lib/Analysis/MemoryDependenceAnalysis.cpp - llvm - Git at Google

 //===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation  --*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements an analysis that determines, for a given memory
 // operation, what preceding memory operations it depends on.  It builds on
 // alias analysis information, and tries to provide a lazy, caching interface to
 // a common kind of alias information query.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Constants.h"
 #include "llvm/Instructions.h"
 #include "llvm/Function.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/ADT/Statistic.h"

 #define DEBUG_TYPE "memdep"

 using namespace llvm;

 // Control the calculation of non-local dependencies by only examining the
 // predecessors if the basic block has less than X amount (50 by default).
 static cl::opt<int>
 PredLimit("nonlocaldep-threshold", cl::Hidden, cl::init(50),
           cl::desc("Control the calculation of non-local"
                    "dependencies (default = 50)"));

 STATISTIC(NumCacheNonlocal, "Number of cached non-local responses");
 STATISTIC(NumUncacheNonlocal, "Number of uncached non-local responses");

 char MemoryDependenceAnalysis::ID = 0;

 Instruction* const MemoryDependenceAnalysis::NonLocal = (Instruction*)-3;
 Instruction* const MemoryDependenceAnalysis::None = (Instruction*)-4;
 Instruction* const MemoryDependenceAnalysis::Dirty = (Instruction*)-5;

 // Register this pass...
 static RegisterPass<MemoryDependenceAnalysis> X("memdep",
                                                 "Memory Dependence Analysis", false, true);

 void MemoryDependenceAnalysis::ping(Instruction *D) {
   for (depMapType::iterator I = depGraphLocal.begin(), E = depGraphLocal.end();
        I != E; ++I) {
     assert(I->first != D);
     assert(I->second.first != D);
   }

   for (nonLocalDepMapType::iterator I = depGraphNonLocal.begin(), E = depGraphNonLocal.end();
        I != E; ++I) {
     assert(I->first != D);
     for (DenseMap<BasicBlock*, Value*>::iterator II = I->second.begin(),
          EE = I->second.end(); II  != EE; ++II)
       assert(II->second != D);
   }

   for (reverseDepMapType::iterator I = reverseDep.begin(), E = reverseDep.end();
        I != E; ++I)
     for (SmallPtrSet<Instruction*, 4>::iterator II = I->second.begin(), EE = I->second.end();
          II != EE; ++II)
       assert(*II != D);

   for (reverseDepMapType::iterator I = reverseDepNonLocal.begin(), E = reverseDepNonLocal.end();
        I != E; ++I)
     for (SmallPtrSet<Instruction*, 4>::iterator II = I->second.begin(), EE = I->second.end();
          II != EE; ++II)
       assert(*II != D);
 }

 /// getAnalysisUsage - Does not modify anything.  It uses Alias Analysis.
 ///
 void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.setPreservesAll();
   AU.addRequiredTransitive<AliasAnalysis>();
   AU.addRequiredTransitive<TargetData>();
 }

 /// getCallSiteDependency - Private helper for finding the local dependencies
 /// of a call site.
 Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C,
                                                            Instruction* start,
                                                             BasicBlock* block) {

   std::pair<Instruction*, bool>& cachedResult =
                                               depGraphLocal[C.getInstruction()];
   AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
   TargetData& TD = getAnalysis<TargetData>();
   BasicBlock::iterator blockBegin = C.getInstruction()->getParent()->begin();
   BasicBlock::iterator QI = C.getInstruction();

   // If the starting point was specified, use it
   if (start) {
     QI = start;
     blockBegin = start->getParent()->begin();
   // If the starting point wasn't specified, but the block was, use it
   } else if (!start && block) {
     QI = block->end();
     blockBegin = block->begin();
   }

   // Walk backwards through the block, looking for dependencies
   while (QI != blockBegin) {
     --QI;

     // If this inst is a memory op, get the pointer it accessed
     Value* pointer = 0;
     uint64_t pointerSize = 0;
     if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
       pointer = S->getPointerOperand();
       pointerSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
     } else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
       pointer = AI;
       if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
         pointerSize = C->getZExtValue() * \
                       TD.getABITypeSize(AI->getAllocatedType());
       else
         pointerSize = ~0UL;
     } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
       pointer = V->getOperand(0);
       pointerSize = TD.getTypeStoreSize(V->getType());
     } else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
       pointer = F->getPointerOperand();

       // FreeInsts erase the entire structure
       pointerSize = ~0UL;
     } else if (CallSite::get(QI).getInstruction() != 0) {
       AliasAnalysis::ModRefBehavior result =
                    AA.getModRefBehavior(CallSite::get(QI));
       if (result != AliasAnalysis::DoesNotAccessMemory) {
         if (!start && !block) {
           cachedResult.first = QI;
           cachedResult.second = true;
           reverseDep[QI].insert(C.getInstruction());
         }
         return QI;
       } else {
         continue;
       }
     } else
       continue;

     if (AA.getModRefInfo(C, pointer, pointerSize) != AliasAnalysis::NoModRef) {
       if (!start && !block) {
         cachedResult.first = QI;
         cachedResult.second = true;
         reverseDep[QI].insert(C.getInstruction());
       }
       return QI;
     }
   }

   // No dependence found
   cachedResult.first = NonLocal;
   cachedResult.second = true;
   reverseDep[NonLocal].insert(C.getInstruction());
   return NonLocal;
 }

 /// nonLocalHelper - Private helper used to calculate non-local dependencies
 /// by doing DFS on the predecessors of a block to find its dependencies
 void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
                                               BasicBlock* block,
                                          DenseMap<BasicBlock*, Value*>& resp) {
   // Set of blocks that we've already visited in our DFS
   SmallPtrSet<BasicBlock*, 4> visited;
   // If we're updating a dirtied cache entry, we don't need to reprocess
   // already computed entries.
   for (DenseMap<BasicBlock*, Value*>::iterator I = resp.begin(),
        E = resp.end(); I != E; ++I)
     if (I->second != Dirty)
       visited.insert(I->first);

   // Current stack of the DFS
   SmallVector<BasicBlock*, 4> stack;
   for (pred_iterator PI = pred_begin(block), PE = pred_end(block);
        PI != PE; ++PI)
     stack.push_back(*PI);

   // Do a basic DFS
   while (!stack.empty()) {
     BasicBlock* BB = stack.back();

     // If we've already visited this block, no need to revist
     if (visited.count(BB)) {
       stack.pop_back();
       continue;
     }

     // If we find a new block with a local dependency for query,
     // then we insert the new dependency and backtrack.
     if (BB != block) {
       visited.insert(BB);

       Instruction* localDep = getDependency(query, 0, BB);
       if (localDep != NonLocal) {
         resp.insert(std::make_pair(BB, localDep));
         stack.pop_back();

         continue;
       }
     // If we re-encounter the starting block, we still need to search it
     // because there might be a dependency in the starting block AFTER
     // the position of the query.  This is necessary to get loops right.
     } else if (BB == block) {
       visited.insert(BB);

       Instruction* localDep = getDependency(query, 0, BB);
       if (localDep != query)
         resp.insert(std::make_pair(BB, localDep));

       stack.pop_back();

       continue;
     }

     // If we didn't find anything, recurse on the precessors of this block
     // Only do this for blocks with a small number of predecessors.
     bool predOnStack = false;
     bool inserted = false;
     if (std::distance(pred_begin(BB), pred_end(BB)) <= PredLimit) {
       for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
            PI != PE; ++PI)
         if (!visited.count(*PI)) {
           stack.push_back(*PI);
           inserted = true;
         } else
           predOnStack = true;
     }

     // If we inserted a new predecessor, then we'll come back to this block
     if (inserted)
       continue;
     // If we didn't insert because we have no predecessors, then this
     // query has no dependency at all.
     else if (!inserted && !predOnStack) {
       resp.insert(std::make_pair(BB, None));
     // If we didn't insert because our predecessors are already on the stack,
     // then we might still have a dependency, but it will be discovered during
     // backtracking.
     } else if (!inserted && predOnStack){
       resp.insert(std::make_pair(BB, NonLocal));
     }

     stack.pop_back();
   }
 }

 /// getNonLocalDependency - Fills the passed-in map with the non-local
 /// dependencies of the queries.  The map will contain NonLocal for
 /// blocks between the query and its dependencies.
 void MemoryDependenceAnalysis::getNonLocalDependency(Instruction* query,
                                          DenseMap<BasicBlock*, Value*>& resp) {
   if (depGraphNonLocal.count(query)) {
     DenseMap<BasicBlock*, Value*>& cached = depGraphNonLocal[query];
     NumCacheNonlocal++;

     SmallVector<BasicBlock*, 4> dirtied;
     for (DenseMap<BasicBlock*, Value*>::iterator I = cached.begin(),
          E = cached.end(); I != E; ++I)
       if (I->second == Dirty)
         dirtied.push_back(I->first);

     for (SmallVector<BasicBlock*, 4>::iterator I = dirtied.begin(),
          E = dirtied.end(); I != E; ++I) {
       Instruction* localDep = getDependency(query, 0, *I);
       if (localDep != NonLocal)
         cached[*I] = localDep;
       else {
         cached.erase(*I);
         nonLocalHelper(query, *I, cached);
       }
     }

     resp = cached;

     // Update the reverse non-local dependency cache
     for (DenseMap<BasicBlock*, Value*>::iterator I = resp.begin(), E = resp.end();
          I != E; ++I)
       reverseDepNonLocal[I->second].insert(query);

     return;
   } else
     NumUncacheNonlocal++;

   // If not, go ahead and search for non-local deps.
   nonLocalHelper(query, query->getParent(), resp);

   // Update the non-local dependency cache
   for (DenseMap<BasicBlock*, Value*>::iterator I = resp.begin(), E = resp.end();
        I != E; ++I) {
     depGraphNonLocal[query].insert(*I);
     reverseDepNonLocal[I->second].insert(query);
   }
 }

 /// getDependency - Return the instruction on which a memory operation
 /// depends.  The local parameter indicates if the query should only
 /// evaluate dependencies within the same basic block.
 Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
                                                      Instruction* start,
                                                      BasicBlock* block) {
   // Start looking for dependencies with the queried inst
   BasicBlock::iterator QI = query;

   // Check for a cached result
   std::pair<Instruction*, bool>& cachedResult = depGraphLocal[query];
   // If we have a _confirmed_ cached entry, return it
   if (!block && !start) {
     if (cachedResult.second)
       return cachedResult.first;
     else if (cachedResult.first && cachedResult.first != NonLocal)
       // If we have an unconfirmed cached entry, we can start our search from there
       QI = cachedResult.first;
   }

   if (start)
     QI = start;
   else if (!start && block)
     QI = block->end();

   AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
   TargetData& TD = getAnalysis<TargetData>();

   // Get the pointer value for which dependence will be determined
   Value* dependee = 0;
   uint64_t dependeeSize = 0;
   bool queryIsVolatile = false;
   if (StoreInst* S = dyn_cast<StoreInst>(query)) {
     dependee = S->getPointerOperand();
     dependeeSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
     queryIsVolatile = S->isVolatile();
   } else if (LoadInst* L = dyn_cast<LoadInst>(query)) {
     dependee = L->getPointerOperand();
     dependeeSize = TD.getTypeStoreSize(L->getType());
     queryIsVolatile = L->isVolatile();
   } else if (VAArgInst* V = dyn_cast<VAArgInst>(query)) {
     dependee = V->getOperand(0);
     dependeeSize = TD.getTypeStoreSize(V->getType());
   } else if (FreeInst* F = dyn_cast<FreeInst>(query)) {
     dependee = F->getPointerOperand();

     // FreeInsts erase the entire structure, not just a field
     dependeeSize = ~0UL;
   } else if (CallSite::get(query).getInstruction() != 0)
     return getCallSiteDependency(CallSite::get(query), start, block);
   else if (isa<AllocationInst>(query))
     return None;
   else
     return None;

   BasicBlock::iterator blockBegin = block ? block->begin()
                                           : query->getParent()->begin();

   // Walk backwards through the basic block, looking for dependencies
   while (QI != blockBegin) {
     --QI;

     // If this inst is a memory op, get the pointer it accessed
     Value* pointer = 0;
     uint64_t pointerSize = 0;
     if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
       // All volatile loads/stores depend on each other
       if (queryIsVolatile && S->isVolatile()) {
         if (!start && !block) {
           cachedResult.first = S;
           cachedResult.second = true;
           reverseDep[S].insert(query);
         }

         return S;
       }

       pointer = S->getPointerOperand();
       pointerSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
     } else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
       // All volatile loads/stores depend on each other
       if (queryIsVolatile && L->isVolatile()) {
         if (!start && !block) {
           cachedResult.first = L;
           cachedResult.second = true;
           reverseDep[L].insert(query);
         }

         return L;
       }

       pointer = L->getPointerOperand();
       pointerSize = TD.getTypeStoreSize(L->getType());
     } else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
       pointer = AI;
       if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
         pointerSize = C->getZExtValue() * \
                       TD.getABITypeSize(AI->getAllocatedType());
       else
         pointerSize = ~0UL;
     } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
       pointer = V->getOperand(0);
       pointerSize = TD.getTypeStoreSize(V->getType());
     } else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
       pointer = F->getPointerOperand();

       // FreeInsts erase the entire structure
       pointerSize = ~0UL;
     } else if (CallSite::get(QI).getInstruction() != 0) {
       // Call insts need special handling. Check if they can modify our pointer
       AliasAnalysis::ModRefResult MR = AA.getModRefInfo(CallSite::get(QI),
                                                       dependee, dependeeSize);

       if (MR != AliasAnalysis::NoModRef) {
         // Loads don't depend on read-only calls
         if (isa<LoadInst>(query) && MR == AliasAnalysis::Ref)
           continue;

         if (!start && !block) {
           cachedResult.first = QI;
           cachedResult.second = true;
           reverseDep[QI].insert(query);
         }

         return QI;
       } else {
         continue;
       }
     }

     // If we found a pointer, check if it could be the same as our pointer
     if (pointer) {
       AliasAnalysis::AliasResult R = AA.alias(pointer, pointerSize,
                                               dependee, dependeeSize);

       if (R != AliasAnalysis::NoAlias) {
         // May-alias loads don't depend on each other
         if (isa<LoadInst>(query) && isa<LoadInst>(QI) &&
             R == AliasAnalysis::MayAlias)
           continue;

         if (!start && !block) {
           cachedResult.first = QI;
           cachedResult.second = true;
           reverseDep[QI].insert(query);
         }

         return QI;
       }
     }
   }

   // If we found nothing, return the non-local flag
   if (!start && !block) {
     cachedResult.first = NonLocal;
     cachedResult.second = true;
     reverseDep[NonLocal].insert(query);
   }

   return NonLocal;
 }

 /// dropInstruction - Remove an instruction from the analysis, making
 /// absolutely conservative assumptions when updating the cache.  This is
 /// useful, for example when an instruction is changed rather than removed.
 void MemoryDependenceAnalysis::dropInstruction(Instruction* drop) {
   depMapType::iterator depGraphEntry = depGraphLocal.find(drop);
   if (depGraphEntry != depGraphLocal.end())
     reverseDep[depGraphEntry->second.first].erase(drop);

   // Drop dependency information for things that depended on this instr
   SmallPtrSet<Instruction*, 4>& set = reverseDep[drop];
   for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
        I != E; ++I)
     depGraphLocal.erase(*I);

   depGraphLocal.erase(drop);
   reverseDep.erase(drop);

   for (DenseMap<BasicBlock*, Value*>::iterator DI =
        depGraphNonLocal[drop].begin(), DE = depGraphNonLocal[drop].end();
        DI != DE; ++DI)
     if (DI->second != None)
       reverseDepNonLocal[DI->second].erase(drop);

   if (reverseDepNonLocal.count(drop)) {
     SmallPtrSet<Instruction*, 4>& set = reverseDepNonLocal[drop];
     for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
          I != E; ++I)
       for (DenseMap<BasicBlock*, Value*>::iterator DI =
            depGraphNonLocal[*I].begin(), DE = depGraphNonLocal[*I].end();
            DI != DE; ++DI)
         if (DI->second == drop)
           DI->second = Dirty;
   }

   reverseDepNonLocal.erase(drop);
   nonLocalDepMapType::iterator I = depGraphNonLocal.find(drop);
   if (I != depGraphNonLocal.end())
     depGraphNonLocal.erase(I);
 }

 /// removeInstruction - Remove an instruction from the dependence analysis,
 /// updating the dependence of instructions that previously depended on it.
 /// This method attempts to keep the cache coherent using the reverse map.
 void MemoryDependenceAnalysis::removeInstruction(Instruction* rem) {
   // Figure out the new dep for things that currently depend on rem
   Instruction* newDep = NonLocal;

   for (DenseMap<BasicBlock*, Value*>::iterator DI =
        depGraphNonLocal[rem].begin(), DE = depGraphNonLocal[rem].end();
        DI != DE; ++DI)
     if (DI->second != None)
       reverseDepNonLocal[DI->second].erase(rem);

   depMapType::iterator depGraphEntry = depGraphLocal.find(rem);

   if (depGraphEntry != depGraphLocal.end()) {
     reverseDep[depGraphEntry->second.first].erase(rem);

     if (depGraphEntry->second.first != NonLocal &&
         depGraphEntry->second.first != None &&
         depGraphEntry->second.second) {
       // If we have dep info for rem, set them to it
       BasicBlock::iterator RI = depGraphEntry->second.first;
       RI++;

       // If RI is rem, then we use rem's immediate successor.
       if (RI == (BasicBlock::iterator)rem) RI++;

       newDep = RI;
     } else if ( (depGraphEntry->second.first == NonLocal ||
                  depGraphEntry->second.first == None ) &&
                depGraphEntry->second.second ) {
       // If we have a confirmed non-local flag, use it
       newDep = depGraphEntry->second.first;
     } else {
       // Otherwise, use the immediate successor of rem
       // NOTE: This is because, when getDependence is called, it will first
       // check the immediate predecessor of what is in the cache.
       BasicBlock::iterator RI = rem;
       RI++;
       newDep = RI;
     }
   } else {
     // Otherwise, use the immediate successor of rem
     // NOTE: This is because, when getDependence is called, it will first
     // check the immediate predecessor of what is in the cache.
     BasicBlock::iterator RI = rem;
     RI++;
     newDep = RI;
   }

   SmallPtrSet<Instruction*, 4>& set = reverseDep[rem];
   for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
        I != E; ++I) {
     // Insert the new dependencies
     // Mark it as unconfirmed as long as it is not the non-local flag
     depGraphLocal[*I] = std::make_pair(newDep, (newDep == NonLocal ||
                                                 newDep == None));
   }

   depGraphLocal.erase(rem);
   reverseDep.erase(rem);

   if (reverseDepNonLocal.count(rem)) {
     SmallPtrSet<Instruction*, 4>& set = reverseDepNonLocal[rem];
     for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
          I != E; ++I)
       for (DenseMap<BasicBlock*, Value*>::iterator DI =
            depGraphNonLocal[*I].begin(), DE = depGraphNonLocal[*I].end();
            DI != DE; ++DI)
         if (DI->second == rem)
           DI->second = Dirty;

   }

   reverseDepNonLocal.erase(rem);
   nonLocalDepMapType::iterator I = depGraphNonLocal.find(rem);
   if (I != depGraphNonLocal.end())
     depGraphNonLocal.erase(I);

   getAnalysis<AliasAnalysis>().deleteValue(rem);
 }
	//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation --- C++ --===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This file implements an analysis that determines, for a given memory
	// operation, what preceding memory operations it depends on. It builds on
	// alias analysis information, and tries to provide a lazy, caching interface to
	// a common kind of alias information query.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/Analysis/MemoryDependenceAnalysis.h"
	#include "llvm/Constants.h"
	#include "llvm/Instructions.h"
	#include "llvm/Function.h"
	#include "llvm/Analysis/AliasAnalysis.h"
	#include "llvm/Support/CFG.h"
	#include "llvm/Support/CommandLine.h"
	#include "llvm/Target/TargetData.h"
	#include "llvm/ADT/Statistic.h"

	#define DEBUG_TYPE "memdep"

	using namespace llvm;

	// Control the calculation of non-local dependencies by only examining the
	// predecessors if the basic block has less than X amount (50 by default).
	static cl::opt<int>
	PredLimit("nonlocaldep-threshold", cl::Hidden, cl::init(50),
	cl::desc("Control the calculation of non-local"
	"dependencies (default = 50)"));

	STATISTIC(NumCacheNonlocal, "Number of cached non-local responses");
	STATISTIC(NumUncacheNonlocal, "Number of uncached non-local responses");

	char MemoryDependenceAnalysis::ID = 0;

	Instruction* const MemoryDependenceAnalysis::NonLocal = (Instruction*)-3;
	Instruction* const MemoryDependenceAnalysis::None = (Instruction*)-4;
	Instruction* const MemoryDependenceAnalysis::Dirty = (Instruction*)-5;

	// Register this pass...
	static RegisterPass<MemoryDependenceAnalysis> X("memdep",
	"Memory Dependence Analysis", false, true);

	void MemoryDependenceAnalysis::ping(Instruction *D) {
	for (depMapType::iterator I = depGraphLocal.begin(), E = depGraphLocal.end();
	I != E; ++I) {
	assert(I->first != D);
	assert(I->second.first != D);
	}

	for (nonLocalDepMapType::iterator I = depGraphNonLocal.begin(), E = depGraphNonLocal.end();
	I != E; ++I) {
	assert(I->first != D);
	for (DenseMap<BasicBlock, Value>::iterator II = I->second.begin(),
	EE = I->second.end(); II != EE; ++II)
	assert(II->second != D);
	}

	for (reverseDepMapType::iterator I = reverseDep.begin(), E = reverseDep.end();
	I != E; ++I)
	for (SmallPtrSet<Instruction*, 4>::iterator II = I->second.begin(), EE = I->second.end();
	II != EE; ++II)
	assert(*II != D);

	for (reverseDepMapType::iterator I = reverseDepNonLocal.begin(), E = reverseDepNonLocal.end();
	I != E; ++I)
	for (SmallPtrSet<Instruction*, 4>::iterator II = I->second.begin(), EE = I->second.end();
	II != EE; ++II)
	assert(*II != D);
	}

	/// getAnalysisUsage - Does not modify anything. It uses Alias Analysis.
	///
	void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
	AU.setPreservesAll();
	AU.addRequiredTransitive<AliasAnalysis>();
	AU.addRequiredTransitive<TargetData>();
	}

	/// getCallSiteDependency - Private helper for finding the local dependencies
	/// of a call site.
	Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C,
	Instruction* start,
	BasicBlock* block) {

	std::pair<Instruction*, bool>& cachedResult =
	depGraphLocal[C.getInstruction()];
	AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
	TargetData& TD = getAnalysis<TargetData>();
	BasicBlock::iterator blockBegin = C.getInstruction()->getParent()->begin();
	BasicBlock::iterator QI = C.getInstruction();

	// If the starting point was specified, use it
	if (start) {
	QI = start;
	blockBegin = start->getParent()->begin();
	// If the starting point wasn't specified, but the block was, use it
	} else if (!start && block) {
	QI = block->end();
	blockBegin = block->begin();
	}

	// Walk backwards through the block, looking for dependencies
	while (QI != blockBegin) {
	--QI;

	// If this inst is a memory op, get the pointer it accessed
	Value* pointer = 0;
	uint64_t pointerSize = 0;
	if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
	pointer = S->getPointerOperand();
	pointerSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
	} else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
	pointer = AI;
	if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
	pointerSize = C->getZExtValue() * \
	TD.getABITypeSize(AI->getAllocatedType());
	else
	pointerSize = ~0UL;
	} else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
	pointer = V->getOperand(0);
	pointerSize = TD.getTypeStoreSize(V->getType());
	} else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
	pointer = F->getPointerOperand();

	// FreeInsts erase the entire structure
	pointerSize = ~0UL;
	} else if (CallSite::get(QI).getInstruction() != 0) {
	AliasAnalysis::ModRefBehavior result =
	AA.getModRefBehavior(CallSite::get(QI));
	if (result != AliasAnalysis::DoesNotAccessMemory) {
	if (!start && !block) {
	cachedResult.first = QI;
	cachedResult.second = true;
	reverseDep[QI].insert(C.getInstruction());
	}
	return QI;
	} else {
	continue;
	}
	} else
	continue;

	if (AA.getModRefInfo(C, pointer, pointerSize) != AliasAnalysis::NoModRef) {
	if (!start && !block) {
	cachedResult.first = QI;
	cachedResult.second = true;
	reverseDep[QI].insert(C.getInstruction());
	}
	return QI;
	}
	}

	// No dependence found
	cachedResult.first = NonLocal;
	cachedResult.second = true;
	reverseDep[NonLocal].insert(C.getInstruction());
	return NonLocal;
	}

	/// nonLocalHelper - Private helper used to calculate non-local dependencies
	/// by doing DFS on the predecessors of a block to find its dependencies
	void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
	BasicBlock* block,
	DenseMap<BasicBlock, Value>& resp) {
	// Set of blocks that we've already visited in our DFS
	SmallPtrSet<BasicBlock*, 4> visited;
	// If we're updating a dirtied cache entry, we don't need to reprocess
	// already computed entries.
	for (DenseMap<BasicBlock, Value>::iterator I = resp.begin(),
	E = resp.end(); I != E; ++I)
	if (I->second != Dirty)
	visited.insert(I->first);

	// Current stack of the DFS
	SmallVector<BasicBlock*, 4> stack;
	for (pred_iterator PI = pred_begin(block), PE = pred_end(block);
	PI != PE; ++PI)
	stack.push_back(*PI);

	// Do a basic DFS
	while (!stack.empty()) {
	BasicBlock* BB = stack.back();

	// If we've already visited this block, no need to revist
	if (visited.count(BB)) {
	stack.pop_back();
	continue;
	}

	// If we find a new block with a local dependency for query,
	// then we insert the new dependency and backtrack.
	if (BB != block) {
	visited.insert(BB);

	Instruction* localDep = getDependency(query, 0, BB);
	if (localDep != NonLocal) {
	resp.insert(std::make_pair(BB, localDep));
	stack.pop_back();

	continue;
	}
	// If we re-encounter the starting block, we still need to search it
	// because there might be a dependency in the starting block AFTER
	// the position of the query. This is necessary to get loops right.
	} else if (BB == block) {
	visited.insert(BB);

	Instruction* localDep = getDependency(query, 0, BB);
	if (localDep != query)
	resp.insert(std::make_pair(BB, localDep));

	stack.pop_back();

	continue;
	}

	// If we didn't find anything, recurse on the precessors of this block
	// Only do this for blocks with a small number of predecessors.
	bool predOnStack = false;
	bool inserted = false;
	if (std::distance(pred_begin(BB), pred_end(BB)) <= PredLimit) {
	for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
	PI != PE; ++PI)
	if (!visited.count(*PI)) {
	stack.push_back(*PI);
	inserted = true;
	} else
	predOnStack = true;
	}

	// If we inserted a new predecessor, then we'll come back to this block
	if (inserted)
	continue;
	// If we didn't insert because we have no predecessors, then this
	// query has no dependency at all.
	else if (!inserted && !predOnStack) {
	resp.insert(std::make_pair(BB, None));
	// If we didn't insert because our predecessors are already on the stack,
	// then we might still have a dependency, but it will be discovered during
	// backtracking.
	} else if (!inserted && predOnStack){
	resp.insert(std::make_pair(BB, NonLocal));
	}

	stack.pop_back();
	}
	}

	/// getNonLocalDependency - Fills the passed-in map with the non-local
	/// dependencies of the queries. The map will contain NonLocal for
	/// blocks between the query and its dependencies.
	void MemoryDependenceAnalysis::getNonLocalDependency(Instruction* query,
	DenseMap<BasicBlock, Value>& resp) {
	if (depGraphNonLocal.count(query)) {
	DenseMap<BasicBlock, Value>& cached = depGraphNonLocal[query];
	NumCacheNonlocal++;

	SmallVector<BasicBlock*, 4> dirtied;
	for (DenseMap<BasicBlock, Value>::iterator I = cached.begin(),
	E = cached.end(); I != E; ++I)
	if (I->second == Dirty)
	dirtied.push_back(I->first);

	for (SmallVector<BasicBlock*, 4>::iterator I = dirtied.begin(),
	E = dirtied.end(); I != E; ++I) {
	Instruction* localDep = getDependency(query, 0, *I);
	if (localDep != NonLocal)
	cached[*I] = localDep;
	else {
	cached.erase(*I);
	nonLocalHelper(query, *I, cached);
	}
	}

	resp = cached;

	// Update the reverse non-local dependency cache
	for (DenseMap<BasicBlock, Value>::iterator I = resp.begin(), E = resp.end();
	I != E; ++I)
	reverseDepNonLocal[I->second].insert(query);

	return;
	} else
	NumUncacheNonlocal++;

	// If not, go ahead and search for non-local deps.
	nonLocalHelper(query, query->getParent(), resp);

	// Update the non-local dependency cache
	for (DenseMap<BasicBlock, Value>::iterator I = resp.begin(), E = resp.end();
	I != E; ++I) {
	depGraphNonLocal[query].insert(*I);
	reverseDepNonLocal[I->second].insert(query);
	}
	}

	/// getDependency - Return the instruction on which a memory operation
	/// depends. The local parameter indicates if the query should only
	/// evaluate dependencies within the same basic block.
	Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
	Instruction* start,
	BasicBlock* block) {
	// Start looking for dependencies with the queried inst
	BasicBlock::iterator QI = query;

	// Check for a cached result
	std::pair<Instruction*, bool>& cachedResult = depGraphLocal[query];
	// If we have a _confirmed_ cached entry, return it
	if (!block && !start) {
	if (cachedResult.second)
	return cachedResult.first;
	else if (cachedResult.first && cachedResult.first != NonLocal)
	// If we have an unconfirmed cached entry, we can start our search from there
	QI = cachedResult.first;
	}

	if (start)
	QI = start;
	else if (!start && block)
	QI = block->end();

	AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
	TargetData& TD = getAnalysis<TargetData>();

	// Get the pointer value for which dependence will be determined
	Value* dependee = 0;
	uint64_t dependeeSize = 0;
	bool queryIsVolatile = false;
	if (StoreInst* S = dyn_cast<StoreInst>(query)) {
	dependee = S->getPointerOperand();
	dependeeSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
	queryIsVolatile = S->isVolatile();
	} else if (LoadInst* L = dyn_cast<LoadInst>(query)) {
	dependee = L->getPointerOperand();
	dependeeSize = TD.getTypeStoreSize(L->getType());
	queryIsVolatile = L->isVolatile();
	} else if (VAArgInst* V = dyn_cast<VAArgInst>(query)) {
	dependee = V->getOperand(0);
	dependeeSize = TD.getTypeStoreSize(V->getType());
	} else if (FreeInst* F = dyn_cast<FreeInst>(query)) {
	dependee = F->getPointerOperand();

	// FreeInsts erase the entire structure, not just a field
	dependeeSize = ~0UL;
	} else if (CallSite::get(query).getInstruction() != 0)
	return getCallSiteDependency(CallSite::get(query), start, block);
	else if (isa<AllocationInst>(query))
	return None;
	else
	return None;

	BasicBlock::iterator blockBegin = block ? block->begin()
	: query->getParent()->begin();

	// Walk backwards through the basic block, looking for dependencies
	while (QI != blockBegin) {
	--QI;

	// If this inst is a memory op, get the pointer it accessed
	Value* pointer = 0;
	uint64_t pointerSize = 0;
	if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
	// All volatile loads/stores depend on each other
	if (queryIsVolatile && S->isVolatile()) {
	if (!start && !block) {
	cachedResult.first = S;
	cachedResult.second = true;
	reverseDep[S].insert(query);
	}

	return S;
	}

	pointer = S->getPointerOperand();
	pointerSize = TD.getTypeStoreSize(S->getOperand(0)->getType());
	} else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
	// All volatile loads/stores depend on each other
	if (queryIsVolatile && L->isVolatile()) {
	if (!start && !block) {
	cachedResult.first = L;
	cachedResult.second = true;
	reverseDep[L].insert(query);
	}

	return L;
	}

	pointer = L->getPointerOperand();
	pointerSize = TD.getTypeStoreSize(L->getType());
	} else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
	pointer = AI;
	if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
	pointerSize = C->getZExtValue() * \
	TD.getABITypeSize(AI->getAllocatedType());
	else
	pointerSize = ~0UL;
	} else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
	pointer = V->getOperand(0);
	pointerSize = TD.getTypeStoreSize(V->getType());
	} else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
	pointer = F->getPointerOperand();

	// FreeInsts erase the entire structure
	pointerSize = ~0UL;
	} else if (CallSite::get(QI).getInstruction() != 0) {
	// Call insts need special handling. Check if they can modify our pointer
	AliasAnalysis::ModRefResult MR = AA.getModRefInfo(CallSite::get(QI),
	dependee, dependeeSize);

	if (MR != AliasAnalysis::NoModRef) {
	// Loads don't depend on read-only calls
	if (isa<LoadInst>(query) && MR == AliasAnalysis::Ref)
	continue;

	if (!start && !block) {
	cachedResult.first = QI;
	cachedResult.second = true;
	reverseDep[QI].insert(query);
	}

	return QI;
	} else {
	continue;
	}
	}

	// If we found a pointer, check if it could be the same as our pointer
	if (pointer) {
	AliasAnalysis::AliasResult R = AA.alias(pointer, pointerSize,
	dependee, dependeeSize);

	if (R != AliasAnalysis::NoAlias) {
	// May-alias loads don't depend on each other
	if (isa<LoadInst>(query) && isa<LoadInst>(QI) &&
	R == AliasAnalysis::MayAlias)
	continue;

	if (!start && !block) {
	cachedResult.first = QI;
	cachedResult.second = true;
	reverseDep[QI].insert(query);
	}

	return QI;
	}
	}
	}

	// If we found nothing, return the non-local flag
	if (!start && !block) {
	cachedResult.first = NonLocal;
	cachedResult.second = true;
	reverseDep[NonLocal].insert(query);
	}

	return NonLocal;
	}

	/// dropInstruction - Remove an instruction from the analysis, making
	/// absolutely conservative assumptions when updating the cache. This is
	/// useful, for example when an instruction is changed rather than removed.
	void MemoryDependenceAnalysis::dropInstruction(Instruction* drop) {
	depMapType::iterator depGraphEntry = depGraphLocal.find(drop);
	if (depGraphEntry != depGraphLocal.end())
	reverseDep[depGraphEntry->second.first].erase(drop);

	// Drop dependency information for things that depended on this instr
	SmallPtrSet<Instruction*, 4>& set = reverseDep[drop];
	for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
	I != E; ++I)
	depGraphLocal.erase(*I);

	depGraphLocal.erase(drop);
	reverseDep.erase(drop);

	for (DenseMap<BasicBlock, Value>::iterator DI =
	depGraphNonLocal[drop].begin(), DE = depGraphNonLocal[drop].end();
	DI != DE; ++DI)
	if (DI->second != None)
	reverseDepNonLocal[DI->second].erase(drop);

	if (reverseDepNonLocal.count(drop)) {
	SmallPtrSet<Instruction*, 4>& set = reverseDepNonLocal[drop];
	for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
	I != E; ++I)
	for (DenseMap<BasicBlock, Value>::iterator DI =
	depGraphNonLocal[I].begin(), DE = depGraphNonLocal[I].end();
	DI != DE; ++DI)
	if (DI->second == drop)
	DI->second = Dirty;
	}

	reverseDepNonLocal.erase(drop);
	nonLocalDepMapType::iterator I = depGraphNonLocal.find(drop);
	if (I != depGraphNonLocal.end())
	depGraphNonLocal.erase(I);
	}

	/// removeInstruction - Remove an instruction from the dependence analysis,
	/// updating the dependence of instructions that previously depended on it.
	/// This method attempts to keep the cache coherent using the reverse map.
	void MemoryDependenceAnalysis::removeInstruction(Instruction* rem) {
	// Figure out the new dep for things that currently depend on rem
	Instruction* newDep = NonLocal;

	for (DenseMap<BasicBlock, Value>::iterator DI =
	depGraphNonLocal[rem].begin(), DE = depGraphNonLocal[rem].end();
	DI != DE; ++DI)
	if (DI->second != None)
	reverseDepNonLocal[DI->second].erase(rem);

	depMapType::iterator depGraphEntry = depGraphLocal.find(rem);

	if (depGraphEntry != depGraphLocal.end()) {
	reverseDep[depGraphEntry->second.first].erase(rem);

	if (depGraphEntry->second.first != NonLocal &&
	depGraphEntry->second.first != None &&
	depGraphEntry->second.second) {
	// If we have dep info for rem, set them to it
	BasicBlock::iterator RI = depGraphEntry->second.first;
	RI++;

	// If RI is rem, then we use rem's immediate successor.
	if (RI == (BasicBlock::iterator)rem) RI++;

	newDep = RI;
	} else if ( (depGraphEntry->second.first == NonLocal \|\|
	depGraphEntry->second.first == None ) &&
	depGraphEntry->second.second ) {
	// If we have a confirmed non-local flag, use it
	newDep = depGraphEntry->second.first;
	} else {
	// Otherwise, use the immediate successor of rem
	// NOTE: This is because, when getDependence is called, it will first
	// check the immediate predecessor of what is in the cache.
	BasicBlock::iterator RI = rem;
	RI++;
	newDep = RI;
	}
	} else {
	// Otherwise, use the immediate successor of rem
	// NOTE: This is because, when getDependence is called, it will first
	// check the immediate predecessor of what is in the cache.
	BasicBlock::iterator RI = rem;
	RI++;
	newDep = RI;
	}

	SmallPtrSet<Instruction*, 4>& set = reverseDep[rem];
	for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
	I != E; ++I) {
	// Insert the new dependencies
	// Mark it as unconfirmed as long as it is not the non-local flag
	depGraphLocal[*I] = std::make_pair(newDep, (newDep == NonLocal \|\|
	newDep == None));
	}

	depGraphLocal.erase(rem);
	reverseDep.erase(rem);

	if (reverseDepNonLocal.count(rem)) {
	SmallPtrSet<Instruction*, 4>& set = reverseDepNonLocal[rem];
	for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end();
	I != E; ++I)
	for (DenseMap<BasicBlock, Value>::iterator DI =
	depGraphNonLocal[I].begin(), DE = depGraphNonLocal[I].end();
	DI != DE; ++DI)
	if (DI->second == rem)
	DI->second = Dirty;

	}

	reverseDepNonLocal.erase(rem);
	nonLocalDepMapType::iterator I = depGraphNonLocal.find(rem);
	if (I != depGraphNonLocal.end())
	depGraphNonLocal.erase(I);

	getAnalysis<AliasAnalysis>().deleteValue(rem);
	}