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/Pass.h" 19 #include "llvm/Support/BranchProbability.h" 20 #include <climits> 21 22 namespace llvm { 23 24 class raw_ostream; 25 class MachineBasicBlock; 26 27 class MachineBranchProbabilityInfo : public ImmutablePass { 28 29 // Default weight value. Used when we don't have information about the edge. 30 // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of 31 // the successors have a weight yet. But it doesn't make sense when providing 32 // weight to an edge that may have siblings with non-zero weights. This can 33 // be handled various ways, but it's probably fine for an edge with unknown 34 // weight to just "inherit" the non-zero weight of an adjacent successor. 35 static const uint32_t DEFAULT_WEIGHT = 16; 36 37 // Get sum of the block successors' weights. 38 uint32_t getSumForBlock(MachineBasicBlock *MBB) const; 39 40 public: 41 static char ID; 42 43 MachineBranchProbabilityInfo() : ImmutablePass(ID) { 44 PassRegistry &Registry = *PassRegistry::getPassRegistry(); 45 initializeMachineBranchProbabilityInfoPass(Registry); 46 } 47 48 void getAnalysisUsage(AnalysisUsage &AU) const { 49 AU.setPreservesAll(); 50 } 51 52 // Return edge weight. If we don't have any informations about it - return 53 // DEFAULT_WEIGHT. 54 uint32_t getEdgeWeight(MachineBasicBlock *Src, MachineBasicBlock *Dst) const; 55 56 // A 'Hot' edge is an edge which probability is >= 80%. 57 bool isEdgeHot(MachineBasicBlock *Src, MachineBasicBlock *Dst) const; 58 59 // Return a hot successor for the block BB or null if there isn't one. 60 MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const; 61 62 // Return a probability as a fraction between 0 (0% probability) and 63 // 1 (100% probability), however the value is never equal to 0, and can be 1 64 // only iff SRC block has only one successor. 65 BranchProbability getEdgeProbability(MachineBasicBlock *Src, 66 MachineBasicBlock *Dst) const; 67 68 // Print value between 0 (0% probability) and 1 (100% probability), 69 // however the value is never equal to 0, and can be 1 only iff SRC block 70 // has only one successor. 71 raw_ostream &printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src, 72 MachineBasicBlock *Dst) const; 73 }; 74 75 } 76 77 78 #endif 79
