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 INITIALIZE_PASS_BEGIN(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
54 "Insert optimal instrumentation for edge profiling",
56 INITIALIZE_PASS_DEPENDENCY(ProfileEstimatorPass)
57 INITIALIZE_AG_DEPENDENCY(ProfileInfo)
58 INITIALIZE_PASS_END(OptimalEdgeProfiler, "insert-optimal-edge-profiling",
59 "Insert optimal instrumentation for edge profiling",
62 ModulePass *llvm::createOptimalEdgeProfilerPass() {
63 return new OptimalEdgeProfiler();
66 inline static void printEdgeCounter(ProfileInfo::Edge e,
69 DEBUG(dbgs() << "--Edge Counter for " << (e) << " in " \
70 << ((b)?(b)->getNameStr():"0") << " (# " << (i) << ")\n");
73 bool OptimalEdgeProfiler::runOnModule(Module &M) {
74 Function *Main = M.getFunction("main");
76 errs() << "WARNING: cannot insert edge profiling into a module"
77 << " with no main function!\n";
78 return false; // No main, no instrumentation!
81 // NumEdges counts all the edges that may be instrumented. Later on its
82 // decided which edges to actually instrument, to achieve optimal profiling.
83 // For the entry block a virtual edge (0,entry) is reserved, for each block
84 // with no successors an edge (BB,0) is reserved. These edges are necessary
85 // to calculate a truly optimal maximum spanning tree and thus an optimal
87 unsigned NumEdges = 0;
89 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
90 if (F->isDeclaration()) continue;
91 // Reserve space for (0,entry) edge.
93 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
94 // Keep track of which blocks need to be instrumented. We don't want to
95 // instrument blocks that are added as the result of breaking critical
97 if (BB->getTerminator()->getNumSuccessors() == 0) {
98 // Reserve space for (BB,0) edge.
101 NumEdges += BB->getTerminator()->getNumSuccessors();
106 // In the profiling output a counter for each edge is reserved, but only few
107 // are used. This is done to be able to read back in the profile without
108 // calulating the maximum spanning tree again, instead each edge counter that
109 // is not used is initialised with -1 to signal that this edge counter has to
110 // be calculated from other edge counters on reading the profile info back
113 const Type *Int32 = Type::getInt32Ty(M.getContext());
114 const ArrayType *ATy = ArrayType::get(Int32, NumEdges);
115 GlobalVariable *Counters =
116 new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
117 Constant::getNullValue(ATy), "OptEdgeProfCounters");
118 NumEdgesInserted = 0;
120 std::vector<Constant*> Initializer(NumEdges);
121 Constant* Zero = ConstantInt::get(Int32, 0);
122 Constant* Uncounted = ConstantInt::get(Int32, ProfileInfoLoader::Uncounted);
124 // Instrument all of the edges not in MST...
126 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
127 if (F->isDeclaration()) continue;
128 DEBUG(dbgs()<<"Working on "<<F->getNameStr()<<"\n");
130 // Calculate a Maximum Spanning Tree with the edge weights determined by
131 // ProfileEstimator. ProfileEstimator also assign weights to the virtual
132 // edges (0,entry) and (BB,0) (for blocks with no successors) and this
133 // edges also participate in the maximum spanning tree calculation.
134 // The third parameter of MaximumSpanningTree() has the effect that not the
135 // actual MST is returned but the edges _not_ in the MST.
137 ProfileInfo::EdgeWeights ECs =
138 getAnalysis<ProfileInfo>(*F).getEdgeWeights(F);
139 std::vector<ProfileInfo::EdgeWeight> EdgeVector(ECs.begin(), ECs.end());
140 MaximumSpanningTree<BasicBlock> MST (EdgeVector);
141 std::stable_sort(MST.begin(),MST.end());
143 // Check if (0,entry) not in the MST. If not, instrument edge
144 // (IncrementCounterInBlock()) and set the counter initially to zero, if
145 // the edge is in the MST the counter is initialised to -1.
147 BasicBlock *entry = &(F->getEntryBlock());
148 ProfileInfo::Edge edge = ProfileInfo::getEdge(0,entry);
149 if (!std::binary_search(MST.begin(), MST.end(), edge)) {
150 printEdgeCounter(edge,entry,i);
151 IncrementCounterInBlock(entry, i, Counters); ++NumEdgesInserted;
152 Initializer[i++] = (Zero);
154 Initializer[i++] = (Uncounted);
157 // InsertedBlocks contains all blocks that were inserted for splitting an
158 // edge, this blocks do not have to be instrumented.
159 DenseSet<BasicBlock*> InsertedBlocks;
160 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
161 // Check if block was not inserted and thus does not have to be
163 if (InsertedBlocks.count(BB)) continue;
165 // Okay, we have to add a counter of each outgoing edge not in MST. If
166 // the outgoing edge is not critical don't split it, just insert the
167 // counter in the source or destination of the edge. Also, if the block
168 // has no successors, the virtual edge (BB,0) is processed.
169 TerminatorInst *TI = BB->getTerminator();
170 if (TI->getNumSuccessors() == 0) {
171 ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,0);
172 if (!std::binary_search(MST.begin(), MST.end(), edge)) {
173 printEdgeCounter(edge,BB,i);
174 IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
175 Initializer[i++] = (Zero);
177 Initializer[i++] = (Uncounted);
180 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
181 BasicBlock *Succ = TI->getSuccessor(s);
182 ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,Succ);
183 if (!std::binary_search(MST.begin(), MST.end(), edge)) {
185 // If the edge is critical, split it.
186 bool wasInserted = SplitCriticalEdge(TI, s, this);
187 Succ = TI->getSuccessor(s);
189 InsertedBlocks.insert(Succ);
191 // Okay, we are guaranteed that the edge is no longer critical. If
192 // we only have a single successor, insert the counter in this block,
193 // otherwise insert it in the successor block.
194 if (TI->getNumSuccessors() == 1) {
195 // Insert counter at the start of the block
196 printEdgeCounter(edge,BB,i);
197 IncrementCounterInBlock(BB, i, Counters); ++NumEdgesInserted;
199 // Insert counter at the start of the block
200 printEdgeCounter(edge,Succ,i);
201 IncrementCounterInBlock(Succ, i, Counters); ++NumEdgesInserted;
203 Initializer[i++] = (Zero);
205 Initializer[i++] = (Uncounted);
211 // Check if the number of edges counted at first was the number of edges we
212 // considered for instrumentation.
213 assert(i==NumEdges && "the number of edges in counting array is wrong");
215 // Assing the now completely defined initialiser to the array.
216 Constant *init = ConstantArray::get(ATy, Initializer);
217 Counters->setInitializer(init);
219 // Add the initialization call to main.
220 InsertProfilingInitCall(Main, "llvm_start_opt_edge_profiling", Counters);