| /* |
| * Copyright (C) 2011-2018 Apple Inc. All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY |
| * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR |
| * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY |
| * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| #include "config.h" |
| #include "DFGCSEPhase.h" |
| |
| #if ENABLE(DFG_JIT) |
| |
| #include "DFGAbstractHeap.h" |
| #include "DFGBlockMapInlines.h" |
| #include "DFGClobberSet.h" |
| #include "DFGClobberize.h" |
| #include "DFGDominators.h" |
| #include "DFGGraph.h" |
| #include "DFGPhase.h" |
| #include "JSCInlines.h" |
| #include <array> |
| |
| namespace JSC { namespace DFG { |
| |
| // This file contains two CSE implementations: local and global. LocalCSE typically runs when we're |
| // in DFG mode, i.e. we want to compile quickly. LocalCSE contains a lot of optimizations for |
| // compile time. GlobalCSE, on the other hand, is fairly straight-forward. It will find more |
| // optimization opportunities by virtue of being global. |
| |
| namespace { |
| |
| namespace DFGCSEPhaseInternal { |
| static const bool verbose = false; |
| } |
| |
| class ImpureDataSlot { |
| WTF_MAKE_NONCOPYABLE(ImpureDataSlot); |
| WTF_MAKE_FAST_ALLOCATED; |
| public: |
| ImpureDataSlot(HeapLocation key, LazyNode value, unsigned hash) |
| : key(key), value(value), hash(hash) |
| { } |
| |
| HeapLocation key; |
| LazyNode value; |
| unsigned hash; |
| }; |
| |
| struct ImpureDataSlotHash : public DefaultHash<std::unique_ptr<ImpureDataSlot>>::Hash { |
| static unsigned hash(const std::unique_ptr<ImpureDataSlot>& key) |
| { |
| return key->hash; |
| } |
| |
| static bool equal(const std::unique_ptr<ImpureDataSlot>& a, const std::unique_ptr<ImpureDataSlot>& b) |
| { |
| // The ImpureDataSlot are unique per table per HeapLocation. This lets us compare the key |
| // by just comparing the pointers of the unique ImpureDataSlots. |
| ASSERT(a != b || a->key == b->key); |
| return a == b; |
| } |
| }; |
| |
| struct ImpureDataTranslator { |
| static unsigned hash(const HeapLocation& key) |
| { |
| return key.hash(); |
| } |
| |
| static bool equal(const std::unique_ptr<ImpureDataSlot>& slot, const HeapLocation& key) |
| { |
| if (!slot) |
| return false; |
| if (HashTraits<std::unique_ptr<ImpureDataSlot>>::isDeletedValue(slot)) |
| return false; |
| return slot->key == key; |
| } |
| |
| static void translate(std::unique_ptr<ImpureDataSlot>& slot, const HeapLocation& key, unsigned hashCode) |
| { |
| new (NotNull, std::addressof(slot)) std::unique_ptr<ImpureDataSlot>(new ImpureDataSlot {key, LazyNode(), hashCode}); |
| } |
| }; |
| |
| class ImpureMap { |
| WTF_MAKE_FAST_ALLOCATED; |
| WTF_MAKE_NONCOPYABLE(ImpureMap); |
| public: |
| ImpureMap() = default; |
| |
| ImpureMap(ImpureMap&& other) |
| { |
| m_abstractHeapStackMap.swap(other.m_abstractHeapStackMap); |
| m_fallbackStackMap.swap(other.m_fallbackStackMap); |
| m_heapMap.swap(other.m_heapMap); |
| #if !defined(NDEBUG) |
| m_debugImpureData.swap(other.m_debugImpureData); |
| #endif |
| } |
| |
| const ImpureDataSlot* add(const HeapLocation& location, const LazyNode& node) |
| { |
| const ImpureDataSlot* result = addImpl(location, node); |
| |
| #if !defined(NDEBUG) |
| auto addResult = m_debugImpureData.add(location, node); |
| ASSERT(!!result == !addResult.isNewEntry); |
| #endif |
| return result; |
| } |
| |
| LazyNode get(const HeapLocation& location) const |
| { |
| LazyNode result = getImpl(location); |
| #if !defined(NDEBUG) |
| ASSERT(result == m_debugImpureData.get(location)); |
| #endif |
| return result; |
| } |
| |
| void clobber(AbstractHeap heap) |
| { |
| switch (heap.kind()) { |
| case World: { |
| clear(); |
| break; |
| } |
| case SideState: |
| break; |
| case Stack: { |
| ASSERT(!heap.payload().isTop()); |
| ASSERT(heap.payload().value() == heap.payload().value32()); |
| m_abstractHeapStackMap.remove(heap.payload().value32()); |
| clobber(m_fallbackStackMap, heap); |
| break; |
| } |
| default: |
| clobber(m_heapMap, heap); |
| break; |
| } |
| #if !defined(NDEBUG) |
| m_debugImpureData.removeIf([heap](const HashMap<HeapLocation, LazyNode>::KeyValuePairType& pair) -> bool { |
| return heap.overlaps(pair.key.heap()); |
| }); |
| ASSERT(m_debugImpureData.size() |
| == (m_heapMap.size() |
| + m_abstractHeapStackMap.size() |
| + m_fallbackStackMap.size())); |
| |
| const bool verifyClobber = false; |
| if (verifyClobber) { |
| for (auto& pair : m_debugImpureData) |
| ASSERT(!!get(pair.key)); |
| } |
| #endif |
| } |
| |
| void clear() |
| { |
| m_abstractHeapStackMap.clear(); |
| m_fallbackStackMap.clear(); |
| m_heapMap.clear(); |
| #if !defined(NDEBUG) |
| m_debugImpureData.clear(); |
| #endif |
| } |
| |
| private: |
| typedef HashSet<std::unique_ptr<ImpureDataSlot>, ImpureDataSlotHash> Map; |
| |
| const ImpureDataSlot* addImpl(const HeapLocation& location, const LazyNode& node) |
| { |
| switch (location.heap().kind()) { |
| case World: |
| case SideState: |
| RELEASE_ASSERT_NOT_REACHED(); |
| case Stack: { |
| AbstractHeap abstractHeap = location.heap(); |
| if (abstractHeap.payload().isTop()) |
| return add(m_fallbackStackMap, location, node); |
| ASSERT(abstractHeap.payload().value() == abstractHeap.payload().value32()); |
| auto addResult = m_abstractHeapStackMap.add(abstractHeap.payload().value32(), nullptr); |
| if (addResult.isNewEntry) { |
| addResult.iterator->value.reset(new ImpureDataSlot {location, node, 0}); |
| return nullptr; |
| } |
| if (addResult.iterator->value->key == location) |
| return addResult.iterator->value.get(); |
| return add(m_fallbackStackMap, location, node); |
| } |
| default: |
| return add(m_heapMap, location, node); |
| } |
| return nullptr; |
| } |
| |
| LazyNode getImpl(const HeapLocation& location) const |
| { |
| switch (location.heap().kind()) { |
| case World: |
| case SideState: |
| RELEASE_ASSERT_NOT_REACHED(); |
| case Stack: { |
| ASSERT(location.heap().payload().value() == location.heap().payload().value32()); |
| auto iterator = m_abstractHeapStackMap.find(location.heap().payload().value32()); |
| if (iterator != m_abstractHeapStackMap.end() |
| && iterator->value->key == location) |
| return iterator->value->value; |
| return get(m_fallbackStackMap, location); |
| } |
| default: |
| return get(m_heapMap, location); |
| } |
| return LazyNode(); |
| } |
| |
| static const ImpureDataSlot* add(Map& map, const HeapLocation& location, const LazyNode& node) |
| { |
| auto result = map.add<ImpureDataTranslator>(location); |
| if (result.isNewEntry) { |
| (*result.iterator)->value = node; |
| return nullptr; |
| } |
| return result.iterator->get(); |
| } |
| |
| static LazyNode get(const Map& map, const HeapLocation& location) |
| { |
| auto iterator = map.find<ImpureDataTranslator>(location); |
| if (iterator != map.end()) |
| return (*iterator)->value; |
| return LazyNode(); |
| } |
| |
| static void clobber(Map& map, AbstractHeap heap) |
| { |
| map.removeIf([heap](const std::unique_ptr<ImpureDataSlot>& slot) -> bool { |
| return heap.overlaps(slot->key.heap()); |
| }); |
| } |
| |
| // The majority of Impure Stack Slots are unique per value. |
| // This is very useful for fast clobber(), we can just remove the slot addressed by AbstractHeap |
| // in O(1). |
| // |
| // When there are conflict, any additional HeapLocation is added in the fallback map. |
| // This works well because fallbackStackMap remains tiny. |
| // |
| // One cannot assume a unique ImpureData is in m_abstractHeapStackMap. It may have been |
| // a duplicate in the past and now only live in m_fallbackStackMap. |
| // |
| // Obviously, TOP always goes into m_fallbackStackMap since it does not have a unique value. |
| HashMap<int32_t, std::unique_ptr<ImpureDataSlot>, DefaultHash<int32_t>::Hash, WTF::SignedWithZeroKeyHashTraits<int32_t>> m_abstractHeapStackMap; |
| Map m_fallbackStackMap; |
| |
| Map m_heapMap; |
| |
| #if !defined(NDEBUG) |
| HashMap<HeapLocation, LazyNode> m_debugImpureData; |
| #endif |
| }; |
| |
| class LocalCSEPhase : public Phase { |
| public: |
| LocalCSEPhase(Graph& graph) |
| : Phase(graph, "local common subexpression elimination") |
| , m_smallBlock(graph) |
| , m_largeBlock(graph) |
| { |
| } |
| |
| bool run() |
| { |
| ASSERT(m_graph.m_fixpointState == FixpointNotConverged); |
| ASSERT(m_graph.m_form == ThreadedCPS || m_graph.m_form == LoadStore); |
| |
| bool changed = false; |
| |
| m_graph.clearReplacements(); |
| |
| for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) { |
| BasicBlock* block = m_graph.block(blockIndex); |
| if (!block) |
| continue; |
| |
| if (block->size() <= SmallMaps::capacity) |
| changed |= m_smallBlock.run(block); |
| else |
| changed |= m_largeBlock.run(block); |
| } |
| |
| return changed; |
| } |
| |
| private: |
| class SmallMaps { |
| public: |
| // This permits SmallMaps to be used for blocks that have up to 100 nodes. In practice, |
| // fewer than half of the nodes in a block have pure defs, and even fewer have impure defs. |
| // Thus, a capacity limit of 100 probably means that somewhere around ~40 things may end up |
| // in one of these "small" list-based maps. That number still seems largeish, except that |
| // the overhead of HashMaps can be quite high currently: clearing them, or even removing |
| // enough things from them, deletes (or resizes) their backing store eagerly. Hence |
| // HashMaps induce a lot of malloc traffic. |
| static const unsigned capacity = 100; |
| |
| SmallMaps() |
| : m_pureLength(0) |
| , m_impureLength(0) |
| { |
| } |
| |
| void clear() |
| { |
| m_pureLength = 0; |
| m_impureLength = 0; |
| } |
| |
| void write(AbstractHeap heap) |
| { |
| if (heap.kind() == SideState) |
| return; |
| |
| for (unsigned i = 0; i < m_impureLength; ++i) { |
| if (heap.overlaps(m_impureMap[i].key.heap())) |
| m_impureMap[i--] = m_impureMap[--m_impureLength]; |
| } |
| } |
| |
| Node* addPure(PureValue value, Node* node) |
| { |
| for (unsigned i = m_pureLength; i--;) { |
| if (m_pureMap[i].key == value) |
| return m_pureMap[i].value; |
| } |
| |
| ASSERT(m_pureLength < capacity); |
| m_pureMap[m_pureLength++] = WTF::KeyValuePair<PureValue, Node*>(value, node); |
| return nullptr; |
| } |
| |
| LazyNode findReplacement(HeapLocation location) |
| { |
| for (unsigned i = m_impureLength; i--;) { |
| if (m_impureMap[i].key == location) |
| return m_impureMap[i].value; |
| } |
| return nullptr; |
| } |
| |
| LazyNode addImpure(HeapLocation location, LazyNode node) |
| { |
| // FIXME: If we are using small maps, we must not def() derived values. |
| // For now the only derived values we def() are constant-based. |
| if (location.index() && !location.index().isNode()) |
| return nullptr; |
| if (LazyNode result = findReplacement(location)) |
| return result; |
| ASSERT(m_impureLength < capacity); |
| m_impureMap[m_impureLength++] = WTF::KeyValuePair<HeapLocation, LazyNode>(location, node); |
| return nullptr; |
| } |
| |
| private: |
| WTF::KeyValuePair<PureValue, Node*> m_pureMap[capacity]; |
| WTF::KeyValuePair<HeapLocation, LazyNode> m_impureMap[capacity]; |
| unsigned m_pureLength; |
| unsigned m_impureLength; |
| }; |
| |
| class LargeMaps { |
| public: |
| LargeMaps() |
| { |
| } |
| |
| void clear() |
| { |
| m_pureMap.clear(); |
| m_impureMap.clear(); |
| } |
| |
| void write(AbstractHeap heap) |
| { |
| m_impureMap.clobber(heap); |
| } |
| |
| Node* addPure(PureValue value, Node* node) |
| { |
| auto result = m_pureMap.add(value, node); |
| if (result.isNewEntry) |
| return nullptr; |
| return result.iterator->value; |
| } |
| |
| LazyNode findReplacement(HeapLocation location) |
| { |
| return m_impureMap.get(location); |
| } |
| |
| LazyNode addImpure(const HeapLocation& location, const LazyNode& node) |
| { |
| if (const ImpureDataSlot* slot = m_impureMap.add(location, node)) |
| return slot->value; |
| return LazyNode(); |
| } |
| |
| private: |
| HashMap<PureValue, Node*> m_pureMap; |
| ImpureMap m_impureMap; |
| }; |
| |
| template<typename Maps> |
| class BlockCSE { |
| public: |
| BlockCSE(Graph& graph) |
| : m_graph(graph) |
| , m_insertionSet(graph) |
| { |
| } |
| |
| bool run(BasicBlock* block) |
| { |
| m_maps.clear(); |
| m_changed = false; |
| m_block = block; |
| |
| for (unsigned nodeIndex = 0; nodeIndex < block->size(); ++nodeIndex) { |
| m_node = block->at(nodeIndex); |
| m_graph.performSubstitution(m_node); |
| |
| if (m_node->op() == Identity || m_node->op() == IdentityWithProfile) { |
| m_node->replaceWith(m_graph, m_node->child1().node()); |
| m_changed = true; |
| } else { |
| // This rule only makes sense for local CSE, since in SSA form we have already |
| // factored the bounds check out of the PutByVal. It's kind of gross, but we |
| // still have reason to believe that PutByValAlias is a good optimization and |
| // that it's better to do it with a single node rather than separating out the |
| // CheckInBounds. |
| if (m_node->op() == PutByVal || m_node->op() == PutByValDirect) { |
| HeapLocation heap; |
| |
| Node* base = m_graph.varArgChild(m_node, 0).node(); |
| Node* index = m_graph.varArgChild(m_node, 1).node(); |
| LocationKind indexedPropertyLoc = indexedPropertyLocForResultType(m_node->result()); |
| |
| ArrayMode mode = m_node->arrayMode(); |
| switch (mode.type()) { |
| case Array::Int32: |
| if (!mode.isInBounds()) |
| break; |
| heap = HeapLocation(indexedPropertyLoc, IndexedInt32Properties, base, index); |
| break; |
| |
| case Array::Double: { |
| if (!mode.isInBounds()) |
| break; |
| LocationKind kind = mode.isSaneChain() ? IndexedPropertyDoubleSaneChainLoc : IndexedPropertyDoubleLoc; |
| heap = HeapLocation(kind, IndexedDoubleProperties, base, index); |
| break; |
| } |
| |
| case Array::Contiguous: |
| if (!mode.isInBounds()) |
| break; |
| heap = HeapLocation(indexedPropertyLoc, IndexedContiguousProperties, base, index); |
| break; |
| |
| case Array::Int8Array: |
| case Array::Int16Array: |
| case Array::Int32Array: |
| case Array::Uint8Array: |
| case Array::Uint8ClampedArray: |
| case Array::Uint16Array: |
| case Array::Uint32Array: |
| case Array::Float32Array: |
| case Array::Float64Array: |
| if (!mode.isInBounds()) |
| break; |
| heap = HeapLocation( |
| indexedPropertyLoc, TypedArrayProperties, base, index); |
| break; |
| |
| default: |
| break; |
| } |
| |
| if (!!heap && m_maps.findReplacement(heap)) |
| m_node->setOp(PutByValAlias); |
| } |
| |
| clobberize(m_graph, m_node, *this); |
| } |
| } |
| |
| m_insertionSet.execute(block); |
| |
| return m_changed; |
| } |
| |
| void read(AbstractHeap) { } |
| |
| void write(AbstractHeap heap) |
| { |
| m_maps.write(heap); |
| } |
| |
| void def(PureValue value) |
| { |
| Node* match = m_maps.addPure(value, m_node); |
| if (!match) |
| return; |
| |
| m_node->replaceWith(m_graph, match); |
| m_changed = true; |
| } |
| |
| void def(const HeapLocation& location, const LazyNode& value) |
| { |
| LazyNode match = m_maps.addImpure(location, value); |
| if (!match) |
| return; |
| |
| if (m_node->op() == GetLocal) { |
| // Usually the CPS rethreading phase does this. But it's OK for us to mess with |
| // locals so long as: |
| // |
| // - We dethread the graph. Any changes we make may invalidate the assumptions of |
| // our CPS form, particularly if this GetLocal is linked to the variablesAtTail. |
| // |
| // - We don't introduce a Phantom for the child of the GetLocal. This wouldn't be |
| // totally wrong but it would pessimize the code. Just because there is a |
| // GetLocal doesn't mean that the child was live. Simply rerouting the all uses |
| // of this GetLocal will preserve the live-at-exit information just fine. |
| // |
| // We accomplish the latter by just clearing the child; then the Phantom that we |
| // introduce won't have children and so it will eventually just be deleted. |
| |
| m_node->child1() = Edge(); |
| m_graph.dethread(); |
| } |
| |
| if (value.isNode() && value.asNode() == m_node) { |
| match.ensureIsNode(m_insertionSet, m_block, 0)->owner = m_block; |
| ASSERT(match.isNode()); |
| m_node->replaceWith(m_graph, match.asNode()); |
| m_changed = true; |
| } |
| } |
| |
| private: |
| Graph& m_graph; |
| |
| bool m_changed; |
| Node* m_node; |
| BasicBlock* m_block; |
| |
| Maps m_maps; |
| |
| InsertionSet m_insertionSet; |
| }; |
| |
| BlockCSE<SmallMaps> m_smallBlock; |
| BlockCSE<LargeMaps> m_largeBlock; |
| }; |
| |
| class GlobalCSEPhase : public Phase { |
| public: |
| GlobalCSEPhase(Graph& graph) |
| : Phase(graph, "global common subexpression elimination") |
| , m_impureDataMap(graph) |
| , m_insertionSet(graph) |
| { |
| } |
| |
| bool run() |
| { |
| ASSERT(m_graph.m_fixpointState == FixpointNotConverged); |
| ASSERT(m_graph.m_form == SSA); |
| |
| m_graph.initializeNodeOwners(); |
| m_graph.ensureSSADominators(); |
| |
| m_preOrder = m_graph.blocksInPreOrder(); |
| |
| // First figure out what gets clobbered by blocks. Node that this uses the preOrder list |
| // for convenience only. |
| for (unsigned i = m_preOrder.size(); i--;) { |
| m_block = m_preOrder[i]; |
| m_impureData = &m_impureDataMap[m_block]; |
| for (unsigned nodeIndex = m_block->size(); nodeIndex--;) |
| addWrites(m_graph, m_block->at(nodeIndex), m_impureData->writes); |
| } |
| |
| // Based on my experience doing this before, what follows might have to be made iterative. |
| // Right now it doesn't have to be iterative because everything is dominator-bsed. But when |
| // validation is enabled, we check if iterating would find new CSE opportunities. |
| |
| bool changed = iterate(); |
| |
| // FIXME: It should be possible to assert that CSE will not find any new opportunities if you |
| // run it a second time. Unfortunately, we cannot assert this right now. Note that if we did |
| // this, we'd have to first reset all of our state. |
| // https://bugs.webkit.org/show_bug.cgi?id=145853 |
| |
| return changed; |
| } |
| |
| bool iterate() |
| { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog("Performing iteration.\n"); |
| |
| m_changed = false; |
| m_graph.clearReplacements(); |
| |
| for (unsigned i = 0; i < m_preOrder.size(); ++i) { |
| m_block = m_preOrder[i]; |
| m_impureData = &m_impureDataMap[m_block]; |
| m_writesSoFar.clear(); |
| |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog("Processing block ", *m_block, ":\n"); |
| |
| for (unsigned nodeIndex = 0; nodeIndex < m_block->size(); ++nodeIndex) { |
| m_nodeIndex = nodeIndex; |
| m_node = m_block->at(nodeIndex); |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Looking at node ", m_node, ":\n"); |
| |
| m_graph.performSubstitution(m_node); |
| |
| if (m_node->op() == Identity || m_node->op() == IdentityWithProfile) { |
| m_node->replaceWith(m_graph, m_node->child1().node()); |
| m_changed = true; |
| } else |
| clobberize(m_graph, m_node, *this); |
| } |
| |
| m_insertionSet.execute(m_block); |
| |
| m_impureData->didVisit = true; |
| } |
| |
| return m_changed; |
| } |
| |
| void read(AbstractHeap) { } |
| |
| void write(AbstractHeap heap) |
| { |
| m_impureData->availableAtTail.clobber(heap); |
| m_writesSoFar.add(heap); |
| } |
| |
| void def(PureValue value) |
| { |
| // With pure values we do not have to worry about the possibility of some control flow path |
| // clobbering the value. So, we just search for all of the like values that have been |
| // computed. We pick one that is in a block that dominates ours. Note that this means that |
| // a PureValue will map to a list of nodes, since there may be many places in the control |
| // flow graph that compute a value but only one of them that dominates us. We may build up |
| // a large list of nodes that compute some value in the case of gnarly control flow. This |
| // is probably OK. |
| |
| auto result = m_pureValues.add(value, Vector<Node*>()); |
| if (result.isNewEntry) { |
| result.iterator->value.append(m_node); |
| return; |
| } |
| |
| for (unsigned i = result.iterator->value.size(); i--;) { |
| Node* candidate = result.iterator->value[i]; |
| if (m_graph.m_ssaDominators->dominates(candidate->owner, m_block)) { |
| m_node->replaceWith(m_graph, candidate); |
| m_changed = true; |
| return; |
| } |
| } |
| |
| result.iterator->value.append(m_node); |
| } |
| |
| LazyNode findReplacement(HeapLocation location) |
| { |
| // At this instant, our "availableAtTail" reflects the set of things that are available in |
| // this block so far. We check this map to find block-local CSE opportunities before doing |
| // a global search. |
| LazyNode match = m_impureData->availableAtTail.get(location); |
| if (!!match) { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Found local match: ", match, "\n"); |
| return match; |
| } |
| |
| // If it's not available at this point in the block, and at some prior point in the block |
| // we have clobbered this heap location, then there is no point in doing a global search. |
| if (m_writesSoFar.overlaps(location.heap())) { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Not looking globally because of local clobber: ", m_writesSoFar, "\n"); |
| return nullptr; |
| } |
| |
| // This perfoms a backward search over the control flow graph to find some possible |
| // non-local def() that matches our heap location. Such a match is only valid if there does |
| // not exist any path from that def() to our block that contains a write() that overlaps |
| // our heap. This algorithm looks for both of these things (the matching def and the |
| // overlapping writes) in one backwards DFS pass. |
| // |
| // This starts by looking at the starting block's predecessors, and then it continues along |
| // their predecessors. As soon as this finds a possible def() - one that defines the heap |
| // location we want while dominating our starting block - it assumes that this one must be |
| // the match. It then lets the DFS over predecessors complete, but it doesn't add the |
| // def()'s predecessors; this ensures that any blocks we visit thereafter are on some path |
| // from the def() to us. As soon as the DFG finds a write() that overlaps the location's |
| // heap, it stops, assuming that there is no possible match. Note that the write() case may |
| // trigger before we find a def(), or after. Either way, the write() case causes this |
| // function to immediately return nullptr. |
| // |
| // If the write() is found before we find the def(), then we know that any def() we would |
| // find would have a path to us that trips over the write() and hence becomes invalid. This |
| // is just a direct outcome of us looking for a def() that dominates us. Given a block A |
| // that dominates block B - so that A is the one that would have the def() and B is our |
| // starting block - we know that any other block must either be on the path from A to B, or |
| // it must be on a path from the root to A, but not both. So, if we haven't found A yet but |
| // we already have found a block C that has a write(), then C must be on some path from A |
| // to B, which means that A's def() is invalid for our purposes. Hence, before we find the |
| // def(), stopping on write() is the right thing to do. |
| // |
| // Stopping on write() is also the right thing to do after we find the def(). After we find |
| // the def(), we don't add that block's predecessors to the search worklist. That means |
| // that henceforth the only blocks we will see in the search are blocks on the path from |
| // the def() to us. If any such block has a write() that clobbers our heap then we should |
| // give up. |
| // |
| // Hence this graph search algorithm ends up being deceptively simple: any overlapping |
| // write() causes us to immediately return nullptr, and a matching def() means that we just |
| // record it and neglect to visit its precessors. |
| |
| Vector<BasicBlock*, 8> worklist; |
| Vector<BasicBlock*, 8> seenList; |
| BitVector seen; |
| |
| for (unsigned i = m_block->predecessors.size(); i--;) { |
| BasicBlock* predecessor = m_block->predecessors[i]; |
| if (!seen.get(predecessor->index)) { |
| worklist.append(predecessor); |
| seen.set(predecessor->index); |
| } |
| } |
| |
| while (!worklist.isEmpty()) { |
| BasicBlock* block = worklist.takeLast(); |
| seenList.append(block); |
| |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Searching in block ", *block, "\n"); |
| ImpureBlockData& data = m_impureDataMap[block]; |
| |
| // We require strict domination because this would only see things in our own block if |
| // they came *after* our position in the block. Clearly, while our block dominates |
| // itself, the things in the block after us don't dominate us. |
| if (m_graph.m_ssaDominators->strictlyDominates(block, m_block)) { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" It strictly dominates.\n"); |
| DFG_ASSERT(m_graph, m_node, data.didVisit); |
| DFG_ASSERT(m_graph, m_node, !match); |
| match = data.availableAtTail.get(location); |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Availability: ", match, "\n"); |
| if (!!match) { |
| // Don't examine the predecessors of a match. At this point we just want to |
| // establish that other blocks on the path from here to there don't clobber |
| // the location we're interested in. |
| continue; |
| } |
| } |
| |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Dealing with write set ", data.writes, "\n"); |
| if (data.writes.overlaps(location.heap())) { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Clobbered.\n"); |
| return nullptr; |
| } |
| |
| for (unsigned i = block->predecessors.size(); i--;) { |
| BasicBlock* predecessor = block->predecessors[i]; |
| if (!seen.get(predecessor->index)) { |
| worklist.append(predecessor); |
| seen.set(predecessor->index); |
| } |
| } |
| } |
| |
| if (!match) |
| return nullptr; |
| |
| // Cache the results for next time. We cache them both for this block and for all of our |
| // predecessors, since even though we've already visited our predecessors, our predecessors |
| // probably have successors other than us. |
| // FIXME: Consider caching failed searches as well, when match is null. It's not clear that |
| // the reduction in compile time would warrant the increase in complexity, though. |
| // https://bugs.webkit.org/show_bug.cgi?id=134876 |
| for (BasicBlock* block : seenList) |
| m_impureDataMap[block].availableAtTail.add(location, match); |
| m_impureData->availableAtTail.add(location, match); |
| |
| return match; |
| } |
| |
| void def(HeapLocation location, LazyNode value) |
| { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Got heap location def: ", location, " -> ", value, "\n"); |
| |
| LazyNode match = findReplacement(location); |
| |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Got match: ", match, "\n"); |
| |
| if (!match) { |
| if (DFGCSEPhaseInternal::verbose) |
| dataLog(" Adding at-tail mapping: ", location, " -> ", value, "\n"); |
| auto result = m_impureData->availableAtTail.add(location, value); |
| ASSERT_UNUSED(result, !result); |
| return; |
| } |
| |
| if (value.isNode() && value.asNode() == m_node) { |
| if (!match.isNode()) { |
| // We need to properly record the constant in order to use an existing one if applicable. |
| // This ensures that re-running GCSE will not find new optimizations. |
| match.ensureIsNode(m_insertionSet, m_block, m_nodeIndex)->owner = m_block; |
| auto result = m_pureValues.add(PureValue(match.asNode(), match->constant()), Vector<Node*>()); |
| bool replaced = false; |
| if (!result.isNewEntry) { |
| for (unsigned i = result.iterator->value.size(); i--;) { |
| Node* candidate = result.iterator->value[i]; |
| if (m_graph.m_ssaDominators->dominates(candidate->owner, m_block)) { |
| ASSERT(candidate); |
| match->replaceWith(m_graph, candidate); |
| match.setNode(candidate); |
| replaced = true; |
| break; |
| } |
| } |
| } |
| if (!replaced) |
| result.iterator->value.append(match.asNode()); |
| } |
| ASSERT(match.asNode()); |
| m_node->replaceWith(m_graph, match.asNode()); |
| m_changed = true; |
| } |
| } |
| |
| struct ImpureBlockData { |
| ImpureBlockData() |
| : didVisit(false) |
| { |
| } |
| |
| ClobberSet writes; |
| ImpureMap availableAtTail; |
| bool didVisit; |
| }; |
| |
| Vector<BasicBlock*> m_preOrder; |
| |
| PureMultiMap m_pureValues; |
| BlockMap<ImpureBlockData> m_impureDataMap; |
| |
| BasicBlock* m_block; |
| Node* m_node; |
| unsigned m_nodeIndex; |
| ImpureBlockData* m_impureData; |
| ClobberSet m_writesSoFar; |
| InsertionSet m_insertionSet; |
| |
| bool m_changed; |
| }; |
| |
| } // anonymous namespace |
| |
| bool performLocalCSE(Graph& graph) |
| { |
| return runPhase<LocalCSEPhase>(graph); |
| } |
| |
| bool performGlobalCSE(Graph& graph) |
| { |
| return runPhase<GlobalCSEPhase>(graph); |
| } |
| |
| } } // namespace JSC::DFG |
| |
| #endif // ENABLE(DFG_JIT) |
