1 2 //==- MachineBranchProbabilityInfo.h - Machine Branch Probability Analysis -==// 3 // 4 // The LLVM Compiler Infrastructure 5 // 6 // This file is distributed under the University of Illinois Open Source 7 // License. See LICENSE.TXT for details. 8 // 9 //===----------------------------------------------------------------------===// 10 // 11 // This pass is used to evaluate branch probabilties on machine basic blocks. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H 16 #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H 17 18 #include "llvm/CodeGen/MachineBasicBlock.h" 19 #include "llvm/Pass.h" 20 #include "llvm/Support/BranchProbability.h" 21 #include <climits> 22 23 namespace llvm { 24 25 class MachineBranchProbabilityInfo : public ImmutablePass { 26 virtual void anchor(); 27 28 // Default weight value. Used when we don't have information about the edge. 29 // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of 30 // the successors have a weight yet. But it doesn't make sense when providing 31 // weight to an edge that may have siblings with non-zero weights. This can 32 // be handled various ways, but it's probably fine for an edge with unknown 33 // weight to just "inherit" the non-zero weight of an adjacent successor. 34 static const uint32_t DEFAULT_WEIGHT = 16; 35 36 public: 37 static char ID; 38 39 MachineBranchProbabilityInfo() : ImmutablePass(ID) { 40 PassRegistry &Registry = *PassRegistry::getPassRegistry(); 41 initializeMachineBranchProbabilityInfoPass(Registry); 42 } 43 44 void getAnalysisUsage(AnalysisUsage &AU) const { 45 AU.setPreservesAll(); 46 } 47 48 // Return edge weight. If we don't have any informations about it - return 49 // DEFAULT_WEIGHT. 50 uint32_t getEdgeWeight(const MachineBasicBlock *Src, 51 const MachineBasicBlock *Dst) const; 52 53 // Same thing, but using a const_succ_iterator from Src. This is faster when 54 // the iterator is already available. 55 uint32_t getEdgeWeight(const MachineBasicBlock *Src, 56 MachineBasicBlock::const_succ_iterator Dst) const; 57 58 // Get sum of the block successors' weights, potentially scaling them to fit 59 // within 32-bits. If scaling is required, sets Scale based on the necessary 60 // adjustment. Any edge weights used with the sum should be divided by Scale. 61 uint32_t getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const; 62 63 // A 'Hot' edge is an edge which probability is >= 80%. 64 bool isEdgeHot(MachineBasicBlock *Src, 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(MachineBasicBlock *Src, 77 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, MachineBasicBlock *Src, 83 MachineBasicBlock *Dst) const; 84 }; 85 86 } 87 88 89 #endif 90
