lib/Transforms/Instrumentation/OptimalEdgeProfiling.cpp

   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)->getNameStr():"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   const Type *Int32 = Type::getInt32Ty(M.getContext());
 116   const 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->getNameStr() << "\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