1 | //===- LazyBranchProbabilityInfo.h - Lazy Branch Probability ----*- 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 is an alternative analysis pass to BranchProbabilityInfoWrapperPass. |
10 | // The difference is that with this pass the branch probabilities are not |
11 | // computed when the analysis pass is executed but rather when the BPI results |
12 | // is explicitly requested by the analysis client. |
13 | // |
14 | //===----------------------------------------------------------------------===// |
15 | |
16 | #ifndef LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
17 | #define LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
18 | |
19 | #include "llvm/Analysis/BranchProbabilityInfo.h" |
20 | #include "llvm/Pass.h" |
21 | |
22 | namespace llvm { |
23 | class AnalysisUsage; |
24 | class Function; |
25 | class LoopInfo; |
26 | class TargetLibraryInfo; |
27 | |
28 | /// This is an alternative analysis pass to |
29 | /// BranchProbabilityInfoWrapperPass. The difference is that with this pass the |
30 | /// branch probabilities are not computed when the analysis pass is executed but |
31 | /// rather when the BPI results is explicitly requested by the analysis client. |
32 | /// |
33 | /// There are some additional requirements for any client pass that wants to use |
34 | /// the analysis: |
35 | /// |
36 | /// 1. The pass needs to initialize dependent passes with: |
37 | /// |
38 | /// INITIALIZE_PASS_DEPENDENCY(LazyBPIPass) |
39 | /// |
40 | /// 2. Similarly, getAnalysisUsage should call: |
41 | /// |
42 | /// LazyBranchProbabilityInfoPass::getLazyBPIAnalysisUsage(AU) |
43 | /// |
44 | /// 3. The computed BPI should be requested with |
45 | /// getAnalysis<LazyBranchProbabilityInfoPass>().getBPI() before LoopInfo |
46 | /// could be invalidated for example by changing the CFG. |
47 | /// |
48 | /// Note that it is expected that we wouldn't need this functionality for the |
49 | /// new PM since with the new PM, analyses are executed on demand. |
50 | class LazyBranchProbabilityInfoPass : public FunctionPass { |
51 | |
52 | /// Wraps a BPI to allow lazy computation of the branch probabilities. |
53 | /// |
54 | /// A pass that only conditionally uses BPI can uncondtionally require the |
55 | /// analysis without paying for the overhead if BPI doesn't end up being used. |
56 | class LazyBranchProbabilityInfo { |
57 | public: |
58 | LazyBranchProbabilityInfo(const Function *F, const LoopInfo *LI, |
59 | const TargetLibraryInfo *TLI) |
60 | : F(F), LI(LI), TLI(TLI) {} |
61 | |
62 | /// Retrieve the BPI with the branch probabilities computed. |
63 | BranchProbabilityInfo &getCalculated() { |
64 | if (!Calculated) { |
65 | assert(F && LI && "call setAnalysis" ); |
66 | BPI.calculate(F: *F, LI: *LI, TLI, DT: nullptr, PDT: nullptr); |
67 | Calculated = true; |
68 | } |
69 | return BPI; |
70 | } |
71 | |
72 | const BranchProbabilityInfo &getCalculated() const { |
73 | return const_cast<LazyBranchProbabilityInfo *>(this)->getCalculated(); |
74 | } |
75 | |
76 | private: |
77 | BranchProbabilityInfo BPI; |
78 | bool Calculated = false; |
79 | const Function *F; |
80 | const LoopInfo *LI; |
81 | const TargetLibraryInfo *TLI; |
82 | }; |
83 | |
84 | std::unique_ptr<LazyBranchProbabilityInfo> LBPI; |
85 | |
86 | public: |
87 | static char ID; |
88 | |
89 | LazyBranchProbabilityInfoPass(); |
90 | |
91 | /// Compute and return the branch probabilities. |
92 | BranchProbabilityInfo &getBPI() { return LBPI->getCalculated(); } |
93 | |
94 | /// Compute and return the branch probabilities. |
95 | const BranchProbabilityInfo &getBPI() const { return LBPI->getCalculated(); } |
96 | |
97 | void getAnalysisUsage(AnalysisUsage &AU) const override; |
98 | |
99 | /// Helper for client passes to set up the analysis usage on behalf of this |
100 | /// pass. |
101 | static void getLazyBPIAnalysisUsage(AnalysisUsage &AU); |
102 | |
103 | bool runOnFunction(Function &F) override; |
104 | void releaseMemory() override; |
105 | void print(raw_ostream &OS, const Module *M) const override; |
106 | }; |
107 | |
108 | /// Helper for client passes to initialize dependent passes for LBPI. |
109 | void initializeLazyBPIPassPass(PassRegistry &Registry); |
110 | |
111 | /// Simple trait class that provides a mapping between BPI passes and the |
112 | /// corresponding BPInfo. |
113 | template <typename PassT> struct BPIPassTrait { |
114 | static PassT &getBPI(PassT *P) { return *P; } |
115 | }; |
116 | |
117 | template <> struct BPIPassTrait<LazyBranchProbabilityInfoPass> { |
118 | static BranchProbabilityInfo &getBPI(LazyBranchProbabilityInfoPass *P) { |
119 | return P->getBPI(); |
120 | } |
121 | }; |
122 | } |
123 | #endif |
124 | |