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219 lines
8.7 KiB
C++
219 lines
8.7 KiB
C++
//===- OptimalEdgeProfiling.cpp - Insert counters for opt. edge profiling -===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass instruments the specified program with counters for edge profiling.
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// Edge profiling can give a reasonable approximation of the hot paths through a
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// program, and is used for a wide variety of program transformations.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "insert-optimal-edge-profiling"
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#include "ProfilingUtils.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/ProfileInfo.h"
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#include "llvm/Analysis/ProfileInfoLoader.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Instrumentation.h"
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "MaximumSpanningTree.h"
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#include <set>
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using namespace llvm;
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STATISTIC(NumEdgesInserted, "The # of edges inserted.");
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namespace {
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class OptimalEdgeProfiler : public ModulePass {
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bool runOnModule(Module &M);
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public:
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static char ID; // Pass identification, replacement for typeid
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OptimalEdgeProfiler() : ModulePass(&ID) {}
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void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(ProfileEstimatorPassID);
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AU.addRequired<ProfileInfo>();
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}
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virtual const char *getPassName() const {
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return "Optimal Edge Profiler";
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}
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};
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}
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char OptimalEdgeProfiler::ID = 0;
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static RegisterPass<OptimalEdgeProfiler>
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X("insert-optimal-edge-profiling",
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"Insert optimal instrumentation for edge profiling");
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ModulePass *llvm::createOptimalEdgeProfilerPass() {
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return new OptimalEdgeProfiler();
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}
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inline static void printEdgeCounter(ProfileInfo::Edge e,
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BasicBlock* b,
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unsigned i) {
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DEBUG(dbgs() << "--Edge Counter for " << (e) << " in " \
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<< ((b)?(b)->getNameStr():"0") << " (# " << (i) << ")\n");
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}
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bool OptimalEdgeProfiler::runOnModule(Module &M) {
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Function *Main = M.getFunction("main");
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if (Main == 0) {
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errs() << "WARNING: cannot insert edge profiling into a module"
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<< " with no main function!\n";
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return false; // No main, no instrumentation!
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}
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// NumEdges counts all the edges that may be instrumented. Later on its
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// decided which edges to actually instrument, to achieve optimal profiling.
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// For the entry block a virtual edge (0,entry) is reserved, for each block
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// with no successors an edge (BB,0) is reserved. These edges are necessary
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// to calculate a truly optimal maximum spanning tree and thus an optimal
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// instrumentation.
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unsigned NumEdges = 0;
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for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
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if (F->isDeclaration()) continue;
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// Reserve space for (0,entry) edge.
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++NumEdges;
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for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
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// Keep track of which blocks need to be instrumented. We don't want to
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// instrument blocks that are added as the result of breaking critical
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// edges!
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if (BB->getTerminator()->getNumSuccessors() == 0) {
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// Reserve space for (BB,0) edge.
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++NumEdges;
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} else {
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NumEdges += BB->getTerminator()->getNumSuccessors();
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}
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}
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}
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// In the profiling output a counter for each edge is reserved, but only few
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// are used. This is done to be able to read back in the profile without
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// calulating the maximum spanning tree again, instead each edge counter that
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// is not used is initialised with -1 to signal that this edge counter has to
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// be calculated from other edge counters on reading the profile info back
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// in.
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const Type *Int32 = Type::getInt32Ty(M.getContext());
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const ArrayType *ATy = ArrayType::get(Int32, NumEdges);
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GlobalVariable *Counters =
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new GlobalVariable(M, ATy, false, GlobalValue::InternalLinkage,
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Constant::getNullValue(ATy), "OptEdgeProfCounters");
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NumEdgesInserted = 0;
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std::vector<Constant*> Initializer(NumEdges);
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Constant* Zero = ConstantInt::get(Int32, 0);
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Constant* Uncounted = ConstantInt::get(Int32, ProfileInfoLoader::Uncounted);
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// Instrument all of the edges not in MST...
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unsigned i = 0;
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for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
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if (F->isDeclaration()) continue;
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DEBUG(dbgs()<<"Working on "<<F->getNameStr()<<"\n");
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// Calculate a Maximum Spanning Tree with the edge weights determined by
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// ProfileEstimator. ProfileEstimator also assign weights to the virtual
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// edges (0,entry) and (BB,0) (for blocks with no successors) and this
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// edges also participate in the maximum spanning tree calculation.
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// The third parameter of MaximumSpanningTree() has the effect that not the
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// actual MST is returned but the edges _not_ in the MST.
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ProfileInfo::EdgeWeights ECs =
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getAnalysis<ProfileInfo>(*F).getEdgeWeights(F);
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std::vector<ProfileInfo::EdgeWeight> EdgeVector(ECs.begin(), ECs.end());
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MaximumSpanningTree<BasicBlock> MST (EdgeVector);
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std::stable_sort(MST.begin(),MST.end());
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// Check if (0,entry) not in the MST. If not, instrument edge
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// (IncrementCounterInBlock()) and set the counter initially to zero, if
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// the edge is in the MST the counter is initialised to -1.
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BasicBlock *entry = &(F->getEntryBlock());
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ProfileInfo::Edge edge = ProfileInfo::getEdge(0,entry);
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if (!std::binary_search(MST.begin(), MST.end(), edge)) {
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printEdgeCounter(edge,entry,i);
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IncrementCounterInBlock(entry, i, Counters); NumEdgesInserted++;
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Initializer[i++] = (Zero);
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} else{
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Initializer[i++] = (Uncounted);
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}
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// InsertedBlocks contains all blocks that were inserted for splitting an
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// edge, this blocks do not have to be instrumented.
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DenseSet<BasicBlock*> InsertedBlocks;
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for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
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// Check if block was not inserted and thus does not have to be
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// instrumented.
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if (InsertedBlocks.count(BB)) continue;
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// Okay, we have to add a counter of each outgoing edge not in MST. If
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// the outgoing edge is not critical don't split it, just insert the
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// counter in the source or destination of the edge. Also, if the block
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// has no successors, the virtual edge (BB,0) is processed.
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TerminatorInst *TI = BB->getTerminator();
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if (TI->getNumSuccessors() == 0) {
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ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,0);
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if (!std::binary_search(MST.begin(), MST.end(), edge)) {
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printEdgeCounter(edge,BB,i);
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IncrementCounterInBlock(BB, i, Counters); NumEdgesInserted++;
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Initializer[i++] = (Zero);
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} else{
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Initializer[i++] = (Uncounted);
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}
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}
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for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
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BasicBlock *Succ = TI->getSuccessor(s);
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ProfileInfo::Edge edge = ProfileInfo::getEdge(BB,Succ);
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if (!std::binary_search(MST.begin(), MST.end(), edge)) {
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// If the edge is critical, split it.
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bool wasInserted = SplitCriticalEdge(TI, s, this);
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Succ = TI->getSuccessor(s);
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if (wasInserted)
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InsertedBlocks.insert(Succ);
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// Okay, we are guaranteed that the edge is no longer critical. If
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// we only have a single successor, insert the counter in this block,
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// otherwise insert it in the successor block.
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if (TI->getNumSuccessors() == 1) {
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// Insert counter at the start of the block
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printEdgeCounter(edge,BB,i);
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IncrementCounterInBlock(BB, i, Counters); NumEdgesInserted++;
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} else {
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// Insert counter at the start of the block
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printEdgeCounter(edge,Succ,i);
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IncrementCounterInBlock(Succ, i, Counters); NumEdgesInserted++;
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}
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Initializer[i++] = (Zero);
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} else {
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Initializer[i++] = (Uncounted);
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}
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}
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}
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}
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// Check if the number of edges counted at first was the number of edges we
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// considered for instrumentation.
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assert(i==NumEdges && "the number of edges in counting array is wrong");
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// Assing the now completely defined initialiser to the array.
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Constant *init = ConstantArray::get(ATy, Initializer);
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Counters->setInitializer(init);
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// Add the initialization call to main.
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InsertProfilingInitCall(Main, "llvm_start_opt_edge_profiling", Counters);
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return true;
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}
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