CodeGenPGO.h

Go to the documentation of this file.

//===--- CodeGenPGO.h - PGO Instrumentation for LLVM CodeGen ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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 "llvm/ProfileData/InstrProfReader.h"
#include <array>
#include <memory>
#include <optional>
 
namespace clang {
namespace CodeGen {
 
/// Per-function PGO state.
class CodeGenPGO {
private:
  CodeGenModule &CGM;
  std::string FuncName;
  llvm::GlobalVariable *FuncNameVar;
 
  std::array <unsigned, llvm::IPVK_Last + 1> NumValueSites;
  unsigned NumRegionCounters;
  uint64_t FunctionHash;
  std::unique_ptr<llvm::DenseMap<const Stmt *, unsigned>> RegionCounterMap;
  std::unique_ptr<llvm::DenseMap<const Stmt *, uint64_t>> StmtCountMap;
  std::unique_ptr<llvm::InstrProfRecord> ProfRecord;
  std::vector<uint64_t> RegionCounts;
  uint64_t CurrentRegionCount;
 
public:
  CodeGenPGO(CodeGenModule &CGModule)
      : CGM(CGModule), FuncNameVar(nullptr), NumValueSites({{0}}),
        NumRegionCounters(0), FunctionHash(0), CurrentRegionCount(0) {}
 
  /// 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.empty(); }
 
  /// 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; }
 
  /// Check if an execution count is known for a given statement. If so, return
  /// true and put the value in Count; else return false.
  std::optional<uint64_t> getStmtCount(const Stmt *S) const {
    if (!StmtCountMap)
      return std::nullopt;
    auto I = StmtCountMap->find(S);
    if (I == StmtCountMap->end())
      return std::nullopt;
    return I->second;
  }
 
  /// If the execution count for the current statement is known, record that
  /// as the current count.
  void setCurrentStmt(const Stmt *S) {
    if (auto Count = getStmtCount(S))
      setCurrentRegionCount(*Count);
  }
 
  /// 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(GlobalDecl GD, llvm::Function *Fn);
  /// Emit a coverage mapping range with a counter zero
  /// for an unused declaration.
  void emitEmptyCounterMapping(const Decl *D, StringRef FuncName,
                               llvm::GlobalValue::LinkageTypes Linkage);
  // Insert instrumentation or attach profile metadata at value sites
  void valueProfile(CGBuilderTy &Builder, uint32_t ValueKind,
                    llvm::Instruction *ValueSite, llvm::Value *ValuePtr);
 
  // Set a module flag indicating if value profiling is enabled.
  void setValueProfilingFlag(llvm::Module &M);
 
private:
  void setFuncName(llvm::Function *Fn);
  void setFuncName(StringRef Name, 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);
  bool skipRegionMappingForDecl(const Decl *D);
  void emitCounterRegionMapping(const Decl *D);
 
public:
  void emitCounterIncrement(CGBuilderTy &Builder, const Stmt *S,
                            llvm::Value *StepV);
 
  /// Return the region count for the counter at the given index.
  uint64_t getRegionCount(const Stmt *S) {
    if (!RegionCounterMap)
      return 0;
    if (!haveRegionCounts())
      return 0;
    // With profiles from a differing version of clang we can have mismatched
    // decl counts. Don't crash in such a case.
    auto Index = (*RegionCounterMap)[S];
    if (Index >= RegionCounts.size())
      return 0;
    return RegionCounts[Index];
  }
};
 
}  // end namespace CodeGen
}  // end namespace clang
 
#endif