Andrew Scull | 5e1ddfa | 2018-08-14 10:06:54 +0100 | [diff] [blame^] | 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 |