allocation algorithm
+// used below, the recalculation of all the distances between instructions and
+// their pool entries can be avoided by noting that there will be a limiting
+// instruction and pool entry pair that does not change when inserting more
+// instructions. Adding more instructions makes the same increase to the
+// distance, between instructions and their pool entries, for all such
+// pairs. This pair is recorded as the limiter, and it is updated when new pool
+// entries are added, see updateLimiter()
+//
+// The pools consist of: a guard instruction that branches around the pool, a
+// header word that helps identify a pool in the instruction stream, and then
+// the pool entries allocated in units of words. The guard instruction could be
+// omitted if control does not reach the pool, and this is referred to as a
+// natural guard below, but for simplicity the guard branch is always
+// emitted. The pool header is an identifiable word that in combination with the
+// guard uniquely identifies a pool in the instruction stream. The header also
+// encodes the pool size and a flag indicating if the guard is natural. It is
+// possible to iterate through the code instructions skipping or examining the
+// pools. E.g. it might be necessary to skip pools when search for, or patching,
+// an instruction sequence.
+//
+// It is often required to keep a reference to a pool entry, to patch it after
+// the buffer is finished. Each pool entry is assigned a unique index, counting
+// up from zero (see the poolEntryCount slot below). These can be mapped back to
+// the offset of the pool entry in the finished buffer, see poolEntryOffset().
+//
+// The code supports no-pool regions, and for these the size of the region, in
+// instructions, must be supplied. This size is used to determine if inserting
+// the instructions would place a pool entry out of range, and if so then a pool
+// is firstly flushed. The DEBUG code checks that the emitted code is within the
+// supplied size to detect programming errors. See enterNoPool() and
+// leaveNoPool().
+
+// The only planned instruction sets that require inline constant pools are the
+// ARM, ARM64, and MIPS, and these all have fixed 32-bit sized instructions so
+// for simplicity the code below is specialized for fixed 32-bit sized
+// instructions and makes no attempt to support variable length
+// instructions. The base assembler buffer which supports variable width
+// instruction is used by the x86 and x64 backends.
+
+// The AssemblerBufferWithConstantPools template class uses static callbacks to
+// the provided Asm template argument class:
+//
+// void Asm::InsertIndexIntoTag(uint8_t* load_, uint32_t index)
+//
+//   When allocEntry() is called to add a constant pool load with an associated
+//   constant pool entry, this callback is called to encode the index of the
+//   allocated constant pool entry into the load instruction.
+//
+//   After the constant pool has been placed, PatchConstantPoolLoad() is called
+//   to update the load instruction with the right load offset.
+//
+// void Asm::WritePoolGuard(BufferOffset branch,
+//                          Instruction* dest,
+//                          BufferOffset afterPool)
+//
+//   Write out the constant pool guard branch before emitting the pool.
+//
+//   branch
+//     Offset of the guard branch in the buffer.
+//
+//   dest
+//     Pointer into the buffer where the guard branch should be emitted. (Same
+//     as getInst(branch)). Space for guardSize_ instructions has been reserved.
+//
+//   afterPool
+//     Offset of the first instruction after the constant pool. This includes
+//     both pool entries and branch veneers added after the pool data.
+//
+// void Asm::WritePoolHeader(uint8_t* start, Pool* p, bool isNatural)
+//
+//   Write out the pool header which follows the guard branch.
+//
+// void Asm::PatchConstantPoolLoad(void* loadAddr, void* constPoolAddr)
+//
+//   Re-encode a load of a constant pool entry after the location of the
+//   constant pool is known.
+//
+//   The load instruction at loadAddr was previously passed to
+//   InsertIndexIntoTag(). The constPoolAddr is the final address of the
+//   constant pool in the assembler buffer.
+//
+// void Asm::PatchShortRangeBranchToVeneer(AssemblerBufferWithConstantPools*,
+//                                         unsigned rangeIdx,
+//                                         BufferOffset deadline,
+//                                         BufferOffset veneer)
+//
+//   Patch a short-range branch to jump through a veneer before it goes out of
+//   range.
+//
+//   rangeIdx, deadline
+//     These arguments were previously passed to registerBranchDeadline(). It is
+//     assumed that PatchShortRangeBranchToVeneer() knows how to compute the
+//     offset of the short-range branch from this information.
+//
+//   veneer
+//     Space for a branch veneer, guaranteed to be <= deadline. At this
+//     position, guardSize_ * InstSize bytes are allocated. They should be
+//     initialized to the proper unconditional branch instruction.
+//
+//   Unbound branches to the same unbound label are organized as a linked list:
+//
+//     Label::offset -> Branch1 -> Branch2 -> Branch3 -> nil
+//
+//   This callback should insert a new veneer branch into the list:
+//
+//     Label::offset -> Branch1 -> Branch2 -> Veneer -> Branch3 -> nil
+//
+//   When Assembler::bind() rewrites the branches with the real label offset, it
+//   probably has to bind Branch2 to target the veneer branch instead of jumping
+//   straight to the label.
+
+namespace js {
+namespace jit {
+
+// BranchDeadlineSet - Keep track of pending branch deadlines.
+//
+// Some architectures like arm and arm64 have branch instructions with limited
+// range. When assembling a forward branch, it is not always known if the final
+// target label will be in range of the branch instruction.
+//
+// The BranchDeadlineSet data structure is used to keep track of the set of
+// pending forward branches. It supports the following fast operations:
+//
+// 1. Get the earliest deadline in the set.
+// 2. Add a new branch deadline.
+// 3. Remove a branch deadline.
+//
+// Architectures may have different branch encodings with different ranges. Each
+// supported range is assigned a small integer starting at 0. This data
+// structure does not care about the actual range of branch instructions, just
+// the latest buffer offset that can be reached - the deadline offset.
+//
+// Branched are stored as (rangeIdx, deadline) tuples. The target-specific code
+// can compute the location of the branch itself from this information. This
+// data structure does not need to know.
+//
+template <unsigned NumRanges>
+class BranchDeadlineSet
+{
+    // Maintain a list of pending deadlines for each range separately.
+    //
+    // The offsets in each vector are always kept in ascending order.
+    //
+    // Because we have a separate vector for different ranges, as forward
+    // branches are added to the assembler buffer, their deadlines will
+    // always be appended to the vector corresponding to their range.
+    //
+    // When binding labels, we expect a more-or-less LIFO order of branch
+    // resolutions. This would always hold if we had strictly structured control
+    // flow.
+    //
+    // We allow branch deadlines to be added and removed in any order, but
+    // performance is best in the expected case of near LIFO order.
+    //
+    typedef Vector<BufferOffset, 8, LifoAllocPolicy<Fallible>> RangeVector;
+
+    // We really just want "RangeVector deadline_[NumRanges];", but each vector
+    // needs to be initialized with a LifoAlloc, and C++ doesn't bend that way.
+    //
+    // Use raw aligned storage instead and explicitly construct NumRanges
+    // vectors in our constructor.
+    mozilla::AlignedStorage2<RangeVector[NumRanges]> deadlineStorage_;
+
+    // Always access the range vectors through this method.
+    RangeVector& vectorForRange(unsigned rangeIdx)
+    {
+        MOZ_ASSERT(rangeIdx < NumRanges, "Invalid branch range index");
+        return (*deadlineStorage_.addr())[rangeIdx];
+    }
+
+    const RangeVector& vectorForRange(unsigned rangeIdx) const
+    {
+        MOZ_ASSERT(rangeIdx < NumRanges, "Invalid branch range index");
+        return (*deadlineStorage_.addr())[rangeIdx];
+    }
+
+    // Maintain a precomputed earliest deadline at all times.
+    // This is unassigned only when all deadline vectors are empty.
+    BufferOffset earliest_;
+
+    // The range vector owning earliest_. Uninitialized when empty.
+    unsigned earliestRange_;
+
+    // Recompute the earliest deadline after it's been invalidated.
+    void recomputeEarliest()
+    {
+        earliest_ = BufferOffset();
+        for (unsigned r = 0; r < NumRanges; r++) {
+            auto& vec = vectorForRange(r);
+            if (!vec.empty() && (!earliest_.assigned() || vec[0] < earliest_)) {
+                earliest_ = vec[0];
+                earliestRange_ = r;
+            }
+        }
+    }
+
+    // Update the earliest deadline if needed after inserting (rangeIdx,
+    // deadline). Always return true for convenience:
+    // return insert() && updateEarliest().
+    bool updateEarliest(unsigned rangeIdx, BufferOffset deadline)
+    {
+        if (!earliest_.assigned() || deadline < earliest_) {
+            earliest_ = deadline;
+            earliestRange_ = rangeIdx;
+        }
+        return true;
+    }
+
+  public:
+    explicit BranchDeadlineSet(LifoAlloc& alloc)
+    {
+        // Manually construct vectors in the uninitialized aligned storage.
+        // This is because C++ arrays can otherwise only be constructed with
+        // the default constructor.
+        for (unsigned r = 0; r < NumRanges; r++)
+            new (&vectorForRange(r)) RangeVector(alloc);
+    }
+
+    ~BranchDeadlineSet()
+    {
+        // Aligned storage doesn't destruct its contents automatically.
+        for (unsigned r = 0; r < NumRanges; r++)
+            vectorForRange(r).~RangeVector();
+    }
+
+    // Is this set completely empty?
+    bool empty() const { return !earliest_.assigned(); }
+
+    // Get the total number of deadlines in the set.
+    size_t size() const
+    {
+        size_t count = 0;
+        for (unsigned r = 0; r < NumRanges; r++)
+            count += vectorForRange(r).length();
+        return count;
+    }
+
+    // Get the number of deadlines for the range with the most elements.
+    size_t maxRangeSize() const
+    {
+        size_t count = 0;
+        for (unsigned r = 0; r < NumRanges; r++)
+            count = std::max(count, vectorForRange(r).length());
+        return count;
+    }
+
+    // Get the first deadline that is still in the set.
+    BufferOffset earliestDeadline() const
+    {
+        MOZ_ASSERT(!empty());
+        return earliest_;
+    }
+
+    // Get the range index corresponding to earliestDeadlineRange().
+    unsigned earliestDeadlineRange() const
+    {
+        MOZ_ASSERT(!empty());
+        return earliestRange_;
+    }
+
+    // Add a (rangeIdx, deadline) tuple to the set.
+    //
+    // It is assumed that this tuple is not already in the set.
+    // This function performs best id the added deadline is later than any
+    // existing deadline for the same range index.
+    //
+    // Return true if the tuple was added, false if the tuple could not be added
+    // because of an OOM error.
+    bool addDeadline(unsigned rangeIdx, BufferOffset deadline)
+    {
+        MOZ_ASSERT(deadline.assigned(), "Can only store assigned buffer offsets");
+        // This is the vector where deadline should be saved.
+        auto& vec = vectorForRange(rangeIdx);
+
+        // Fast case: Simple append to the relevant array. This never affects
+        // the earliest deadline.
+        if (!vec.empty() && vec.back() < deadline)
+            return vec.append(deadline);
+
+        // Fast case: First entry to the vector. We need to update earliest_.
+        if (vec.empty())
+            return vec.append(deadline) && updateEarliest(rangeIdx, deadline);
+
+        return addDeadlineSlow(rangeIdx, deadline);
+    }
+
+  private:
+    // General case of addDeadline. This is split into two functions such that
+    // the common case in addDeadline can be inlined while this part probably
+    // won't inline.
+    bool addDeadlineSlow(unsigned rangeIdx, BufferOffset deadline)
+    {
+        auto& vec = vectorForRange(rangeIdx);
+
+        // Inserting into the middle of the vector. Use a log time binary search
+        // and a linear time insert().
+        // Is it worthwhile special-casing the empty vector?
+        auto at = std::lower_bound(vec.begin(), vec.end(), deadline);
+        MOZ_ASSERT(at == vec.end() || *at != deadline, "Cannot insert duplicate deadlines");
+        return vec.insert(at, deadline) && updateEarliest(rangeIdx, deadline);
+    }
+
+  public:
+    // Remove a deadline from the set.
+    // If (rangeIdx, deadline) is not in the set, nothing happens.
+    void removeDeadline(unsigned rangeIdx, BufferOffset deadline)
+    {
+        auto& vec = vectorForRange(rangeIdx);
+
+        if (vec.empty())
+            return;
+
+        if (deadline == vec.back()) {
+            // Expected fast case: Structured control flow causes forward
+            // branches to be bound in reverse order.
+            vec.popBack();
+        } else {
+            // Slow case: Binary search + linear erase.
+            auto where = std::lower_bound(vec.begin(), vec.end(), deadline);
+            if (where == vec.end() || *where != deadline)
+                return;
+            vec.erase(where);
+        }
+        if (deadline == earliest_)
+            recomputeEarliest();
+    }
+};
+
+// Specialization for architectures that don't need to track short-range
+// branches.
+template <>
+class BranchDeadlineSet<0u>
+{
+  public:
+    explicit BranchDeadlineSet(LifoAlloc& alloc) {}
+    bool empty() const { return true; }
+    size_t size() const { return 0; }
+    size_t maxRangeSize() const { return 0; }
+    BufferOffset earliestDeadline() const { MOZ_CRASH(); }
+    unsigned earliestDeadlineRange() const { MOZ_CRASH(); }
+    bool addDeadline(unsigned rangeIdx, BufferOffset deadline) { MOZ_CRASH(); }
+    void removeDeadline(unsigned rangeIdx, BufferOffset deadline) { MOZ_CRASH(); }
+};
+
+// The allocation unit size for pools.
+typedef int32_t PoolAllocUnit;
+
+// Hysteresis given to short-range branches.
+//
+// If any short-range branches will go out of range in the next N bytes,
+// generate a veneer for them in the current pool. The hysteresis prevents the
+// creation of many tiny constant pools for branch veneers.
+const size_t ShortRangeBranchHysteresis = 128;
+
+struct Pool
+{
+  private:
+    // The maximum program-counter relative offset below which the instruction
+    // set can encode. Different classes of intructions might support different
+    // ranges but for simplicity the minimum is used here, and for the ARM this
+    // is constrained to 1024 by the float load instructions.
+    const size_t maxOffset_;
+    // An offset to apply to program-counter relative offsets. The ARM has a
+    // bias of 8.
+    const unsigned bias_;
+
+    // The content of the pool entries.
+    Vector<PoolAllocUnit, 8, LifoAllocPolicy<Fallible>> poolData_;
+
+    // Flag that tracks OOM conditions. This is set after any append failed.
+    bool oom_;
+
+    // The limiting instruction and pool-entry pair. The instruction program
+    // counter relative offset of this limiting instruction will go out of range
+    // first as the pool position moves forward. It is more efficient to track
+    // just this limiting pair than to recheck all offsets when testing if the
+    // pool needs to be dumped.
+    //
+    // 1. The actual offset of the limiting instruction referencing the limiting
+    // pool entry.
+    BufferOffset limitingUser;
+    // 2. The pool entry index of the limiting pool entry.
+    unsigned limitingUsee;
+
+  public:
+    // A record of the code offset of instructions that reference pool
+    // entries. These instructions need to be patched when the actual position
+    // of the instructions and pools are known, and for the code below this
+    // occurs when each pool is finished, see finishPool().
+    Vector<BufferOffset, 8, LifoAllocPolicy<Fallible>> loadOffsets;
+
+    // Create a Pool. Don't allocate anything from lifoAloc, just capture its reference.
+    explicit Pool(size_t maxOffset, unsigned bias, LifoAlloc& lifoAlloc)
+      : maxOffset_(maxOffset),
+        bias_(bias),
+        poolData_(lifoAlloc),
+        oom_(false),
+        limitingUser(),
+        limitingUsee(INT_MIN),
+        loadOffsets(lifoAlloc)
+    {
+    }
+
+    // If poolData() returns nullptr then oom_ will also be true.
+    const PoolAllocUnit* poolData() const {
+        return poolData_.begin();
+    }
+
+    unsigned numEntries() const {
+        return poolData_.length();
+    }
+
+    size_t getPoolSize() const {
+        return numEntries() * sizeof(PoolAllocUnit);
+    }
+
+    bool oom() const {
+        return oom_;
+    }
+
+    // Update the instruction/pool-entry pair that limits the position of the
+    // pool. The nextInst is the actual offset of the new instruction being
+    // allocated.
+    //
+    // This is comparing the offsets, see checkFull() below for the equation,
+    // but common expressions on both sides have been canceled from the ranges
+    // being compared. Notably, the poolOffset cancels out, so the limiting pair
+    // does not depend on where the pool is placed.
+    void updateLimiter(BufferOffset nextInst) {
+        ptrdiff_t oldRange = limitingUsee * sizeof(PoolAllocUnit) - limitingUser.getOffset();
+        ptrdiff_t newRange = getPoolSize() - nextInst.getOffset();
+        if (!limitingUser.assigned() || newRange > oldRange) {
+            // We have a new largest range!
+            limitingUser = nextInst;
+            limitingUsee = numEntries();
+        }
+    }
+
+    // Check if inserting a pool at the actual offset poolOffset would place
+    // pool entries out of reach. This is called before inserting instructions
+    // to check that doing so would not push pool entries out of reach, and if
+    // so then the pool would need to be firstly dumped. The poolOffset is the
+    // first word of the pool, after the guard and header and alignment fill.
+    bool checkFull(size_t poolOffset) const {
+        // Not full if there are no uses.
+        if (!limitingUser.assigned())
+            return false;
+        size_t offset = poolOffset + limitingUsee * sizeof(PoolAllocUnit)
+                        - (limitingUser.getOffset() + bias_);
+        return offset >= maxOffset_;
+    }
+
+    static const unsigned OOM_FAIL = unsigned(-1);
+
+    unsigned insertEntry(unsigned num, uint8_t* data, BufferOffset off, LifoAlloc& lifoAlloc) {
+        if (oom_)
+            return OOM_FAIL;
+        unsigned ret = numEntries();
+        if (!poolData_.append((PoolAllocUnit*)data, num) || !loadOffsets.append(off)) {
+            oom_ = true;
+            return OOM_FAIL;
+        }
+        return ret;
+    }
+
+    void reset() {
+        poolData_.clear();
+        loadOffsets.clear();
+
+        limitingUser = BufferOffset();
+        limitingUsee = -1;
+    }
+};
+
+
+// Template arguments:
+//
+// SliceSize
+//   Number of bytes in each allocated BufferSlice. See
+//   AssemblerBuffer::SliceSize.
+//
+// InstSize
+//   Size in bytes of the fixed-size instructions. This should be equal to
+//   sizeof(Inst). This is only needed here because the buffer is defined before
+//   the Instruction.
+//
+// Inst
+//   The actual type used to represent instructions. This is only really used as
+//   the return type of the getInst() method.
+//
+// Asm
+//   Class defining the needed static callback functions. See documentation of
+//   the Asm::* callbacks above.
+//
+// NumShortBranchRanges
+//   The number of short branch ranges to support. This can be 0 if no support
+//   for tracking short range branches is needed. The
+//   AssemblerBufferWithConstantPools class does not need to know what the range
+//   of branches is - it deals in branch 'deadlines' which is the last buffer
+//   position that a short-range forward branch can reach. It is assumed that
+//   the Asm class is able to find the actual branch instruction given a
+//   (range-index, deadline) pair.
+//
+//
+template <size_t SliceSize, size_t InstSize, class Inst, class Asm,
+          unsigned NumShortBranchRanges = 0>
+struct AssemblerBufferWithConstantPools : public AssemblerBuffer<SliceSize, Inst>
+{
+  private:
+    // The PoolEntry index counter. Each PoolEntry is given a unique index,
+    // counting up from zero, and these can be mapped back to the actual pool
+    // entry offset after finishing the buffer, see poolEntryOffset().
+    size_t poolEntryCount;
+
+  public:
+    class PoolEntry
+    {
+        size_t index_;
+
+      public:
+        explicit PoolEntry(size_t index)
+          : index_(index)
+        { }
+
+        PoolEntry()
+          : index_(-1)
+        { }
+
+        size_t index() const {
+            return index_;
+        }
+    };
+
+  private:
+    typedef AssemblerBuffer<SliceSize, Inst> Parent;
+    using typename Parent::Slice;
+
+    // The size of a pool guard, in instructions. A branch around the pool.
+    const unsigned guardSize_;
+    // The size of the header that is put at the beginning of a full pool, in
+    // instruction sized units.
+    const unsigned headerSize_;
+
+    // The maximum pc relative offset encoded in instructions that reference
+    // pool entries. This is generally set to the maximum offset that can be
+    // encoded by the instructions, but for testing can be lowered to affect the
+    // pool placement and frequency of pool placement.
+    const size_t poolMaxOffset_;
+
+    // The bias on pc relative addressing mode offsets, in units of bytes. The
+    // ARM has a bias of 8 bytes.
+    const unsigned pcBias_;
+
+    // The current working pool. Copied out as needed before resetting.
+    Pool pool_;
+
+    // The buffer should be aligned to this address.
+    const size_t instBufferAlign_;
+
+    struct PoolInfo {
+        // The index of the first entry in this pool.
+        // Pool entries are numbered uniquely across all pools, starting from 0.
+        unsigned firstEntryIndex;
+
+        // The location of this pool's first entry in the main assembler buffer.
+        // Note that the pool guard and header come before this offset which
+        // points directly at the data.
+        BufferOffset offset;
+
+        explicit PoolInfo(unsigned index, BufferOffset data)
+          : firstEntryIndex(index)
+          , offset(data)
+        {
+        }
+    };
+
+    // Info for each pool that has already been dumped. This does not include
+    // any entries in pool_.
+    Vector<PoolInfo, 8, LifoAllocPolicy<Fallible>> poolInfo_;
+
+    // Set of short-range forward branches that have not yet been bound.
+    // We may need to insert veneers if the final label turns out to be out of
+    // range.
+    //
+    // This set stores (rangeIdx, deadline) pairs instead of the actual branch
+    // locations.
+    BranchDeadlineSet<NumShortBranchRanges> branchDeadlines_;
+
+    // When true dumping pools is inhibited.
+    bool canNotPlacePool_;
+
+#ifdef DEBUG
+    // State for validating the 'maxInst' argument to enterNoPool().
+    // The buffer offset when entering the no-pool region.
+    size_t canNotPlacePoolStartOffset_;
+    // The maximum number of word sized instructions declared for the no-pool
+    // region.
+    size_t canNotPlacePoolMaxInst_;
+#endif
+
+    // Instruction to use for alignment fill.
+    const uint32_t alignFillInst_;
+
+    // Insert a number of NOP instructions between each requested instruction at
+    // all locations at which a pool can potentially spill. This is useful for
+    // checking that instruction locations are correctly referenced and/or
+    // followed.
+    const uint32_t nopFillInst_;
+    const unsigned nopFill_;
+    // For inhibiting the insertion of fill NOPs in the dynamic context in which
+    // they are being inserted.
+    bool inhibitNops_;
+
+  public:
+    // A unique id within each JitContext, to identify pools in the debug
+    // spew. Set by the MacroAssembler, see getNextAssemblerId().
+    int id;
+
+  private:
+    // The buffer slices are in a double linked list.
+    Slice* getHead() const {
+        return this->head;
+    }
+    Slice* getTail() const {
+        return this->tail;
+    }
+
+  public:
+    // Create an assembler buffer.
+    // Note that this constructor is not allowed to actually allocate memory from this->lifoAlloc_
+    // because the MacroAssembler constructor has not yet created an AutoJitContextAlloc.
+    AssemblerBufferWithConstantPools(unsigned guardSize, unsigned headerSize,
+                                     size_t instBufferAlign, size_t poolMaxOffset,
+                                     unsigned pcBias, uint32_t alignFillInst, uint32_t nopFillInst,
+                                     unsigned nopFill = 0)
+      : poolEntryCount(0),
+        guardSize_(guardSize),
+        headerSize_(headerSize),
+        poolMaxOffset_(poolMaxOffset),
+        pcBias_(pcBias),
+        pool_(poolMaxOffset, pcBias, this->lifoAlloc_),
+        instBufferAlign_(instBufferAlign),
+        poolInfo_(this->lifoAlloc_),
+        branchDeadlines_(this->lifoAlloc_),
+        canNotPlacePool_(false),
+#ifdef DEBUG
+        canNotPlacePoolStartOffset_(0),
+        canNotPlacePoolMaxInst_(0),
+#endif
+        alignFillInst_(alignFillInst),
+        nopFillInst_(nopFillInst),
+        nopFill_(nopFill),
+        inhibitNops_(false),
+        id(-1)
+    { }
+
+    // We need to wait until an AutoJitContextAlloc is created by the
+    // MacroAssembler before allocating any space.
+    void initWithAllocator() {
+        // We hand out references to lifoAlloc_ in the constructor.
+        // Check that no allocations were made then.
+        MOZ_ASSERT(this->lifoAlloc_.isEmpty(), "Illegal LIFO allocations before AutoJitContextAlloc");
+    }
+
+  private:
+    size_t sizeExcludingCurrentPool() const {
+        // Return the actual size of the buffer, excluding the current pending
+        // pool.
+        return this->nextOffset().getOffset();
+    }
+
+  public:
+    size_t size() const {
+        // Return the current actual size of the buffer. This is only accurate
+        // if there are no pending pool entries to dump, check.
+        MOZ_ASSERT_IF(!this->oom(), pool_.numEntries() == 0);
+        return sizeExcludingCurrentPool();
+    }
+
+  private:
+    void insertNopFill() {
+        // Insert fill for testing.
+        if (nopFill_ > 0 && !inhibitNops_ && !canNotPlacePool_) {
+            inhibitNops_ = true;
+
+            // Fill using a branch-nop rather than a NOP so this can be
+            // distinguished and skipped.
+            for (size_t i = 0; i < nopFill_; i++)
+                putInt(nopFillInst_);
+
+            inhibitNops_ = false;
+        }
+    }
+
+    static const unsigned OOM_FAIL = unsigned(-1);
+    static const unsigned DUMMY_INDEX = unsigned(-2);
+
+    // Check if it is possible to add numInst instructions and numPoolEntries
+    // constant pool entries without needing to flush the current pool.
+    bool hasSpaceForInsts(unsigned numInsts, unsigned numPoolEntries) const
+    {
+        size_t nextOffset = sizeExcludingCurrentPool();
+        // Earliest starting offset for the current pool after adding numInsts.
+        // This is the beginning of the pool entries proper, after inserting a
+        // guard branch + pool header.
+        size_t poolOffset = nextOffset + (numInsts + guardSize_ + headerSize_) * InstSize;
+
+        // Any constant pool loads that would go out of range?
+        if (pool_.checkFull(poolOffset))
+            return false;
+
+        // Any short-range branch that would go out of range?
+        if (!branchDeadlines_.empty()) {
+            size_t deadline = branchDeadlines_.earliestDeadline().getOffset();
+            size_t poolEnd =
+              poolOffset + pool_.getPoolSize() + numPoolEntries * sizeof(PoolAllocUnit);
+
+            // When NumShortBranchRanges > 1, is is possible for branch deadlines to expire faster
+            // than we can insert veneers. Suppose branches are 4 bytes each, we could have the
+            // following deadline set:
+            //
+            //   Range 0: 40, 44, 48
+            //   Range 1: 44, 48
+            //
+            // It is not good enough to start inserting veneers at the 40 deadline; we would not be
+            // able to create veneers for the second 44 deadline. Instead, we need to start at 32:
+            //
+            //   32: veneer(40)
+            //   36: veneer(44)
+            //   40: veneer(44)
+            //   44: veneer(48)
+            //   48: veneer(48)
+            //
+            // This is a pretty conservative solution to the problem: If we begin at the earliest
+            // deadline, we can always emit all veneers for the range that currently has the most
+            // pending deadlines. That may not leave room for veneers for the remaining ranges, so
+            // reserve space for those secondary range veneers assuming the worst case deadlines.
+
+            // Total pending secondary range veneer size.
+            size_t secondaryVeneers =
+              guardSize_ * (branchDeadlines_.size() - branchDeadlines_.maxRangeSize());
+
+            if (deadline < poolEnd + secondaryVeneers)
+                return false;
+        }
+
+        return true;
+    }
+
+    unsigned insertEntryForwards(unsigned numInst, unsigned numPoolEntries, uint8_t* inst, uint8_t* data) {
+        // If inserting pool entries then find a new limiter before we do the
+        // range check.
+        if (numPoolEntries)
+            pool_.updateLimiter(BufferOffset(sizeExcludingCurrentPool()));
+
+        if (!hasSpaceForInsts(numInst, numPoolEntries)) {
+            if (numPoolEntries)
+                JitSpew(JitSpew_Pools, "[%d] Inserting pool entry caused a spill", id);
+            else
+                JitSpew(JitSpew_Pools, "[%d] Inserting instruction(%" PRIuSIZE ") caused a spill", id,
+                        sizeExcludingCurrentPool());
+
+            finishPool();
+            if (this->oom())
+                return OOM_FAIL;
+            return insertEntryForwards(numInst, numPoolEntries, inst, data);
+        }
+        if (numPoolEntries) {
+            unsigned result = pool_.insertEntry(numPoolEntries, data, this->nextOffset(), this->lifoAlloc_);
+            if (result == Pool::OOM_FAIL) {
+                this->fail_oom();
+                return OOM_FAIL;
+            }
+            return result;
+        }
+
+        // The pool entry index is returned above when allocating an entry, but
+        // when not allocating an entry a dummy value is returned - it is not
+        // expected to be used by the caller.
+        return DUMMY_INDEX;
+    }
+
+  public:
+    // Get the next buffer offset where an instruction would be inserted.
+    // This may flush the current constant pool before returning nextOffset().
+    BufferOffset nextInstrOffset()
+    {
+        if (!hasSpaceForInsts(/* numInsts= */ 1, /* numPoolEntries= */ 0)) {
+            JitSpew(JitSpew_Pools, "[%d] nextInstrOffset @ %d caused a constant pool spill", id,
+                    this->nextOffset().getOffset());
+            finishPool();
+        }
+        return this->nextOffset();
+    }
+
+    BufferOffset allocEntry(size_t numInst, unsigned numPoolEntries,
+                            uint8_t* inst, uint8_t* data, PoolEntry* pe = nullptr,
+                            bool markAsBranch = false)
+    {
+        // The allocation of pool entries is not supported in a no-pool region,
+        // check.
+        MOZ_ASSERT_IF(numPoolEntries, !canNotPlacePool_);
+
+        if (this->oom() && !this->bail())
+            return BufferOffset();
+
+        insertNopFill();
+
+#ifdef JS_JITSPEW
+        if (numPoolEntries && JitSpewEnabled(JitSpew_Pools)) {
+            JitSpew(JitSpew_Pools, "[%d] Inserting %d entries into pool", id, numPoolEntries);
+            JitSpewStart(JitSpew_Pools, "[%d] data is: 0x", id);
+            size_t length = numPoolEntries * sizeof(PoolAllocUnit);
+            for (unsigned idx = 0; idx < length; idx++) {
+                JitSpewCont(JitSpew_Pools, "%02x", data[length - idx - 1]);
+                if (((idx & 3) == 3) && (idx + 1 != length))
+                    JitSpewCont(JitSpew_Pools, "_");
+            }
+            JitSpewFin(JitSpew_Pools);
+        }
+#endif
+
+        // Insert the pool value.
+        unsigned index = insertEntryForwards(numInst, numPoolEntries, inst, data);
+        if (this->oom())
+            return BufferOffset();
+
+        // Now to get an instruction to write.
+        PoolEntry retPE;
+        if (numPoolEntries) {
+            JitSpew(JitSpew_Pools, "[%d] Entry has index %u, offset %" PRIuSIZE, id, index,
+                    sizeExcludingCurrentPool());
+            Asm::InsertIndexIntoTag(inst, index);
+            // Figure out the offset within the pool entries.
+            retPE = PoolEntry(poolEntryCount);
+            poolEntryCount += numPoolEntries;
+        }
+        // Now inst is a valid thing to insert into the instruction stream.
+        if (pe != nullptr)
+            *pe = retPE;
+        return this->putBytes(numInst * InstSize, inst);
+    }
+
+    BufferOffset putInt(uint32_t value, bool markAsBranch = false) {
+        return allocEntry(1, 0, (uint8_t*)&value, nullptr, nullptr, markAsBranch);
+    }
+
+    // Register a short-range branch deadline.
+    //
+    // After inserting a short-range forward branch, call this method to
+    // register the branch 'deadline' which is the last buffer offset that the
+    // branch instruction can reach.
+    //
+    // When the branch is bound to a destination label, call
+    // unregisterBranchDeadline() to stop tracking this branch,
+    //
+    // If the assembled code is about to exceed the registered branch deadline,
+    // and unregisterBranchDeadline() has not yet been called, an
+    // instruction-sized constant pool entry is allocated before the branch
+    // deadline.
+    //
+    // rangeIdx
+    //   A number < NumShortBranchRanges identifying the range of the branch.
+    //
+    // deadline
+    //   The highest buffer offset the the short-range branch can reach
+    //   directly.
+    //
+    void registerBranchDeadline(unsigned rangeIdx, BufferOffset deadline)
+    {
+        if (!this->oom() && !branchDeadlines_.addDeadline(rangeIdx, deadline))
+            this->fail_oom();
+    }
+
+    // Un-register a short-range branch deadline.
+    //
+    // When a short-range branch has been successfully bound to its destination
+    // label, call this function to stop traching the branch.
+    //
+    // The (rangeIdx, deadline) pair must be previously registered.
+    //
+    void unregisterBranchDeadline(unsigned rangeIdx, BufferOffset deadline)
+    {
+        if (!this->oom())
+            branchDeadlines_.removeDeadline(rangeIdx, deadline);
+    }
+
+  private:
+    // Are any short-range branches about to expire?
+    bool hasExpirableShortRangeBranches() const
+    {
+        if (branchDeadlines_.empty())
+            return false;
+
+        // Include branches that would expire in the next N bytes.
+        // The hysteresis avoids the needless creation of many tiny constant
+        // pools.
+        return this->nextOffset().getOffset() + ShortRangeBranchHysteresis >
+               size_t(branchDeadlines_.earliestDeadline().getOffset());
+    }
+
+    void finishPool() {
+        JitSpew(JitSpew_Pools, "[%d] Attempting to finish pool %" PRIuSIZE " with %u entries.",
+                id, poolInfo_.length(), pool_.numEntries());
+
+        if (pool_.numEntries() == 0 && !hasExpirableShortRangeBranches()) {
+            // If there is no data in the pool being dumped, don't dump anything.
+            JitSpew(JitSpew_Pools, "[%d] Aborting because the pool is empty", id);
+            return;
+        }
+
+        // Should not be placing a pool in a no-pool region, check.
+        MOZ_ASSERT(!canNotPlacePool_);
+
+        // Dump the pool with a guard branch around the pool.
+        BufferOffset guard = this->putBytes(guardSize_ * InstSize, nullptr);
+        BufferOffset header = this->putBytes(headerSize_ * InstSize, nullptr);
+        BufferOffset data =
+          this->putBytesLarge(pool_.getPoolSize(), (const uint8_t*)pool_.poolData());
+        if (this->oom())
+            return;
+
+        // Now generate branch veneers for any short-range branches that are
+        // about to expire.
+        while (hasExpirableShortRangeBranches()) {
+            unsigned rangeIdx = branchDeadlines_.earliestDeadlineRange();
+            BufferOffset deadline = branchDeadlines_.earliestDeadline();
+
+            // Stop tracking this branch. The Asm callback below may register
+            // new branches to track.
+            branchDeadlines_.removeDeadline(rangeIdx, deadline);
+
+            // Make room for the veneer. Same as a pool guard branch.
+            BufferOffset veneer = this->putBytes(guardSize_ * InstSize, nullptr);
+            if (this->oom())
+                return;
+
+            // Fix the branch so it targets the veneer.
+            // The Asm class knows how to find the original branch given the
+            // (rangeIdx, deadline) pair.
+            Asm::PatchShortRangeBranchToVeneer(this, rangeIdx, deadline, veneer);
+        }
+
+        // We only reserved space for the guard branch and pool header.
+        // Fill them in.
+        BufferOffset afterPool = this->nextOffset();
+        Asm::WritePoolGuard(guard, this->getInst(guard), afterPool);
+        Asm::WritePoolHeader((uint8_t*)this->getInst(header), &pool_, false);
+
+        // With the pool's final position determined it is now possible to patch
+        // the instructions that reference entries in this pool, and this is
+        // done incrementally as each pool is finished.
+        size_t poolOffset = data.getOffset();
+
+        unsigned idx = 0;
+        for (BufferOffset* iter = pool_.loadOffsets.begin();
+             iter != pool_.loadOffsets.end();
+             ++iter, ++idx)
+        {
+            // All entries should be before the pool.
+            MOZ_ASSERT(iter->getOffset() < guard.getOffset());
+
+            // Everything here is known so we can safely do the necessary
+            // substitutions.
+            Inst* inst = this->getInst(*iter);
+            size_t codeOffset = poolOffset - iter->getOffset();
+
+            // That is, PatchConstantPoolLoad wants to be handed the address of
+            // the pool entry that is being loaded.  We need to do a non-trivial
+            // amount of math here, since the pool that we've made does not
+            // actually reside there in memory.
+            JitSpew(JitSpew_Pools, "[%d] Fixing entry %d offset to %" PRIuSIZE, id, idx, codeOffset);
+            Asm::PatchConstantPoolLoad(inst, (uint8_t*)inst + codeOffset);
+        }
+
+        // Record the pool info.
+        unsigned firstEntry = poolEntryCount - pool_.numEntries();
+        if (!poolInfo_.append(PoolInfo(firstEntry, data))) {
+            this->fail_oom();
+            return;
+        }
+
+        // Reset everything to the state that it was in when we started.
+        pool_.reset();
+    }
+
+  public:
+    void flushPool() {
+        if (this->oom())
+            return;
+        JitSpew(JitSpew_Pools, "[%d] Requesting a pool flush", id);
+        finishPool();
+    }
+
+    void enterNoPool(size_t maxInst) {
+        // Don't allow re-entry.
+        MOZ_ASSERT(!canNotPlacePool_);
+        insertNopFill();
+
+        // Check if the pool will spill by adding maxInst instructions, and if
+        // so then finish the pool before entering the no-pool region. It is
+        // assumed that no pool entries are allocated in a no-pool region and
+        // this is asserted when allocating entries.
+        if (!hasSpaceForInsts(maxInst, 0)) {
+            JitSpew(JitSpew_Pools, "[%d] No-Pool instruction(%" PRIuSIZE ") caused a spill.", id,
+                    sizeExcludingCurrentPool());
+            finishPool();
+        }
+
+#ifdef DEBUG
+        // Record the buffer position to allow validating maxInst when leaving
+        // the region.
+        canNotPlacePoolStartOffset_ = this->nextOffset().getOffset();
+        canNotPlacePoolMaxInst_ = maxInst;
+#endif
+
+        canNotPlacePool_ = true;
+    }
+
+    void leaveNoPool() {
+        MOZ_ASSERT(canNotPlacePool_);
+        canNotPlacePool_ = false;
+
+        // Validate the maxInst argument supplied to enterNoPool().
+        MOZ_ASSERT(this->nextOffset().getOffset() - canNotPlacePoolStartOffset_ <= canNotPlacePoolMaxInst_ * InstSize);
+    }
+
+    void align(unsigned alignment) {
+        MOZ_ASSERT(mozilla::IsPowerOfTwo(alignment));
+        MOZ_ASSERT(alignment >= InstSize);
+
+        // A pool many need to be dumped at this point, so insert NOP fill here.
+        insertNopFill();
+
+        // Check if the code position can be aligned without dumping a pool.
+        unsigned requiredFill = sizeExcludingCurrentPool() & (alignment - 1);
+        if (requiredFill == 0)
+            return;
+        requiredFill = alignment - requiredFill;
+
+        // Add an InstSize because it is probably not useful for a pool to be
+        // dumped at the aligned code position.
+        if (!hasSpaceForInsts(requiredFill / InstSize + 1, 0)) {
+            // Alignment would cause a pool dump, so dump the pool now.
+            JitSpew(JitSpew_Pools, "[%d] Alignment of %d at %" PRIuSIZE " caused a spill.",
+                    id, alignment, sizeExcludingCurrentPool());
+            finishPool();
+        }
+
+        inhibitNops_ = true;
+        while ((sizeExcludingCurrentPool() & (alignment - 1)) && !this->oom())
+            putInt(alignFillInst_);
+        inhibitNops_ = false;
+    }
+
+  public:
+    void executableCopy(uint8_t* dest) {
+        if (this->oom())
+            return;
+        // The pools should have all been flushed, check.
+        MOZ_ASSERT(pool_.numEntries() == 0);
+        for (Slice* cur = getHead(); cur != nullptr; cur = cur->getNext()) {
+            memcpy(dest, &cur->instructions[0], cur->length());
+            dest += cur->length();
+        }
+    }
+
+    bool appendBuffer(const AssemblerBufferWithConstantPools& other) {
+        if (this->oom())
+            return false;
+        // The pools should have all been flushed, check.
+        MOZ_ASSERT(pool_.numEntries() == 0);
+        for (Slice* cur = other.getHead(); cur != nullptr; cur = cur->getNext()) {
+            this->putBytes(cur->length(), &cur->instructions[0]);
+            if (this->oom())
+                return false;
+        }
+        return true;
+    }
+
+  public:
+    size_t poolEntryOffset(PoolEntry pe) const {
+        MOZ_ASSERT(pe.index() < poolEntryCount - pool_.numEntries(),
+                   "Invalid pool entry, or not flushed yet.");
+        // Find the pool containing pe.index().
+        // The array is sorted, so we can use a binary search.
+        auto b = poolInfo_.begin(), e = poolInfo_.end();
+        // A note on asymmetric types in the upper_bound comparator:
+        // http://permalink.gmane.org/gmane.comp.compilers.clang.devel/10101
+        auto i = std::upper_bound(b, e, pe.index(), [](size_t value, const PoolInfo& entry) {
+            return value < entry.firstEntryIndex;
+        });
+        // Since upper_bound finds the first pool greater than pe,
+        // we want the previous one which is the last one less than or equal.
+        MOZ_ASSERT(i != b, "PoolInfo not sorted or empty?");
+        --i;
+        // The i iterator now points to the pool containing pe.index.
+        MOZ_ASSERT(i->firstEntryIndex <= pe.index() &&
+                   (i + 1 == e || (i + 1)->firstEntryIndex > pe.index()));
+        // Compute the byte offset into the pool.
+        unsigned relativeIndex = pe.index() - i->firstEntryIndex;
+        return i->offset.getOffset() + relativeIndex * sizeof(PoolAllocUnit);
+    }
+};
+
+} // namespace ion
+} // namespace js
+
+#endif // jit_shared_IonAssemblerBufferWithConstantPools_h