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      1 //===- 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 
     24 namespace llvm {
     25 class AnalysisUsage;
     26 class BranchProbabilityInfo;
     27 class Function;
     28 class 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.
     34 template <typename FunctionT, typename BranchProbabilityInfoPassT,
     35           typename LoopInfoT, typename BlockFrequencyInfoT>
     36 class LazyBlockFrequencyInfo {
     37 public:
     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 
     70 private:
     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 
    101 class LazyBlockFrequencyInfoPass : public FunctionPass {
    102 private:
    103   LazyBlockFrequencyInfo<Function, LazyBranchProbabilityInfoPass, LoopInfo,
    104                          BlockFrequencyInfo>
    105       LBFI;
    106 
    107 public:
    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.
    130 void initializeLazyBFIPassPass(PassRegistry &Registry);
    131 }
    132 #endif
    133