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