diff -r 000000000000 -r 6474c204b198 js/src/ds/LifoAlloc.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/ds/LifoAlloc.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,525 @@
+/* -*- 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 ds_LifoAlloc_h
+#define ds_LifoAlloc_h
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/MemoryChecking.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/TemplateLib.h"
+#include "mozilla/TypeTraits.h"
+
+// This data structure supports stacky LIFO allocation (mark/release and
+// LifoAllocScope). It does not maintain one contiguous segment; instead, it
+// maintains a bunch of linked memory segments. In order to prevent malloc/free
+// thrashing, unused segments are deallocated when garbage collection occurs.
+
+#include "jsutil.h"
+
+namespace js {
+
+namespace detail {
+
+static const size_t LIFO_ALLOC_ALIGN = 8;
+
+MOZ_ALWAYS_INLINE
+char *
+AlignPtr(void *orig)
+{
+    static_assert(mozilla::tl::FloorLog2<LIFO_ALLOC_ALIGN>::value ==
+                  mozilla::tl::CeilingLog2<LIFO_ALLOC_ALIGN>::value,
+                  "LIFO_ALLOC_ALIGN must be a power of two");
+
+    char *result = (char *) ((uintptr_t(orig) + (LIFO_ALLOC_ALIGN - 1)) & (~LIFO_ALLOC_ALIGN + 1));
+    JS_ASSERT(uintptr_t(result) % LIFO_ALLOC_ALIGN == 0);
+    return result;
+}
+
+// Header for a chunk of memory wrangled by the LifoAlloc.
+class BumpChunk
+{
+    char        *bump;          // start of the available data
+    char        *limit;         // end of the data
+    BumpChunk   *next_;         // the next BumpChunk
+    size_t      bumpSpaceSize;  // size of the data area
+
+    char *headerBase() { return reinterpret_cast<char *>(this); }
+    char *bumpBase() const { return limit - bumpSpaceSize; }
+
+    explicit BumpChunk(size_t bumpSpaceSize)
+      : bump(reinterpret_cast<char *>(MOZ_THIS_IN_INITIALIZER_LIST()) + sizeof(BumpChunk)),
+        limit(bump + bumpSpaceSize),
+        next_(nullptr), bumpSpaceSize(bumpSpaceSize)
+    {
+        JS_ASSERT(bump == AlignPtr(bump));
+    }
+
+    void setBump(void *ptr) {
+        JS_ASSERT(bumpBase() <= ptr);
+        JS_ASSERT(ptr <= limit);
+#if defined(DEBUG) || defined(MOZ_HAVE_MEM_CHECKS)
+        char* prevBump = bump;
+#endif
+        bump = static_cast<char *>(ptr);
+#ifdef DEBUG
+        JS_ASSERT(contains(prevBump));
+
+        // Clobber the now-free space.
+        if (prevBump > bump)
+            memset(bump, 0xcd, prevBump - bump);
+#endif
+
+        // Poison/Unpoison memory that we just free'd/allocated.
+#if defined(MOZ_HAVE_MEM_CHECKS)
+        if (prevBump > bump)
+            MOZ_MAKE_MEM_NOACCESS(bump, prevBump - bump);
+        else if (bump > prevBump)
+            MOZ_MAKE_MEM_UNDEFINED(prevBump, bump - prevBump);
+#endif
+    }
+
+  public:
+    BumpChunk *next() const { return next_; }
+    void setNext(BumpChunk *succ) { next_ = succ; }
+
+    size_t used() const { return bump - bumpBase(); }
+
+    void *start() const { return bumpBase(); }
+    void *end() const { return limit; }
+
+    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) {
+        return mallocSizeOf(this);
+    }
+
+    size_t computedSizeOfIncludingThis() {
+        return limit - headerBase();
+    }
+
+    void resetBump() {
+        setBump(headerBase() + sizeof(BumpChunk));
+    }
+
+    void *mark() const { return bump; }
+
+    void release(void *mark) {
+        JS_ASSERT(contains(mark));
+        JS_ASSERT(mark <= bump);
+        setBump(mark);
+    }
+
+    bool contains(void *mark) const {
+        return bumpBase() <= mark && mark <= limit;
+    }
+
+    bool canAlloc(size_t n);
+
+    size_t unused() {
+        return limit - AlignPtr(bump);
+    }
+
+    // Try to perform an allocation of size |n|, return null if not possible.
+    MOZ_ALWAYS_INLINE
+    void *tryAlloc(size_t n) {
+        char *aligned = AlignPtr(bump);
+        char *newBump = aligned + n;
+
+        if (newBump > limit)
+            return nullptr;
+
+        // Check for overflow.
+        if (MOZ_UNLIKELY(newBump < bump))
+            return nullptr;
+
+        JS_ASSERT(canAlloc(n)); // Ensure consistency between "can" and "try".
+        setBump(newBump);
+        return aligned;
+    }
+
+    static BumpChunk *new_(size_t chunkSize);
+    static void delete_(BumpChunk *chunk);
+};
+
+} // namespace detail
+
+// LIFO bump allocator: used for phase-oriented and fast LIFO allocations.
+//
+// Note: |latest| is not necessary "last". We leave BumpChunks latent in the
+// chain after they've been released to avoid thrashing before a GC.
+class LifoAlloc
+{
+    typedef detail::BumpChunk BumpChunk;
+
+    BumpChunk   *first;
+    BumpChunk   *latest;
+    BumpChunk   *last;
+    size_t      markCount;
+    size_t      defaultChunkSize_;
+    size_t      curSize_;
+    size_t      peakSize_;
+
+    void operator=(const LifoAlloc &) MOZ_DELETE;
+    LifoAlloc(const LifoAlloc &) MOZ_DELETE;
+
+    // Return a BumpChunk that can perform an allocation of at least size |n|
+    // and add it to the chain appropriately.
+    //
+    // Side effect: if retval is non-null, |first| and |latest| are initialized
+    // appropriately.
+    BumpChunk *getOrCreateChunk(size_t n);
+
+    void reset(size_t defaultChunkSize) {
+        JS_ASSERT(mozilla::RoundUpPow2(defaultChunkSize) == defaultChunkSize);
+        first = latest = last = nullptr;
+        defaultChunkSize_ = defaultChunkSize;
+        markCount = 0;
+        curSize_ = 0;
+    }
+
+    // Append unused chunks to the end of this LifoAlloc.
+    void appendUnused(BumpChunk *start, BumpChunk *end) {
+        JS_ASSERT(start && end);
+        if (last)
+            last->setNext(start);
+        else
+            first = latest = start;
+        last = end;
+    }
+
+    // Append used chunks to the end of this LifoAlloc. We act as if all the
+    // chunks in |this| are used, even if they're not, so memory may be wasted.
+    void appendUsed(BumpChunk *start, BumpChunk *latest, BumpChunk *end) {
+        JS_ASSERT(start && latest &&  end);
+        if (last)
+            last->setNext(start);
+        else
+            first = latest = start;
+        last = end;
+        this->latest = latest;
+    }
+
+    void incrementCurSize(size_t size) {
+        curSize_ += size;
+        if (curSize_ > peakSize_)
+            peakSize_ = curSize_;
+    }
+    void decrementCurSize(size_t size) {
+        JS_ASSERT(curSize_ >= size);
+        curSize_ -= size;
+    }
+
+  public:
+    explicit LifoAlloc(size_t defaultChunkSize)
+      : peakSize_(0)
+    {
+        reset(defaultChunkSize);
+    }
+
+    // Steal allocated chunks from |other|.
+    void steal(LifoAlloc *other) {
+        JS_ASSERT(!other->markCount);
+
+        // Copy everything from |other| to |this| except for |peakSize_|, which
+        // requires some care.
+        size_t oldPeakSize = peakSize_;
+        mozilla::PodAssign(this, other);
+        peakSize_ = Max(oldPeakSize, curSize_);
+
+        other->reset(defaultChunkSize_);
+    }
+
+    // Append all chunks from |other|. They are removed from |other|.
+    void transferFrom(LifoAlloc *other);
+
+    // Append unused chunks from |other|. They are removed from |other|.
+    void transferUnusedFrom(LifoAlloc *other);
+
+    ~LifoAlloc() { freeAll(); }
+
+    size_t defaultChunkSize() const { return defaultChunkSize_; }
+
+    // Frees all held memory.
+    void freeAll();
+
+    static const unsigned HUGE_ALLOCATION = 50 * 1024 * 1024;
+    void freeAllIfHugeAndUnused() {
+        if (markCount == 0 && curSize_ > HUGE_ALLOCATION)
+            freeAll();
+    }
+
+    MOZ_ALWAYS_INLINE
+    void *alloc(size_t n) {
+        JS_OOM_POSSIBLY_FAIL();
+
+        void *result;
+        if (latest && (result = latest->tryAlloc(n)))
+            return result;
+
+        if (!getOrCreateChunk(n))
+            return nullptr;
+
+        // Since we just created a large enough chunk, this can't fail.
+        result = latest->tryAlloc(n);
+        MOZ_ASSERT(result);
+        return result;
+    }
+
+    // Ensures that enough space exists to satisfy N bytes worth of
+    // allocation requests, not necessarily contiguous. Note that this does
+    // not guarantee a successful single allocation of N bytes.
+    MOZ_ALWAYS_INLINE
+    bool ensureUnusedApproximate(size_t n) {
+        size_t total = 0;
+        for (BumpChunk *chunk = latest; chunk; chunk = chunk->next()) {
+            total += chunk->unused();
+            if (total >= n)
+                return true;
+        }
+        BumpChunk *latestBefore = latest;
+        if (!getOrCreateChunk(n))
+            return false;
+        if (latestBefore)
+            latest = latestBefore;
+        return true;
+    }
+
+    template <typename T>
+    T *newArray(size_t count) {
+        JS_STATIC_ASSERT(mozilla::IsPod<T>::value);
+        return newArrayUninitialized<T>(count);
+    }
+
+    // Create an array with uninitialized elements of type |T|.
+    // The caller is responsible for initialization.
+    template <typename T>
+    T *newArrayUninitialized(size_t count) {
+        if (count & mozilla::tl::MulOverflowMask<sizeof(T)>::value)
+            return nullptr;
+        return static_cast<T *>(alloc(sizeof(T) * count));
+    }
+
+    class Mark {
+        BumpChunk *chunk;
+        void *markInChunk;
+        friend class LifoAlloc;
+        Mark(BumpChunk *chunk, void *markInChunk) : chunk(chunk), markInChunk(markInChunk) {}
+      public:
+        Mark() : chunk(nullptr), markInChunk(nullptr) {}
+    };
+
+    Mark mark() {
+        markCount++;
+        return latest ? Mark(latest, latest->mark()) : Mark();
+    }
+
+    void release(Mark mark) {
+        markCount--;
+        if (!mark.chunk) {
+            latest = first;
+            if (latest)
+                latest->resetBump();
+        } else {
+            latest = mark.chunk;
+            latest->release(mark.markInChunk);
+        }
+    }
+
+    void releaseAll() {
+        JS_ASSERT(!markCount);
+        latest = first;
+        if (latest)
+            latest->resetBump();
+    }
+
+    // Get the total "used" (occupied bytes) count for the arena chunks.
+    size_t used() const {
+        size_t accum = 0;
+        for (BumpChunk *chunk = first; chunk; chunk = chunk->next()) {
+            accum += chunk->used();
+            if (chunk == latest)
+                break;
+        }
+        return accum;
+    }
+
+    // Return true if the LifoAlloc does not currently contain any allocations.
+    bool isEmpty() const {
+        return !latest || !latest->used();
+    }
+
+    // Return the number of bytes remaining to allocate in the current chunk.
+    // e.g. How many bytes we can allocate before needing a new block.
+    size_t availableInCurrentChunk() const {
+        if (!latest)
+            return 0;
+        return latest->unused();
+    }
+
+    // Get the total size of the arena chunks (including unused space).
+    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
+        size_t n = 0;
+        for (BumpChunk *chunk = first; chunk; chunk = chunk->next())
+            n += chunk->sizeOfIncludingThis(mallocSizeOf);
+        return n;
+    }
+
+    // Like sizeOfExcludingThis(), but includes the size of the LifoAlloc itself.
+    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
+        return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
+    }
+
+    // Get the peak size of the arena chunks (including unused space and
+    // bookkeeping space).
+    size_t peakSizeOfExcludingThis() const { return peakSize_; }
+
+    // Doesn't perform construction; useful for lazily-initialized POD types.
+    template <typename T>
+    MOZ_ALWAYS_INLINE
+    T *newPod() {
+        return static_cast<T *>(alloc(sizeof(T)));
+    }
+
+    JS_DECLARE_NEW_METHODS(new_, alloc, MOZ_ALWAYS_INLINE)
+
+    // A mutable enumeration of the allocated data.
+    class Enum
+    {
+        friend class LifoAlloc;
+        friend class detail::BumpChunk;
+
+        LifoAlloc *alloc_;  // The LifoAlloc being traversed.
+        BumpChunk *chunk_;  // The current chunk.
+        char *position_;    // The current position (must be within chunk_).
+
+        // If there is not enough room in the remaining block for |size|,
+        // advance to the next block and update the position.
+        void ensureSpaceAndAlignment(size_t size) {
+            JS_ASSERT(!empty());
+            char *aligned = detail::AlignPtr(position_);
+            if (aligned + size > chunk_->end()) {
+                chunk_ = chunk_->next();
+                position_ = static_cast<char *>(chunk_->start());
+            } else {
+                position_ = aligned;
+            }
+            JS_ASSERT(uintptr_t(position_) + size <= uintptr_t(chunk_->end()));
+        }
+
+      public:
+        Enum(LifoAlloc &alloc)
+          : alloc_(&alloc),
+            chunk_(alloc.first),
+            position_(static_cast<char *>(alloc.first ? alloc.first->start() : nullptr))
+        {}
+
+        // Return true if there are no more bytes to enumerate.
+        bool empty() {
+            return !chunk_ || (chunk_ == alloc_->latest && position_ >= chunk_->mark());
+        }
+
+        // Move the read position forward by the size of one T.
+        template <typename T>
+        void popFront() {
+            popFront(sizeof(T));
+        }
+
+        // Move the read position forward by |size| bytes.
+        void popFront(size_t size) {
+            ensureSpaceAndAlignment(size);
+            position_ = position_ + size;
+        }
+
+        // Update the bytes at the current position with a new value.
+        template <typename T>
+        void updateFront(const T &t) {
+            ensureSpaceAndAlignment(sizeof(T));
+            memmove(position_, &t, sizeof(T));
+        }
+
+        // Return a pointer to the item at the current position. This
+        // returns a pointer to the inline storage, not a copy.
+        template <typename T>
+        T *get(size_t size = sizeof(T)) {
+            ensureSpaceAndAlignment(size);
+            return reinterpret_cast<T *>(position_);
+        }
+
+        // Return a Mark at the current position of the Enum.
+        Mark mark() {
+            alloc_->markCount++;
+            return Mark(chunk_, position_);
+        }
+    };
+};
+
+class LifoAllocScope
+{
+    LifoAlloc       *lifoAlloc;
+    LifoAlloc::Mark mark;
+    bool            shouldRelease;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+
+  public:
+    explicit LifoAllocScope(LifoAlloc *lifoAlloc
+                            MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : lifoAlloc(lifoAlloc),
+        mark(lifoAlloc->mark()),
+        shouldRelease(true)
+    {
+        MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    }
+
+    ~LifoAllocScope() {
+        if (shouldRelease)
+            lifoAlloc->release(mark);
+    }
+
+    LifoAlloc &alloc() {
+        return *lifoAlloc;
+    }
+
+    void releaseEarly() {
+        JS_ASSERT(shouldRelease);
+        lifoAlloc->release(mark);
+        shouldRelease = false;
+    }
+};
+
+class LifoAllocPolicy
+{
+    LifoAlloc &alloc_;
+
+  public:
+    LifoAllocPolicy(LifoAlloc &alloc)
+      : alloc_(alloc)
+    {}
+    void *malloc_(size_t bytes) {
+        return alloc_.alloc(bytes);
+    }
+    void *calloc_(size_t bytes) {
+        void *p = malloc_(bytes);
+        if (p)
+            memset(p, 0, bytes);
+        return p;
+    }
+    void *realloc_(void *p, size_t oldBytes, size_t bytes) {
+        void *n = malloc_(bytes);
+        if (!n)
+            return n;
+        memcpy(n, p, Min(oldBytes, bytes));
+        return n;
+    }
+    void free_(void *p) {
+    }
+    void reportAllocOverflow() const {
+    }
+};
+
+} // namespace js
+
+#endif /* ds_LifoAlloc_h */