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| 14 | pmbaty | 1 | //===- LazyBranchProbabilityInfo.h - Lazy Branch Probability ----*- C++ -*-===// |
| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This is an alternative analysis pass to BranchProbabilityInfoWrapperPass. |
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| 10 | // The difference is that with this pass the branch probabilities are not |
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| 11 | // computed when the analysis pass is executed but rather when the BPI results |
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| 12 | // is explicitly requested by the analysis client. |
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| 13 | // |
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| 14 | //===----------------------------------------------------------------------===// |
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| 15 | |||
| 16 | #ifndef LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
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| 17 | #define LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
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| 18 | |||
| 19 | #include "llvm/Analysis/BranchProbabilityInfo.h" |
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| 20 | #include "llvm/Pass.h" |
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| 21 | |||
| 22 | namespace llvm { |
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| 23 | class AnalysisUsage; |
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| 24 | class Function; |
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| 25 | class LoopInfo; |
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| 26 | class TargetLibraryInfo; |
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| 27 | |||
| 28 | /// This is an alternative analysis pass to |
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| 29 | /// BranchProbabilityInfoWrapperPass. The difference is that with this pass the |
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| 30 | /// branch probabilities are not computed when the analysis pass is executed but |
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| 31 | /// rather when the BPI results is explicitly requested by the analysis client. |
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| 32 | /// |
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| 33 | /// There are some additional requirements for any client pass that wants to use |
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| 34 | /// the analysis: |
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| 35 | /// |
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| 36 | /// 1. The pass needs to initialize dependent passes with: |
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| 37 | /// |
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| 38 | /// INITIALIZE_PASS_DEPENDENCY(LazyBPIPass) |
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| 39 | /// |
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| 40 | /// 2. Similarly, getAnalysisUsage should call: |
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| 41 | /// |
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| 42 | /// LazyBranchProbabilityInfoPass::getLazyBPIAnalysisUsage(AU) |
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| 43 | /// |
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| 44 | /// 3. The computed BPI should be requested with |
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| 45 | /// getAnalysis<LazyBranchProbabilityInfoPass>().getBPI() before LoopInfo |
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| 46 | /// could be invalidated for example by changing the CFG. |
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| 47 | /// |
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| 48 | /// Note that it is expected that we wouldn't need this functionality for the |
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| 49 | /// new PM since with the new PM, analyses are executed on demand. |
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| 50 | class LazyBranchProbabilityInfoPass : public FunctionPass { |
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| 51 | |||
| 52 | /// Wraps a BPI to allow lazy computation of the branch probabilities. |
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| 53 | /// |
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| 54 | /// A pass that only conditionally uses BPI can uncondtionally require the |
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| 55 | /// analysis without paying for the overhead if BPI doesn't end up being used. |
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| 56 | class LazyBranchProbabilityInfo { |
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| 57 | public: |
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| 58 | LazyBranchProbabilityInfo(const Function *F, const LoopInfo *LI, |
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| 59 | const TargetLibraryInfo *TLI) |
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| 60 | : F(F), LI(LI), TLI(TLI) {} |
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| 61 | |||
| 62 | /// Retrieve the BPI with the branch probabilities computed. |
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| 63 | BranchProbabilityInfo &getCalculated() { |
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| 64 | if (!Calculated) { |
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| 65 | assert(F && LI && "call setAnalysis"); |
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| 66 | BPI.calculate(*F, *LI, TLI, nullptr, nullptr); |
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| 67 | Calculated = true; |
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| 68 | } |
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| 69 | return BPI; |
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| 70 | } |
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| 71 | |||
| 72 | const BranchProbabilityInfo &getCalculated() const { |
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| 73 | return const_cast<LazyBranchProbabilityInfo *>(this)->getCalculated(); |
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| 74 | } |
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| 75 | |||
| 76 | private: |
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| 77 | BranchProbabilityInfo BPI; |
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| 78 | bool Calculated = false; |
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| 79 | const Function *F; |
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| 80 | const LoopInfo *LI; |
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| 81 | const TargetLibraryInfo *TLI; |
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| 82 | }; |
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| 83 | |||
| 84 | std::unique_ptr<LazyBranchProbabilityInfo> LBPI; |
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| 85 | |||
| 86 | public: |
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| 87 | static char ID; |
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| 88 | |||
| 89 | LazyBranchProbabilityInfoPass(); |
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| 90 | |||
| 91 | /// Compute and return the branch probabilities. |
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| 92 | BranchProbabilityInfo &getBPI() { return LBPI->getCalculated(); } |
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| 93 | |||
| 94 | /// Compute and return the branch probabilities. |
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| 95 | const BranchProbabilityInfo &getBPI() const { return LBPI->getCalculated(); } |
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| 96 | |||
| 97 | void getAnalysisUsage(AnalysisUsage &AU) const override; |
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| 98 | |||
| 99 | /// Helper for client passes to set up the analysis usage on behalf of this |
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| 100 | /// pass. |
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| 101 | static void getLazyBPIAnalysisUsage(AnalysisUsage &AU); |
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| 102 | |||
| 103 | bool runOnFunction(Function &F) override; |
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| 104 | void releaseMemory() override; |
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| 105 | void print(raw_ostream &OS, const Module *M) const override; |
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| 106 | }; |
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| 107 | |||
| 108 | /// Helper for client passes to initialize dependent passes for LBPI. |
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| 109 | void initializeLazyBPIPassPass(PassRegistry &Registry); |
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| 110 | |||
| 111 | /// Simple trait class that provides a mapping between BPI passes and the |
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| 112 | /// corresponding BPInfo. |
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| 113 | template <typename PassT> struct BPIPassTrait { |
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| 114 | static PassT &getBPI(PassT *P) { return *P; } |
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| 115 | }; |
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| 116 | |||
| 117 | template <> struct BPIPassTrait<LazyBranchProbabilityInfoPass> { |
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| 118 | static BranchProbabilityInfo &getBPI(LazyBranchProbabilityInfoPass *P) { |
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| 119 | return P->getBPI(); |
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| 120 | } |
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| 121 | }; |
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| 122 | } |
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| 123 | #endif |