1 //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass is used to evaluate branch probabilties on machine basic blocks. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H 15 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H 16 17 #include "llvm/CodeGen/MachineBasicBlock.h" 18 #include "llvm/Pass.h" 19 #include "llvm/Support/BranchProbability.h" 20 #include <climits> 21 22 namespace llvm { 23 24 class MachineBranchProbabilityInfo : public ImmutablePass { 25 virtual void anchor(); 26 27 // Default weight value. Used when we don't have information about the edge. 28 // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of 29 // the successors have a weight yet. But it doesn't make sense when providing 30 // weight to an edge that may have siblings with non-zero weights. This can 31 // be handled various ways, but it's probably fine for an edge with unknown 32 // weight to just "inherit" the non-zero weight of an adjacent successor. 33 static const uint32_t DEFAULT_WEIGHT = 16; 34 35 public: 36 static char ID; 37 38 MachineBranchProbabilityInfo() : ImmutablePass(ID) { 39 PassRegistry &Registry = *PassRegistry::getPassRegistry(); 40 initializeMachineBranchProbabilityInfoPass(Registry); 41 } 42 43 void getAnalysisUsage(AnalysisUsage &AU) const override { 44 AU.setPreservesAll(); 45 } 46 47 // Return edge weight. If we don't have any informations about it - return 48 // DEFAULT_WEIGHT. 49 uint32_t getEdgeWeight(const MachineBasicBlock *Src, 50 const MachineBasicBlock *Dst) const; 51 52 // Same thing, but using a const_succ_iterator from Src. This is faster when 53 // the iterator is already available. 54 uint32_t getEdgeWeight(const MachineBasicBlock *Src, 55 MachineBasicBlock::const_succ_iterator Dst) const; 56 57 // Get sum of the block successors' weights, potentially scaling them to fit 58 // within 32-bits. If scaling is required, sets Scale based on the necessary 59 // adjustment. Any edge weights used with the sum should be divided by Scale. 60 uint32_t getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const; 61 62 // A 'Hot' edge is an edge which probability is >= 80%. 63 bool isEdgeHot(const MachineBasicBlock *Src, 64 const MachineBasicBlock *Dst) const; 65 66 // Return a hot successor for the block BB or null if there isn't one. 67 // NB: This routine's complexity is linear on the number of successors. 68 MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const; 69 70 // Return a probability as a fraction between 0 (0% probability) and 71 // 1 (100% probability), however the value is never equal to 0, and can be 1 72 // only iff SRC block has only one successor. 73 // NB: This routine's complexity is linear on the number of successors of 74 // Src. Querying sequentially for each successor's probability is a quadratic 75 // query pattern. 76 BranchProbability getEdgeProbability(const MachineBasicBlock *Src, 77 const MachineBasicBlock *Dst) const; 78 79 // Print value between 0 (0% probability) and 1 (100% probability), 80 // however the value is never equal to 0, and can be 1 only iff SRC block 81 // has only one successor. 82 raw_ostream &printEdgeProbability(raw_ostream &OS, 83 const MachineBasicBlock *Src, 84 const MachineBasicBlock *Dst) const; 85 }; 86 87 } 88 89 90 #endif 91
