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
22namespace llvm {
23class AnalysisUsage;
24class Function;
25class LoopInfo;
26class 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.
50class 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        : Calculated(false), 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, *LI, TLI, nullptr, 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;
79    const Function *F;
80    const LoopInfo *LI;
81    const TargetLibraryInfo *TLI;
82  };
83
84  std::unique_ptr<LazyBranchProbabilityInfo> LBPI;
85
86public:
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.
109void initializeLazyBPIPassPass(PassRegistry &Registry);
110
111/// Simple trait class that provides a mapping between BPI passes and the
112/// corresponding BPInfo.
113template <typename PassT> struct BPIPassTrait {
114  static PassT &getBPI(PassT *P) { return *P; }
115};
116
117template <> struct BPIPassTrait<LazyBranchProbabilityInfoPass> {
118  static BranchProbabilityInfo &getBPI(LazyBranchProbabilityInfoPass *P) {
119    return P->getBPI();
120  }
121};
122}
123#endif
124