1 //===- EdgeProfiling.cpp - Insert counters for edge profiling -------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
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.
18 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "insert-edge-profiling"
20 #include "ProfilingUtils.h"
21 #include "llvm/Module.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Support/raw_ostream.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/Transforms/Instrumentation.h"
26 #include "llvm/ADT/Statistic.h"
30 STATISTIC(NumEdgesInserted, "The # of edges inserted.");
33 class EdgeProfiler : public ModulePass {
34 bool runOnModule(Module &M);
36 static char ID; // Pass identification, replacement for typeid
37 EdgeProfiler() : ModulePass(&ID) {}
39 virtual const char *getPassName() const {
40 return "Edge Profiler";
45 char EdgeProfiler::ID = 0;
46 static RegisterPass<EdgeProfiler>
47 X("insert-edge-profiling", "Insert instrumentation for edge profiling");
49 ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
51 bool EdgeProfiler::runOnModule(Module &M) {
52 Function *Main = M.getFunction("main");
54 errs() << "WARNING: cannot insert edge profiling into a module"
55 << " with no main function!\n";
56 return false; // No main, no instrumentation!
59 std::set<BasicBlock*> BlocksToInstrument;
60 unsigned NumEdges = 0;
61 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
62 if (F->isDeclaration()) continue;
63 // Reserve space for (0,entry) edge.
65 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
66 // Keep track of which blocks need to be instrumented. We don't want to
67 // instrument blocks that are added as the result of breaking critical
69 BlocksToInstrument.insert(BB);
70 NumEdges += BB->getTerminator()->getNumSuccessors();
74 const Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), NumEdges);
75 GlobalVariable *Counters =
76 new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
77 Constant::getNullValue(ATy), "EdgeProfCounters");
78 NumEdgesInserted = NumEdges;
80 // Instrument all of the edges...
82 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
83 if (F->isDeclaration()) continue;
84 // Create counter for (0,entry) edge.
85 IncrementCounterInBlock(&F->getEntryBlock(), i++, Counters);
86 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
87 if (BlocksToInstrument.count(BB)) { // Don't instrument inserted blocks
88 // Okay, we have to add a counter of each outgoing edge. If the
89 // outgoing edge is not critical don't split it, just insert the counter
90 // in the source or destination of the edge.
91 TerminatorInst *TI = BB->getTerminator();
92 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
93 // If the edge is critical, split it.
94 SplitCriticalEdge(TI, s, this);
96 // Okay, we are guaranteed that the edge is no longer critical. If we
97 // only have a single successor, insert the counter in this block,
98 // otherwise insert it in the successor block.
99 if (TI->getNumSuccessors() == 1) {
100 // Insert counter at the start of the block
101 IncrementCounterInBlock(BB, i++, Counters);
103 // Insert counter at the start of the block
104 IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
110 // Add the initialization call to main.
111 InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);