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 BranchProbabilityInfo;
26 class Function;
27 class LoopInfo;
28 
29 /// Wraps a BFI to allow lazy computation of the block frequencies.
30 ///
31 /// A pass that only conditionally uses BFI can uncondtionally require the
32 /// analysis without paying for the overhead if BFI doesn't end up being used.
33 template <typename FunctionT, typename BranchProbabilityInfoPassT,
34           typename LoopInfoT, typename BlockFrequencyInfoT>
35 class LazyBlockFrequencyInfo {
36 public:
37   LazyBlockFrequencyInfo()
38       : Calculated(false), F(nullptr), BPIPass(nullptr), LI(nullptr) {}
39 
40   /// Set up the per-function input.
41   void setAnalysis(const FunctionT *F, BranchProbabilityInfoPassT *BPIPass,
42                    const LoopInfoT *LI) {
43     this->F = F;
44     this->BPIPass = BPIPass;
45     this->LI = LI;
46   }
47 
48   /// Retrieve the BFI with the block frequencies computed.
49   BlockFrequencyInfoT &getCalculated() {
50     if (!Calculated) {
51       assert(F && BPIPass && LI && "call setAnalysis");
52       BFI.calculate(
53           *F, BPIPassTrait<BranchProbabilityInfoPassT>::getBPI(BPIPass), *LI);
54       Calculated = true;
55     }
56     return BFI;
57   }
58 
59   const BlockFrequencyInfoT &getCalculated() const {
60     return const_cast<LazyBlockFrequencyInfo *>(this)->getCalculated();
61   }
62 
63   void releaseMemory() {
64     BFI.releaseMemory();
65     Calculated = false;
66     setAnalysis(nullptr, nullptr, nullptr);
67   }
68 
69 private:
70   BlockFrequencyInfoT BFI;
71   bool Calculated;
72   const FunctionT *F;
73   BranchProbabilityInfoPassT *BPIPass;
74   const LoopInfoT *LI;
75 };
76 
77 /// This is an alternative analysis pass to
78 /// BlockFrequencyInfoWrapperPass.  The difference is that with this pass the
79 /// block frequencies are not computed when the analysis pass is executed but
80 /// rather when the BFI result is explicitly requested by the analysis client.
81 ///
82 /// There are some additional requirements for any client pass that wants to use
83 /// the analysis:
84 ///
85 /// 1. The pass needs to initialize dependent passes with:
86 ///
87 ///   INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
88 ///
89 /// 2. Similarly, getAnalysisUsage should call:
90 ///
91 ///   LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
92 ///
93 /// 3. The computed BFI should be requested with
94 ///    getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
95 ///    or BPI could be invalidated for example by changing the CFG.
96 ///
97 /// Note that it is expected that we wouldn't need this functionality for the
98 /// new PM since with the new PM, analyses are executed on demand.
99 
100 class LazyBlockFrequencyInfoPass : public FunctionPass {
101 private:
102   LazyBlockFrequencyInfo<Function, LazyBranchProbabilityInfoPass, LoopInfo,
103                          BlockFrequencyInfo>
104       LBFI;
105 
106 public:
107   static char ID;
108 
109   LazyBlockFrequencyInfoPass();
110 
111   /// Compute and return the block frequencies.
112   BlockFrequencyInfo &getBFI() { return LBFI.getCalculated(); }
113 
114   /// Compute and return the block frequencies.
115   const BlockFrequencyInfo &getBFI() const { return LBFI.getCalculated(); }
116 
117   void getAnalysisUsage(AnalysisUsage &AU) const override;
118 
119   /// Helper for client passes to set up the analysis usage on behalf of this
120   /// pass.
121   static void getLazyBFIAnalysisUsage(AnalysisUsage &AU);
122 
123   bool runOnFunction(Function &F) override;
124   void releaseMemory() override;
125   void print(raw_ostream &OS, const Module *M) const override;
126 };
127 
128 /// Helper for client passes to initialize dependent passes for LBFI.
129 void initializeLazyBFIPassPass(PassRegistry &Registry);
130 }
131 #endif
132