1 //===-- ProfilePaths.cpp - interface to insert instrumentation ---*- C++ -*--=//
3 // This inserts intrumentation for counting
4 // execution of paths though a given function
5 // Its implemented as a "Function" Pass, and called using opt
7 // This pass is implemented by using algorithms similar to
8 // 1."Efficient Path Profiling": Ball, T. and Larus, J. R.,
9 // Proceedings of Micro-29, Dec 1996, Paris, France.
10 // 2."Efficiently Counting Program events with support for on-line
11 // "queries": Ball T., ACM Transactions on Programming Languages
12 // and systems, Sep 1994.
14 // The algorithms work on a Graph constructed over the nodes
15 // made from Basic Blocks: The transformations then take place on
16 // the constucted graph (implementation in Graph.cpp and GraphAuxillary.cpp)
17 // and finally, appropriate instrumentation is placed over suitable edges.
18 // (code inserted through EdgeCode.cpp).
20 // The algorithm inserts code such that every acyclic path in the CFG
21 // of a function is identified through a unique number. the code insertion
22 // is optimal in the sense that its inserted over a minimal set of edges. Also,
23 // the algorithm makes sure than initialization, path increment and counter
24 // update can be collapsed into minimum number of edges.
25 //===----------------------------------------------------------------------===//
27 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
28 #include "llvm/Support/CFG.h"
29 #include "llvm/Constants.h"
30 #include "llvm/DerivedTypes.h"
31 #include "llvm/iMemory.h"
32 #include "llvm/Module.h"
38 struct ProfilePaths : public FunctionPass {
39 bool runOnFunction(Function &F);
41 // Before this pass, make sure that there is only one
42 // entry and only one exit node for the function in the CFG of the function
44 void ProfilePaths::getAnalysisUsage(AnalysisUsage &AU) const {
45 AU.addRequired<UnifyFunctionExitNodes>();
49 static RegisterOpt<ProfilePaths> X("paths", "Profile Paths");
51 static Node *findBB(std::vector<Node *> &st, BasicBlock *BB){
52 for(std::vector<Node *>::iterator si=st.begin(); si!=st.end(); ++si){
53 if(((*si)->getElement())==BB){
60 //Per function pass for inserting counters and trigger code
61 bool ProfilePaths::runOnFunction(Function &F){
69 //increment counter for instrumented functions. mn is now function#
72 // Transform the cfg s.t. we have just one exit node
73 BasicBlock *ExitNode = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
75 //iterating over BBs and making graph
76 std::vector<Node *> nodes;
77 std::vector<Edge> edges;
80 Node *exitNode = 0, *startNode = 0;
82 // The nodes must be uniquesly identified:
83 // That is, no two nodes must hav same BB*
85 for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE; ++BB) {
86 Node *nd=new Node(BB);
94 // now do it againto insert edges
95 for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE; ++BB){
96 Node *nd=findBB(nodes, BB);
97 assert(nd && "No node for this edge!");
99 for(BasicBlock::succ_iterator s=succ_begin(BB), se=succ_end(BB);
101 Node *nd2=findBB(nodes,*s);
102 assert(nd2 && "No node for this edge!");
108 Graph g(nodes,edges, startNode, exitNode);
110 #ifdef DEBUG_PATH_PROFILES
111 std::cerr<<"Original graph\n";
115 BasicBlock *fr = &F.front();
117 // The graph is made acyclic: this is done
118 // by removing back edges for now, and adding them later on
120 std::map<Node *, int> nodePriority; //it ranks nodes in depth first order traversal
121 g.getBackEdges(be, nodePriority);
123 #ifdef DEBUG_PATH_PROFILES
124 std::cerr<<"BackEdges-------------\n";
125 for(vector<Edge>::iterator VI=be.begin(); VI!=be.end(); ++VI){
129 std::cerr<<"------\n";
132 #ifdef DEBUG_PATH_PROFILES
133 cerr<<"Backedges:"<<be.size()<<endl;
135 //Now we need to reflect the effect of back edges
136 //This is done by adding dummy edges
137 //If a->b is a back edge
138 //Then we add 2 back edges for it:
139 //1. from root->b (in vector stDummy)
140 //and 2. from a->exit (in vector exDummy)
141 vector<Edge> stDummy;
142 vector<Edge> exDummy;
143 addDummyEdges(stDummy, exDummy, g, be);
145 #ifdef DEBUG_PATH_PROFILES
146 std::cerr<<"After adding dummy edges\n";
150 // Now, every edge in the graph is assigned a weight
151 // This weight later adds on to assign path
152 // numbers to different paths in the graph
153 // All paths for now are acyclic,
154 // since no back edges in the graph now
155 // numPaths is the number of acyclic paths in the graph
156 int numPaths=valueAssignmentToEdges(g, nodePriority, be);
158 //if(numPaths<=1) return false;
160 if(numPaths<=1 || numPaths >5000) return false;
162 #ifdef DEBUG_PATH_PROFILES
166 //create instruction allocation r and count
167 //r is the variable that'll act like an accumulator
168 //all along the path, we just add edge values to r
169 //and at the end, r reflects the path number
170 //count is an array: count[x] would store
171 //the number of executions of path numbered x
173 Instruction *rVar=new
174 AllocaInst(Type::IntTy,
175 ConstantUInt::get(Type::UIntTy,1),"R");
177 //Instruction *countVar=new
178 //AllocaInst(Type::IntTy,
179 // ConstantUInt::get(Type::UIntTy, numPaths), "Count");
181 //initialize counter array!
182 std::vector<Constant*> arrayInitialize;
183 for(int xi=0; xi<numPaths; xi++)
184 arrayInitialize.push_back(ConstantSInt::get(Type::IntTy, 0));
186 const ArrayType *ATy = ArrayType::get(Type::IntTy, numPaths);
187 Constant *initializer = ConstantArray::get(ATy, arrayInitialize);
188 GlobalVariable *countVar = new GlobalVariable(ATy, false,
189 GlobalValue::InternalLinkage,
190 initializer, "Count",
192 static GlobalVariable *threshold = NULL;
193 static bool insertedThreshold = false;
195 if(!insertedThreshold){
196 threshold = new GlobalVariable(Type::IntTy, false,
197 GlobalValue::ExternalLinkage, 0,
200 F.getParent()->getGlobalList().push_back(threshold);
201 insertedThreshold = true;
204 assert(threshold && "GlobalVariable threshold not defined!");
206 // insert initialization code in first (entry) BB
207 // this includes initializing r and count
208 insertInTopBB(&F.getEntryNode(),numPaths, rVar, threshold);
210 //now process the graph: get path numbers,
211 //get increments along different paths,
212 //and assign "increments" and "updates" (to r and count)
213 //"optimally". Finally, insert llvm code along various edges
214 processGraph(g, rVar, countVar, be, stDummy, exDummy, numPaths, mn,
217 return true; // Always modifies function