llvm/lib/Analysis/BlockFrequencyInfo.cpp

   1 //===- BlockFrequencyInfo.cpp - Block Frequency Analysis ------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Loops should be simplified before this analysis.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Analysis/BlockFrequencyInfo.h"
  14 #include "llvm/ADT/APInt.h"
  15 #include "llvm/ADT/iterator.h"
  16 #include "llvm/Analysis/BlockFrequencyInfoImpl.h"
  17 #include "llvm/Analysis/BranchProbabilityInfo.h"
  18 #include "llvm/Analysis/LoopInfo.h"
  19 #include "llvm/IR/CFG.h"
  20 #include "llvm/IR/Function.h"
  21 #include "llvm/IR/PassManager.h"
  22 #include "llvm/InitializePasses.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/Support/CommandLine.h"
  25 #include "llvm/Support/GraphWriter.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include <cassert>
  28 #include <optional>
  29 #include <string>
  30
  31 using namespace llvm;
  32
  33 #define DEBUG_TYPE "block-freq"
  34
  35 static cl::opt<GVDAGType> ViewBlockFreqPropagationDAG(
  36     "view-block-freq-propagation-dags", cl::Hidden,
  37     cl::desc("Pop up a window to show a dag displaying how block "
  38              "frequencies propagation through the CFG."),
  39     cl::values(clEnumValN(GVDT_None, "none", "do not display graphs."),
  40                clEnumValN(GVDT_Fraction, "fraction",
  41                           "display a graph using the "
  42                           "fractional block frequency representation."),
  43                clEnumValN(GVDT_Integer, "integer",
  44                           "display a graph using the raw "
  45                           "integer fractional block frequency representation."),
  46                clEnumValN(GVDT_Count, "count", "display a graph using the real "
  47                                                "profile count if available.")));
  48
  49 namespace llvm {
  50 cl::opt<std::string>
  51     ViewBlockFreqFuncName("view-bfi-func-name", cl::Hidden,
  52                           cl::desc("The option to specify "
  53                                    "the name of the function "
  54                                    "whose CFG will be displayed."));
  55
  56 cl::opt<unsigned>
  57     ViewHotFreqPercent("view-hot-freq-percent", cl::init(10), cl::Hidden,
  58                        cl::desc("An integer in percent used to specify "
  59                                 "the hot blocks/edges to be displayed "
  60                                 "in red: a block or edge whose frequency "
  61                                 "is no less than the max frequency of the "
  62                                 "function multiplied by this percent."));
  63
  64 // Command line option to turn on CFG dot or text dump after profile annotation.
  65 cl::opt<PGOViewCountsType> PGOViewCounts(
  66     "pgo-view-counts", cl::Hidden,
  67     cl::desc("A boolean option to show CFG dag or text with "
  68              "block profile counts and branch probabilities "
  69              "right after PGO profile annotation step. The "
  70              "profile counts are computed using branch "
  71              "probabilities from the runtime profile data and "
  72              "block frequency propagation algorithm. To view "
  73              "the raw counts from the profile, use option "
  74              "-pgo-view-raw-counts instead. To limit graph "
  75              "display to only one function, use filtering option "
  76              "-view-bfi-func-name."),
  77     cl::values(clEnumValN(PGOVCT_None, "none", "do not show."),
  78                clEnumValN(PGOVCT_Graph, "graph", "show a graph."),
  79                clEnumValN(PGOVCT_Text, "text", "show in text.")));
  80
  81 static cl::opt<bool> PrintBFI("print-bfi", cl::init(false), cl::Hidden,
  82                               cl::desc("Print the block frequency info."));
  83
  84 cl::opt<std::string>
  85     PrintBFIFuncName("print-bfi-func-name", cl::Hidden,
  86                      cl::desc("The option to specify the name of the function "
  87                               "whose block frequency info is printed."));
  88 } // namespace llvm
  89
  90 namespace llvm {
  91
  92 static GVDAGType getGVDT() {
  93   if (PGOViewCounts == PGOVCT_Graph)
  94     return GVDT_Count;
  95   return ViewBlockFreqPropagationDAG;
  96 }
  97
  98 template <>
  99 struct GraphTraits<BlockFrequencyInfo *> {
 100   using NodeRef = const BasicBlock *;
 101   using ChildIteratorType = const_succ_iterator;
 102   using nodes_iterator = pointer_iterator<Function::const_iterator>;
 103
 104   static NodeRef getEntryNode(const BlockFrequencyInfo *G) {
 105     return &G->getFunction()->front();
 106   }
 107
 108   static ChildIteratorType child_begin(const NodeRef N) {
 109     return succ_begin(N);
 110   }
 111
 112   static ChildIteratorType child_end(const NodeRef N) { return succ_end(N); }
 113
 114   static nodes_iterator nodes_begin(const BlockFrequencyInfo *G) {
 115     return nodes_iterator(G->getFunction()->begin());
 116   }
 117
 118   static nodes_iterator nodes_end(const BlockFrequencyInfo *G) {
 119     return nodes_iterator(G->getFunction()->end());
 120   }
 121 };
 122
 123 using BFIDOTGTraitsBase =
 124     BFIDOTGraphTraitsBase<BlockFrequencyInfo, BranchProbabilityInfo>;
 125
 126 template <>
 127 struct DOTGraphTraits<BlockFrequencyInfo *> : public BFIDOTGTraitsBase {
 128   explicit DOTGraphTraits(bool isSimple = false)
 129       : BFIDOTGTraitsBase(isSimple) {}
 130
 131   std::string getNodeLabel(const BasicBlock *Node,
 132                            const BlockFrequencyInfo *Graph) {
 133
 134     return BFIDOTGTraitsBase::getNodeLabel(Node, Graph, getGVDT());
 135   }
 136
 137   std::string getNodeAttributes(const BasicBlock *Node,
 138                                 const BlockFrequencyInfo *Graph) {
 139     return BFIDOTGTraitsBase::getNodeAttributes(Node, Graph,
 140                                                 ViewHotFreqPercent);
 141   }
 142
 143   std::string getEdgeAttributes(const BasicBlock *Node, EdgeIter EI,
 144                                 const BlockFrequencyInfo *BFI) {
 145     return BFIDOTGTraitsBase::getEdgeAttributes(Node, EI, BFI, BFI->getBPI(),
 146                                                 ViewHotFreqPercent);
 147   }
 148 };
 149
 150 } // end namespace llvm
 151
 152 BlockFrequencyInfo::BlockFrequencyInfo() = default;
 153
 154 BlockFrequencyInfo::BlockFrequencyInfo(const Function &F,
 155                                        const BranchProbabilityInfo &BPI,
 156                                        const LoopInfo &LI) {
 157   calculate(F, BPI, LI);
 158 }
 159
 160 BlockFrequencyInfo::BlockFrequencyInfo(BlockFrequencyInfo &&Arg)
 161     : BFI(std::move(Arg.BFI)) {}
 162
 163 BlockFrequencyInfo &BlockFrequencyInfo::operator=(BlockFrequencyInfo &&RHS) {
 164   releaseMemory();
 165   BFI = std::move(RHS.BFI);
 166   return *this;
 167 }
 168
 169 // Explicitly define the default constructor otherwise it would be implicitly
 170 // defined at the first ODR-use which is the BFI member in the
 171 // LazyBlockFrequencyInfo header.  The dtor needs the BlockFrequencyInfoImpl
 172 // template instantiated which is not available in the header.
 173 BlockFrequencyInfo::~BlockFrequencyInfo() = default;
 174
 175 bool BlockFrequencyInfo::invalidate(Function &F, const PreservedAnalyses &PA,
 176                                     FunctionAnalysisManager::Invalidator &) {
 177   // Check whether the analysis, all analyses on functions, or the function's
 178   // CFG have been preserved.
 179   auto PAC = PA.getChecker<BlockFrequencyAnalysis>();
 180   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
 181            PAC.preservedSet<CFGAnalyses>());
 182 }
 183
 184 void BlockFrequencyInfo::calculate(const Function &F,
 185                                    const BranchProbabilityInfo &BPI,
 186                                    const LoopInfo &LI) {
 187   if (!BFI)
 188     BFI.reset(new ImplType);
 189   BFI->calculate(F, BPI, LI);
 190   if (ViewBlockFreqPropagationDAG != GVDT_None &&
 191       (ViewBlockFreqFuncName.empty() ||
 192        F.getName().equals(ViewBlockFreqFuncName))) {
 193     view();
 194   }
 195   if (PrintBFI &&
 196       (PrintBFIFuncName.empty() || F.getName().equals(PrintBFIFuncName))) {
 197     print(dbgs());
 198   }
 199 }
 200
 201 BlockFrequency BlockFrequencyInfo::getBlockFreq(const BasicBlock *BB) const {
 202   return BFI ? BFI->getBlockFreq(BB) : BlockFrequency(0);
 203 }
 204
 205 std::optional<uint64_t>
 206 BlockFrequencyInfo::getBlockProfileCount(const BasicBlock *BB,
 207                                          bool AllowSynthetic) const {
 208   if (!BFI)
 209     return std::nullopt;
 210
 211   return BFI->getBlockProfileCount(*getFunction(), BB, AllowSynthetic);
 212 }
 213
 214 std::optional<uint64_t>
 215 BlockFrequencyInfo::getProfileCountFromFreq(BlockFrequency Freq) const {
 216   if (!BFI)
 217     return std::nullopt;
 218   return BFI->getProfileCountFromFreq(*getFunction(), Freq);
 219 }
 220
 221 bool BlockFrequencyInfo::isIrrLoopHeader(const BasicBlock *BB) {
 222   assert(BFI && "Expected analysis to be available");
 223   return BFI->isIrrLoopHeader(BB);
 224 }
 225
 226 void BlockFrequencyInfo::setBlockFreq(const BasicBlock *BB,
 227                                       BlockFrequency Freq) {
 228   assert(BFI && "Expected analysis to be available");
 229   BFI->setBlockFreq(BB, Freq);
 230 }
 231
 232 void BlockFrequencyInfo::setBlockFreqAndScale(
 233     const BasicBlock *ReferenceBB, BlockFrequency Freq,
 234     SmallPtrSetImpl<BasicBlock *> &BlocksToScale) {
 235   assert(BFI && "Expected analysis to be available");
 236   // Use 128 bits APInt to avoid overflow.
 237   APInt NewFreq(128, Freq.getFrequency());
 238   APInt OldFreq(128, BFI->getBlockFreq(ReferenceBB).getFrequency());
 239   APInt BBFreq(128, 0);
 240   for (auto *BB : BlocksToScale) {
 241     BBFreq = BFI->getBlockFreq(BB).getFrequency();
 242     // Multiply first by NewFreq and then divide by OldFreq
 243     // to minimize loss of precision.
 244     BBFreq *= NewFreq;
 245     // udiv is an expensive operation in the general case. If this ends up being
 246     // a hot spot, one of the options proposed in
 247     // https://reviews.llvm.org/D28535#650071 could be used to avoid this.
 248     BBFreq = BBFreq.udiv(OldFreq);
 249     BFI->setBlockFreq(BB, BlockFrequency(BBFreq.getLimitedValue()));
 250   }
 251   BFI->setBlockFreq(ReferenceBB, Freq);
 252 }
 253
 254 /// Pop up a ghostview window with the current block frequency propagation
 255 /// rendered using dot.
 256 void BlockFrequencyInfo::view(StringRef title) const {
 257   ViewGraph(const_cast<BlockFrequencyInfo *>(this), title);
 258 }
 259
 260 const Function *BlockFrequencyInfo::getFunction() const {
 261   return BFI ? BFI->getFunction() : nullptr;
 262 }
 263
 264 const BranchProbabilityInfo *BlockFrequencyInfo::getBPI() const {
 265   return BFI ? &BFI->getBPI() : nullptr;
 266 }
 267
 268 BlockFrequency BlockFrequencyInfo::getEntryFreq() const {
 269   return BFI ? BFI->getEntryFreq() : BlockFrequency(0);
 270 }
 271
 272 void BlockFrequencyInfo::releaseMemory() { BFI.reset(); }
 273
 274 void BlockFrequencyInfo::print(raw_ostream &OS) const {
 275   if (BFI)
 276     BFI->print(OS);
 277 }
 278
 279 void BlockFrequencyInfo::verifyMatch(BlockFrequencyInfo &Other) const {
 280   if (BFI)
 281     BFI->verifyMatch(*Other.BFI);
 282 }
 283
 284 Printable llvm::printBlockFreq(const BlockFrequencyInfo &BFI,
 285                                BlockFrequency Freq) {
 286   return Printable([&BFI, Freq](raw_ostream &OS) {
 287     printBlockFreqImpl(OS, BFI.getEntryFreq(), Freq);
 288   });
 289 }
 290
 291 Printable llvm::printBlockFreq(const BlockFrequencyInfo &BFI,
 292                                const BasicBlock &BB) {
 293   return printBlockFreq(BFI, BFI.getBlockFreq(&BB));
 294 }
 295
 296 INITIALIZE_PASS_BEGIN(BlockFrequencyInfoWrapperPass, "block-freq",
 297                       "Block Frequency Analysis", true, true)
 298 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
 299 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 300 INITIALIZE_PASS_END(BlockFrequencyInfoWrapperPass, "block-freq",
 301                     "Block Frequency Analysis", true, true)
 302
 303 char BlockFrequencyInfoWrapperPass::ID = 0;
 304
 305 BlockFrequencyInfoWrapperPass::BlockFrequencyInfoWrapperPass()
 306     : FunctionPass(ID) {
 307   initializeBlockFrequencyInfoWrapperPassPass(*PassRegistry::getPassRegistry());
 308 }
 309
 310 BlockFrequencyInfoWrapperPass::~BlockFrequencyInfoWrapperPass() = default;
 311
 312 void BlockFrequencyInfoWrapperPass::print(raw_ostream &OS,
 313                                           const Module *) const {
 314   BFI.print(OS);
 315 }
 316
 317 void BlockFrequencyInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
 318   AU.addRequired<BranchProbabilityInfoWrapperPass>();
 319   AU.addRequired<LoopInfoWrapperPass>();
 320   AU.setPreservesAll();
 321 }
 322
 323 void BlockFrequencyInfoWrapperPass::releaseMemory() { BFI.releaseMemory(); }
 324
 325 bool BlockFrequencyInfoWrapperPass::runOnFunction(Function &F) {
 326   BranchProbabilityInfo &BPI =
 327       getAnalysis<BranchProbabilityInfoWrapperPass>().getBPI();
 328   LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
 329   BFI.calculate(F, BPI, LI);
 330   return false;
 331 }
 332
 333 AnalysisKey BlockFrequencyAnalysis::Key;
 334 BlockFrequencyInfo BlockFrequencyAnalysis::run(Function &F,
 335                                                FunctionAnalysisManager &AM) {
 336   auto &BP = AM.getResult<BranchProbabilityAnalysis>(F);
 337   auto &LI = AM.getResult<LoopAnalysis>(F);
 338   BlockFrequencyInfo BFI;
 339   BFI.calculate(F, BP, LI);
 340   return BFI;
 341 }
 342
 343 PreservedAnalyses
 344 BlockFrequencyPrinterPass::run(Function &F, FunctionAnalysisManager &AM) {
 345   OS << "Printing analysis results of BFI for function "
 346      << "'" << F.getName() << "':"
 347      << "\n";
 348   AM.getResult<BlockFrequencyAnalysis>(F).print(OS);
 349   return PreservedAnalyses::all();
 350 }