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