CodeGenPGO.h

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//===--- CodeGenPGO.h - PGO Instrumentation for LLVM CodeGen ----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Instrumentation-based profile-guided optimization
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_LIB_CODEGEN_CODEGENPGO_H
#define LLVM_CLANG_LIB_CODEGEN_CODEGENPGO_H

#include "CGBuilder.h"
#include "CodeGenModule.h"
#include "CodeGenTypes.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/MemoryBuffer.h"
#include <memory>

namespace clang {
namespace CodeGen {
class RegionCounter;

/// Per-function PGO state. This class should generally not be used directly,
/// but instead through the CodeGenFunction and RegionCounter types.
class CodeGenPGO {
private:
  CodeGenModule &CGM;
  std::unique_ptr<std::string> PrefixedFuncName;
  StringRef RawFuncName;
  llvm::GlobalValue::LinkageTypes VarLinkage;

  unsigned NumRegionCounters;
  uint64_t FunctionHash;
  llvm::GlobalVariable *RegionCounters;
  std::unique_ptr<llvm::DenseMap<const Stmt *, unsigned>> RegionCounterMap;
  std::unique_ptr<llvm::DenseMap<const Stmt *, uint64_t>> StmtCountMap;
  std::unique_ptr<std::vector<uint64_t>> RegionCounts;
  uint64_t CurrentRegionCount;
  std::string CoverageMapping;
  /// \brief A flag that is set to true when this function doesn't need
  /// to have coverage mapping data.
  bool SkipCoverageMapping;

public:
  CodeGenPGO(CodeGenModule &CGM)
      : CGM(CGM), NumRegionCounters(0), FunctionHash(0),
        RegionCounters(nullptr), CurrentRegionCount(0),
        SkipCoverageMapping(false) {}

  /// Whether or not we have PGO region data for the current function. This is
  /// false both when we have no data at all and when our data has been
  /// discarded.
  bool haveRegionCounts() const { return RegionCounts != nullptr; }

  /// Get the string used to identify this function in the profile data.
  /// For functions with local linkage, this includes the main file name.
  StringRef getFuncName() const { return StringRef(*PrefixedFuncName); }
  std::string getFuncVarName(StringRef VarName) const {
    return ("__llvm_profile_" + VarName + "_" + RawFuncName).str();
  }

  /// Return the counter value of the current region.
  uint64_t getCurrentRegionCount() const { return CurrentRegionCount; }

  /// Set the counter value for the current region. This is used to keep track
  /// of changes to the most recent counter from control flow and non-local
  /// exits.
  void setCurrentRegionCount(uint64_t Count) { CurrentRegionCount = Count; }

  /// Indicate that the current region is never reached, and thus should have a
  /// counter value of zero. This is important so that subsequent regions can
  /// correctly track their parent counts.
  void setCurrentRegionUnreachable() { setCurrentRegionCount(0); }

  /// Check if an execution count is known for a given statement. If so, return
  /// true and put the value in Count; else return false.
  bool getStmtCount(const Stmt *S, uint64_t &Count) {
    if (!StmtCountMap)
      return false;
    llvm::DenseMap<const Stmt*, uint64_t>::const_iterator
      I = StmtCountMap->find(S);
    if (I == StmtCountMap->end())
      return false;
    Count = I->second;
    return true;
  }

  /// If the execution count for the current statement is known, record that
  /// as the current count.
  void setCurrentStmt(const Stmt *S) {
    uint64_t Count;
    if (getStmtCount(S, Count))
      setCurrentRegionCount(Count);
  }

  /// Calculate branch weights appropriate for PGO data
  llvm::MDNode *createBranchWeights(uint64_t TrueCount, uint64_t FalseCount);
  llvm::MDNode *createBranchWeights(ArrayRef<uint64_t> Weights);
  llvm::MDNode *createLoopWeights(const Stmt *Cond, RegionCounter &Cnt);

  /// Check if we need to emit coverage mapping for a given declaration
  void checkGlobalDecl(GlobalDecl GD);
  /// Assign counters to regions and configure them for PGO of a given
  /// function. Does nothing if instrumentation is not enabled and either
  /// generates global variables or associates PGO data with each of the
  /// counters depending on whether we are generating or using instrumentation.
  void assignRegionCounters(const Decl *D, llvm::Function *Fn);
  /// Emit static data structures for instrumentation data.
  void emitInstrumentationData();
  /// Clean up region counter state. Must be called if assignRegionCounters is
  /// used.
  void destroyRegionCounters();
  /// Emit static initialization code, if any.
  static llvm::Function *emitInitialization(CodeGenModule &CGM);
  /// Emit a coverage mapping range with a counter zero
  /// for an unused declaration.
  void emitEmptyCounterMapping(const Decl *D, StringRef FuncName,
                               llvm::GlobalValue::LinkageTypes Linkage);
private:
  void setFuncName(llvm::Function *Fn);
  void setFuncName(StringRef Name, llvm::GlobalValue::LinkageTypes Linkage);
  void setVarLinkage(llvm::GlobalValue::LinkageTypes Linkage);
  void mapRegionCounters(const Decl *D);
  void computeRegionCounts(const Decl *D);
  void applyFunctionAttributes(llvm::IndexedInstrProfReader *PGOReader,
                               llvm::Function *Fn);
  void loadRegionCounts(llvm::IndexedInstrProfReader *PGOReader,
                        bool IsInMainFile);
  void emitCounterVariables();
  llvm::GlobalVariable *buildDataVar();
  void emitCounterRegionMapping(const Decl *D);

  /// Emit code to increment the counter at the given index
  void emitCounterIncrement(CGBuilderTy &Builder, unsigned Counter);

  /// Return the region counter for the given statement. This should only be
  /// called on statements that have a dedicated counter.
  unsigned getRegionCounter(const Stmt *S) {
    if (!RegionCounterMap)
      return 0;
    return (*RegionCounterMap)[S];
  }

  /// Return the region count for the counter at the given index.
  uint64_t getRegionCount(unsigned Counter) {
    if (!haveRegionCounts())
      return 0;
    return (*RegionCounts)[Counter];
  }

  friend class RegionCounter;
};

/// A counter for a particular region. This is the primary interface through
/// which clients manage PGO counters and their values.
class RegionCounter {
  CodeGenPGO *PGO;
  unsigned Counter;
  uint64_t Count;
  uint64_t ParentCount;
  uint64_t RegionCount;
  int64_t Adjust;

  RegionCounter(CodeGenPGO &PGO, unsigned CounterIndex)
    : PGO(&PGO), Counter(CounterIndex), Count(PGO.getRegionCount(Counter)),
      ParentCount(PGO.getCurrentRegionCount()), Adjust(0) {}

public:
  RegionCounter(CodeGenPGO &PGO, const Stmt *S)
    : PGO(&PGO), Counter(PGO.getRegionCounter(S)),
      Count(PGO.getRegionCount(Counter)),
      ParentCount(PGO.getCurrentRegionCount()), Adjust(0) {}

  /// Get the value of the counter. In most cases this is the number of times
  /// the region of the counter was entered, but for switch labels it's the
  /// number of direct jumps to that label.
  uint64_t getCount() const { return Count; }

  /// Get the value of the counter with adjustments applied. Adjustments occur
  /// when control enters or leaves the region abnormally; i.e., if there is a
  /// jump to a label within the region, or if the function can return from
  /// within the region. The adjusted count, then, is the value of the counter
  /// at the end of the region.
  uint64_t getAdjustedCount() const {
    return Count + Adjust;
  }

  /// Get the value of the counter in this region's parent, i.e., the region
  /// that was active when this region began. This is useful for deriving
  /// counts in implicitly counted regions, like the false case of a condition
  /// or the normal exits of a loop.
  uint64_t getParentCount() const { return ParentCount; }

  /// Activate the counter by emitting an increment and starting to track
  /// adjustments. If AddIncomingFallThrough is true, the current region count
  /// will be added to the counter for the purposes of tracking the region.
  void beginRegion(CGBuilderTy &Builder, bool AddIncomingFallThrough=false) {
    beginRegion(AddIncomingFallThrough);
    PGO->emitCounterIncrement(Builder, Counter);
  }
  void beginRegion(bool AddIncomingFallThrough=false) {
    RegionCount = Count;
    if (AddIncomingFallThrough)
      RegionCount += PGO->getCurrentRegionCount();
    PGO->setCurrentRegionCount(RegionCount);
  }

  /// For counters on boolean branches, begins tracking adjustments for the
  /// uncounted path.
  void beginElseRegion() {
    RegionCount = ParentCount - Count;
    PGO->setCurrentRegionCount(RegionCount);
  }

  /// Reset the current region count.
  void setCurrentRegionCount(uint64_t CurrentCount) {
    RegionCount = CurrentCount;
    PGO->setCurrentRegionCount(RegionCount);
  }

  /// Adjust for non-local control flow after emitting a subexpression or
  /// substatement. This must be called to account for constructs such as gotos,
  /// labels, and returns, so that we can ensure that our region's count is
  /// correct in the code that follows.
  void adjustForControlFlow() {
    Adjust += PGO->getCurrentRegionCount() - RegionCount;
    // Reset the region count in case this is called again later.
    RegionCount = PGO->getCurrentRegionCount();
  }

  /// Commit all adjustments to the current region. If the region is a loop,
  /// the LoopAdjust value should be the count of all the breaks and continues
  /// from the loop, to compensate for those counts being deducted from the
  /// adjustments for the body of the loop.
  void applyAdjustmentsToRegion(uint64_t LoopAdjust) {
    PGO->setCurrentRegionCount(ParentCount + Adjust + LoopAdjust);
  }
};

}  // end namespace CodeGen
}  // end namespace clang

#endif