1 //===- OptimalEdgeProfiling.cpp - Insert counters for opt. edge profiling -===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass instruments the specified program with counters for edge profiling. 11 // Edge profiling can give a reasonable approximation of the hot paths through a 12 // program, and is used for a wide variety of program transformations. 13 // 14 //===----------------------------------------------------------------------===// 15 #define DEBUG_TYPE "insert-optimal-edge-profiling" 16 #include "ProfilingUtils.h" 17 #include "llvm/Constants.h" 18 #include "llvm/Module.h" 19 #include "llvm/Pass.h" 20 #include "llvm/Analysis/Passes.h" 21 #include "llvm/Analysis/ProfileInfo.h" 22 #include "llvm/Analysis/ProfileInfoLoader.h" 23 #include "llvm/Support/raw_ostream.h" 24 #include "llvm/Support/Debug.h" 25 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 26 #include "llvm/Transforms/Instrumentation.h" 27 #include "llvm/ADT/DenseSet.h" 28 #include "llvm/ADT/Statistic.h" 29 #include "MaximumSpanningTree.h" 30 using namespace llvm; 31 32 STATISTIC(NumEdgesInserted, "The # of edges inserted."); 33 34 namespace { 35 class OptimalEdgeProfiler : public ModulePass { 36 bool runOnModule(Module &M); 37 public: 38 static char ID; // Pass identification, replacement for typeid 39 OptimalEdgeProfiler() : ModulePass(ID) { 40 initializeOptimalEdgeProfilerPass(*PassRegistry::getPassRegistry()); 41 } 42 43 void getAnalysisUsage(AnalysisUsage &AU) const { 44 AU.addRequiredID(ProfileEstimatorPassID); 45 AU.addRequired<ProfileInfo>(); 46 } 47 48 virtual const char *getPassName() const { 49 return "Optimal Edge Profiler"; 50 } 51 }; 52 } 53 54 char OptimalEdgeProfiler::ID = 0; 55 INITIALIZE_PASS_BEGIN(OptimalEdgeProfiler, "insert-optimal-edge-profiling", 56 "Insert optimal instrumentation for edge profiling", 57 false, false) 58 INITIALIZE_PASS_DEPENDENCY(ProfileEstimatorPass) 59 INITIALIZE_AG_DEPENDENCY(ProfileInfo) 60 INITIALIZE_PASS_END(OptimalEdgeProfiler, "insert-optimal-edge-profiling", 61 "Insert optimal instrumentation for edge profiling", 62 false, false) 63 64 ModulePass *llvm::createOptimalEdgeProfilerPass() { 65 return new OptimalEdgeProfiler(); 66 } 67 68 inline static void printEdgeCounter(ProfileInfo::Edge e, 69 BasicBlock* b, 70 unsigned i) { 71 DEBUG(dbgs() << "--Edge Counter for " << (e) << " in " \ 72 << ((b)?(b)->getName():"0") << " (# " << (i) << ")\n"); 73 } 74 75 bool OptimalEdgeProfiler::runOnModule(Module &M) { 76 Function *Main = M.getFunction("main"); 77 if (Main == 0) { 78 errs() << "WARNING: cannot insert edge profiling into a module" 79 << " with no main function!\n"; 80 return false; // No main, no instrumentation! 81 } 82 83 // NumEdges counts all the edges that may be instrumented. Later on its 84 // decided which edges to actually instrument, to achieve optimal profiling. 85 // For the entry block a virtual edge (0,entry) is reserved, for each block 86 // with no successors an edge (BB,0) is reserved. These edges are necessary 87 // to calculate a truly optimal maximum spanning tree and thus an optimal 88 // instrumentation. 89 unsigned NumEdges = 0; 90 91 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { 92 if (F->isDeclaration()) continue; 93 // Reserve space for (0,entry) edge. 94 ++NumEdges; 95 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 96 // Keep track of which blocks need to be instrumented. We don't want to 97 // instrument blocks that are added as the result of breaking critical 98 // edges! 99 if (BB->getTerminator()->getNumSuccessors() == 0) { 100 // Reserve space for (BB,0) edge. 101 ++NumEdges; 102 } else { 103 NumEdges += BB->getTerminator()->getNumSuccessors(); 104 } 105 } 106 } 107 108 // In the profiling output a counter for each edge is reserved, but only few 109 // are used. This is done to be able to read back in the profile without 110 // calulating the maximum spanning tree again, instead each edge counter that 111 // is not used is initialised with -1 to signal that this edge counter has to 112 // be calculated from other edge counters on reading the profile info back 113 // in. 114 115 Type *Int32 = Type::getInt32Ty(M.getContext()); 116 ArrayType *ATy = ArrayType::get(Int32, NumEdges); 117 GlobalVariable *Counters = 118 new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage, 119 Constant::getNullValue(ATy), "OptEdgeProfCounters"); 120 NumEdgesInserted = 0; 121 122 std::vector<Constant*> Initializer(NumEdges); 123 Constant *Zero = ConstantInt::get(Int32, 0); 124 Constant *Uncounted = ConstantInt::get(Int32, ProfileInfoLoader::Uncounted); 125 126 // Instrument all of the edges not in MST... 127 unsigned i = 0; 128 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) { 129 if (F->isDeclaration()) continue; 130 DEBUG(dbgs() << "Working on " << F->getName() << "\n"); 131 132 // Calculate a Maximum Spanning Tree with the edge weights determined by 133 // ProfileEstimator. ProfileEstimator also assign weights to the virtual 134 // edges (0,entry) and (BB,0) (for blocks with no successors) and this 135 // edges also participate in the maximum spanning tree calculation. 136 // The third parameter of MaximumSpanningTree() has the effect that not the 137 // actual MST is returned but the edges _not_ in the MST. 138 139 ProfileInfo::EdgeWeights ECs = 140 getAnalysis<ProfileInfo>(*F).getEdgeWeights(F); 141 std::vector<ProfileInfo::EdgeWeight> EdgeVector(ECs.begin(), ECs.end()); 142 MaximumSpanningTree<BasicBlock> MST(EdgeVector); 143 std::stable_sort(MST.begin(), MST.end()); 144 145 // Check if (0,entry) not in the MST. If not, instrument edge 146 // (IncrementCounterInBlock()) and set the counter initially to zero, if 147 // the edge is in the MST the counter is initialised to -1. 148 149 BasicBlock *entry = &(F->getEntryBlock()); 150 ProfileInfo::Edge edge = ProfileInfo::getEdge(0, entry); 151 if (!std::binary_search(MST.begin(), MST.end(), edge)) { 152 printEdgeCounter(edge, entry, i); 153 IncrementCounterInBlock(entry, i, Counters); ++NumEdgesInserted; 154 Initializer[i++] = (Zero); 155 } else{ 156 Initializer[i++] = (Uncounted); 157 } 158 159 // InsertedBlocks contains all blocks that were inserted for splitting an 160 // edge, this blocks do not have to be instrumented. 161 DenseSet<BasicBlock*> InsertedBlocks; 162 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 163 // Check if block was not inserted and thus does not have to be 164 // instrumented. 165 if (InsertedBlocks.count(BB)) continue; 166 167 // Okay, we have to add a counter of each outgoing edge not in MST. If 168 // the outgoing edge is not critical don't split it, just insert the 169 // counter in the source or destination of the edge. Also, if the block 170 // has no successors, the virtual edge (BB,0) is processed. 171 TerminatorInst *TI = BB->getTerminator(); 172 if (TI->getNumSuccessors() == 0) { 173 ProfileInfo::Edge edge = ProfileInfo::getEdge(BB, 0); 174 if (!std::binary_search(MST.begin(), MST.end(), edge)) { 175 printEdgeCounter(edge, BB, i); 176 IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted; 177 Initializer[i++] = (Zero); 178 } else{ 179 Initializer[i++] = (Uncounted); 180 } 181 } 182 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) { 183 BasicBlock *Succ = TI->getSuccessor(s); 184 ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,Succ); 185 if (!std::binary_search(MST.begin(), MST.end(), edge)) { 186 187 // If the edge is critical, split it. 188 bool wasInserted = SplitCriticalEdge(TI, s, this); 189 Succ = TI->getSuccessor(s); 190 if (wasInserted) 191 InsertedBlocks.insert(Succ); 192 193 // Okay, we are guaranteed that the edge is no longer critical. If 194 // we only have a single successor, insert the counter in this block, 195 // otherwise insert it in the successor block. 196 if (TI->getNumSuccessors() == 1) { 197 // Insert counter at the start of the block 198 printEdgeCounter(edge, BB, i); 199 IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted; 200 } else { 201 // Insert counter at the start of the block 202 printEdgeCounter(edge, Succ, i); 203 IncrementCounterInBlock(Succ, i, Counters); ++NumEdgesInserted; 204 } 205 Initializer[i++] = (Zero); 206 } else { 207 Initializer[i++] = (Uncounted); 208 } 209 } 210 } 211 } 212 213 // Check if the number of edges counted at first was the number of edges we 214 // considered for instrumentation. 215 assert(i == NumEdges && "the number of edges in counting array is wrong"); 216 217 // Assign the now completely defined initialiser to the array. 218 Constant *init = ConstantArray::get(ATy, Initializer); 219 Counters->setInitializer(init); 220 221 // Add the initialization call to main. 222 InsertProfilingInitCall(Main, "llvm_start_opt_edge_profiling", Counters); 223 return true; 224 } 225 226
