BlockFrequencyInfo.cpp

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//===- BlockFrequencyInfo.cpp - Block Frequency Analysis ------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Loops should be simplified before this analysis.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "AnalysisOptions.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/CycleAnalysis.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/GraphWriter.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <optional>
#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.")));
 
StringRef llvm::getViewBlockFreqFuncName(const LLVMContext &C) {
  return getAnalysisOptions(C).view_bfi_func_name;
}
unsigned llvm::getViewHotFreqPercent(const LLVMContext &C) {
  return getAnalysisOptions(C).view_hot_freq_percent;
}
PGOViewCountsType llvm::getPGOViewCounts(const LLVMContext &C) {
  return getAnalysisOptions(C).pgo_view_counts;
}
StringRef llvm::getPrintBFIFuncName(const LLVMContext &C) {
  return getAnalysisOptions(C).print_bfi_func_name;
}
 
namespace llvm {
 
static GVDAGType getGVDT(const LLVMContext &C) {
  if (getPGOViewCounts(C) == PGOViewCountsType::Graph)
    return GVDT_Count;
  return ViewBlockFreqPropagationDAG;
}
 
template <>
struct GraphTraits<BlockFrequencyInfo *> {
  using NodeRef = const BasicBlock *;
  using ChildIteratorType = const_succ_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(Node->getContext()));
  }
 
  std::string getNodeAttributes(const BasicBlock *Node,
                                const BlockFrequencyInfo *Graph) {
    return BFIDOTGTraitsBase::getNodeAttributes(
        Node, Graph, getViewHotFreqPercent(Node->getContext()));
  }
 
  std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
                                const BlockFrequencyInfo *BFI) {
    return BFIDOTGTraitsBase::getEdgeAttributes(
        Node, EI, BFI, BFI->getBPI(),
        getViewHotFreqPercent(Node->getContext()));
  }
};
 
} // end namespace llvm
 
BlockFrequencyInfo::BlockFrequencyInfo() = default;
 
BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
                                       const BranchProbabilityInfo &BPI,
                                       const CycleInfo &CI) {
  calculate(F, BPI, CI);
}
 
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 CycleInfo &CI) {
  if (!BFI)
    BFI.reset(new ImplType);
  BFI->calculate(F, BPI, CI);
  const AnalysisOptions &Opts = getAnalysisOptions(F);
  if (ViewBlockFreqPropagationDAG != GVDT_None &&
      (Opts.view_bfi_func_name.empty() ||
       F.getName() == Opts.view_bfi_func_name)) {
    view();
  }
  if (Opts.print_bfi && (Opts.print_bfi_func_name.empty() ||
                         F.getName() == Opts.print_bfi_func_name)) {
    print(dbgs());
  }
}
 
BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
  return BFI ? BFI->getBlockFreq(BB) : BlockFrequency(0);
}
 
std::optional<uint64_t>
BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB) const {
  if (!BFI)
    return std::nullopt;
 
  return BFI->getBlockProfileCount(*getFunction(), BB);
}
 
std::optional<uint64_t>
BlockFrequencyInfo::getProfileCountFromFreq(BlockFrequency Freq) const {
  if (!BFI)
    return std::nullopt;
  return BFI->getProfileCountFromFreq(*getFunction(), Freq);
}
 
bool BlockFrequencyInfo::isIrrLoopHeader(const BasicBlock *BB) {
  assert(BFI && "Expected analysis to be available");
  return BFI->isIrrLoopHeader(BB);
}
 
void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB,
                                      BlockFrequency Freq) {
  assert(BFI && "Expected analysis to be available");
  BFI->setBlockFreq(BB, Freq);
}
 
void BlockFrequencyInfo::setBlockFreqAndScale(
    const BasicBlock *ReferenceBB, BlockFrequency Freq,
    SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
  assert(BFI && "Expected analysis to be available");
  // Use 128 bits APInt to avoid overflow.
  APInt NewFreq(128, Freq.getFrequency());
  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, BlockFrequency(BBFreq.getLimitedValue()));
  }
  BFI->setBlockFreq(ReferenceBB, Freq);
}
 
/// Pop up a ghostview window with the current block frequency propagation
/// rendered using dot.
void BlockFrequencyInfo::view(StringRef title) const {
  ViewGraph(const_cast<BlockFrequencyInfo *>(this), title);
}
 
const Function *BlockFrequencyInfo::getFunction() const {
  return BFI ? BFI->getFunction() : nullptr;
}
 
const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
  return BFI ? &BFI->getBPI() : nullptr;
}
 
BlockFrequency BlockFrequencyInfo::getEntryFreq() const {
  return BFI ? BFI->getEntryFreq() : BlockFrequency(0);
}
 
void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
 
void BlockFrequencyInfo::print(raw_ostream &OS) const {
  if (BFI)
    BFI->print(OS);
}
 
void BlockFrequencyInfo::verifyMatch(BlockFrequencyInfo &Other) const {
  if (BFI)
    BFI->verifyMatch(*Other.BFI);
}
 
Printable llvm::printBlockFreq(const BlockFrequencyInfo &BFI,
                               BlockFrequency Freq) {
  return Printable([&BFI, Freq](raw_ostream &OS) {
    printRelativeBlockFreq(OS, BFI.getEntryFreq(), Freq);
  });
}
 
Printable llvm::printBlockFreq(const BlockFrequencyInfo &BFI,
                               const BasicBlock &BB) {
  return printBlockFreq(BFI, BFI.getBlockFreq(&BB));
}
 
INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
                      "Block Frequency Analysis", true, true)
INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(CycleInfoWrapperPass)
INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
                    "Block Frequency Analysis", true, true)
 
char BlockFrequencyInfoWrapperPass::ID = 0;
 
BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
    : FunctionPass(ID) {}
 
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<CycleInfoWrapperPass>();
  AU.setPreservesAll();
}
 
void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
 
bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
  BranchProbabilityInfo &BPI =
      getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
  CycleInfo &LI = getAnalysis<CycleInfoWrapperPass>().getResult();
  BFI.calculate(F, BPI, LI);
  return false;
}
 
AnalysisKey BlockFrequencyAnalysis::Key;
BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
                                               FunctionAnalysisManager &AM) {
  auto &BP = AM.getResult<BranchProbabilityAnalysis>(F);
  auto &LI = AM.getResult<CycleAnalysis>(F);
  BlockFrequencyInfo BFI;
  BFI.calculate(F, BP, LI);
  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();
}