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