lib/Transforms/Instrumentation/EdgeProfiling.cpp

   1 //===- EdgeProfiling.cpp - Insert counters for 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 // Note that this implementation is very naive.  We insert a counter for *every*
  15 // edge in the program, instead of using control flow information to prune the
  16 // number of counters inserted.
  17 //
  18 //===----------------------------------------------------------------------===//
  19 #define DEBUG_TYPE "insert-edge-profiling"
  20
  21 #include "ProfilingUtils.h"
  22 #include "llvm/Module.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/Support/raw_ostream.h"
  25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  26 #include "llvm/Transforms/Instrumentation.h"
  27 #include "llvm/ADT/Statistic.h"
  28 #include <set>
  29 using namespace llvm;
  30
  31 STATISTIC(NumEdgesInserted, "The # of edges inserted.");
  32
  33 namespace {
  34   class EdgeProfiler : public ModulePass {
  35     bool runOnModule(Module &M);
  36   public:
  37     static char ID; // Pass identification, replacement for typeid
  38     EdgeProfiler() : ModulePass(ID) {
  39       initializeEdgeProfilerPass(*PassRegistry::getPassRegistry());
  40     }
  41
  42     virtual const char *getPassName() const {
  43       return "Edge Profiler";
  44     }
  45   };
  46 }
  47
  48 char EdgeProfiler::ID = 0;
  49 INITIALIZE_PASS(EdgeProfiler, "insert-edge-profiling",
  50                 "Insert instrumentation for edge profiling", false, false)
  51
  52 ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
  53
  54 bool EdgeProfiler::runOnModule(Module &M) {
  55   Function *Main = M.getFunction("main");
  56   if (Main == 0) {
  57     errs() << "WARNING: cannot insert edge profiling into a module"
  58            << " with no main function!\n";
  59     return false;  // No main, no instrumentation!
  60   }
  61
  62   std::set<BasicBlock*> BlocksToInstrument;
  63   unsigned NumEdges = 0;
  64   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
  65     if (F->isDeclaration()) continue;
  66     // Reserve space for (0,entry) edge.
  67     ++NumEdges;
  68     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
  69       // Keep track of which blocks need to be instrumented.  We don't want to
  70       // instrument blocks that are added as the result of breaking critical
  71       // edges!
  72       BlocksToInstrument.insert(BB);
  73       NumEdges += BB->getTerminator()->getNumSuccessors();
  74     }
  75   }
  76
  77   const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), NumEdges);
  78   GlobalVariable *Counters =
  79     new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
  80                        Constant::getNullValue(ATy), "EdgeProfCounters");
  81   NumEdgesInserted = NumEdges;
  82
  83   // Instrument all of the edges...
  84   unsigned i = 0;
  85   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
  86     if (F->isDeclaration()) continue;
  87     // Create counter for (0,entry) edge.
  88     IncrementCounterInBlock(&F->getEntryBlock(), i++, Counters);
  89     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
  90       if (BlocksToInstrument.count(BB)) {  // Don't instrument inserted blocks
  91         // Okay, we have to add a counter of each outgoing edge.  If the
  92         // outgoing edge is not critical don't split it, just insert the counter
  93         // in the source or destination of the edge.
  94         TerminatorInst *TI = BB->getTerminator();
  95         for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
  96           // If the edge is critical, split it.
  97           SplitCriticalEdge(TI, s, this);
  98
  99           // Okay, we are guaranteed that the edge is no longer critical.  If we
 100           // only have a single successor, insert the counter in this block,
 101           // otherwise insert it in the successor block.
 102           if (TI->getNumSuccessors() == 1) {
 103             // Insert counter at the start of the block
 104             IncrementCounterInBlock(BB, i++, Counters, false);
 105           } else {
 106             // Insert counter at the start of the block
 107             IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
 108           }
 109         }
 110       }
 111   }
 112
 113   // Add the initialization call to main.
 114   InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);
 115   return true;
 116 }
 117