lib/Analysis/DataStructure/PgmDependenceGraph.cpp

//===- PgmDependenceGraph.cpp - Enumerate PDG for a function ----*- C++ -*-===//
// 
//                     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.
// 
//===----------------------------------------------------------------------===//
// 
// The Program Dependence Graph (PDG) for a single function represents all
// data and control dependences for the function.  This file provides an
// iterator to enumerate all these dependences.  In particular, it enumerates:
// 
// -- Data dependences on memory locations, computed using the
//    MemoryDepAnalysis pass;
// -- Data dependences on SSA registers, directly from Def-Use edges of Values;
// -- Control dependences, computed using postdominance frontiers
//    (NOT YET IMPLEMENTED).
// 
// Note that this file does not create an explicit dependence graph --
// it only provides an iterator to traverse the PDG conceptually.
// The MemoryDepAnalysis does build an explicit graph, which is used internally
// here.  That graph could be augmented with the other dependences above if
// desired, but for most uses there will be little need to do that.
//
//===----------------------------------------------------------------------===//

#include "PgmDependenceGraph.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Function.h"
#include <iostream>

namespace llvm {

//----------------------------------------------------------------------------
// class DepIterState
//----------------------------------------------------------------------------

const DepIterState::IterStateFlags DepIterState::NoFlag  = 0x0;
const DepIterState::IterStateFlags DepIterState::MemDone = 0x1;
const DepIterState::IterStateFlags DepIterState::SSADone = 0x2;
const DepIterState::IterStateFlags DepIterState::AllDone = 0x4;
const DepIterState::IterStateFlags DepIterState::FirstTimeFlag= 0x8;

// Find the first memory dependence for the current Mem In/Out iterators.
// Find the first memory dependence for the current Mem In/Out iterators.
// Sets dep to that dependence and returns true if one is found.
// 
bool DepIterState::SetFirstMemoryDep()
{
  if (! (depFlags & MemoryDeps))
    return false;

  bool doIncomingDeps = dep.getDepType() & IncomingFlag;

  if (( doIncomingDeps && memDepIter == memDepGraph->inDepEnd( *depNode)) ||
      (!doIncomingDeps && memDepIter == memDepGraph->outDepEnd(*depNode)))
    {
      iterFlags |= MemDone;
      return false;
    }

  dep = *memDepIter;     // simple copy from dependence in memory DepGraph

  return true;
}


// Find the first valid data dependence for the current SSA In/Out iterators.
// A valid data dependence is one that is to/from an Instruction.
// E.g., an SSA edge from a formal parameter is not a valid dependence.
// Sets dep to that dependence and returns true if a valid one is found.
// Returns false and leaves dep unchanged otherwise.
// 
bool DepIterState::SetFirstSSADep()
{
  if (! (depFlags & SSADeps))
    return false;

  bool doIncomingDeps = dep.getDepType() & IncomingFlag;
  Instruction* firstTarget = NULL;

  // Increment the In or Out iterator till it runs out or we find a valid dep
  if (doIncomingDeps)
    for (Instruction::op_iterator E = depNode->getInstr().op_end();
         ssaInEdgeIter != E &&
           (firstTarget = dyn_cast<Instruction>(ssaInEdgeIter))== NULL; )
      ++ssaInEdgeIter;
  else
    for (Value::use_iterator E = depNode->getInstr().use_end();
         ssaOutEdgeIter != E &&
           (firstTarget = dyn_cast<Instruction>(*ssaOutEdgeIter)) == NULL; )
      ++ssaOutEdgeIter;

  // If the iterator ran out before we found a valid dep, there isn't one.
  if (!firstTarget)
    {
      iterFlags |= SSADone;
      return false;
    }

  // Create a simple dependence object to represent this SSA dependence.
  dep = Dependence(memDepGraph->getNode(*firstTarget, /*create*/ true),
                   TrueDependence, doIncomingDeps);

  return true;
}


DepIterState::DepIterState(DependenceGraph* _memDepGraph,
                           Instruction&     I, 
                           bool             incomingDeps,
                           PDGIteratorFlags whichDeps)
  : memDepGraph(_memDepGraph),
    depFlags(whichDeps),
    iterFlags(NoFlag)
{
  depNode = memDepGraph->getNode(I, /*create*/ true);

  if (incomingDeps)
    {
      if (whichDeps & MemoryDeps) memDepIter= memDepGraph->inDepBegin(*depNode);
      if (whichDeps & SSADeps)    ssaInEdgeIter = I.op_begin();
      /* Initialize control dependence iterator here. */
    }
  else
    {
      if (whichDeps & MemoryDeps) memDepIter=memDepGraph->outDepBegin(*depNode);
      if (whichDeps & SSADeps)    ssaOutEdgeIter = I.use_begin();
      /* Initialize control dependence iterator here. */
    }

  // Set the dependence to the first of a memory dep or an SSA dep
  // and set the done flag if either is found.  Otherwise, set the
  // init flag to indicate that the iterators have just been initialized.
  // 
  if (!SetFirstMemoryDep() && !SetFirstSSADep())
    iterFlags |= AllDone;
  else
    iterFlags |= FirstTimeFlag;
}


// Helper function for ++ operator that bumps iterator by 1 (to next
// dependence) and resets the dep field to represent the new dependence.
// 
void DepIterState::Next()
{
  // firstMemDone and firstSsaDone are used to indicate when the memory or
  // SSA iterators just ran out, or when this is the very first increment.
  // In either case, the next iterator (if any) should not be incremented.
  // 
  bool firstMemDone = iterFlags & FirstTimeFlag;
  bool firstSsaDone = iterFlags & FirstTimeFlag;
  bool doIncomingDeps = dep.getDepType() & IncomingFlag;

  if (depFlags & MemoryDeps && ! (iterFlags & MemDone))
    {
      iterFlags &= ~FirstTimeFlag;           // clear "firstTime" flag
      ++memDepIter;
      if (SetFirstMemoryDep())
        return;
      firstMemDone = true;              // flags that we _just_ rolled over
    }

  if (depFlags & SSADeps && ! (iterFlags & SSADone))
    {
      // Don't increment the SSA iterator if we either just rolled over from
      // the memory dep iterator, or if the SSA iterator is already done.
      iterFlags &= ~FirstTimeFlag;           // clear "firstTime" flag
      if (! firstMemDone)
        if (doIncomingDeps) ++ssaInEdgeIter;
        else ++ssaOutEdgeIter;
      if (SetFirstSSADep())
        return;
      firstSsaDone = true;                   // flags if we just rolled over
    } 

  if (depFlags & ControlDeps != 0)
    {
      assert(0 && "Cannot handle control deps");
      // iterFlags &= ~FirstTimeFlag;           // clear "firstTime" flag
    }

  // This iterator is now complete.
  iterFlags |= AllDone;
}


//----------------------------------------------------------------------------
// class PgmDependenceGraph
//----------------------------------------------------------------------------


// MakeIterator -- Create and initialize an iterator as specified.
// 
PDGIterator PgmDependenceGraph::MakeIterator(Instruction& I,
                                             bool incomingDeps,
                                             PDGIteratorFlags whichDeps)
{
  assert(memDepGraph && "Function not initialized!");
  return PDGIterator(new DepIterState(memDepGraph, I, incomingDeps, whichDeps));
}


void PgmDependenceGraph::printOutgoingSSADeps(Instruction& I,
                                              std::ostream &O)
{
  iterator SI = this->outDepBegin(I, SSADeps);
  iterator SE = this->outDepEnd(I, SSADeps);
  if (SI == SE)
    return;

  O << "\n    Outgoing SSA dependences:\n";
  for ( ; SI != SE; ++SI)
    {
      O << "\t";
      SI->print(O);
      O << " to instruction:";
      O << SI->getSink()->getInstr();
    }
}


void PgmDependenceGraph::print(std::ostream &O, const Module*) const
{
  MemoryDepAnalysis& graphSet = getAnalysis<MemoryDepAnalysis>();

  // TEMPORARY LOOP
  for (hash_map<Function*, DependenceGraph*>::iterator
         I = graphSet.funcMap.begin(), E = graphSet.funcMap.end();
       I != E; ++I)
    {
      Function* func = I->first;
      DependenceGraph* depGraph = I->second;
      const_cast<PgmDependenceGraph*>(this)->runOnFunction(*func);

  O << "DEPENDENCE GRAPH FOR FUNCTION " << func->getName() << ":\n";
  for (Function::iterator BB=func->begin(), FE=func->end(); BB != FE; ++BB)
    for (BasicBlock::iterator II=BB->begin(), IE=BB->end(); II !=IE; ++II)
      {
        DepGraphNode* dgNode = depGraph->getNode(*II, /*create*/ true);
        dgNode->print(O);
        const_cast<PgmDependenceGraph*>(this)->printOutgoingSSADeps(*II, O);
      }
    } // END TEMPORARY LOOP
}


void PgmDependenceGraph::dump() const
{
  this->print(std::cerr);
}

static RegisterAnalysis<PgmDependenceGraph>
Z("pgmdep", "Enumerate Program Dependence Graph (data and control)");

} // End llvm namespace