android / platform / prebuilts / clang / darwin-x86 / sdk / 3.5 / 031fad734623c88aa9e66c36bc426c09bff4e7e8 / . / include / llvm / Analysis / BranchProbabilityInfo.h

//===--- 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/IR/CFG.h" | |

#include "llvm/InitializePasses.h" | |

#include "llvm/Pass.h" | |

#include "llvm/Support/BranchProbability.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 override; | |

bool runOnFunction(Function &F) override; | |

void print(raw_ostream &OS, const Module *M = nullptr) const override; | |

/// \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 |