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Andrew Scull5e1ddfa2018-08-14 10:06:54 +01001//===- LazyBlockFrequencyInfo.h - Lazy Block Frequency Analysis -*- C++ -*-===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This is an alternative analysis pass to BlockFrequencyInfoWrapperPass. The
11// difference is that with this pass the block frequencies are not computed when
12// the analysis pass is executed but rather when the BFI result is explicitly
13// requested by the analysis client.
14//
15//===----------------------------------------------------------------------===//
16
17#ifndef LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
18#define LLVM_ANALYSIS_LAZYBLOCKFREQUENCYINFO_H
19
20#include "llvm/Analysis/BlockFrequencyInfo.h"
21#include "llvm/Analysis/LazyBranchProbabilityInfo.h"
22#include "llvm/Pass.h"
23
24namespace llvm {
25class AnalysisUsage;
26class BranchProbabilityInfo;
27class Function;
28class LoopInfo;
29
30/// Wraps a BFI to allow lazy computation of the block frequencies.
31///
32/// A pass that only conditionally uses BFI can uncondtionally require the
33/// analysis without paying for the overhead if BFI doesn't end up being used.
34template <typename FunctionT, typename BranchProbabilityInfoPassT,
35 typename LoopInfoT, typename BlockFrequencyInfoT>
36class LazyBlockFrequencyInfo {
37public:
38 LazyBlockFrequencyInfo()
39 : Calculated(false), F(nullptr), BPIPass(nullptr), LI(nullptr) {}
40
41 /// Set up the per-function input.
42 void setAnalysis(const FunctionT *F, BranchProbabilityInfoPassT *BPIPass,
43 const LoopInfoT *LI) {
44 this->F = F;
45 this->BPIPass = BPIPass;
46 this->LI = LI;
47 }
48
49 /// Retrieve the BFI with the block frequencies computed.
50 BlockFrequencyInfoT &getCalculated() {
51 if (!Calculated) {
52 assert(F && BPIPass && LI && "call setAnalysis");
53 BFI.calculate(
54 *F, BPIPassTrait<BranchProbabilityInfoPassT>::getBPI(BPIPass), *LI);
55 Calculated = true;
56 }
57 return BFI;
58 }
59
60 const BlockFrequencyInfoT &getCalculated() const {
61 return const_cast<LazyBlockFrequencyInfo *>(this)->getCalculated();
62 }
63
64 void releaseMemory() {
65 BFI.releaseMemory();
66 Calculated = false;
67 setAnalysis(nullptr, nullptr, nullptr);
68 }
69
70private:
71 BlockFrequencyInfoT BFI;
72 bool Calculated;
73 const FunctionT *F;
74 BranchProbabilityInfoPassT *BPIPass;
75 const LoopInfoT *LI;
76};
77
78/// \brief This is an alternative analysis pass to
79/// BlockFrequencyInfoWrapperPass. The difference is that with this pass the
80/// block frequencies are not computed when the analysis pass is executed but
81/// rather when the BFI result is explicitly requested by the analysis client.
82///
83/// There are some additional requirements for any client pass that wants to use
84/// the analysis:
85///
86/// 1. The pass needs to initialize dependent passes with:
87///
88/// INITIALIZE_PASS_DEPENDENCY(LazyBFIPass)
89///
90/// 2. Similarly, getAnalysisUsage should call:
91///
92/// LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU)
93///
94/// 3. The computed BFI should be requested with
95/// getAnalysis<LazyBlockFrequencyInfoPass>().getBFI() before either LoopInfo
96/// or BPI could be invalidated for example by changing the CFG.
97///
98/// Note that it is expected that we wouldn't need this functionality for the
99/// new PM since with the new PM, analyses are executed on demand.
100
101class LazyBlockFrequencyInfoPass : public FunctionPass {
102private:
103 LazyBlockFrequencyInfo<Function, LazyBranchProbabilityInfoPass, LoopInfo,
104 BlockFrequencyInfo>
105 LBFI;
106
107public:
108 static char ID;
109
110 LazyBlockFrequencyInfoPass();
111
112 /// \brief Compute and return the block frequencies.
113 BlockFrequencyInfo &getBFI() { return LBFI.getCalculated(); }
114
115 /// \brief Compute and return the block frequencies.
116 const BlockFrequencyInfo &getBFI() const { return LBFI.getCalculated(); }
117
118 void getAnalysisUsage(AnalysisUsage &AU) const override;
119
120 /// Helper for client passes to set up the analysis usage on behalf of this
121 /// pass.
122 static void getLazyBFIAnalysisUsage(AnalysisUsage &AU);
123
124 bool runOnFunction(Function &F) override;
125 void releaseMemory() override;
126 void print(raw_ostream &OS, const Module *M) const override;
127};
128
129/// \brief Helper for client passes to initialize dependent passes for LBFI.
130void initializeLazyBFIPassPass(PassRegistry &Registry);
131}
132#endif