1 //===- LazyBlockFrequencyInfo.h - Lazy Block Frequency 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 is an alternative analysis pass to BlockFrequencyInfoWrapperPass.  The
10 // difference is that with this pass the block frequencies are not computed when
11 // the analysis pass is executed but rather when the BFI result is explicitly
12 // requested by the analysis client.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
17 #define LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
18 
19 #include "llvm/Analysis/BlockFrequencyInfo.h"
20 #include "llvm/Analysis/LazyBranchProbabilityInfo.h"
21 #include "llvm/Pass.h"
22 
23 namespace llvm {
24 class AnalysisUsage;
25 class Function;
26 class LoopInfo;
27 
28 /// Wraps a BFI to allow lazy computation of the block frequencies.
29 ///
30 /// A pass that only conditionally uses BFI can uncondtionally require the
31 /// analysis without paying for the overhead if BFI doesn't end up being used.
32 template <typename FunctionT, typename BranchProbabilityInfoPassT,
33           typename LoopInfoT, typename BlockFrequencyInfoT>
34 class LazyBlockFrequencyInfo {
35 public:
36   LazyBlockFrequencyInfo() = default;
37 
38   /// Set up the per-function input.
39   void setAnalysis(const FunctionT *F, BranchProbabilityInfoPassT *BPIPass,
40                    const LoopInfoT *LI) {
41     this->F = F;
42     this->BPIPass = BPIPass;
43     this->LI = LI;
44   }
45 
46   /// Retrieve the BFI with the block frequencies computed.
47   BlockFrequencyInfoT &getCalculated() {
48     if (!Calculated) {
49       assert(F && BPIPass && LI && "call setAnalysis");
50       BFI.calculate(
51           *F, BPIPassTrait<BranchProbabilityInfoPassT>::getBPI(BPIPass), *LI);
52       Calculated = true;
53     }
54     return BFI;
55   }
56 
57   const BlockFrequencyInfoT &getCalculated() const {
58     return const_cast<LazyBlockFrequencyInfo *>(this)->getCalculated();
59   }
60 
61   void releaseMemory() {
62     BFI.releaseMemory();
63     Calculated = false;
64     setAnalysis(nullptr, nullptr, nullptr);
65   }
66 
67 private:
68   BlockFrequencyInfoT BFI;
69   bool Calculated = false;
70   const FunctionT *F = nullptr;
71   BranchProbabilityInfoPassT *BPIPass = nullptr;
72   const LoopInfoT *LI = nullptr;
73 };
74 
75 /// This is an alternative analysis pass to
76 /// BlockFrequencyInfoWrapperPass.  The difference is that with this pass the
77 /// block frequencies are not computed when the analysis pass is executed but
78 /// rather when the BFI result is explicitly requested by the analysis client.
79 ///
80 /// There are some additional requirements for any client pass that wants to use
81 /// the analysis:
82 ///
83 /// 1. The pass needs to initialize dependent passes with:
84 ///
85 ///   INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
86 ///
87 /// 2. Similarly, getAnalysisUsage should call:
88 ///
89 ///   LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
90 ///
91 /// 3. The computed BFI should be requested with
92 ///    getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
93 ///    or BPI could be invalidated for example by changing the CFG.
94 ///
95 /// Note that it is expected that we wouldn't need this functionality for the
96 /// new PM since with the new PM, analyses are executed on demand.
97 
98 class LazyBlockFrequencyInfoPass : public FunctionPass {
99 private:
100   LazyBlockFrequencyInfo<Function, LazyBranchProbabilityInfoPass, LoopInfo,
101                          BlockFrequencyInfo>
102       LBFI;
103 
104 public:
105   static char ID;
106 
107   LazyBlockFrequencyInfoPass();
108 
109   /// Compute and return the block frequencies.
110   BlockFrequencyInfo &getBFI() { return LBFI.getCalculated(); }
111 
112   /// Compute and return the block frequencies.
113   const BlockFrequencyInfo &getBFI() const { return LBFI.getCalculated(); }
114 
115   void getAnalysisUsage(AnalysisUsage &AU) const override;
116 
117   /// Helper for client passes to set up the analysis usage on behalf of this
118   /// pass.
119   static void getLazyBFIAnalysisUsage(AnalysisUsage &AU);
120 
121   bool runOnFunction(Function &F) override;
122   void releaseMemory() override;
123   void print(raw_ostream &OS, const Module *M) const override;
124 };
125 
126 /// Helper for client passes to initialize dependent passes for LBFI.
127 void initializeLazyBFIPassPass(PassRegistry &Registry);
128 }
129 #endif
130