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llvm-mirror/lib/Transforms/Instrumentation/ProfilePaths/ProfilePaths.cpp

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//===-- ProfilePaths.cpp - interface to insert instrumentation ---*- C++ -*--=//
//
// This inserts intrumentation for counting
// execution of paths though a given function
// Its implemented as a "Function" Pass, and called using opt
//
// This pass is implemented by using algorithms similar to
// 1."Efficient Path Profiling": Ball, T. and Larus, J. R.,
// Proceedings of Micro-29, Dec 1996, Paris, France.
// 2."Efficiently Counting Program events with support for on-line
// "queries": Ball T., ACM Transactions on Programming Languages
// and systems, Sep 1994.
//
// The algorithms work on a Graph constructed over the nodes
// made from Basic Blocks: The transformations then take place on
// the constucted graph (implementation in Graph.cpp and GraphAuxillary.cpp)
// and finally, appropriate instrumentation is placed over suitable edges.
// (code inserted through EdgeCode.cpp).
//
// The algorithm inserts code such that every acyclic path in the CFG
// of a function is identified through a unique number. the code insertion
// is optimal in the sense that its inserted over a minimal set of edges. Also,
// the algorithm makes sure than initialization, path increment and counter
// update can be collapsed into minmimum number of edges.
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Instrumentation/ProfilePaths.h"
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#include "llvm/Transforms/UnifyFunctionExitNodes.h"
#include "llvm/Support/CFG.h"
#include "llvm/Function.h"
#include "llvm/BasicBlock.h"
#include "llvm/ConstantVals.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iMemory.h"
#include "llvm/Pass.h"
#include "Graph.h"
using std::vector;
class ProfilePaths: public FunctionPass {
public:
bool runOnFunction(Function *F);
// Before this pass, make sure that there is only one
// entry and only one exit node for the function in the CFG of the function
//
void ProfilePaths::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired(UnifyFunctionExitNodes::ID);
}
};
// createProfilePathsPass - Create a new pass to add path profiling
//
Pass *createProfilePathsPass() {
return new ProfilePaths();
}
static Node *findBB(std::set<Node *> &st, BasicBlock *BB){
for(std::set<Node *>::iterator si=st.begin(); si!=st.end(); ++si){
if(((*si)->getElement())==BB){
return *si;
}
}
return NULL;
}
//Per function pass for inserting counters and trigger code
bool ProfilePaths::runOnFunction(Function *M){
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// Transform the cfg s.t. we have just one exit node
BasicBlock *ExitNode = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
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// iterating over BBs and making graph
std::set<Node *> nodes;
std::set<Edge> edges;
Node *tmp;
Node *exitNode, *startNode;
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// The nodes must be uniquesly identified:
// That is, no two nodes must hav same BB*
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// First enter just nodes: later enter edges
for (Function::iterator BB = M->begin(), BE=M->end(); BB != BE; ++BB){
Node *nd=new Node(*BB);
nodes.insert(nd);
if(*BB==ExitNode)
exitNode=nd;
if(*BB==M->front())
startNode=nd;
}
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// now do it againto insert edges
for (Function::iterator BB = M->begin(), BE=M->end(); BB != BE; ++BB){
Node *nd=findBB(nodes, *BB);
assert(nd && "No node for this edge!");
for(BasicBlock::succ_iterator s=succ_begin(*BB), se=succ_end(*BB);
s!=se; ++s){
Node *nd2=findBB(nodes,*s);
assert(nd2 && "No node for this edge!");
Edge ed(nd,nd2,0);
edges.insert(ed);
}
}
Graph g(nodes,edges, startNode, exitNode);
#ifdef DEBUG_PATH_PROFILES
printGraph(g);
#endif
BasicBlock *fr=M->front();
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// If only one BB, don't instrument
if (M->getBasicBlocks().size() == 1) {
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// The graph is made acyclic: this is done
// by removing back edges for now, and adding them later on
vector<Edge> be;
g.getBackEdges(be);
#ifdef DEBUG_PATH_PROFILES
cerr<<"Backedges:"<<be.size()<<endl;
#endif
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// Now we need to reflect the effect of back edges
// This is done by adding dummy edges
// If a->b is a back edge
// Then we add 2 back edges for it:
// 1. from root->b (in vector stDummy)
// and 2. from a->exit (in vector exDummy)
vector<Edge> stDummy;
vector<Edge> exDummy;
addDummyEdges(stDummy, exDummy, g, be);
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// Now, every edge in the graph is assigned a weight
// This weight later adds on to assign path
// numbers to different paths in the graph
// All paths for now are acyclic,
// since no back edges in the graph now
// numPaths is the number of acyclic paths in the graph
int numPaths=valueAssignmentToEdges(g);
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// create instruction allocation r and count
// r is the variable that'll act like an accumulator
// all along the path, we just add edge values to r
// and at the end, r reflects the path number
// count is an array: count[x] would store
// the number of executions of path numbered x
Instruction *rVar=new
AllocaInst(PointerType::get(Type::IntTy),
ConstantUInt::get(Type::UIntTy,1),"R");
Instruction *countVar=new
AllocaInst(PointerType::get(Type::IntTy),
ConstantUInt::get(Type::UIntTy, numPaths), "Count");
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// insert initialization code in first (entry) BB
// this includes initializing r and count
insertInTopBB(M->getEntryNode(),numPaths, rVar, countVar);
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// now process the graph: get path numbers,
// get increments along different paths,
// and assign "increments" and "updates" (to r and count)
// "optimally". Finally, insert llvm code along various edges
processGraph(g, rVar, countVar, be, stDummy, exDummy);
}
return true; // Always modifies function
}