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1a4d82fc | 1 | //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=// |
223e47cc LB |
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 | ||
223e47cc | 17 | #include "llvm/CodeGen/MachineBasicBlock.h" |
970d7e83 | 18 | #include "llvm/Pass.h" |
223e47cc LB |
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 | ||
1a4d82fc | 43 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
223e47cc LB |
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%. | |
1a4d82fc JJ |
63 | bool isEdgeHot(const MachineBasicBlock *Src, |
64 | const MachineBasicBlock *Dst) const; | |
223e47cc LB |
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. | |
1a4d82fc JJ |
76 | BranchProbability getEdgeProbability(const MachineBasicBlock *Src, |
77 | const MachineBasicBlock *Dst) const; | |
223e47cc LB |
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. | |
1a4d82fc JJ |
82 | raw_ostream &printEdgeProbability(raw_ostream &OS, |
83 | const MachineBasicBlock *Src, | |
84 | const MachineBasicBlock *Dst) const; | |
223e47cc LB |
85 | }; |
86 | ||
87 | } | |
88 | ||
89 | ||
90 | #endif |