BlockFrequencyInfo.cpp

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//===- BlockFrequencyInfo.cpp - Block Frequency Analysis ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Loops should be simplified before this analysis.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <string>

using namespace llvm;

#define DEBUG_TYPE "block-freq"

static cl::opt<GVDAGType> ViewBlockFreqPropagationDAG(
    "view-block-freq-propagation-dags", cl::Hidden,
    cl::desc("Pop up a window to show a dag displaying how block "
             "frequencies propagation through the CFG."),
    cl::values(clEnumValN(GVDT_None, "none", "do not display graphs."),
               clEnumValN(GVDT_Fraction, "fraction",
                          "display a graph using the "
                          "fractional block frequency representation."),
               clEnumValN(GVDT_Integer, "integer",
                          "display a graph using the raw "
                          "integer fractional block frequency representation."),
               clEnumValN(GVDT_Count, "count", "display a graph using the real "
                                               "profile count if available.")));

cl::opt<std::string>
    ViewBlockFreqFuncName("view-bfi-func-name", cl::Hidden,
                          cl::desc("The option to specify "
                                   "the name of the function "
                                   "whose CFG will be displayed."));

cl::opt<unsigned>
    ViewHotFreqPercent("view-hot-freq-percent", cl::init(10), cl::Hidden,
                       cl::desc("An integer in percent used to specify "
                                "the hot blocks/edges to be displayed "
                                "in red: a block or edge whose frequency "
                                "is no less than the max frequency of the "
                                "function multiplied by this percent."));

// Command line option to turn on CFG dot dump after profile annotation.
cl::opt<bool>
    PGOViewCounts("pgo-view-counts", cl::init(false), cl::Hidden,
                  cl::desc("A boolean option to show CFG dag with "
                           "block profile counts and branch probabilities "
                           "right after PGO profile annotation step. The "
                           "profile counts are computed using branch "
                           "probabilities from the runtime profile data and "
                           "block frequency propagation algorithm. To view "
                           "the raw counts from the profile, use option "
                           "-pgo-view-raw-counts instead. To limit graph "
                           "display to only one function, use filtering option "
                           "-view-bfi-func-name."));

namespace llvm {

static GVDAGType getGVDT() {
  if (PGOViewCounts)
    return GVDT_Count;
  return ViewBlockFreqPropagationDAG;
}

template <>
struct GraphTraits<BlockFrequencyInfo *> {
  using NodeRef = const BasicBlock *;
  using ChildIteratorType = succ_const_iterator;
  using nodes_iterator = pointer_iterator<Function::const_iterator>;

  static NodeRef getEntryNode(const BlockFrequencyInfo *G) {
    return &G->getFunction()->front();
  }

  static ChildIteratorType child_begin(const NodeRef N) {
    return succ_begin(N);
  }

  static ChildIteratorType child_end(const NodeRef N) { return succ_end(N); }

  static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
    return nodes_iterator(G->getFunction()->begin());
  }

  static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
    return nodes_iterator(G->getFunction()->end());
  }
};

using BFIDOTGTraitsBase =
    BFIDOTGraphTraitsBase<BlockFrequencyInfo, BranchProbabilityInfo>;

template <>
struct DOTGraphTraits<BlockFrequencyInfo *> : public BFIDOTGTraitsBase {
  explicit DOTGraphTraits(bool isSimple = false)
      : BFIDOTGTraitsBase(isSimple) {}

  std::string getNodeLabel(const BasicBlock *Node,
                           const BlockFrequencyInfo *Graph) {

    return BFIDOTGTraitsBase::getNodeLabel(Node, Graph, getGVDT());
  }

  std::string getNodeAttributes(const BasicBlock *Node,
                                const BlockFrequencyInfo *Graph) {
    return BFIDOTGTraitsBase::getNodeAttributes(Node, Graph,
                                                ViewHotFreqPercent);
  }

  std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
                                const BlockFrequencyInfo *BFI) {
    return BFIDOTGTraitsBase::getEdgeAttributes(Node, EI, BFI, BFI->getBPI(),
                                                ViewHotFreqPercent);
  }
};

} // end namespace llvm

BlockFrequencyInfo::BlockFrequencyInfo() = default;

BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
                                       const BranchProbabilityInfo &BPI,
                                       const LoopInfo &LI) {
  calculate(F, BPI, LI);
}

BlockFrequencyInfo::BlockFrequencyInfo(BlockFrequencyInfo &&Arg)
    : BFI(std::move(Arg.BFI)) {}

BlockFrequencyInfo &BlockFrequencyInfo::operator=(BlockFrequencyInfo &&RHS) {
  releaseMemory();
  BFI = std::move(RHS.BFI);
  return *this;
}

// Explicitly define the default constructor otherwise it would be implicitly
// defined at the first ODR-use which is the BFI member in the
// LazyBlockFrequencyInfo header.  The dtor needs the BlockFrequencyInfoImpl
// template instantiated which is not available in the header.
BlockFrequencyInfo::~BlockFrequencyInfo() = default;

bool BlockFrequencyInfo::invalidate(Function &F, const PreservedAnalyses &PA,
                                    FunctionAnalysisManager::Invalidator &) {
  // Check whether the analysis, all analyses on functions, or the function's
  // CFG have been preserved.
  auto PAC = PA.getChecker<BlockFrequencyAnalysis>();
  return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
           PAC.preservedSet<CFGAnalyses>());
}

void BlockFrequencyInfo::calculate(const Function &F,
                                   const BranchProbabilityInfo &BPI,
                                   const LoopInfo &LI) {
  if (!BFI)
    BFI.reset(new ImplType);
  BFI->calculate(F, BPI, LI);
  if (ViewBlockFreqPropagationDAG != GVDT_None &&
      (ViewBlockFreqFuncName.empty() ||
       F.getName().equals(ViewBlockFreqFuncName))) {
    view();
  }
}

BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
  return BFI ? BFI->getBlockFreq(BB) : 0;
}

Optional<uint64_t>
BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB) const {
  if (!BFI)
    return None;

  return BFI->getBlockProfileCount(*getFunction(), BB);
}

Optional<uint64_t>
BlockFrequencyInfo::getProfileCountFromFreq(uint64_t Freq) const {
  if (!BFI)
    return None;
  return BFI->getProfileCountFromFreq(*getFunction(), Freq);
}

void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB, uint64_t Freq) {
  assert(BFI && "Expected analysis to be available");
  BFI->setBlockFreq(BB, Freq);
}

void BlockFrequencyInfo::setBlockFreqAndScale(
    const BasicBlock *ReferenceBB, uint64_t Freq,
    SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
  assert(BFI && "Expected analysis to be available");
  // Use 128 bits APInt to avoid overflow.
  APInt NewFreq(128, Freq);
  APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
  APInt BBFreq(128, 0);
  for (auto *BB : BlocksToScale) {
    BBFreq = BFI->getBlockFreq(BB).getFrequency();
    // Multiply first by NewFreq and then divide by OldFreq
    // to minimize loss of precision.
    BBFreq *= NewFreq;
    // udiv is an expensive operation in the general case. If this ends up being
    // a hot spot, one of the options proposed in
    // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
    BBFreq = BBFreq.udiv(OldFreq);
    BFI->setBlockFreq(BB, BBFreq.getLimitedValue());
  }
  BFI->setBlockFreq(ReferenceBB, Freq);
}

/// Pop up a ghostview window with the current block frequency propagation
/// rendered using dot.
void BlockFrequencyInfo::view() const {
  ViewGraph(const_cast<BlockFrequencyInfo *>(this), "BlockFrequencyDAGs");
}

const Function *BlockFrequencyInfo::getFunction() const {
  return BFI ? BFI->getFunction() : nullptr;
}

const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
  return BFI ? &BFI->getBPI() : nullptr;
}

raw_ostream &BlockFrequencyInfo::
printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const {
  return BFI ? BFI->printBlockFreq(OS, Freq) : OS;
}

raw_ostream &
BlockFrequencyInfo::printBlockFreq(raw_ostream &OS,
                                   const BasicBlock *BB) const {
  return BFI ? BFI->printBlockFreq(OS, BB) : OS;
}

uint64_t BlockFrequencyInfo::getEntryFreq() const {
  return BFI ? BFI->getEntryFreq() : 0;
}

void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }

void BlockFrequencyInfo::print(raw_ostream &OS) const {
  if (BFI)
    BFI->print(OS);
}

INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
                      "Block Frequency Analysis", true, true)
INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
                    "Block Frequency Analysis", true, true)

char BlockFrequencyInfoWrapperPass::ID = 0;

BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
    : FunctionPass(ID) {
  initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
}

BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() = default;

void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
                                          const Module *) const {
  BFI.print(OS);
}

void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<BranchProbabilityInfoWrapperPass>();
  AU.addRequired<LoopInfoWrapperPass>();
  AU.setPreservesAll();
}

void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }

bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
  BranchProbabilityInfo &BPI =
      getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
  LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
  BFI.calculate(F, BPI, LI);
  return false;
}

AnalysisKey BlockFrequencyAnalysis::Key;
BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
                                               FunctionAnalysisManager &AM) {
  BlockFrequencyInfo BFI;
  BFI.calculate(F, AM.getResult<BranchProbabilityAnalysis>(F),
                AM.getResult<LoopAnalysis>(F));
  return BFI;
}

PreservedAnalyses
BlockFrequencyPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
  OS << "Printing analysis results of BFI for function "
     << "'" << F.getName() << "':"
     << "\n";
  AM.getResult<BlockFrequencyAnalysis>(F).print(OS);
  return PreservedAnalyses::all();
}