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/Instrumentation/ProfilePaths.h"
28 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
29 #include "llvm/Transforms/Instrumentation/Graph.h"
30 #include "llvm/Support/CFG.h"
31 #include "llvm/Constants.h"
32 #include "llvm/DerivedTypes.h"
33 #include "llvm/iMemory.h"
34 #include "llvm/GlobalVariable.h"
35 #include "llvm/Module.h"
41 struct ProfilePaths : public FunctionPass {
42 bool runOnFunction(Function &F);
44 // Before this pass, make sure that there is only one
45 // entry and only one exit node for the function in the CFG of the function
47 void ProfilePaths::getAnalysisUsage(AnalysisUsage &AU) const {
48 AU.addRequired<UnifyFunctionExitNodes>();
52 static RegisterOpt<ProfilePaths> X("paths", "Profile Paths");
54 // createProfilePathsPass - Create a new pass to add path profiling
56 Pass *createProfilePathsPass() {
57 return new ProfilePaths();
61 static Node *findBB(std::vector<Node *> &st, BasicBlock *BB){
62 for(std::vector<Node *>::iterator si=st.begin(); si!=st.end(); ++si){
63 if(((*si)->getElement())==BB){
70 //Per function pass for inserting counters and trigger code
71 bool ProfilePaths::runOnFunction(Function &F){
79 //increment counter for instrumented functions. mn is now function#
82 // Transform the cfg s.t. we have just one exit node
83 BasicBlock *ExitNode = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
85 //iterating over BBs and making graph
86 std::vector<Node *> nodes;
87 std::vector<Edge> edges;
90 Node *exitNode, *startNode;
92 // The nodes must be uniquesly identified:
93 // That is, no two nodes must hav same BB*
95 for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE; ++BB) {
96 Node *nd=new Node(BB);
104 // now do it againto insert edges
105 for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE; ++BB){
106 Node *nd=findBB(nodes, BB);
107 assert(nd && "No node for this edge!");
109 for(BasicBlock::succ_iterator s=succ_begin(BB), se=succ_end(BB);
111 Node *nd2=findBB(nodes,*s);
112 assert(nd2 && "No node for this edge!");
118 Graph g(nodes,edges, startNode, exitNode);
120 #ifdef DEBUG_PATH_PROFILES
121 std::cerr<<"Original graph\n";
125 BasicBlock *fr = &F.front();
127 // The graph is made acyclic: this is done
128 // by removing back edges for now, and adding them later on
130 std::map<Node *, int> nodePriority; //it ranks nodes in depth first order traversal
131 g.getBackEdges(be, nodePriority);
133 #ifdef DEBUG_PATH_PROFILES
134 std::cerr<<"BackEdges-------------\n";
135 for(vector<Edge>::iterator VI=be.begin(); VI!=be.end(); ++VI){
139 std::cerr<<"------\n";
142 #ifdef DEBUG_PATH_PROFILES
143 cerr<<"Backedges:"<<be.size()<<endl;
145 //Now we need to reflect the effect of back edges
146 //This is done by adding dummy edges
147 //If a->b is a back edge
148 //Then we add 2 back edges for it:
149 //1. from root->b (in vector stDummy)
150 //and 2. from a->exit (in vector exDummy)
151 vector<Edge> stDummy;
152 vector<Edge> exDummy;
153 addDummyEdges(stDummy, exDummy, g, be);
155 #ifdef DEBUG_PATH_PROFILES
156 std::cerr<<"After adding dummy edges\n";
160 // Now, every edge in the graph is assigned a weight
161 // This weight later adds on to assign path
162 // numbers to different paths in the graph
163 // All paths for now are acyclic,
164 // since no back edges in the graph now
165 // numPaths is the number of acyclic paths in the graph
166 int numPaths=valueAssignmentToEdges(g, nodePriority, be);
168 if(numPaths<=1 || numPaths >5000) return false;
170 #ifdef DEBUG_PATH_PROFILES
174 //create instruction allocation r and count
175 //r is the variable that'll act like an accumulator
176 //all along the path, we just add edge values to r
177 //and at the end, r reflects the path number
178 //count is an array: count[x] would store
179 //the number of executions of path numbered x
181 Instruction *rVar=new
182 AllocaInst(Type::IntTy,
183 ConstantUInt::get(Type::UIntTy,1),"R");
185 Instruction *countVar=new
186 AllocaInst(Type::IntTy,
187 ConstantUInt::get(Type::UIntTy, numPaths), "Count");
189 static GlobalVariable *threshold = NULL;
190 static bool insertedThreshold = false;
192 if(!insertedThreshold){
193 threshold = new GlobalVariable(Type::IntTy, false, false, 0,
196 F.getParent()->getGlobalList().push_back(threshold);
197 insertedThreshold = true;
200 assert(threshold && "GlobalVariable threshold not defined!");
202 // insert initialization code in first (entry) BB
203 // this includes initializing r and count
204 insertInTopBB(&F.getEntryNode(),numPaths, rVar, countVar, threshold);
206 //now process the graph: get path numbers,
207 //get increments along different paths,
208 //and assign "increments" and "updates" (to r and count)
209 //"optimally". Finally, insert llvm code along various edges
210 processGraph(g, rVar, countVar, be, stDummy, exDummy, numPaths, mn,
213 return true; // Always modifies function