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