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