Add m-esr52 at 52.6.0

1 files changed, 622 insertions, 0 deletions

diff --git a/dom/canvas/WebGLElementArrayCache.cpp b/dom/canvas/WebGLElementArrayCache.cpp
new file mode 100644
index 000000000..a0591445a
--- /dev/null
+++ b/dom/canvas/WebGLElementArrayCache.cpp
@@ -0,0 +1,622 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* 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/. */
+
+#include "WebGLElementArrayCache.h"
+
+#include <algorithm>
+#include <cstdlib>
+#include <cstring>
+#include <limits>
+#include "mozilla/Assertions.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/MemoryReporting.h"
+
+namespace mozilla {
+
+/* WebGLElementArrayCacheTree contains most of the implementation of
+ * WebGLElementArrayCache, which performs WebGL element array buffer validation
+ * for drawElements.
+ *
+ * Attention: Here lie nontrivial data structures, bug-prone algorithms, and
+ * non-canonical tweaks! Whence the explanatory comments, and compiled unit
+ * test.
+ *
+ * *** What problem are we solving here? ***
+ *
+ * WebGL::DrawElements has to validate that the elements are in range wrt the
+ * current vertex attribs. This boils down to the problem, given an array of
+ * integers, of computing the maximum in an arbitrary sub-array. The naive
+ * algorithm has linear complexity; this has been a major performance problem,
+ * see bug 569431. In that bug, we took the approach of caching the max for the
+ * whole array, which does cover most cases (DrawElements typically consumes the
+ * whole element array buffer) but doesn't help in other use cases:
+ *  - when doing "partial DrawElements" i.e. consuming only part of the element
+ *    array buffer
+ *  - when doing frequent "partial buffer updates" i.e. bufferSubData calls
+ *    updating parts of the element array buffer
+ *
+ * *** The solution: A binary tree ***
+ *
+ * The solution implemented here is to use a binary tree as the cache data
+ * structure. Each tree node contains the max of its two children nodes. In this
+ * way, finding the maximum in any contiguous sub-array has log complexity
+ * instead of linear complexity.
+ *
+ * Simplistically, if the element array is:
+ *
+ *    [1   4   3   2]
+ *
+ * then the corresponding tree is:
+ *
+ *           4
+ *         _/ \_
+ *       4       3
+ *      / \     / \
+ *     1   4   3   2
+ *
+ * In practice, the bottom-most levels of the tree are both the largest to store
+ * (because they have more nodes), and the least useful performance-wise
+ * (because each node in the bottom levels concerns only few entries in the
+ * elements array buffer, it is cheap to compute).
+ *
+ * For this reason, we stop the tree a few levels above, so that each tree leaf
+ * actually corresponds to more than one element array entry.
+ *
+ * The number of levels that we "drop" is |kSkippedBottomTreeLevels| and the
+ * number of element array entries that each leaf corresponds to, is
+ * |kElementsPerLeaf|. This being a binary tree, we have:
+ *
+ *   kElementsPerLeaf = 2 ^ kSkippedBottomTreeLevels.
+ *
+ * *** Storage layout of the binary tree ***
+ *
+ * We take advantage of the specifics of the situation to avoid generalist tree
+ * storage and instead store the tree entries in a vector, mTreeData.
+ *
+ * TreeData is always a vector of length:
+ *
+ *    2 * (number of leaves).
+ *
+ * Its data layout is as follows: mTreeData[0] is unused, mTreeData[1] is the
+ * root node, then at offsets 2..3 is the tree level immediately below the root
+ * node, then at offsets 4..7 is the tree level below that, etc.
+ *
+ * The figure below illustrates this by writing at each tree node the offset
+ * into mTreeData at which it is stored:
+ *
+ *           1
+ *         _/ \_
+ *       2       3
+ *      / \     / \
+ *     4   5   6   7
+ *    ...
+ *
+ * Thus, under the convention that the root level is level 0, we see that level
+ * N is stored at offsets:
+ *
+ *    [ 2^n .. 2^(n+1) - 1 ]
+ *
+ * in mTreeData. Likewise, all the usual tree operations have simple
+ * mathematical expressions in terms of mTreeData offsets, see all the methods
+ * such as ParentNode, LeftChildNode, etc.
+ *
+ * *** Design constraint: Element types aren't known at buffer-update time ***
+ *
+ * Note that a key constraint that we're operating under, is that we don't know
+ * the types of the elements by the time WebGL bufferData/bufferSubData methods
+ * are called. The type of elements is only specified in the drawElements call.
+ * This means that we may potentially have to store caches for multiple element
+ * types, for the same element array buffer. Since we don't know yet how many
+ * element types we'll eventually support (extensions add more), the concern
+ * about memory usage is serious. This is addressed by kSkippedBottomTreeLevels
+ * as explained above. Of course, in the typical case where each element array
+ * buffer is only ever used with one type, this is also addressed by having
+ * WebGLElementArrayCache lazily create trees for each type only upon first use.
+ *
+ * Another consequence of this constraint is that when updating the trees, we
+ * have to update all existing trees. So if trees for types uint8_t, uint16_t
+ * and uint32_t have ever been constructed for this buffer, every subsequent
+ * update will have to update all trees even if one of the types is never used
+ * again. That's inefficient, but content should not put indices of different
+ * types in the same element array buffer anyways. Different index types can
+ * only be consumed in separate drawElements calls, so nothing particular is
+ * to be achieved by lumping them in the same buffer object.
+ */
+template<typename T>
+struct WebGLElementArrayCacheTree
+{
+    /* A too-high kSkippedBottomTreeLevels would harm the performance of small
+     * drawElements calls. A too-low kSkippedBottomTreeLevels would cause undue
+     * memory usage. The current value has been validated by some benchmarking.
+     * See bug 732660.
+     */
+    static const size_t kSkippedBottomTreeLevels = 3;
+    static const size_t kElementsPerLeaf = 1 << kSkippedBottomTreeLevels;
+    // Since kElementsPerLeaf is POT:
+    static const size_t kElementsPerLeafMask = kElementsPerLeaf - 1;
+
+private:
+    // The WebGLElementArrayCache that owns this tree:
+    WebGLElementArrayCache& mParent;
+
+    // The tree's internal data storage. Its length is 2 * (number of leaves)
+    // because of its data layout explained in the above class comment.
+    FallibleTArray<T> mTreeData;
+
+public:
+    // Constructor. Takes a reference to the WebGLElementArrayCache that is to be
+    // the parent. Does not initialize the tree. Should be followed by a call
+    // to Update() to attempt initializing the tree.
+    explicit WebGLElementArrayCacheTree(WebGLElementArrayCache& value)
+        : mParent(value)
+    {
+    }
+
+    T GlobalMaximum() const {
+        return mTreeData[1];
+    }
+
+    // returns the index of the parent node; if treeIndex=1 (the root node),
+    // the return value is 0.
+    static size_t ParentNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex > 1);
+        return treeIndex >> 1;
+    }
+
+    static bool IsRightNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex > 1);
+        return treeIndex & 1;
+    }
+
+    static bool IsLeftNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex > 1);
+        return !IsRightNode(treeIndex);
+    }
+
+    static size_t SiblingNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex > 1);
+        return treeIndex ^ 1;
+    }
+
+    static size_t LeftChildNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex);
+        return treeIndex << 1;
+    }
+
+    static size_t RightChildNode(size_t treeIndex) {
+        MOZ_ASSERT(treeIndex);
+        return SiblingNode(LeftChildNode(treeIndex));
+    }
+
+    static size_t LeftNeighborNode(size_t treeIndex, size_t distance = 1) {
+        MOZ_ASSERT(treeIndex > 1);
+        return treeIndex - distance;
+    }
+
+    static size_t RightNeighborNode(size_t treeIndex, size_t distance = 1) {
+        MOZ_ASSERT(treeIndex > 1);
+        return treeIndex + distance;
+    }
+
+    size_t NumLeaves() const {
+        // See class comment for why we the tree storage size is 2 * numLeaves.
+        return mTreeData.Length() >> 1;
+    }
+
+    size_t LeafForElement(size_t element) const {
+        size_t leaf = element / kElementsPerLeaf;
+        MOZ_ASSERT(leaf < NumLeaves());
+        return leaf;
+    }
+
+    size_t LeafForByte(size_t byte) const {
+        return LeafForElement(byte / sizeof(T));
+    }
+
+    // Returns the index, into the tree storage, where a given leaf is stored.
+    size_t TreeIndexForLeaf(size_t leaf) const {
+        // See above class comment. The tree storage is an array of length
+        // 2 * numLeaves. The leaves are stored in its second half.
+        return leaf + NumLeaves();
+    }
+
+    static size_t LastElementUnderSameLeaf(size_t element) {
+        return element | kElementsPerLeafMask;
+    }
+
+    static size_t FirstElementUnderSameLeaf(size_t element) {
+        return element & ~kElementsPerLeafMask;
+    }
+
+    static size_t NextMultipleOfElementsPerLeaf(size_t numElements) {
+        MOZ_ASSERT(numElements >= 1);
+        return ((numElements - 1) | kElementsPerLeafMask) + 1;
+    }
+
+    bool Validate(T maxAllowed, size_t firstLeaf, size_t lastLeaf)
+    {
+        size_t firstTreeIndex = TreeIndexForLeaf(firstLeaf);
+        size_t lastTreeIndex  = TreeIndexForLeaf(lastLeaf);
+
+        while (true) {
+            // Given that we tweak these values in nontrivial ways, it doesn't
+            // hurt to do this sanity check.
+            MOZ_ASSERT(firstTreeIndex <= lastTreeIndex);
+
+            // Final case where there is only one node to validate at the
+            // current tree level:
+            if (lastTreeIndex == firstTreeIndex) {
+                const T& curData = mTreeData[firstTreeIndex];
+                return curData <= maxAllowed;
+            }
+
+            // If the first node at current tree level is a right node, handle
+            // it individually and replace it with its right neighbor, which is
+            // a left node.
+            if (IsRightNode(firstTreeIndex)) {
+                const T& curData = mTreeData[firstTreeIndex];
+                if (curData > maxAllowed)
+                  return false;
+
+                firstTreeIndex = RightNeighborNode(firstTreeIndex);
+            }
+
+            // If the last node at current tree level is a left node, handle it
+            // individually and replace it with its left neighbor, which is a
+            // right node.
+            if (IsLeftNode(lastTreeIndex)) {
+                const T& curData = mTreeData[lastTreeIndex];
+                if (curData > maxAllowed)
+                    return false;
+
+                lastTreeIndex = LeftNeighborNode(lastTreeIndex);
+            }
+
+            /* At this point it can happen that firstTreeIndex and lastTreeIndex
+             * "crossed" eachother. That happens if firstTreeIndex was a right
+             * node and lastTreeIndex was its right neighor: In that case, both
+             * above tweaks happened and as a result, they ended up being
+             * swapped: LastTreeIndex is now the _left_ neighbor of
+             * firstTreeIndex. When that happens, there is nothing left to
+             * validate.
+             */
+            if (lastTreeIndex == LeftNeighborNode(firstTreeIndex))
+                return true;
+
+            // Walk up one level.
+            firstTreeIndex = ParentNode(firstTreeIndex);
+            lastTreeIndex = ParentNode(lastTreeIndex);
+        }
+    }
+
+    // Updates the tree from the parent's buffer contents. Fallible, as it
+    // may have to resize the tree storage.
+    bool Update(size_t firstByte, size_t lastByte);
+
+    size_t SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
+    {
+        return mallocSizeOf(this) +
+               mTreeData.ShallowSizeOfExcludingThis(mallocSizeOf);
+    }
+};
+
+// TreeForType: just a template helper to select the right tree object for a given
+// element type.
+template<typename T>
+struct TreeForType {};
+
+template<>
+struct TreeForType<uint8_t>
+{
+    static UniquePtr<WebGLElementArrayCacheTree<uint8_t>>&
+    Value(WebGLElementArrayCache* b) {
+        return b->mUint8Tree;
+    }
+};
+
+template<>
+struct TreeForType<uint16_t>
+{
+    static UniquePtr<WebGLElementArrayCacheTree<uint16_t>>&
+    Value(WebGLElementArrayCache* b) {
+        return b->mUint16Tree;
+    }
+};
+
+template<>
+struct TreeForType<uint32_t>
+{
+    static UniquePtr<WebGLElementArrayCacheTree<uint32_t>>&
+    Value(WebGLElementArrayCache* b) {
+        return b->mUint32Tree;
+    }
+};
+
+// Calling this method will 1) update the leaves in this interval
+// from the raw buffer data, and 2) propagate this update up the tree.
+template<typename T>
+bool
+WebGLElementArrayCacheTree<T>::Update(size_t firstByte, size_t lastByte)
+{
+    MOZ_ASSERT(firstByte <= lastByte);
+    MOZ_ASSERT(lastByte < mParent.mBytes.Length());
+
+    size_t numberOfElements = mParent.mBytes.Length() / sizeof(T);
+    size_t requiredNumLeaves = 0;
+    if (numberOfElements > 0) {
+        /* If we didn't require the number of leaves to be a power of two, then
+         * it would just be equal to
+         *
+         *    ceil(numberOfElements / kElementsPerLeaf)
+         *
+         * The way we implement this (division+ceil) operation in integer
+         * arithmetic
+         * is as follows:
+         */
+        size_t numLeavesNonPOT = (numberOfElements + kElementsPerLeaf - 1) / kElementsPerLeaf;
+        // It only remains to round that up to the next power of two:
+        requiredNumLeaves = RoundUpPow2(numLeavesNonPOT);
+    }
+
+    // Step #0: If needed, resize our tree data storage.
+    if (requiredNumLeaves != NumLeaves()) {
+        // See class comment for why we the tree storage size is 2 * numLeaves.
+        if (!mTreeData.SetLength(2 * requiredNumLeaves, fallible)) {
+            mTreeData.Clear();
+            return false;
+        }
+        MOZ_ASSERT(NumLeaves() == requiredNumLeaves);
+
+        if (NumLeaves()) {
+            // When resizing, update the whole tree, not just the subset
+            // corresponding to the part of the buffer being updated.
+            memset(mTreeData.Elements(), 0, mTreeData.Length() * sizeof(T));
+            firstByte = 0;
+            lastByte = mParent.mBytes.Length() - 1;
+        }
+    }
+
+    if (NumLeaves() == 0)
+        return true;
+
+    lastByte = std::min(lastByte, NumLeaves() * kElementsPerLeaf * sizeof(T) - 1);
+    if (firstByte > lastByte)
+        return true;
+
+    size_t firstLeaf = LeafForByte(firstByte);
+    size_t lastLeaf = LeafForByte(lastByte);
+
+    MOZ_ASSERT(firstLeaf <= lastLeaf && lastLeaf < NumLeaves());
+
+    size_t firstTreeIndex = TreeIndexForLeaf(firstLeaf);
+    size_t lastTreeIndex = TreeIndexForLeaf(lastLeaf);
+
+    // Step #1: Initialize the tree leaves from plain buffer data.
+    // That is, each tree leaf must be set to the max of the |kElementsPerLeaf|
+    // corresponding buffer entries.
+
+    // Condition-less scope to prevent leaking this scope's variables into the
+    // code below:
+    {
+        // TreeIndex is the index of the tree leaf we're writing, i.e. the
+        // destination index.
+        size_t treeIndex = firstTreeIndex;
+        // srcIndex is the index in the source buffer.
+        size_t srcIndex = firstLeaf * kElementsPerLeaf;
+        while (treeIndex <= lastTreeIndex) {
+            T m = 0;
+            size_t a = srcIndex;
+            size_t srcIndexNextLeaf = std::min(a + kElementsPerLeaf, numberOfElements);
+            for (; srcIndex < srcIndexNextLeaf; srcIndex++) {
+                m = std::max(m, mParent.Element<T>(srcIndex));
+            }
+            mTreeData[treeIndex] = m;
+            treeIndex++;
+        }
+    }
+
+    // Step #2: Propagate the values up the tree. This is simply a matter of
+    // walking up the tree and setting each node to the max of its two children.
+    while (firstTreeIndex > 1) {
+        // Move up one level.
+        firstTreeIndex = ParentNode(firstTreeIndex);
+        lastTreeIndex = ParentNode(lastTreeIndex);
+
+        // Fast-exit case where only one node is updated at the current level.
+        if (firstTreeIndex == lastTreeIndex) {
+            mTreeData[firstTreeIndex] = std::max(mTreeData[LeftChildNode(firstTreeIndex)], mTreeData[RightChildNode(firstTreeIndex)]);
+            continue;
+        }
+
+        size_t child = LeftChildNode(firstTreeIndex);
+        size_t parent = firstTreeIndex;
+        while (parent <= lastTreeIndex) {
+            T a = mTreeData[child];
+            child = RightNeighborNode(child);
+            T b = mTreeData[child];
+            child = RightNeighborNode(child);
+            mTreeData[parent] = std::max(a, b);
+            parent = RightNeighborNode(parent);
+        }
+    }
+
+    return true;
+}
+
+WebGLElementArrayCache::WebGLElementArrayCache()
+{
+}
+
+WebGLElementArrayCache::~WebGLElementArrayCache()
+{
+}
+
+bool
+WebGLElementArrayCache::BufferData(const void* ptr, size_t byteLength)
+{
+    if (mBytes.Length() != byteLength) {
+        if (!mBytes.SetLength(byteLength, fallible)) {
+            mBytes.Clear();
+            return false;
+        }
+    }
+    MOZ_ASSERT(mBytes.Length() == byteLength);
+    return BufferSubData(0, ptr, byteLength);
+}
+
+bool
+WebGLElementArrayCache::BufferSubData(size_t pos, const void* ptr,
+                                      size_t updateByteLength)
+{
+    MOZ_ASSERT(pos + updateByteLength <= mBytes.Length());
+    if (!updateByteLength)
+        return true;
+
+    // Note, using memcpy on shared racy data is not well-defined, this
+    // will need to use safe-for-races operations when those become available.
+    // See bug 1225033.
+    if (ptr)
+        memcpy(mBytes.Elements() + pos, ptr, updateByteLength);
+    else
+        memset(mBytes.Elements() + pos, 0, updateByteLength);
+    return UpdateTrees(pos, pos + updateByteLength - 1);
+}
+
+bool
+WebGLElementArrayCache::UpdateTrees(size_t firstByte, size_t lastByte)
+{
+    bool result = true;
+    if (mUint8Tree)
+        result &= mUint8Tree->Update(firstByte, lastByte);
+    if (mUint16Tree)
+        result &= mUint16Tree->Update(firstByte, lastByte);
+    if (mUint32Tree)
+        result &= mUint32Tree->Update(firstByte, lastByte);
+    return result;
+}
+
+template<typename T>
+bool
+WebGLElementArrayCache::Validate(uint32_t maxAllowed, size_t firstElement,
+                                 size_t countElements)
+{
+    // If maxAllowed is >= the max T value, then there is no way that a T index
+    // could be invalid.
+    uint32_t maxTSize = std::numeric_limits<T>::max();
+    if (maxAllowed >= maxTSize)
+        return true;
+
+    T maxAllowedT(maxAllowed);
+
+    // Integer overflow must have been handled earlier, so we assert that
+    // maxAllowedT is exactly the max allowed value.
+    MOZ_ASSERT(uint32_t(maxAllowedT) == maxAllowed);
+
+    if (!mBytes.Length() || !countElements)
+      return true;
+
+    UniquePtr<WebGLElementArrayCacheTree<T>>& tree = TreeForType<T>::Value(this);
+    if (!tree) {
+        tree = MakeUnique<WebGLElementArrayCacheTree<T>>(*this);
+        if (mBytes.Length()) {
+            bool valid = tree->Update(0, mBytes.Length() - 1);
+            if (!valid) {
+                // Do not assert here. This case would happen if an allocation
+                // failed. We've already settled on fallible allocations around
+                // here.
+                tree = nullptr;
+                return false;
+            }
+        }
+    }
+
+    size_t lastElement = firstElement + countElements - 1;
+
+    // Fast-exit path when the global maximum for the whole element array buffer
+    // falls in the allowed range:
+    T globalMax = tree->GlobalMaximum();
+    if (globalMax <= maxAllowedT)
+        return true;
+
+    const T* elements = Elements<T>();
+
+    // Before calling tree->Validate, we have to validate ourselves the
+    // boundaries of the elements span, to round them to the nearest multiple of
+    // kElementsPerLeaf.
+    size_t firstElementAdjustmentEnd = std::min(lastElement,
+                                                tree->LastElementUnderSameLeaf(firstElement));
+    while (firstElement <= firstElementAdjustmentEnd) {
+        const T& curData = elements[firstElement];
+        if (curData > maxAllowedT)
+            return false;
+
+        firstElement++;
+    }
+    size_t lastElementAdjustmentEnd = std::max(firstElement,
+                                               tree->FirstElementUnderSameLeaf(lastElement));
+    while (lastElement >= lastElementAdjustmentEnd) {
+        const T& curData = elements[lastElement];
+        if (curData > maxAllowedT)
+            return false;
+
+        lastElement--;
+    }
+
+    // at this point, for many tiny validations, we're already done.
+    if (firstElement > lastElement)
+        return true;
+
+    // general case
+    return tree->Validate(maxAllowedT, tree->LeafForElement(firstElement),
+                          tree->LeafForElement(lastElement));
+}
+
+bool
+WebGLElementArrayCache::Validate(GLenum type, uint32_t maxAllowed,
+                                 size_t firstElement, size_t countElements)
+{
+    if (type == LOCAL_GL_UNSIGNED_BYTE)
+        return Validate<uint8_t>(maxAllowed, firstElement, countElements);
+    if (type == LOCAL_GL_UNSIGNED_SHORT)
+        return Validate<uint16_t>(maxAllowed, firstElement, countElements);
+    if (type == LOCAL_GL_UNSIGNED_INT)
+        return Validate<uint32_t>(maxAllowed, firstElement, countElements);
+
+    MOZ_ASSERT(false, "Invalid type.");
+    return false;
+}
+
+template<typename T>
+static size_t
+SizeOfNullable(mozilla::MallocSizeOf mallocSizeOf, const T& obj)
+{
+    if (!obj)
+        return 0;
+    return obj->SizeOfIncludingThis(mallocSizeOf);
+}
+
+size_t
+WebGLElementArrayCache::SizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const
+{
+    return mallocSizeOf(this) +
+           mBytes.ShallowSizeOfExcludingThis(mallocSizeOf) +
+           SizeOfNullable(mallocSizeOf, mUint8Tree) +
+           SizeOfNullable(mallocSizeOf, mUint16Tree) +
+           SizeOfNullable(mallocSizeOf, mUint32Tree);
+}
+
+bool
+WebGLElementArrayCache::BeenUsedWithMultipleTypes() const
+{
+  // C++ Standard ($4.7)
+  // "If the source type is bool, the value false is converted to zero and
+  //  the value true is converted to one."
+  const int num_types_used = (mUint8Tree  != nullptr) +
+                             (mUint16Tree != nullptr) +
+                             (mUint32Tree != nullptr);
+  return num_types_used > 1;
+}
+
+} // end namespace mozilla