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 #include <numeric> 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 override { 45 AU.setPreservesAll(); 46 } 47 48 // Return edge probability. 49 BranchProbability getEdgeProbability(const MachineBasicBlock *Src, 50 const MachineBasicBlock *Dst) const; 51 52 // Same as above, but using a const_succ_iterator from Src. This is faster 53 // when the iterator is already available. 54 BranchProbability 55 getEdgeProbability(const MachineBasicBlock *Src, 56 MachineBasicBlock::const_succ_iterator Dst) const; 57 58 // A 'Hot' edge is an edge which probability is >= 80%. 59 bool isEdgeHot(const MachineBasicBlock *Src, 60 const MachineBasicBlock *Dst) const; 61 62 // Return a hot successor for the block BB or null if there isn't one. 63 // NB: This routine's complexity is linear on the number of successors. 64 MachineBasicBlock *getHotSucc(MachineBasicBlock *MBB) const; 65 66 // Print value between 0 (0% probability) and 1 (100% probability), 67 // however the value is never equal to 0, and can be 1 only iff SRC block 68 // has only one successor. 69 raw_ostream &printEdgeProbability(raw_ostream &OS, 70 const MachineBasicBlock *Src, 71 const MachineBasicBlock *Dst) const; 72 }; 73 74 } 75 76 77 #endif 78
