1//===- OptimalEdgeProfiling.cpp - Insert counters for opt. 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//===----------------------------------------------------------------------===//
15#define DEBUG_TYPE "insert-optimal-edge-profiling"
16#include "llvm/Transforms/Instrumentation.h"
17#include "MaximumSpanningTree.h"
18#include "ProfilingUtils.h"
19#include "llvm/ADT/DenseSet.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/Analysis/Passes.h"
22#include "llvm/Analysis/ProfileInfo.h"
23#include "llvm/Analysis/ProfileInfoLoader.h"
24#include "llvm/IR/Constants.h"
25#include "llvm/IR/Module.h"
26#include "llvm/Pass.h"
27#include "llvm/Support/Debug.h"
28#include "llvm/Support/raw_ostream.h"
29#include "llvm/Transforms/Utils/BasicBlockUtils.h"
30using namespace llvm;
31
32STATISTIC(NumEdgesInserted, "The # of edges inserted.");
33
34namespace {
35  class OptimalEdgeProfiler : public ModulePass {
36    bool runOnModule(Module &M);
37  public:
38    static char ID; // Pass identification, replacement for typeid
39    OptimalEdgeProfiler() : ModulePass(ID) {
40      initializeOptimalEdgeProfilerPass(*PassRegistry::getPassRegistry());
41    }
42
43    void getAnalysisUsage(AnalysisUsage &AU) const {
44      AU.addRequiredID(ProfileEstimatorPassID);
45      AU.addRequired<ProfileInfo>();
46    }
47
48    virtual const char *getPassName() const {
49      return "Optimal Edge Profiler";
50    }
51  };
52}
53
54char OptimalEdgeProfiler::ID = 0;
55INITIALIZE_PASS_BEGIN(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
56                "Insert optimal instrumentation for edge profiling",
57                false, false)
58INITIALIZE_PASS_DEPENDENCY(ProfileEstimatorPass)
59INITIALIZE_AG_DEPENDENCY(ProfileInfo)
60INITIALIZE_PASS_END(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
61                "Insert optimal instrumentation for edge profiling",
62                false, false)
63
64ModulePass *llvm::createOptimalEdgeProfilerPass() {
65  return new OptimalEdgeProfiler();
66}
67
68inline static void printEdgeCounter(ProfileInfo::Edge e,
69                                    BasicBlock* b,
70                                    unsigned i) {
71  DEBUG(dbgs() << "--Edge Counter for " << (e) << " in " \
72               << ((b)?(b)->getName():"0") << " (# " << (i) << ")\n");
73}
74
75bool OptimalEdgeProfiler::runOnModule(Module &M) {
76  Function *Main = M.getFunction("main");
77  if (Main == 0) {
78    errs() << "WARNING: cannot insert edge profiling into a module"
79           << " with no main function!\n";
80    return false;  // No main, no instrumentation!
81  }
82
83  // NumEdges counts all the edges that may be instrumented. Later on its
84  // decided which edges to actually instrument, to achieve optimal profiling.
85  // For the entry block a virtual edge (0,entry) is reserved, for each block
86  // with no successors an edge (BB,0) is reserved. These edges are necessary
87  // to calculate a truly optimal maximum spanning tree and thus an optimal
88  // instrumentation.
89  unsigned NumEdges = 0;
90
91  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
92    if (F->isDeclaration()) continue;
93    // Reserve space for (0,entry) edge.
94    ++NumEdges;
95    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
96      // Keep track of which blocks need to be instrumented.  We don't want to
97      // instrument blocks that are added as the result of breaking critical
98      // edges!
99      if (BB->getTerminator()->getNumSuccessors() == 0) {
100        // Reserve space for (BB,0) edge.
101        ++NumEdges;
102      } else {
103        NumEdges += BB->getTerminator()->getNumSuccessors();
104      }
105    }
106  }
107
108  // In the profiling output a counter for each edge is reserved, but only few
109  // are used. This is done to be able to read back in the profile without
110  // calulating the maximum spanning tree again, instead each edge counter that
111  // is not used is initialised with -1 to signal that this edge counter has to
112  // be calculated from other edge counters on reading the profile info back
113  // in.
114
115  Type *Int32 = Type::getInt32Ty(M.getContext());
116  ArrayType *ATy = ArrayType::get(Int32, NumEdges);
117  GlobalVariable *Counters =
118    new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
119                       Constant::getNullValue(ATy), "OptEdgeProfCounters");
120  NumEdgesInserted = 0;
121
122  std::vector<Constant*> Initializer(NumEdges);
123  Constant *Zero = ConstantInt::get(Int32, 0);
124  Constant *Uncounted = ConstantInt::get(Int32, ProfileInfoLoader::Uncounted);
125
126  // Instrument all of the edges not in MST...
127  unsigned i = 0;
128  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
129    if (F->isDeclaration()) continue;
130    DEBUG(dbgs() << "Working on " << F->getName() << "\n");
131
132    // Calculate a Maximum Spanning Tree with the edge weights determined by
133    // ProfileEstimator. ProfileEstimator also assign weights to the virtual
134    // edges (0,entry) and (BB,0) (for blocks with no successors) and this
135    // edges also participate in the maximum spanning tree calculation.
136    // The third parameter of MaximumSpanningTree() has the effect that not the
137    // actual MST is returned but the edges _not_ in the MST.
138
139    ProfileInfo::EdgeWeights ECs =
140      getAnalysis<ProfileInfo>(*F).getEdgeWeights(F);
141    std::vector<ProfileInfo::EdgeWeight> EdgeVector(ECs.begin(), ECs.end());
142    MaximumSpanningTree<BasicBlock> MST(EdgeVector);
143    std::stable_sort(MST.begin(), MST.end());
144
145    // Check if (0,entry) not in the MST. If not, instrument edge
146    // (IncrementCounterInBlock()) and set the counter initially to zero, if
147    // the edge is in the MST the counter is initialised to -1.
148
149    BasicBlock *entry = &(F->getEntryBlock());
150    ProfileInfo::Edge edge = ProfileInfo::getEdge(0, entry);
151    if (!std::binary_search(MST.begin(), MST.end(), edge)) {
152      printEdgeCounter(edge, entry, i);
153      IncrementCounterInBlock(entry, i, Counters); ++NumEdgesInserted;
154      Initializer[i++] = (Zero);
155    } else{
156      Initializer[i++] = (Uncounted);
157    }
158
159    // InsertedBlocks contains all blocks that were inserted for splitting an
160    // edge, this blocks do not have to be instrumented.
161    DenseSet<BasicBlock*> InsertedBlocks;
162    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
163      // Check if block was not inserted and thus does not have to be
164      // instrumented.
165      if (InsertedBlocks.count(BB)) continue;
166
167      // Okay, we have to add a counter of each outgoing edge not in MST. If
168      // the outgoing edge is not critical don't split it, just insert the
169      // counter in the source or destination of the edge. Also, if the block
170      // has no successors, the virtual edge (BB,0) is processed.
171      TerminatorInst *TI = BB->getTerminator();
172      if (TI->getNumSuccessors() == 0) {
173        ProfileInfo::Edge edge = ProfileInfo::getEdge(BB, 0);
174        if (!std::binary_search(MST.begin(), MST.end(), edge)) {
175          printEdgeCounter(edge, BB, i);
176          IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
177          Initializer[i++] = (Zero);
178        } else{
179          Initializer[i++] = (Uncounted);
180        }
181      }
182      for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
183        BasicBlock *Succ = TI->getSuccessor(s);
184        ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,Succ);
185        if (!std::binary_search(MST.begin(), MST.end(), edge)) {
186
187          // If the edge is critical, split it.
188          bool wasInserted = SplitCriticalEdge(TI, s, this);
189          Succ = TI->getSuccessor(s);
190          if (wasInserted)
191            InsertedBlocks.insert(Succ);
192
193          // Okay, we are guaranteed that the edge is no longer critical.  If
194          // we only have a single successor, insert the counter in this block,
195          // otherwise insert it in the successor block.
196          if (TI->getNumSuccessors() == 1) {
197            // Insert counter at the start of the block
198            printEdgeCounter(edge, BB, i);
199            IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
200          } else {
201            // Insert counter at the start of the block
202            printEdgeCounter(edge, Succ, i);
203            IncrementCounterInBlock(Succ, i, Counters); ++NumEdgesInserted;
204          }
205          Initializer[i++] = (Zero);
206        } else {
207          Initializer[i++] = (Uncounted);
208        }
209      }
210    }
211  }
212
213  // Check if the number of edges counted at first was the number of edges we
214  // considered for instrumentation.
215  assert(i == NumEdges && "the number of edges in counting array is wrong");
216
217  // Assign the now completely defined initialiser to the array.
218  Constant *init = ConstantArray::get(ATy, Initializer);
219  Counters->setInitializer(init);
220
221  // Add the initialization call to main.
222  InsertProfilingInitCall(Main, "llvm_start_opt_edge_profiling", Counters);
223  return true;
224}
225
226