EdgeProfiling.cpp revision 089efffd7d1ca0d10522ace38d36e0a67f4fac2d 
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>
30using namespace llvm;
31
32namespace {
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((intptr_t)&ID) {}
38  };
39}
40
41char EdgeProfiler::ID = 0;
42static RegisterPass<EdgeProfiler>
43X("insert-edge-profiling", "Insert instrumentation for edge profiling");
44
45ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
46
47bool 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
102