lib/Analysis/DataStructure/BottomUpClosure.cpp

//===- BottomUpClosure.cpp - Compute bottom-up interprocedural closure ----===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This file implements the BUDataStructures class, which represents the
// Bottom-Up Interprocedural closure of the data structure graph over the
// program.  This is useful for applications like pool allocation, but **not**
// applications like alias analysis.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/DataStructure.h"
#include "llvm/Module.h"
#include "Support/Statistic.h"
#include "Support/Debug.h"
#include "DSCallSiteIterator.h"

namespace llvm {

namespace {
  Statistic<> MaxSCC("budatastructure", "Maximum SCC Size in Call Graph");
  Statistic<> NumBUInlines("budatastructures", "Number of graphs inlined");
  Statistic<> NumCallEdges("budatastructures", "Number of 'actual' call edges");
  
  RegisterAnalysis<BUDataStructures>
  X("budatastructure", "Bottom-up Data Structure Analysis");
}

using namespace DS;

// run - Calculate the bottom up data structure graphs for each function in the
// program.
//
bool BUDataStructures::run(Module &M) {
  LocalDataStructures &LocalDSA = getAnalysis<LocalDataStructures>();
  GlobalsGraph = new DSGraph(LocalDSA.getGlobalsGraph());
  GlobalsGraph->setPrintAuxCalls();

  Function *MainFunc = M.getMainFunction();
  if (MainFunc)
    calculateReachableGraphs(MainFunc);

  // Calculate the graphs for any functions that are unreachable from main...
  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
    if (!I->isExternal() && !DSInfo.count(I)) {
#ifndef NDEBUG
      if (MainFunc)
        std::cerr << "*** Function unreachable from main: "
                  << I->getName() << "\n";
#endif
      calculateReachableGraphs(I);    // Calculate all graphs...
    }

  NumCallEdges += ActualCallees.size();

  // At the end of the bottom-up pass, the globals graph becomes complete.
  // FIXME: This is not the right way to do this, but it is sorta better than
  // nothing!  In particular, externally visible globals and unresolvable call
  // nodes at the end of the BU phase should make things that they point to
  // incomplete in the globals graph.
  // 
  GlobalsGraph->maskIncompleteMarkers();
  return false;
}

void BUDataStructures::calculateReachableGraphs(Function *F) {
  std::vector<Function*> Stack;
  hash_map<Function*, unsigned> ValMap;
  unsigned NextID = 1;
  calculateGraphs(F, Stack, NextID, ValMap);
}

DSGraph &BUDataStructures::getOrCreateGraph(Function *F) {
  // Has the graph already been created?
  DSGraph *&Graph = DSInfo[F];
  if (Graph) return *Graph;

  // Copy the local version into DSInfo...
  Graph = new DSGraph(getAnalysis<LocalDataStructures>().getDSGraph(*F));

  Graph->setGlobalsGraph(GlobalsGraph);
  Graph->setPrintAuxCalls();

  // Start with a copy of the original call sites...
  Graph->getAuxFunctionCalls() = Graph->getFunctionCalls();
  return *Graph;
}

unsigned BUDataStructures::calculateGraphs(Function *F,
                                           std::vector<Function*> &Stack,
                                           unsigned &NextID, 
                                     hash_map<Function*, unsigned> &ValMap) {
  assert(ValMap.find(F) == ValMap.end() && "Shouldn't revisit functions!");
  unsigned Min = NextID++, MyID = Min;
  ValMap[F] = Min;
  Stack.push_back(F);

  if (F->isExternal()) {   // sprintf, fprintf, sscanf, etc...
    // No callees!
    Stack.pop_back();
    ValMap[F] = ~0;
    return Min;
  }

  DSGraph &Graph = getOrCreateGraph(F);

  // The edges out of the current node are the call site targets...
  for (DSCallSiteIterator I = DSCallSiteIterator::begin_aux(Graph),
         E = DSCallSiteIterator::end_aux(Graph); I != E; ++I) {
    Function *Callee = *I;
    unsigned M;
    // Have we visited the destination function yet?
    hash_map<Function*, unsigned>::iterator It = ValMap.find(Callee);
    if (It == ValMap.end())  // No, visit it now.
      M = calculateGraphs(Callee, Stack, NextID, ValMap);
    else                    // Yes, get it's number.
      M = It->second;
    if (M < Min) Min = M;
  }

  assert(ValMap[F] == MyID && "SCC construction assumption wrong!");
  if (Min != MyID)
    return Min;         // This is part of a larger SCC!

  // If this is a new SCC, process it now.
  if (Stack.back() == F) {           // Special case the single "SCC" case here.
    DEBUG(std::cerr << "Visiting single node SCC #: " << MyID << " fn: "
                    << F->getName() << "\n");
    Stack.pop_back();
    DSGraph &G = getDSGraph(*F);
    DEBUG(std::cerr << "  [BU] Calculating graph for: " << F->getName()<< "\n");
    calculateGraph(G);
    DEBUG(std::cerr << "  [BU] Done inlining: " << F->getName() << " ["
                    << G.getGraphSize() << "+" << G.getAuxFunctionCalls().size()
                    << "]\n");

    if (MaxSCC < 1) MaxSCC = 1;

    // Should we revisit the graph?
    if (DSCallSiteIterator::begin_aux(G) != DSCallSiteIterator::end_aux(G)) {
      ValMap.erase(F);
      return calculateGraphs(F, Stack, NextID, ValMap);
    } else {
      ValMap[F] = ~0U;
    }
    return MyID;

  } else {
    // SCCFunctions - Keep track of the functions in the current SCC
    //
    hash_set<Function*> SCCFunctions;

    Function *NF;
    std::vector<Function*>::iterator FirstInSCC = Stack.end();
    DSGraph *SCCGraph = 0;
    do {
      NF = *--FirstInSCC;
      ValMap[NF] = ~0U;
      SCCFunctions.insert(NF);

      // Figure out which graph is the largest one, in order to speed things up
      // a bit in situations where functions in the SCC have widely different
      // graph sizes.
      DSGraph &NFGraph = getDSGraph(*NF);
      if (!SCCGraph || SCCGraph->getGraphSize() < NFGraph.getGraphSize())
        SCCGraph = &NFGraph;
    } while (NF != F);

    std::cerr << "Calculating graph for SCC #: " << MyID << " of size: "
              << SCCFunctions.size() << "\n";

    // Compute the Max SCC Size...
    if (MaxSCC < SCCFunctions.size())
      MaxSCC = SCCFunctions.size();

    // First thing first, collapse all of the DSGraphs into a single graph for
    // the entire SCC.  We computed the largest graph, so clone all of the other
    // (smaller) graphs into it.  Discard all of the old graphs.
    //
    for (hash_set<Function*>::iterator I = SCCFunctions.begin(),
           E = SCCFunctions.end(); I != E; ++I) {
      DSGraph &G = getDSGraph(**I);
      if (&G != SCCGraph) {
        DSGraph::NodeMapTy NodeMap;
        SCCGraph->cloneInto(G, SCCGraph->getScalarMap(),
                            SCCGraph->getReturnNodes(), NodeMap, 0);
        // Update the DSInfo map and delete the old graph...
        DSInfo[*I] = SCCGraph;
        delete &G;
      }
    }

    // Clean up the graph before we start inlining a bunch again...
    SCCGraph->removeTriviallyDeadNodes();

    // Now that we have one big happy family, resolve all of the call sites in
    // the graph...
    calculateGraph(*SCCGraph);
    DEBUG(std::cerr << "  [BU] Done inlining SCC  [" << SCCGraph->getGraphSize()
                    << "+" << SCCGraph->getAuxFunctionCalls().size() << "]\n");

    std::cerr << "DONE with SCC #: " << MyID << "\n";

    // We never have to revisit "SCC" processed functions...
    
    // Drop the stuff we don't need from the end of the stack
    Stack.erase(FirstInSCC, Stack.end());
    return MyID;
  }

  return MyID;  // == Min
}


// releaseMemory - If the pass pipeline is done with this pass, we can release
// our memory... here...
//
void BUDataStructures::releaseMemory() {
  for (hash_map<Function*, DSGraph*>::iterator I = DSInfo.begin(),
         E = DSInfo.end(); I != E; ++I) {
    I->second->getReturnNodes().erase(I->first);
    if (I->second->getReturnNodes().empty())
      delete I->second;
  }

  // Empty map so next time memory is released, data structures are not
  // re-deleted.
  DSInfo.clear();
  delete GlobalsGraph;
  GlobalsGraph = 0;
}

void BUDataStructures::calculateGraph(DSGraph &Graph) {
  // Move our call site list into TempFCs so that inline call sites go into the
  // new call site list and doesn't invalidate our iterators!
  std::vector<DSCallSite> TempFCs;
  std::vector<DSCallSite> &AuxCallsList = Graph.getAuxFunctionCalls();
  TempFCs.swap(AuxCallsList);

  DSGraph::ReturnNodesTy &ReturnNodes = Graph.getReturnNodes();

  // Loop over all of the resolvable call sites
  unsigned LastCallSiteIdx = ~0U;
  for (DSCallSiteIterator I = DSCallSiteIterator::begin(TempFCs),
         E = DSCallSiteIterator::end(TempFCs); I != E; ++I) {
    // If we skipped over any call sites, they must be unresolvable, copy them
    // to the real call site list.
    LastCallSiteIdx++;
    for (; LastCallSiteIdx < I.getCallSiteIdx(); ++LastCallSiteIdx)
      AuxCallsList.push_back(TempFCs[LastCallSiteIdx]);
    LastCallSiteIdx = I.getCallSiteIdx();
    
    // Resolve the current call...
    Function *Callee = *I;
    DSCallSite CS = I.getCallSite();

    if (Callee->isExternal()) {
      // Ignore this case, simple varargs functions we cannot stub out!
    } else if (ReturnNodes.find(Callee) != ReturnNodes.end()) {
      // Self recursion... simply link up the formal arguments with the
      // actual arguments...
      DEBUG(std::cerr << "    Self Inlining: " << Callee->getName() << "\n");

      // Handle self recursion by resolving the arguments and return value
      Graph.mergeInGraph(CS, *Callee, Graph, 0);

    } else {
      ActualCallees.insert(std::make_pair(CS.getCallSite().getInstruction(),
                                          Callee));

      // Get the data structure graph for the called function.
      //
      DSGraph &GI = getDSGraph(*Callee);  // Graph to inline
      
      DEBUG(std::cerr << "    Inlining graph for " << Callee->getName()
            << "[" << GI.getGraphSize() << "+"
            << GI.getAuxFunctionCalls().size() << "] into '"
            << Graph.getFunctionNames() << "' [" << Graph.getGraphSize() << "+"
            << Graph.getAuxFunctionCalls().size() << "]\n");
      
      // Handle self recursion by resolving the arguments and return value
      Graph.mergeInGraph(CS, *Callee, GI,
                         DSGraph::KeepModRefBits | 
                         DSGraph::StripAllocaBit | DSGraph::DontCloneCallNodes);
      ++NumBUInlines;

#if 0
      Graph.writeGraphToFile(std::cerr, "bu_" + F.getName() + "_after_" +
                             Callee->getName());
#endif
    }
  }

  // Make sure to catch any leftover unresolvable calls...
  for (++LastCallSiteIdx; LastCallSiteIdx < TempFCs.size(); ++LastCallSiteIdx)
    AuxCallsList.push_back(TempFCs[LastCallSiteIdx]);

  TempFCs.clear();

  // Re-materialize nodes from the globals graph.
  // Do not ignore globals inlined from callees -- they are not up-to-date!
  Graph.getInlinedGlobals().clear();
  Graph.updateFromGlobalGraph();

  // Recompute the Incomplete markers
  Graph.maskIncompleteMarkers();
  Graph.markIncompleteNodes(DSGraph::MarkFormalArgs);

  // Delete dead nodes.  Treat globals that are unreachable but that can
  // reach live nodes as live.
  Graph.removeDeadNodes(DSGraph::KeepUnreachableGlobals);

  //Graph.writeGraphToFile(std::cerr, "bu_" + F.getName());
}

} // End llvm namespace