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#define DEBUG_TYPE "insert-edge-profiling"
20
21#include "llvm/Transforms/Instrumentation.h"
22#include "ProfilingUtils.h"
23#include "llvm/ADT/Statistic.h"
24#include "llvm/IR/Module.h"
25#include "llvm/Pass.h"
26#include "llvm/Support/raw_ostream.h"
27#include "llvm/Transforms/Utils/BasicBlockUtils.h"
28#include <set>
29using namespace llvm;
30
31STATISTIC(NumEdgesInserted, "The # of edges inserted.");
32
33namespace {
34  class EdgeProfiler : public ModulePass {
35    bool runOnModule(Module &M);
36  public:
37    static char ID; // Pass identification, replacement for typeid
38    EdgeProfiler() : ModulePass(ID) {
39      initializeEdgeProfilerPass(*PassRegistry::getPassRegistry());
40    }
41
42    virtual const char *getPassName() const {
43      return "Edge Profiler";
44    }
45  };
46}
47
48char EdgeProfiler::ID = 0;
49INITIALIZE_PASS(EdgeProfiler, "insert-edge-profiling",
50                "Insert instrumentation for edge profiling", false, false)
51
52ModulePass *llvm::createEdgeProfilerPass() { return new EdgeProfiler(); }
53
54bool EdgeProfiler::runOnModule(Module &M) {
55  Function *Main = M.getFunction("main");
56  if (Main == 0) {
57    errs() << "WARNING: cannot insert edge profiling into a module"
58           << " with no main function!\n";
59    return false;  // No main, no instrumentation!
60  }
61
62  std::set<BasicBlock*> BlocksToInstrument;
63  unsigned NumEdges = 0;
64  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
65    if (F->isDeclaration()) continue;
66    // Reserve space for (0,entry) edge.
67    ++NumEdges;
68    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
69      // Keep track of which blocks need to be instrumented.  We don't want to
70      // instrument blocks that are added as the result of breaking critical
71      // edges!
72      BlocksToInstrument.insert(BB);
73      NumEdges += BB->getTerminator()->getNumSuccessors();
74    }
75  }
76
77  Type *ATy = ArrayType::get(Type::getInt32Ty(M.getContext()), NumEdges);
78  GlobalVariable *Counters =
79    new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
80                       Constant::getNullValue(ATy), "EdgeProfCounters");
81  NumEdgesInserted = NumEdges;
82
83  // Instrument all of the edges...
84  unsigned i = 0;
85  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
86    if (F->isDeclaration()) continue;
87    // Create counter for (0,entry) edge.
88    IncrementCounterInBlock(&F->getEntryBlock(), i++, Counters);
89    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
90      if (BlocksToInstrument.count(BB)) {  // Don't instrument inserted blocks
91        // Okay, we have to add a counter of each outgoing edge.  If the
92        // outgoing edge is not critical don't split it, just insert the counter
93        // in the source or destination of the edge.
94        TerminatorInst *TI = BB->getTerminator();
95        for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
96          // If the edge is critical, split it.
97          SplitCriticalEdge(TI, s, this);
98
99          // Okay, we are guaranteed that the edge is no longer critical.  If we
100          // only have a single successor, insert the counter in this block,
101          // otherwise insert it in the successor block.
102          if (TI->getNumSuccessors() == 1) {
103            // Insert counter at the start of the block
104            IncrementCounterInBlock(BB, i++, Counters, false);
105          } else {
106            // Insert counter at the start of the block
107            IncrementCounterInBlock(TI->getSuccessor(s), i++, Counters);
108          }
109        }
110      }
111  }
112
113  // Add the initialization call to main.
114  InsertProfilingInitCall(Main, "llvm_start_edge_profiling", Counters);
115  return true;
116}
117
118