LCOV - code coverage report
Current view: top level - include/llvm/Analysis - BranchProbabilityInfo.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 26 26 100.0 %
Date: 2017-09-14 15:23:50 Functions: 8 9 88.9 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- BranchProbabilityInfo.h - Branch Probability 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 pass is used to evaluate branch probabilties.
      11             : //
      12             : //===----------------------------------------------------------------------===//
      13             : 
      14             : #ifndef LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
      15             : #define LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H
      16             : 
      17             : #include "llvm/ADT/DenseMap.h"
      18             : #include "llvm/ADT/DenseMapInfo.h"
      19             : #include "llvm/ADT/DenseSet.h"
      20             : #include "llvm/ADT/SmallPtrSet.h"
      21             : #include "llvm/IR/BasicBlock.h"
      22             : #include "llvm/IR/CFG.h"
      23             : #include "llvm/IR/PassManager.h"
      24             : #include "llvm/IR/ValueHandle.h"
      25             : #include "llvm/Pass.h"
      26             : #include "llvm/Support/BranchProbability.h"
      27             : #include "llvm/Support/Casting.h"
      28             : #include <algorithm>
      29             : #include <cassert>
      30             : #include <cstdint>
      31             : #include <utility>
      32             : 
      33             : namespace llvm {
      34             : 
      35             : class Function;
      36             : class LoopInfo;
      37             : class raw_ostream;
      38             : class TargetLibraryInfo;
      39             : class Value;
      40             : 
      41             : /// \brief Analysis providing branch probability information.
      42             : ///
      43             : /// This is a function analysis which provides information on the relative
      44             : /// probabilities of each "edge" in the function's CFG where such an edge is
      45             : /// defined by a pair (PredBlock and an index in the successors). The
      46             : /// probability of an edge from one block is always relative to the
      47             : /// probabilities of other edges from the block. The probabilites of all edges
      48             : /// from a block sum to exactly one (100%).
      49             : /// We use a pair (PredBlock and an index in the successors) to uniquely
      50             : /// identify an edge, since we can have multiple edges from Src to Dst.
      51             : /// As an example, we can have a switch which jumps to Dst with value 0 and
      52             : /// value 10.
      53     2033150 : class BranchProbabilityInfo {
      54             : public:
      55     2025565 :   BranchProbabilityInfo() = default;
      56             : 
      57         165 :   BranchProbabilityInfo(const Function &F, const LoopInfo &LI,
      58         825 :                         const TargetLibraryInfo *TLI = nullptr) {
      59         165 :     calculate(F, LI, TLI);
      60         165 :   }
      61             : 
      62        1598 :   BranchProbabilityInfo(BranchProbabilityInfo &&Arg)
      63        4794 :       : Probs(std::move(Arg.Probs)), LastF(Arg.LastF),
      64        1598 :         PostDominatedByUnreachable(std::move(Arg.PostDominatedByUnreachable)),
      65        9588 :         PostDominatedByColdCall(std::move(Arg.PostDominatedByColdCall)) {}
      66             : 
      67             :   BranchProbabilityInfo(const BranchProbabilityInfo &) = delete;
      68             :   BranchProbabilityInfo &operator=(const BranchProbabilityInfo &) = delete;
      69             : 
      70             :   BranchProbabilityInfo &operator=(BranchProbabilityInfo &&RHS) {
      71             :     releaseMemory();
      72             :     Probs = std::move(RHS.Probs);
      73             :     PostDominatedByColdCall = std::move(RHS.PostDominatedByColdCall);
      74             :     PostDominatedByUnreachable = std::move(RHS.PostDominatedByUnreachable);
      75             :     return *this;
      76             :   }
      77             : 
      78             :   void releaseMemory();
      79             : 
      80             :   void print(raw_ostream &OS) const;
      81             : 
      82             :   /// \brief Get an edge's probability, relative to other out-edges of the Src.
      83             :   ///
      84             :   /// This routine provides access to the fractional probability between zero
      85             :   /// (0%) and one (100%) of this edge executing, relative to other edges
      86             :   /// leaving the 'Src' block. The returned probability is never zero, and can
      87             :   /// only be one if the source block has only one successor.
      88             :   BranchProbability getEdgeProbability(const BasicBlock *Src,
      89             :                                        unsigned IndexInSuccessors) const;
      90             : 
      91             :   /// \brief Get the probability of going from Src to Dst.
      92             :   ///
      93             :   /// It returns the sum of all probabilities for edges from Src to Dst.
      94             :   BranchProbability getEdgeProbability(const BasicBlock *Src,
      95             :                                        const BasicBlock *Dst) const;
      96             : 
      97             :   BranchProbability getEdgeProbability(const BasicBlock *Src,
      98             :                                        succ_const_iterator Dst) const;
      99             : 
     100             :   /// \brief Test if an edge is hot relative to other out-edges of the Src.
     101             :   ///
     102             :   /// Check whether this edge out of the source block is 'hot'. We define hot
     103             :   /// as having a relative probability >= 80%.
     104             :   bool isEdgeHot(const BasicBlock *Src, const BasicBlock *Dst) const;
     105             : 
     106             :   /// \brief Retrieve the hot successor of a block if one exists.
     107             :   ///
     108             :   /// Given a basic block, look through its successors and if one exists for
     109             :   /// which \see isEdgeHot would return true, return that successor block.
     110             :   const BasicBlock *getHotSucc(const BasicBlock *BB) const;
     111             : 
     112             :   /// \brief Print an edge's probability.
     113             :   ///
     114             :   /// Retrieves an edge's probability similarly to \see getEdgeProbability, but
     115             :   /// then prints that probability to the provided stream. That stream is then
     116             :   /// returned.
     117             :   raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
     118             :                                     const BasicBlock *Dst) const;
     119             : 
     120             :   /// \brief Set the raw edge probability for the given edge.
     121             :   ///
     122             :   /// This allows a pass to explicitly set the edge probability for an edge. It
     123             :   /// can be used when updating the CFG to update and preserve the branch
     124             :   /// probability information. Read the implementation of how these edge
     125             :   /// probabilities are calculated carefully before using!
     126             :   void setEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors,
     127             :                           BranchProbability Prob);
     128             : 
     129        1180 :   static BranchProbability getBranchProbStackProtector(bool IsLikely) {
     130        1180 :     static const BranchProbability LikelyProb((1u << 20) - 1, 1u << 20);
     131        2360 :     return IsLikely ? LikelyProb : LikelyProb.getCompl();
     132             :   }
     133             : 
     134             :   void calculate(const Function &F, const LoopInfo &LI,
     135             :                  const TargetLibraryInfo *TLI = nullptr);
     136             : 
     137             :   /// Forget analysis results for the given basic block.
     138             :   void eraseBlock(const BasicBlock *BB);
     139             : 
     140             : private:
     141             :   // We need to store CallbackVH's in order to correctly handle basic block
     142             :   // removal.
     143    12699952 :   class BasicBlockCallbackVH final : public CallbackVH {
     144             :     BranchProbabilityInfo *BPI;
     145             : 
     146       10547 :     void deleted() override {
     147             :       assert(BPI != nullptr);
     148       21094 :       BPI->eraseBlock(cast<BasicBlock>(getValPtr()));
     149       21094 :       BPI->Handles.erase(*this);
     150       10547 :     }
     151             : 
     152             :   public:
     153             :     BasicBlockCallbackVH(const Value *V, BranchProbabilityInfo *BPI = nullptr)
     154     5834116 :         : CallbackVH(const_cast<Value *>(V)), BPI(BPI) {}
     155             :   };
     156             : 
     157             :   DenseSet<BasicBlockCallbackVH, DenseMapInfo<Value*>> Handles;
     158             : 
     159             :   // Since we allow duplicate edges from one basic block to another, we use
     160             :   // a pair (PredBlock and an index in the successors) to specify an edge.
     161             :   using Edge = std::pair<const BasicBlock *, unsigned>;
     162             : 
     163             :   // Default weight value. Used when we don't have information about the edge.
     164             :   // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
     165             :   // the successors have a weight yet. But it doesn't make sense when providing
     166             :   // weight to an edge that may have siblings with non-zero weights. This can
     167             :   // be handled various ways, but it's probably fine for an edge with unknown
     168             :   // weight to just "inherit" the non-zero weight of an adjacent successor.
     169             :   static const uint32_t DEFAULT_WEIGHT = 16;
     170             : 
     171             :   DenseMap<Edge, BranchProbability> Probs;
     172             : 
     173             :   /// \brief Track the last function we run over for printing.
     174             :   const Function *LastF;
     175             : 
     176             :   /// \brief Track the set of blocks directly succeeded by a returning block.
     177             :   SmallPtrSet<const BasicBlock *, 16> PostDominatedByUnreachable;
     178             : 
     179             :   /// \brief Track the set of blocks that always lead to a cold call.
     180             :   SmallPtrSet<const BasicBlock *, 16> PostDominatedByColdCall;
     181             : 
     182             :   void updatePostDominatedByUnreachable(const BasicBlock *BB);
     183             :   void updatePostDominatedByColdCall(const BasicBlock *BB);
     184             :   bool calcUnreachableHeuristics(const BasicBlock *BB);
     185             :   bool calcMetadataWeights(const BasicBlock *BB);
     186             :   bool calcColdCallHeuristics(const BasicBlock *BB);
     187             :   bool calcPointerHeuristics(const BasicBlock *BB);
     188             :   bool calcLoopBranchHeuristics(const BasicBlock *BB, const LoopInfo &LI);
     189             :   bool calcZeroHeuristics(const BasicBlock *BB, const TargetLibraryInfo *TLI);
     190             :   bool calcFloatingPointHeuristics(const BasicBlock *BB);
     191             :   bool calcInvokeHeuristics(const BasicBlock *BB);
     192             : };
     193             : 
     194             : /// \brief Analysis pass which computes \c BranchProbabilityInfo.
     195             : class BranchProbabilityAnalysis
     196             :     : public AnalysisInfoMixin<BranchProbabilityAnalysis> {
     197             :   friend AnalysisInfoMixin<BranchProbabilityAnalysis>;
     198             : 
     199             :   static AnalysisKey Key;
     200             : 
     201             : public:
     202             :   /// \brief Provide the result type for this analysis pass.
     203             :   using Result = BranchProbabilityInfo;
     204             : 
     205             :   /// \brief Run the analysis pass over a function and produce BPI.
     206             :   BranchProbabilityInfo run(Function &F, FunctionAnalysisManager &AM);
     207             : };
     208             : 
     209             : /// \brief Printer pass for the \c BranchProbabilityAnalysis results.
     210             : class BranchProbabilityPrinterPass
     211             :     : public PassInfoMixin<BranchProbabilityPrinterPass> {
     212             :   raw_ostream &OS;
     213             : 
     214             : public:
     215           7 :   explicit BranchProbabilityPrinterPass(raw_ostream &OS) : OS(OS) {}
     216             : 
     217             :   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
     218             : };
     219             : 
     220             : /// \brief Legacy analysis pass which computes \c BranchProbabilityInfo.
     221       73630 : class BranchProbabilityInfoWrapperPass : public FunctionPass {
     222             :   BranchProbabilityInfo BPI;
     223             : 
     224             : public:
     225             :   static char ID;
     226             : 
     227       74034 :   BranchProbabilityInfoWrapperPass() : FunctionPass(ID) {
     228       37017 :     initializeBranchProbabilityInfoWrapperPassPass(
     229       37017 :         *PassRegistry::getPassRegistry());
     230       37017 :   }
     231             : 
     232      339535 :   BranchProbabilityInfo &getBPI() { return BPI; }
     233             :   const BranchProbabilityInfo &getBPI() const { return BPI; }
     234             : 
     235             :   void getAnalysisUsage(AnalysisUsage &AU) const override;
     236             :   bool runOnFunction(Function &F) override;
     237             :   void releaseMemory() override;
     238             :   void print(raw_ostream &OS, const Module *M = nullptr) const override;
     239             : };
     240             : 
     241             : } // end namespace llvm
     242             : 
     243             : #endif // LLVM_ANALYSIS_BRANCHPROBABILITYINFO_H

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