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
  20 #include "ProfilingUtils.h"
  21 #include "llvm/Constants.h"
  22 #include "llvm/DerivedTypes.h"
  23 #include "llvm/Module.h"
  24 #include "llvm/Pass.h"
  25 #include "llvm/Support/Compiler.h"
  26 #include "llvm/Support/Streams.h"
  27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  28 #include "llvm/Transforms/Instrumentation.h"
  29 #include <set>
  30 using namespace llvm;
  31
  32 namespace {
  33   class VISIBILITY_HIDDEN EdgeProfiler : public ModulePass {
  34     bool runOnModule(Module &M);
  35   public:
  36     static char ID; // Pass identification, replacement for typeid
  37     EdgeProfiler() : ModulePass(&ID) {}
  38   };
  39 }
  40
  41 char EdgeProfiler::ID = 0;
  42 static RegisterPass<EdgeProfiler>
  43 X("insert-edge-profiling", "Insert instrumentation for edge profiling");
  44
  45 ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
  46
  47 bool EdgeProfiler::runOnModule(Module &M) {
  48   Function *Main = M.getFunction("main");
  49   if (Main == 0) {
  50     cerr << "WARNING: cannot insert edge profiling into a module"
  51          << " with no main function!\n";
  52     return false;  // No main, no instrumentation!
  53   }
  54
  55   std::set<BasicBlock*> BlocksToInstrument;
  56   unsigned NumEdges = 0;
  57   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
  58     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
  59       // Keep track of which blocks need to be instrumented.  We don't want to
  60       // instrument blocks that are added as the result of breaking critical
  61       // edges!
  62       BlocksToInstrument.insert(BB);
  63       NumEdges += BB->getTerminator()->getNumSuccessors();
  64     }
  65
  66   const Type *ATy = ArrayType::get(Type::Int32Ty, NumEdges);
  67   GlobalVariable *Counters =
  68     new GlobalVariable(ATy, false, GlobalValue::InternalLinkage,
  69                        Constant::getNullValue(ATy), "EdgeProfCounters", &M);
  70
  71   // Instrument all of the edges...
  72   unsigned i = 0;
  73   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
  74     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
  75       if (BlocksToInstrument.count(BB)) {  // Don't instrument inserted blocks
  76         // Okay, we have to add a counter of each outgoing edge.  If the
  77         // outgoing edge is not critical don't split it, just insert the counter
  78         // in the source or destination of the edge.
  79         TerminatorInst *TI = BB->getTerminator();
  80         for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
  81           // If the edge is critical, split it.
  82           SplitCriticalEdge(TI, s, this);
  83
  84           // Okay, we are guaranteed that the edge is no longer critical.  If we
  85           // only have a single successor, insert the counter in this block,
  86           // otherwise insert it in the successor block.
  87           if (TI->getNumSuccessors() == 1) {
  88             // Insert counter at the start of the block
  89             IncrementCounterInBlock(BB, i++, Counters);
  90           } else {
  91             // Insert counter at the start of the block
  92             IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
  93           }
  94         }
  95       }
  96
  97   // Add the initialization call to main.
  98   InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);
  99   return true;
 100 }
 101