LLVM API Documentation
00001 //===- EdgeProfiling.cpp - Insert counters for edge profiling -------------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This pass instruments the specified program with counters for edge profiling. 00011 // Edge profiling can give a reasonable approximation of the hot paths through a 00012 // program, and is used for a wide variety of program transformations. 00013 // 00014 // Note that this implementation is very naive. We insert a counter for *every* 00015 // edge in the program, instead of using control flow information to prune the 00016 // number of counters inserted. 00017 // 00018 //===----------------------------------------------------------------------===// 00019 00020 #include "llvm/Constants.h" 00021 #include "llvm/DerivedTypes.h" 00022 #include "llvm/Module.h" 00023 #include "llvm/Pass.h" 00024 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 00025 #include "llvm/Transforms/Instrumentation.h" 00026 #include "ProfilingUtils.h" 00027 #include <iostream> 00028 #include <set> 00029 using namespace llvm; 00030 00031 namespace { 00032 class EdgeProfiler : public ModulePass { 00033 bool runOnModule(Module &M); 00034 }; 00035 00036 RegisterOpt<EdgeProfiler> X("insert-edge-profiling", 00037 "Insert instrumentation for edge profiling"); 00038 } 00039 00040 ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); } 00041 00042 bool EdgeProfiler::runOnModule(Module &M) { 00043 Function *Main = M.getMainFunction(); 00044 if (Main == 0) { 00045 std::cerr << "WARNING: cannot insert edge profiling into a module" 00046 << " with no main function!\n"; 00047 return false; // No main, no instrumentation! 00048 } 00049 00050 std::set<BasicBlock*> BlocksToInstrument; 00051 unsigned NumEdges = 0; 00052 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) 00053 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { 00054 // Keep track of which blocks need to be instrumented. We don't want to 00055 // instrument blocks that are added as the result of breaking critical 00056 // edges! 00057 BlocksToInstrument.insert(BB); 00058 NumEdges += BB->getTerminator()->getNumSuccessors(); 00059 } 00060 00061 const Type *ATy = ArrayType::get(Type::UIntTy, NumEdges); 00062 GlobalVariable *Counters = 00063 new GlobalVariable(ATy, false, GlobalValue::InternalLinkage, 00064 Constant::getNullValue(ATy), "EdgeProfCounters", &M); 00065 00066 // Instrument all of the edges... 00067 unsigned i = 0; 00068 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) 00069 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) 00070 if (BlocksToInstrument.count(BB)) { // Don't instrument inserted blocks 00071 // Okay, we have to add a counter of each outgoing edge. If the 00072 // outgoing edge is not critical don't split it, just insert the counter 00073 // in the source or destination of the edge. 00074 TerminatorInst *TI = BB->getTerminator(); 00075 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) { 00076 // If the edge is critical, split it. 00077 SplitCriticalEdge(TI, s, this); 00078 00079 // Okay, we are guaranteed that the edge is no longer critical. If we 00080 // only have a single successor, insert the counter in this block, 00081 // otherwise insert it in the successor block. 00082 if (TI->getNumSuccessors() == 0) { 00083 // Insert counter at the start of the block 00084 IncrementCounterInBlock(BB, i++, Counters); 00085 } else { 00086 // Insert counter at the start of the block 00087 IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters); 00088 } 00089 } 00090 } 00091 00092 // Add the initialization call to main. 00093 InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters); 00094 return true; 00095 } 00096