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