1 | //=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | // |
9 | // This pass is used to evaluate branch probabilties on machine basic blocks. |
10 | // |
11 | //===----------------------------------------------------------------------===// |
12 | |
13 | #ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H |
14 | #define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H |
15 | |
16 | #include "llvm/CodeGen/MachineBasicBlock.h" |
17 | #include "llvm/Pass.h" |
18 | #include "llvm/Support/BranchProbability.h" |
19 | |
20 | namespace llvm { |
21 | |
22 | class MachineBranchProbabilityInfo : public ImmutablePass { |
23 | virtual void anchor(); |
24 | |
25 | // Default weight value. Used when we don't have information about the edge. |
26 | // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of |
27 | // the successors have a weight yet. But it doesn't make sense when providing |
28 | // weight to an edge that may have siblings with non-zero weights. This can |
29 | // be handled various ways, but it's probably fine for an edge with unknown |
30 | // weight to just "inherit" the non-zero weight of an adjacent successor. |
31 | static const uint32_t DEFAULT_WEIGHT = 16; |
32 | |
33 | public: |
34 | static char ID; |
35 | |
36 | MachineBranchProbabilityInfo(); |
37 | |
38 | void getAnalysisUsage(AnalysisUsage &AU) const override { |
39 | AU.setPreservesAll(); |
40 | } |
41 | |
42 | // Return edge probability. |
43 | BranchProbability getEdgeProbability(const MachineBasicBlock *Src, |
44 | const MachineBasicBlock *Dst) const; |
45 | |
46 | // Same as above, but using a const_succ_iterator from Src. This is faster |
47 | // when the iterator is already available. |
48 | BranchProbability |
49 | getEdgeProbability(const MachineBasicBlock *Src, |
50 | MachineBasicBlock::const_succ_iterator Dst) const; |
51 | |
52 | // A 'Hot' edge is an edge which probability is >= 80%. |
53 | bool isEdgeHot(const MachineBasicBlock *Src, |
54 | const MachineBasicBlock *Dst) const; |
55 | |
56 | // Print value between 0 (0% probability) and 1 (100% probability), |
57 | // however the value is never equal to 0, and can be 1 only iff SRC block |
58 | // has only one successor. |
59 | raw_ostream &printEdgeProbability(raw_ostream &OS, |
60 | const MachineBasicBlock *Src, |
61 | const MachineBasicBlock *Dst) const; |
62 | }; |
63 | |
64 | } |
65 | |
66 | |
67 | #endif |
68 | |