include/llvm/Analysis/LazyBlockFrequencyInfo.h

   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