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diff --git a/include/llvm/Analysis/BlockFrequencyInfoImpl.h b/include/llvm/Analysis/BlockFrequencyInfoImpl.h new file mode 100644 index 000000000000..bb256c7bbcc8 --- /dev/null +++ b/include/llvm/Analysis/BlockFrequencyInfoImpl.h @@ -0,0 +1,1181 @@ +//==- BlockFrequencyInfoImpl.h - Block Frequency Implementation -*- C++ -*-===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// Shared implementation of BlockFrequency for IR and Machine Instructions. +// See the documentation below for BlockFrequencyInfoImpl for details. +// +//===----------------------------------------------------------------------===// + +#ifndef LLVM_ANALYSIS_BLOCKFREQUENCYINFOIMPL_H +#define LLVM_ANALYSIS_BLOCKFREQUENCYINFOIMPL_H + +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/iterator_range.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/Support/BlockFrequency.h" +#include "llvm/Support/BranchProbability.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ScaledNumber.h" +#include "llvm/Support/raw_ostream.h" +#include <deque> +#include <list> +#include <string> +#include <vector> + +#define DEBUG_TYPE "block-freq" + +namespace llvm { + +class BasicBlock; +class BranchProbabilityInfo; +class Function; +class Loop; +class LoopInfo; +class MachineBasicBlock; +class MachineBranchProbabilityInfo; +class MachineFunction; +class MachineLoop; +class MachineLoopInfo; + +namespace bfi_detail { + +struct IrreducibleGraph; + +// This is part of a workaround for a GCC 4.7 crash on lambdas. +template <class BT> struct BlockEdgesAdder; + +/// \brief Mass of a block. +/// +/// This class implements a sort of fixed-point fraction always between 0.0 and +/// 1.0. getMass() == UINT64_MAX indicates a value of 1.0. +/// +/// Masses can be added and subtracted. Simple saturation arithmetic is used, +/// so arithmetic operations never overflow or underflow. +/// +/// Masses can be multiplied. Multiplication treats full mass as 1.0 and uses +/// an inexpensive floating-point algorithm that's off-by-one (almost, but not +/// quite, maximum precision). +/// +/// Masses can be scaled by \a BranchProbability at maximum precision. +class BlockMass { + uint64_t Mass; + +public: + BlockMass() : Mass(0) {} + explicit BlockMass(uint64_t Mass) : Mass(Mass) {} + + static BlockMass getEmpty() { return BlockMass(); } + static BlockMass getFull() { return BlockMass(UINT64_MAX); } + + uint64_t getMass() const { return Mass; } + + bool isFull() const { return Mass == UINT64_MAX; } + bool isEmpty() const { return !Mass; } + + bool operator!() const { return isEmpty(); } + + /// \brief Add another mass. + /// + /// Adds another mass, saturating at \a isFull() rather than overflowing. + BlockMass &operator+=(const BlockMass &X) { + uint64_t Sum = Mass + X.Mass; + Mass = Sum < Mass ? UINT64_MAX : Sum; + return *this; + } + + /// \brief Subtract another mass. + /// + /// Subtracts another mass, saturating at \a isEmpty() rather than + /// undeflowing. + BlockMass &operator-=(const BlockMass &X) { + uint64_t Diff = Mass - X.Mass; + Mass = Diff > Mass ? 0 : Diff; + return *this; + } + + BlockMass &operator*=(const BranchProbability &P) { + Mass = P.scale(Mass); + return *this; + } + + bool operator==(const BlockMass &X) const { return Mass == X.Mass; } + bool operator!=(const BlockMass &X) const { return Mass != X.Mass; } + bool operator<=(const BlockMass &X) const { return Mass <= X.Mass; } + bool operator>=(const BlockMass &X) const { return Mass >= X.Mass; } + bool operator<(const BlockMass &X) const { return Mass < X.Mass; } + bool operator>(const BlockMass &X) const { return Mass > X.Mass; } + + /// \brief Convert to scaled number. + /// + /// Convert to \a ScaledNumber. \a isFull() gives 1.0, while \a isEmpty() + /// gives slightly above 0.0. + ScaledNumber<uint64_t> toScaled() const; + + void dump() const; + raw_ostream &print(raw_ostream &OS) const; +}; + +inline BlockMass operator+(const BlockMass &L, const BlockMass &R) { + return BlockMass(L) += R; +} +inline BlockMass operator-(const BlockMass &L, const BlockMass &R) { + return BlockMass(L) -= R; +} +inline BlockMass operator*(const BlockMass &L, const BranchProbability &R) { + return BlockMass(L) *= R; +} +inline BlockMass operator*(const BranchProbability &L, const BlockMass &R) { + return BlockMass(R) *= L; +} + +inline raw_ostream &operator<<(raw_ostream &OS, const BlockMass &X) { + return X.print(OS); +} + +} // end namespace bfi_detail + +template <> struct isPodLike<bfi_detail::BlockMass> { + static const bool value = true; +}; + +/// \brief Base class for BlockFrequencyInfoImpl +/// +/// BlockFrequencyInfoImplBase has supporting data structures and some +/// algorithms for BlockFrequencyInfoImplBase. Only algorithms that depend on +/// the block type (or that call such algorithms) are skipped here. +/// +/// Nevertheless, the majority of the overall algorithm documention lives with +/// BlockFrequencyInfoImpl. See there for details. +class BlockFrequencyInfoImplBase { +public: + typedef ScaledNumber<uint64_t> Scaled64; + typedef bfi_detail::BlockMass BlockMass; + + /// \brief Representative of a block. + /// + /// This is a simple wrapper around an index into the reverse-post-order + /// traversal of the blocks. + /// + /// Unlike a block pointer, its order has meaning (location in the + /// topological sort) and it's class is the same regardless of block type. + struct BlockNode { + typedef uint32_t IndexType; + IndexType Index; + + bool operator==(const BlockNode &X) const { return Index == X.Index; } + bool operator!=(const BlockNode &X) const { return Index != X.Index; } + bool operator<=(const BlockNode &X) const { return Index <= X.Index; } + bool operator>=(const BlockNode &X) const { return Index >= X.Index; } + bool operator<(const BlockNode &X) const { return Index < X.Index; } + bool operator>(const BlockNode &X) const { return Index > X.Index; } + + BlockNode() : Index(UINT32_MAX) {} + BlockNode(IndexType Index) : Index(Index) {} + + bool isValid() const { return Index <= getMaxIndex(); } + static size_t getMaxIndex() { return UINT32_MAX - 1; } + }; + + /// \brief Stats about a block itself. + struct FrequencyData { + Scaled64 Scaled; + uint64_t Integer; + }; + + /// \brief Data about a loop. + /// + /// Contains the data necessary to represent represent a loop as a + /// pseudo-node once it's packaged. + struct LoopData { + typedef SmallVector<std::pair<BlockNode, BlockMass>, 4> ExitMap; + typedef SmallVector<BlockNode, 4> NodeList; + LoopData *Parent; ///< The parent loop. + bool IsPackaged; ///< Whether this has been packaged. + uint32_t NumHeaders; ///< Number of headers. + ExitMap Exits; ///< Successor edges (and weights). + NodeList Nodes; ///< Header and the members of the loop. + BlockMass BackedgeMass; ///< Mass returned to loop header. + BlockMass Mass; + Scaled64 Scale; + + LoopData(LoopData *Parent, const BlockNode &Header) + : Parent(Parent), IsPackaged(false), NumHeaders(1), Nodes(1, Header) {} + template <class It1, class It2> + LoopData(LoopData *Parent, It1 FirstHeader, It1 LastHeader, It2 FirstOther, + It2 LastOther) + : Parent(Parent), IsPackaged(false), Nodes(FirstHeader, LastHeader) { + NumHeaders = Nodes.size(); + Nodes.insert(Nodes.end(), FirstOther, LastOther); + } + bool isHeader(const BlockNode &Node) const { + if (isIrreducible()) + return std::binary_search(Nodes.begin(), Nodes.begin() + NumHeaders, + Node); + return Node == Nodes[0]; + } + BlockNode getHeader() const { return Nodes[0]; } + bool isIrreducible() const { return NumHeaders > 1; } + + NodeList::const_iterator members_begin() const { + return Nodes.begin() + NumHeaders; + } + NodeList::const_iterator members_end() const { return Nodes.end(); } + iterator_range<NodeList::const_iterator> members() const { + return make_range(members_begin(), members_end()); + } + }; + + /// \brief Index of loop information. + struct WorkingData { + BlockNode Node; ///< This node. + LoopData *Loop; ///< The loop this block is inside. + BlockMass Mass; ///< Mass distribution from the entry block. + + WorkingData(const BlockNode &Node) : Node(Node), Loop(nullptr) {} + + bool isLoopHeader() const { return Loop && Loop->isHeader(Node); } + bool isDoubleLoopHeader() const { + return isLoopHeader() && Loop->Parent && Loop->Parent->isIrreducible() && + Loop->Parent->isHeader(Node); + } + + LoopData *getContainingLoop() const { + if (!isLoopHeader()) + return Loop; + if (!isDoubleLoopHeader()) + return Loop->Parent; + return Loop->Parent->Parent; + } + + /// \brief Resolve a node to its representative. + /// + /// Get the node currently representing Node, which could be a containing + /// loop. + /// + /// This function should only be called when distributing mass. As long as + /// there are no irreducilbe edges to Node, then it will have complexity + /// O(1) in this context. + /// + /// In general, the complexity is O(L), where L is the number of loop + /// headers Node has been packaged into. Since this method is called in + /// the context of distributing mass, L will be the number of loop headers + /// an early exit edge jumps out of. + BlockNode getResolvedNode() const { + auto L = getPackagedLoop(); + return L ? L->getHeader() : Node; + } + LoopData *getPackagedLoop() const { + if (!Loop || !Loop->IsPackaged) + return nullptr; + auto L = Loop; + while (L->Parent && L->Parent->IsPackaged) + L = L->Parent; + return L; + } + + /// \brief Get the appropriate mass for a node. + /// + /// Get appropriate mass for Node. If Node is a loop-header (whose loop + /// has been packaged), returns the mass of its pseudo-node. If it's a + /// node inside a packaged loop, it returns the loop's mass. + BlockMass &getMass() { + if (!isAPackage()) + return Mass; + if (!isADoublePackage()) + return Loop->Mass; + return Loop->Parent->Mass; + } + + /// \brief Has ContainingLoop been packaged up? + bool isPackaged() const { return getResolvedNode() != Node; } + /// \brief Has Loop been packaged up? + bool isAPackage() const { return isLoopHeader() && Loop->IsPackaged; } + /// \brief Has Loop been packaged up twice? + bool isADoublePackage() const { + return isDoubleLoopHeader() && Loop->Parent->IsPackaged; + } + }; + + /// \brief Unscaled probability weight. + /// + /// Probability weight for an edge in the graph (including the + /// successor/target node). + /// + /// All edges in the original function are 32-bit. However, exit edges from + /// loop packages are taken from 64-bit exit masses, so we need 64-bits of + /// space in general. + /// + /// In addition to the raw weight amount, Weight stores the type of the edge + /// in the current context (i.e., the context of the loop being processed). + /// Is this a local edge within the loop, an exit from the loop, or a + /// backedge to the loop header? + struct Weight { + enum DistType { Local, Exit, Backedge }; + DistType Type; + BlockNode TargetNode; + uint64_t Amount; + Weight() : Type(Local), Amount(0) {} + Weight(DistType Type, BlockNode TargetNode, uint64_t Amount) + : Type(Type), TargetNode(TargetNode), Amount(Amount) {} + }; + + /// \brief Distribution of unscaled probability weight. + /// + /// Distribution of unscaled probability weight to a set of successors. + /// + /// This class collates the successor edge weights for later processing. + /// + /// \a DidOverflow indicates whether \a Total did overflow while adding to + /// the distribution. It should never overflow twice. + struct Distribution { + typedef SmallVector<Weight, 4> WeightList; + WeightList Weights; ///< Individual successor weights. + uint64_t Total; ///< Sum of all weights. + bool DidOverflow; ///< Whether \a Total did overflow. + + Distribution() : Total(0), DidOverflow(false) {} + void addLocal(const BlockNode &Node, uint64_t Amount) { + add(Node, Amount, Weight::Local); + } + void addExit(const BlockNode &Node, uint64_t Amount) { + add(Node, Amount, Weight::Exit); + } + void addBackedge(const BlockNode &Node, uint64_t Amount) { + add(Node, Amount, Weight::Backedge); + } + + /// \brief Normalize the distribution. + /// + /// Combines multiple edges to the same \a Weight::TargetNode and scales + /// down so that \a Total fits into 32-bits. + /// + /// This is linear in the size of \a Weights. For the vast majority of + /// cases, adjacent edge weights are combined by sorting WeightList and + /// combining adjacent weights. However, for very large edge lists an + /// auxiliary hash table is used. + void normalize(); + + private: + void add(const BlockNode &Node, uint64_t Amount, Weight::DistType Type); + }; + + /// \brief Data about each block. This is used downstream. + std::vector<FrequencyData> Freqs; + + /// \brief Loop data: see initializeLoops(). + std::vector<WorkingData> Working; + + /// \brief Indexed information about loops. + std::list<LoopData> Loops; + + /// \brief Add all edges out of a packaged loop to the distribution. + /// + /// Adds all edges from LocalLoopHead to Dist. Calls addToDist() to add each + /// successor edge. + /// + /// \return \c true unless there's an irreducible backedge. + bool addLoopSuccessorsToDist(const LoopData *OuterLoop, LoopData &Loop, + Distribution &Dist); + + /// \brief Add an edge to the distribution. + /// + /// Adds an edge to Succ to Dist. If \c LoopHead.isValid(), then whether the + /// edge is local/exit/backedge is in the context of LoopHead. Otherwise, + /// every edge should be a local edge (since all the loops are packaged up). + /// + /// \return \c true unless aborted due to an irreducible backedge. + bool addToDist(Distribution &Dist, const LoopData *OuterLoop, + const BlockNode &Pred, const BlockNode &Succ, uint64_t Weight); + + LoopData &getLoopPackage(const BlockNode &Head) { + assert(Head.Index < Working.size()); + assert(Working[Head.Index].isLoopHeader()); + return *Working[Head.Index].Loop; + } + + /// \brief Analyze irreducible SCCs. + /// + /// Separate irreducible SCCs from \c G, which is an explict graph of \c + /// OuterLoop (or the top-level function, if \c OuterLoop is \c nullptr). + /// Insert them into \a Loops before \c Insert. + /// + /// \return the \c LoopData nodes representing the irreducible SCCs. + iterator_range<std::list<LoopData>::iterator> + analyzeIrreducible(const bfi_detail::IrreducibleGraph &G, LoopData *OuterLoop, + std::list<LoopData>::iterator Insert); + + /// \brief Update a loop after packaging irreducible SCCs inside of it. + /// + /// Update \c OuterLoop. Before finding irreducible control flow, it was + /// partway through \a computeMassInLoop(), so \a LoopData::Exits and \a + /// LoopData::BackedgeMass need to be reset. Also, nodes that were packaged + /// up need to be removed from \a OuterLoop::Nodes. + void updateLoopWithIrreducible(LoopData &OuterLoop); + + /// \brief Distribute mass according to a distribution. + /// + /// Distributes the mass in Source according to Dist. If LoopHead.isValid(), + /// backedges and exits are stored in its entry in Loops. + /// + /// Mass is distributed in parallel from two copies of the source mass. + void distributeMass(const BlockNode &Source, LoopData *OuterLoop, + Distribution &Dist); + + /// \brief Compute the loop scale for a loop. + void computeLoopScale(LoopData &Loop); + + /// \brief Package up a loop. + void packageLoop(LoopData &Loop); + + /// \brief Unwrap loops. + void unwrapLoops(); + + /// \brief Finalize frequency metrics. + /// + /// Calculates final frequencies and cleans up no-longer-needed data + /// structures. + void finalizeMetrics(); + + /// \brief Clear all memory. + void clear(); + + virtual std::string getBlockName(const BlockNode &Node) const; + std::string getLoopName(const LoopData &Loop) const; + + virtual raw_ostream &print(raw_ostream &OS) const { return OS; } + void dump() const { print(dbgs()); } + + Scaled64 getFloatingBlockFreq(const BlockNode &Node) const; + + BlockFrequency getBlockFreq(const BlockNode &Node) const; + + raw_ostream &printBlockFreq(raw_ostream &OS, const BlockNode &Node) const; + raw_ostream &printBlockFreq(raw_ostream &OS, + const BlockFrequency &Freq) const; + + uint64_t getEntryFreq() const { + assert(!Freqs.empty()); + return Freqs[0].Integer; + } + /// \brief Virtual destructor. + /// + /// Need a virtual destructor to mask the compiler warning about + /// getBlockName(). + virtual ~BlockFrequencyInfoImplBase() {} +}; + +namespace bfi_detail { +template <class BlockT> struct TypeMap {}; +template <> struct TypeMap<BasicBlock> { + typedef BasicBlock BlockT; + typedef Function FunctionT; + typedef BranchProbabilityInfo BranchProbabilityInfoT; + typedef Loop LoopT; + typedef LoopInfo LoopInfoT; +}; +template <> struct TypeMap<MachineBasicBlock> { + typedef MachineBasicBlock BlockT; + typedef MachineFunction FunctionT; + typedef MachineBranchProbabilityInfo BranchProbabilityInfoT; + typedef MachineLoop LoopT; + typedef MachineLoopInfo LoopInfoT; +}; + +/// \brief Get the name of a MachineBasicBlock. +/// +/// Get the name of a MachineBasicBlock. It's templated so that including from +/// CodeGen is unnecessary (that would be a layering issue). +/// +/// This is used mainly for debug output. The name is similar to +/// MachineBasicBlock::getFullName(), but skips the name of the function. +template <class BlockT> std::string getBlockName(const BlockT *BB) { + assert(BB && "Unexpected nullptr"); + auto MachineName = "BB" + Twine(BB->getNumber()); + if (BB->getBasicBlock()) + return (MachineName + "[" + BB->getName() + "]").str(); + return MachineName.str(); +} +/// \brief Get the name of a BasicBlock. +template <> inline std::string getBlockName(const BasicBlock *BB) { + assert(BB && "Unexpected nullptr"); + return BB->getName().str(); +} + +/// \brief Graph of irreducible control flow. +/// +/// This graph is used for determining the SCCs in a loop (or top-level +/// function) that has irreducible control flow. +/// +/// During the block frequency algorithm, the local graphs are defined in a +/// light-weight way, deferring to the \a BasicBlock or \a MachineBasicBlock +/// graphs for most edges, but getting others from \a LoopData::ExitMap. The +/// latter only has successor information. +/// +/// \a IrreducibleGraph makes this graph explicit. It's in a form that can use +/// \a GraphTraits (so that \a analyzeIrreducible() can use \a scc_iterator), +/// and it explicitly lists predecessors and successors. The initialization +/// that relies on \c MachineBasicBlock is defined in the header. +struct IrreducibleGraph { + typedef BlockFrequencyInfoImplBase BFIBase; + + BFIBase &BFI; + + typedef BFIBase::BlockNode BlockNode; + struct IrrNode { + BlockNode Node; + unsigned NumIn; + std::deque<const IrrNode *> Edges; + IrrNode(const BlockNode &Node) : Node(Node), NumIn(0) {} + + typedef std::deque<const IrrNode *>::const_iterator iterator; + iterator pred_begin() const { return Edges.begin(); } + iterator succ_begin() const { return Edges.begin() + NumIn; } + iterator pred_end() const { return succ_begin(); } + iterator succ_end() const { return Edges.end(); } + }; + BlockNode Start; + const IrrNode *StartIrr; + std::vector<IrrNode> Nodes; + SmallDenseMap<uint32_t, IrrNode *, 4> Lookup; + + /// \brief Construct an explicit graph containing irreducible control flow. + /// + /// Construct an explicit graph of the control flow in \c OuterLoop (or the + /// top-level function, if \c OuterLoop is \c nullptr). Uses \c + /// addBlockEdges to add block successors that have not been packaged into + /// loops. + /// + /// \a BlockFrequencyInfoImpl::computeIrreducibleMass() is the only expected + /// user of this. + template <class BlockEdgesAdder> + IrreducibleGraph(BFIBase &BFI, const BFIBase::LoopData *OuterLoop, + BlockEdgesAdder addBlockEdges) + : BFI(BFI), StartIrr(nullptr) { + initialize(OuterLoop, addBlockEdges); + } + + template <class BlockEdgesAdder> + void initialize(const BFIBase::LoopData *OuterLoop, + BlockEdgesAdder addBlockEdges); + void addNodesInLoop(const BFIBase::LoopData &OuterLoop); + void addNodesInFunction(); + void addNode(const BlockNode &Node) { + Nodes.emplace_back(Node); + BFI.Working[Node.Index].getMass() = BlockMass::getEmpty(); + } + void indexNodes(); + template <class BlockEdgesAdder> + void addEdges(const BlockNode &Node, const BFIBase::LoopData *OuterLoop, + BlockEdgesAdder addBlockEdges); + void addEdge(IrrNode &Irr, const BlockNode &Succ, + const BFIBase::LoopData *OuterLoop); +}; +template <class BlockEdgesAdder> +void IrreducibleGraph::initialize(const BFIBase::LoopData *OuterLoop, + BlockEdgesAdder addBlockEdges) { + if (OuterLoop) { + addNodesInLoop(*OuterLoop); + for (auto N : OuterLoop->Nodes) + addEdges(N, OuterLoop, addBlockEdges); + } else { + addNodesInFunction(); + for (uint32_t Index = 0; Index < BFI.Working.size(); ++Index) + addEdges(Index, OuterLoop, addBlockEdges); + } + StartIrr = Lookup[Start.Index]; +} +template <class BlockEdgesAdder> +void IrreducibleGraph::addEdges(const BlockNode &Node, + const BFIBase::LoopData *OuterLoop, + BlockEdgesAdder addBlockEdges) { + auto L = Lookup.find(Node.Index); + if (L == Lookup.end()) + return; + IrrNode &Irr = *L->second; + const auto &Working = BFI.Working[Node.Index]; + + if (Working.isAPackage()) + for (const auto &I : Working.Loop->Exits) + addEdge(Irr, I.first, OuterLoop); + else + addBlockEdges(*this, Irr, OuterLoop); +} +} + +/// \brief Shared implementation for block frequency analysis. +/// +/// This is a shared implementation of BlockFrequencyInfo and +/// MachineBlockFrequencyInfo, and calculates the relative frequencies of +/// blocks. +/// +/// LoopInfo defines a loop as a "non-trivial" SCC dominated by a single block, +/// which is called the header. A given loop, L, can have sub-loops, which are +/// loops within the subgraph of L that exclude its header. (A "trivial" SCC +/// consists of a single block that does not have a self-edge.) +/// +/// In addition to loops, this algorithm has limited support for irreducible +/// SCCs, which are SCCs with multiple entry blocks. Irreducible SCCs are +/// discovered on they fly, and modelled as loops with multiple headers. +/// +/// The headers of irreducible sub-SCCs consist of its entry blocks and all +/// nodes that are targets of a backedge within it (excluding backedges within +/// true sub-loops). Block frequency calculations act as if a block is +/// inserted that intercepts all the edges to the headers. All backedges and +/// entries point to this block. Its successors are the headers, which split +/// the frequency evenly. +/// +/// This algorithm leverages BlockMass and ScaledNumber to maintain precision, +/// separates mass distribution from loop scaling, and dithers to eliminate +/// probability mass loss. +/// +/// The implementation is split between BlockFrequencyInfoImpl, which knows the +/// type of graph being modelled (BasicBlock vs. MachineBasicBlock), and +/// BlockFrequencyInfoImplBase, which doesn't. The base class uses \a +/// BlockNode, a wrapper around a uint32_t. BlockNode is numbered from 0 in +/// reverse-post order. This gives two advantages: it's easy to compare the +/// relative ordering of two nodes, and maps keyed on BlockT can be represented +/// by vectors. +/// +/// This algorithm is O(V+E), unless there is irreducible control flow, in +/// which case it's O(V*E) in the worst case. +/// +/// These are the main stages: +/// +/// 0. Reverse post-order traversal (\a initializeRPOT()). +/// +/// Run a single post-order traversal and save it (in reverse) in RPOT. +/// All other stages make use of this ordering. Save a lookup from BlockT +/// to BlockNode (the index into RPOT) in Nodes. +/// +/// 1. Loop initialization (\a initializeLoops()). +/// +/// Translate LoopInfo/MachineLoopInfo into a form suitable for the rest of +/// the algorithm. In particular, store the immediate members of each loop +/// in reverse post-order. +/// +/// 2. Calculate mass and scale in loops (\a computeMassInLoops()). +/// +/// For each loop (bottom-up), distribute mass through the DAG resulting +/// from ignoring backedges and treating sub-loops as a single pseudo-node. +/// Track the backedge mass distributed to the loop header, and use it to +/// calculate the loop scale (number of loop iterations). Immediate +/// members that represent sub-loops will already have been visited and +/// packaged into a pseudo-node. +/// +/// Distributing mass in a loop is a reverse-post-order traversal through +/// the loop. Start by assigning full mass to the Loop header. For each +/// node in the loop: +/// +/// - Fetch and categorize the weight distribution for its successors. +/// If this is a packaged-subloop, the weight distribution is stored +/// in \a LoopData::Exits. Otherwise, fetch it from +/// BranchProbabilityInfo. +/// +/// - Each successor is categorized as \a Weight::Local, a local edge +/// within the current loop, \a Weight::Backedge, a backedge to the +/// loop header, or \a Weight::Exit, any successor outside the loop. +/// The weight, the successor, and its category are stored in \a +/// Distribution. There can be multiple edges to each successor. +/// +/// - If there's a backedge to a non-header, there's an irreducible SCC. +/// The usual flow is temporarily aborted. \a +/// computeIrreducibleMass() finds the irreducible SCCs within the +/// loop, packages them up, and restarts the flow. +/// +/// - Normalize the distribution: scale weights down so that their sum +/// is 32-bits, and coalesce multiple edges to the same node. +/// +/// - Distribute the mass accordingly, dithering to minimize mass loss, +/// as described in \a distributeMass(). +/// +/// Finally, calculate the loop scale from the accumulated backedge mass. +/// +/// 3. Distribute mass in the function (\a computeMassInFunction()). +/// +/// Finally, distribute mass through the DAG resulting from packaging all +/// loops in the function. This uses the same algorithm as distributing +/// mass in a loop, except that there are no exit or backedge edges. +/// +/// 4. Unpackage loops (\a unwrapLoops()). +/// +/// Initialize each block's frequency to a floating point representation of +/// its mass. +/// +/// Visit loops top-down, scaling the frequencies of its immediate members +/// by the loop's pseudo-node's frequency. +/// +/// 5. Convert frequencies to a 64-bit range (\a finalizeMetrics()). +/// +/// Using the min and max frequencies as a guide, translate floating point +/// frequencies to an appropriate range in uint64_t. +/// +/// It has some known flaws. +/// +/// - Loop scale is limited to 4096 per loop (2^12) to avoid exhausting +/// BlockFrequency's 64-bit integer precision. +/// +/// - The model of irreducible control flow is a rough approximation. +/// +/// Modelling irreducible control flow exactly involves setting up and +/// solving a group of infinite geometric series. Such precision is +/// unlikely to be worthwhile, since most of our algorithms give up on +/// irreducible control flow anyway. +/// +/// Nevertheless, we might find that we need to get closer. Here's a sort +/// of TODO list for the model with diminishing returns, to be completed as +/// necessary. +/// +/// - The headers for the \a LoopData representing an irreducible SCC +/// include non-entry blocks. When these extra blocks exist, they +/// indicate a self-contained irreducible sub-SCC. We could treat them +/// as sub-loops, rather than arbitrarily shoving the problematic +/// blocks into the headers of the main irreducible SCC. +/// +/// - Backedge frequencies are assumed to be evenly split between the +/// headers of a given irreducible SCC. Instead, we could track the +/// backedge mass separately for each header, and adjust their relative +/// frequencies. +/// +/// - Entry frequencies are assumed to be evenly split between the +/// headers of a given irreducible SCC, which is the only option if we +/// need to compute mass in the SCC before its parent loop. Instead, +/// we could partially compute mass in the parent loop, and stop when +/// we get to the SCC. Here, we have the correct ratio of entry +/// masses, which we can use to adjust their relative frequencies. +/// Compute mass in the SCC, and then continue propagation in the +/// parent. +/// +/// - We can propagate mass iteratively through the SCC, for some fixed +/// number of iterations. Each iteration starts by assigning the entry +/// blocks their backedge mass from the prior iteration. The final +/// mass for each block (and each exit, and the total backedge mass +/// used for computing loop scale) is the sum of all iterations. +/// (Running this until fixed point would "solve" the geometric +/// series by simulation.) +template <class BT> class BlockFrequencyInfoImpl : BlockFrequencyInfoImplBase { + typedef typename bfi_detail::TypeMap<BT>::BlockT BlockT; + typedef typename bfi_detail::TypeMap<BT>::FunctionT FunctionT; + typedef typename bfi_detail::TypeMap<BT>::BranchProbabilityInfoT + BranchProbabilityInfoT; + typedef typename bfi_detail::TypeMap<BT>::LoopT LoopT; + typedef typename bfi_detail::TypeMap<BT>::LoopInfoT LoopInfoT; + + // This is part of a workaround for a GCC 4.7 crash on lambdas. + friend struct bfi_detail::BlockEdgesAdder<BT>; + + typedef GraphTraits<const BlockT *> Successor; + typedef GraphTraits<Inverse<const BlockT *>> Predecessor; + + const BranchProbabilityInfoT *BPI; + const LoopInfoT *LI; + const FunctionT *F; + + // All blocks in reverse postorder. + std::vector<const BlockT *> RPOT; + DenseMap<const BlockT *, BlockNode> Nodes; + + typedef typename std::vector<const BlockT *>::const_iterator rpot_iterator; + + rpot_iterator rpot_begin() const { return RPOT.begin(); } + rpot_iterator rpot_end() const { return RPOT.end(); } + + size_t getIndex(const rpot_iterator &I) const { return I - rpot_begin(); } + + BlockNode getNode(const rpot_iterator &I) const { + return BlockNode(getIndex(I)); + } + BlockNode getNode(const BlockT *BB) const { return Nodes.lookup(BB); } + + const BlockT *getBlock(const BlockNode &Node) const { + assert(Node.Index < RPOT.size()); + return RPOT[Node.Index]; + } + + /// \brief Run (and save) a post-order traversal. + /// + /// Saves a reverse post-order traversal of all the nodes in \a F. + void initializeRPOT(); + + /// \brief Initialize loop data. + /// + /// Build up \a Loops using \a LoopInfo. \a LoopInfo gives us a mapping from + /// each block to the deepest loop it's in, but we need the inverse. For each + /// loop, we store in reverse post-order its "immediate" members, defined as + /// the header, the headers of immediate sub-loops, and all other blocks in + /// the loop that are not in sub-loops. + void initializeLoops(); + + /// \brief Propagate to a block's successors. + /// + /// In the context of distributing mass through \c OuterLoop, divide the mass + /// currently assigned to \c Node between its successors. + /// + /// \return \c true unless there's an irreducible backedge. + bool propagateMassToSuccessors(LoopData *OuterLoop, const BlockNode &Node); + + /// \brief Compute mass in a particular loop. + /// + /// Assign mass to \c Loop's header, and then for each block in \c Loop in + /// reverse post-order, distribute mass to its successors. Only visits nodes + /// that have not been packaged into sub-loops. + /// + /// \pre \a computeMassInLoop() has been called for each subloop of \c Loop. + /// \return \c true unless there's an irreducible backedge. + bool computeMassInLoop(LoopData &Loop); + + /// \brief Try to compute mass in the top-level function. + /// + /// Assign mass to the entry block, and then for each block in reverse + /// post-order, distribute mass to its successors. Skips nodes that have + /// been packaged into loops. + /// + /// \pre \a computeMassInLoops() has been called. + /// \return \c true unless there's an irreducible backedge. + bool tryToComputeMassInFunction(); + + /// \brief Compute mass in (and package up) irreducible SCCs. + /// + /// Find the irreducible SCCs in \c OuterLoop, add them to \a Loops (in front + /// of \c Insert), and call \a computeMassInLoop() on each of them. + /// + /// If \c OuterLoop is \c nullptr, it refers to the top-level function. + /// + /// \pre \a computeMassInLoop() has been called for each subloop of \c + /// OuterLoop. + /// \pre \c Insert points at the the last loop successfully processed by \a + /// computeMassInLoop(). + /// \pre \c OuterLoop has irreducible SCCs. + void computeIrreducibleMass(LoopData *OuterLoop, + std::list<LoopData>::iterator Insert); + + /// \brief Compute mass in all loops. + /// + /// For each loop bottom-up, call \a computeMassInLoop(). + /// + /// \a computeMassInLoop() aborts (and returns \c false) on loops that + /// contain a irreducible sub-SCCs. Use \a computeIrreducibleMass() and then + /// re-enter \a computeMassInLoop(). + /// + /// \post \a computeMassInLoop() has returned \c true for every loop. + void computeMassInLoops(); + + /// \brief Compute mass in the top-level function. + /// + /// Uses \a tryToComputeMassInFunction() and \a computeIrreducibleMass() to + /// compute mass in the top-level function. + /// + /// \post \a tryToComputeMassInFunction() has returned \c true. + void computeMassInFunction(); + + std::string getBlockName(const BlockNode &Node) const override { + return bfi_detail::getBlockName(getBlock(Node)); + } + +public: + const FunctionT *getFunction() const { return F; } + + void doFunction(const FunctionT *F, const BranchProbabilityInfoT *BPI, + const LoopInfoT *LI); + BlockFrequencyInfoImpl() : BPI(nullptr), LI(nullptr), F(nullptr) {} + + using BlockFrequencyInfoImplBase::getEntryFreq; + BlockFrequency getBlockFreq(const BlockT *BB) const { + return BlockFrequencyInfoImplBase::getBlockFreq(getNode(BB)); + } + Scaled64 getFloatingBlockFreq(const BlockT *BB) const { + return BlockFrequencyInfoImplBase::getFloatingBlockFreq(getNode(BB)); + } + + /// \brief Print the frequencies for the current function. + /// + /// Prints the frequencies for the blocks in the current function. + /// + /// Blocks are printed in the natural iteration order of the function, rather + /// than reverse post-order. This provides two advantages: writing -analyze + /// tests is easier (since blocks come out in source order), and even + /// unreachable blocks are printed. + /// + /// \a BlockFrequencyInfoImplBase::print() only knows reverse post-order, so + /// we need to override it here. + raw_ostream &print(raw_ostream &OS) const override; + using BlockFrequencyInfoImplBase::dump; + + using BlockFrequencyInfoImplBase::printBlockFreq; + raw_ostream &printBlockFreq(raw_ostream &OS, const BlockT *BB) const { + return BlockFrequencyInfoImplBase::printBlockFreq(OS, getNode(BB)); + } +}; + +template <class BT> +void BlockFrequencyInfoImpl<BT>::doFunction(const FunctionT *F, + const BranchProbabilityInfoT *BPI, + const LoopInfoT *LI) { + // Save the parameters. + this->BPI = BPI; + this->LI = LI; + this->F = F; + + // Clean up left-over data structures. + BlockFrequencyInfoImplBase::clear(); + RPOT.clear(); + Nodes.clear(); + + // Initialize. + DEBUG(dbgs() << "\nblock-frequency: " << F->getName() << "\n=================" + << std::string(F->getName().size(), '=') << "\n"); + initializeRPOT(); + initializeLoops(); + + // Visit loops in post-order to find thelocal mass distribution, and then do + // the full function. + computeMassInLoops(); + computeMassInFunction(); + unwrapLoops(); + finalizeMetrics(); +} + +template <class BT> void BlockFrequencyInfoImpl<BT>::initializeRPOT() { + const BlockT *Entry = F->begin(); + RPOT.reserve(F->size()); + std::copy(po_begin(Entry), po_end(Entry), std::back_inserter(RPOT)); + std::reverse(RPOT.begin(), RPOT.end()); + + assert(RPOT.size() - 1 <= BlockNode::getMaxIndex() && + "More nodes in function than Block Frequency Info supports"); + + DEBUG(dbgs() << "reverse-post-order-traversal\n"); + for (rpot_iterator I = rpot_begin(), E = rpot_end(); I != E; ++I) { + BlockNode Node = getNode(I); + DEBUG(dbgs() << " - " << getIndex(I) << ": " << getBlockName(Node) << "\n"); + Nodes[*I] = Node; + } + + Working.reserve(RPOT.size()); + for (size_t Index = 0; Index < RPOT.size(); ++Index) + Working.emplace_back(Index); + Freqs.resize(RPOT.size()); +} + +template <class BT> void BlockFrequencyInfoImpl<BT>::initializeLoops() { + DEBUG(dbgs() << "loop-detection\n"); + if (LI->empty()) + return; + + // Visit loops top down and assign them an index. + std::deque<std::pair<const LoopT *, LoopData *>> Q; + for (const LoopT *L : *LI) + Q.emplace_back(L, nullptr); + while (!Q.empty()) { + const LoopT *Loop = Q.front().first; + LoopData *Parent = Q.front().second; + Q.pop_front(); + + BlockNode Header = getNode(Loop->getHeader()); + assert(Header.isValid()); + + Loops.emplace_back(Parent, Header); + Working[Header.Index].Loop = &Loops.back(); + DEBUG(dbgs() << " - loop = " << getBlockName(Header) << "\n"); + + for (const LoopT *L : *Loop) + Q.emplace_back(L, &Loops.back()); + } + + // Visit nodes in reverse post-order and add them to their deepest containing + // loop. + for (size_t Index = 0; Index < RPOT.size(); ++Index) { + // Loop headers have already been mostly mapped. + if (Working[Index].isLoopHeader()) { + LoopData *ContainingLoop = Working[Index].getContainingLoop(); + if (ContainingLoop) + ContainingLoop->Nodes.push_back(Index); + continue; + } + + const LoopT *Loop = LI->getLoopFor(RPOT[Index]); + if (!Loop) + continue; + + // Add this node to its containing loop's member list. + BlockNode Header = getNode(Loop->getHeader()); + assert(Header.isValid()); + const auto &HeaderData = Working[Header.Index]; + assert(HeaderData.isLoopHeader()); + + Working[Index].Loop = HeaderData.Loop; + HeaderData.Loop->Nodes.push_back(Index); + DEBUG(dbgs() << " - loop = " << getBlockName(Header) + << ": member = " << getBlockName(Index) << "\n"); + } +} + +template <class BT> void BlockFrequencyInfoImpl<BT>::computeMassInLoops() { + // Visit loops with the deepest first, and the top-level loops last. + for (auto L = Loops.rbegin(), E = Loops.rend(); L != E; ++L) { + if (computeMassInLoop(*L)) + continue; + auto Next = std::next(L); + computeIrreducibleMass(&*L, L.base()); + L = std::prev(Next); + if (computeMassInLoop(*L)) + continue; + llvm_unreachable("unhandled irreducible control flow"); + } +} + +template <class BT> +bool BlockFrequencyInfoImpl<BT>::computeMassInLoop(LoopData &Loop) { + // Compute mass in loop. + DEBUG(dbgs() << "compute-mass-in-loop: " << getLoopName(Loop) << "\n"); + + if (Loop.isIrreducible()) { + BlockMass Remaining = BlockMass::getFull(); + for (uint32_t H = 0; H < Loop.NumHeaders; ++H) { + auto &Mass = Working[Loop.Nodes[H].Index].getMass(); + Mass = Remaining * BranchProbability(1, Loop.NumHeaders - H); + Remaining -= Mass; + } + for (const BlockNode &M : Loop.Nodes) + if (!propagateMassToSuccessors(&Loop, M)) + llvm_unreachable("unhandled irreducible control flow"); + } else { + Working[Loop.getHeader().Index].getMass() = BlockMass::getFull(); + if (!propagateMassToSuccessors(&Loop, Loop.getHeader())) + llvm_unreachable("irreducible control flow to loop header!?"); + for (const BlockNode &M : Loop.members()) + if (!propagateMassToSuccessors(&Loop, M)) + // Irreducible backedge. + return false; + } + + computeLoopScale(Loop); + packageLoop(Loop); + return true; +} + +template <class BT> +bool BlockFrequencyInfoImpl<BT>::tryToComputeMassInFunction() { + // Compute mass in function. + DEBUG(dbgs() << "compute-mass-in-function\n"); + assert(!Working.empty() && "no blocks in function"); + assert(!Working[0].isLoopHeader() && "entry block is a loop header"); + + Working[0].getMass() = BlockMass::getFull(); + for (rpot_iterator I = rpot_begin(), IE = rpot_end(); I != IE; ++I) { + // Check for nodes that have been packaged. + BlockNode Node = getNode(I); + if (Working[Node.Index].isPackaged()) + continue; + + if (!propagateMassToSuccessors(nullptr, Node)) + return false; + } + return true; +} + +template <class BT> void BlockFrequencyInfoImpl<BT>::computeMassInFunction() { + if (tryToComputeMassInFunction()) + return; + computeIrreducibleMass(nullptr, Loops.begin()); + if (tryToComputeMassInFunction()) + return; + llvm_unreachable("unhandled irreducible control flow"); +} + +/// \note This should be a lambda, but that crashes GCC 4.7. +namespace bfi_detail { +template <class BT> struct BlockEdgesAdder { + typedef BT BlockT; + typedef BlockFrequencyInfoImplBase::LoopData LoopData; + typedef GraphTraits<const BlockT *> Successor; + + const BlockFrequencyInfoImpl<BT> &BFI; + explicit BlockEdgesAdder(const BlockFrequencyInfoImpl<BT> &BFI) + : BFI(BFI) {} + void operator()(IrreducibleGraph &G, IrreducibleGraph::IrrNode &Irr, + const LoopData *OuterLoop) { + const BlockT *BB = BFI.RPOT[Irr.Node.Index]; + for (auto I = Successor::child_begin(BB), E = Successor::child_end(BB); + I != E; ++I) + G.addEdge(Irr, BFI.getNode(*I), OuterLoop); + } +}; +} +template <class BT> +void BlockFrequencyInfoImpl<BT>::computeIrreducibleMass( + LoopData *OuterLoop, std::list<LoopData>::iterator Insert) { + DEBUG(dbgs() << "analyze-irreducible-in-"; + if (OuterLoop) dbgs() << "loop: " << getLoopName(*OuterLoop) << "\n"; + else dbgs() << "function\n"); + + using namespace bfi_detail; + // Ideally, addBlockEdges() would be declared here as a lambda, but that + // crashes GCC 4.7. + BlockEdgesAdder<BT> addBlockEdges(*this); + IrreducibleGraph G(*this, OuterLoop, addBlockEdges); + + for (auto &L : analyzeIrreducible(G, OuterLoop, Insert)) + computeMassInLoop(L); + + if (!OuterLoop) + return; + updateLoopWithIrreducible(*OuterLoop); +} + +template <class BT> +bool +BlockFrequencyInfoImpl<BT>::propagateMassToSuccessors(LoopData *OuterLoop, + const BlockNode &Node) { + DEBUG(dbgs() << " - node: " << getBlockName(Node) << "\n"); + // Calculate probability for successors. + Distribution Dist; + if (auto *Loop = Working[Node.Index].getPackagedLoop()) { + assert(Loop != OuterLoop && "Cannot propagate mass in a packaged loop"); + if (!addLoopSuccessorsToDist(OuterLoop, *Loop, Dist)) + // Irreducible backedge. + return false; + } else { + const BlockT *BB = getBlock(Node); + for (auto SI = Successor::child_begin(BB), SE = Successor::child_end(BB); + SI != SE; ++SI) + // Do not dereference SI, or getEdgeWeight() is linear in the number of + // successors. + if (!addToDist(Dist, OuterLoop, Node, getNode(*SI), + BPI->getEdgeWeight(BB, SI))) + // Irreducible backedge. + return false; + } + + // Distribute mass to successors, saving exit and backedge data in the + // loop header. + distributeMass(Node, OuterLoop, Dist); + return true; +} + +template <class BT> +raw_ostream &BlockFrequencyInfoImpl<BT>::print(raw_ostream &OS) const { + if (!F) + return OS; + OS << "block-frequency-info: " << F->getName() << "\n"; + for (const BlockT &BB : *F) + OS << " - " << bfi_detail::getBlockName(&BB) + << ": float = " << getFloatingBlockFreq(&BB) + << ", int = " << getBlockFreq(&BB).getFrequency() << "\n"; + + // Add an extra newline for readability. + OS << "\n"; + return OS; +} + +} // end namespace llvm + +#undef DEBUG_TYPE + +#endif |