//===--- BranchProbabilityInfo.h - Branch Probability Analysis --*- C++ -*-===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass is used to evaluate branch probabilties. // //===----------------------------------------------------------------------===// #ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H #define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/InitializePasses.h" #include "llvm/Pass.h" #include "llvm/Support/BranchProbability.h" #include "llvm/Support/CFG.h" namespace llvm { class LoopInfo; class raw_ostream; /// \brief Analysis pass providing branch probability information. /// /// This is a function analysis pass which provides information on the relative /// probabilities of each "edge" in the function's CFG where such an edge is /// defined by a pair (PredBlock and an index in the successors). The /// probability of an edge from one block is always relative to the /// probabilities of other edges from the block. The probabilites of all edges /// from a block sum to exactly one (100%). /// We use a pair (PredBlock and an index in the successors) to uniquely /// identify an edge, since we can have multiple edges from Src to Dst. /// As an example, we can have a switch which jumps to Dst with value 0 and /// value 10. class BranchProbabilityInfo : public FunctionPass { public: static char ID; BranchProbabilityInfo() : FunctionPass(ID) { initializeBranchProbabilityInfoPass(*PassRegistry::getPassRegistry()); } void getAnalysisUsage(AnalysisUsage &AU) const; bool runOnFunction(Function &F); void print(raw_ostream &OS, const Module *M = 0) const; /// \brief Get an edge's probability, relative to other out-edges of the Src. /// /// This routine provides access to the fractional probability between zero /// (0%) and one (100%) of this edge executing, relative to other edges /// leaving the 'Src' block. The returned probability is never zero, and can /// only be one if the source block has only one successor. BranchProbability getEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors) const; /// \brief Get the probability of going from Src to Dst. /// /// It returns the sum of all probabilities for edges from Src to Dst. BranchProbability getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const; /// \brief Test if an edge is hot relative to other out-edges of the Src. /// /// Check whether this edge out of the source block is 'hot'. We define hot /// as having a relative probability >= 80%. bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const; /// \brief Retrieve the hot successor of a block if one exists. /// /// Given a basic block, look through its successors and if one exists for /// which \see isEdgeHot would return true, return that successor block. BasicBlock *getHotSucc(BasicBlock *BB) const; /// \brief Print an edge's probability. /// /// Retrieves an edge's probability similarly to \see getEdgeProbability, but /// then prints that probability to the provided stream. That stream is then /// returned. raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src, const BasicBlock *Dst) const; /// \brief Get the raw edge weight calculated for the edge. /// /// This returns the raw edge weight. It is guaranteed to fall between 1 and /// UINT32_MAX. Note that the raw edge weight is not meaningful in isolation. /// This interface should be very carefully, and primarily by routines that /// are updating the analysis by later calling setEdgeWeight. uint32_t getEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors) const; /// \brief Get the raw edge weight calculated for the block pair. /// /// This returns the sum of all raw edge weights from Src to Dst. /// It is guaranteed to fall between 1 and UINT32_MAX. uint32_t getEdgeWeight(const BasicBlock *Src, const BasicBlock *Dst) const; uint32_t getEdgeWeight(const BasicBlock *Src, succ_const_iterator Dst) const; /// \brief Set the raw edge weight for a given edge. /// /// This allows a pass to explicitly set the edge weight for an edge. It can /// be used when updating the CFG to update and preserve the branch /// probability information. Read the implementation of how these edge /// weights are calculated carefully before using! void setEdgeWeight(const BasicBlock *Src, unsigned IndexInSuccessors, uint32_t Weight); private: // Since we allow duplicate edges from one basic block to another, we use // a pair (PredBlock and an index in the successors) to specify an edge. typedef std::pair<const BasicBlock *, unsigned> Edge; // Default weight value. Used when we don't have information about the edge. // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of // the successors have a weight yet. But it doesn't make sense when providing // weight to an edge that may have siblings with non-zero weights. This can // be handled various ways, but it's probably fine for an edge with unknown // weight to just "inherit" the non-zero weight of an adjacent successor. static const uint32_t DEFAULT_WEIGHT = 16; DenseMap<Edge, uint32_t> Weights; /// \brief Handle to the LoopInfo analysis. LoopInfo *LI; /// \brief Track the last function we run over for printing. Function *LastF; /// \brief Track the set of blocks directly succeeded by a returning block. SmallPtrSet<BasicBlock *, 16> PostDominatedByUnreachable; /// \brief Track the set of blocks that always lead to a cold call. SmallPtrSet<BasicBlock *, 16> PostDominatedByColdCall; /// \brief Get sum of the block successors' weights. uint32_t getSumForBlock(const BasicBlock *BB) const; bool calcUnreachableHeuristics(BasicBlock *BB); bool calcMetadataWeights(BasicBlock *BB); bool calcColdCallHeuristics(BasicBlock *BB); bool calcPointerHeuristics(BasicBlock *BB); bool calcLoopBranchHeuristics(BasicBlock *BB); bool calcZeroHeuristics(BasicBlock *BB); bool calcFloatingPointHeuristics(BasicBlock *BB); bool calcInvokeHeuristics(BasicBlock *BB); }; } #endif