//
// 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
+// alias analysis information, and tries to provide a lazy, caching interface to
// a common kind of alias information query.
//
//===----------------------------------------------------------------------===//
#include "llvm/Instructions.h"
#include "llvm/Function.h"
#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Support/CFG.h"
#include "llvm/Target/TargetData.h"
+#include "llvm/ADT/Statistic.h"
+
+#define DEBUG_TYPE "memdep"
using namespace llvm;
+STATISTIC(NumCacheNonlocal, "Number of cached non-local responses");
+STATISTIC(NumUncacheNonlocal, "Number of uncached non-local responses");
+
char MemoryDependenceAnalysis::ID = 0;
-Instruction* MemoryDependenceAnalysis::NonLocal = (Instruction*)0;
-Instruction* MemoryDependenceAnalysis::None = (Instruction*)~0;
+Instruction* const MemoryDependenceAnalysis::NonLocal = (Instruction*)-3;
+Instruction* const MemoryDependenceAnalysis::None = (Instruction*)-4;
+Instruction* const MemoryDependenceAnalysis::Dirty = (Instruction*)-5;
// Register this pass...
-RegisterPass<MemoryDependenceAnalysis> X("memdep",
- "Memory Dependence Analysis");
+static RegisterPass<MemoryDependenceAnalysis> X("memdep",
+ "Memory Dependence Analysis");
/// getAnalysisUsage - Does not modify anything. It uses Alias Analysis.
///
AU.addRequiredTransitive<TargetData>();
}
-// Find the dependency of a CallSite
-Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C, bool local) {
- assert(local && "Non-local memory dependence analysis not yet implemented");
+/// getCallSiteDependency - Private helper for finding the local dependencies
+/// of a call site.
+Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C,
+ Instruction* start,
+ BasicBlock* block) {
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 specifiy, use it
+ if (start) {
+ QI = start;
+ blockBegin = start->getParent()->end();
+ // If the starting point wasn't specified, but the block was, use it
+ } else if (!start && block) {
+ QI = block->end();
+ blockBegin = block->end();
+ }
+
+ // Walk backwards through the block, looking for dependencies
while (QI != blockBegin) {
--QI;
} else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
pointer = AI;
if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
- pointerSize = C->getZExtValue();
+ pointerSize = C->getZExtValue() * \
+ TD.getTypeSize(AI->getAllocatedType());
else
pointerSize = ~0UL;
+ } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
+ pointer = V->getOperand(0);
+ pointerSize = TD.getTypeSize(V->getType());
} else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
pointer = F->getPointerOperand();
pointerSize = ~0UL;
} else if (CallSite::get(QI).getInstruction() != 0) {
if (AA.getModRefInfo(C, CallSite::get(QI)) != AliasAnalysis::NoModRef) {
- depGraphLocal.insert(std::make_pair(C.getInstruction(), std::make_pair(QI, true)));
- reverseDep.insert(std::make_pair(QI, C.getInstruction()));
+ if (!start && !block) {
+ depGraphLocal.insert(std::make_pair(C.getInstruction(),
+ std::make_pair(QI, true)));
+ reverseDep[QI].insert(C.getInstruction());
+ }
return QI;
} else {
continue;
}
- }
+ } else
+ continue;
if (AA.getModRefInfo(C, pointer, pointerSize) != AliasAnalysis::NoModRef) {
- depGraphLocal.insert(std::make_pair(C.getInstruction(), std::make_pair(QI, true)));
- reverseDep.insert(std::make_pair(QI, C.getInstruction()));
+ if (!start && !block) {
+ depGraphLocal.insert(std::make_pair(C.getInstruction(),
+ std::make_pair(QI, true)));
+ reverseDep[QI].insert(C.getInstruction());
+ }
return QI;
}
}
// No dependence found
- depGraphLocal.insert(std::make_pair(C.getInstruction(), std::make_pair(NonLocal, true)));
- reverseDep.insert(std::make_pair(NonLocal, C.getInstruction()));
+ depGraphLocal.insert(std::make_pair(C.getInstruction(),
+ std::make_pair(NonLocal, 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;
+ stack.push_back(block);
+
+ // 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 && stack.size() > 1) {
+ 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
+ bool predOnStack = false;
+ bool inserted = false;
+ 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;
+
+ 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 paramter indicates if the query should only
/// evaluate dependencies within the same basic block.
Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
- bool local) {
- if (!local)
- assert(0 && "Non-local memory dependence is not yet supported.");
-
+ Instruction* start,
+ BasicBlock* block) {
// Start looking for dependencies with the queried inst
BasicBlock::iterator QI = query;
// If we have a _confirmed_ cached entry, return it
if (cachedResult.second)
return cachedResult.first;
- else if (cachedResult.first != NonLocal)
+ 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;
- if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
+ bool queryIsVolatile = false;
+ if (StoreInst* S = dyn_cast<StoreInst>(query)) {
dependee = S->getPointerOperand();
dependeeSize = TD.getTypeSize(S->getOperand(0)->getType());
- } else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
+ queryIsVolatile = S->isVolatile();
+ } else if (LoadInst* L = dyn_cast<LoadInst>(query)) {
dependee = L->getPointerOperand();
dependeeSize = TD.getTypeSize(L->getType());
- } else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
+ queryIsVolatile = L->isVolatile();
+ } else if (VAArgInst* V = dyn_cast<VAArgInst>(query)) {
+ dependee = V->getOperand(0);
+ dependeeSize = TD.getTypeSize(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(QI).getInstruction() != 0)
- return getCallSiteDependency(CallSite::get(QI));
+ } 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 = query->getParent()->begin();
+ BasicBlock::iterator blockBegin = block ? block->begin()
+ : query->getParent()->begin();
+ // Walk backwards through the basic block, looking for dependencies
while (QI != blockBegin) {
--QI;
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) {
+ depGraphLocal.insert(std::make_pair(query, std::make_pair(S, true)));
+ reverseDep[S].insert(query);
+ }
+
+ return S;
+ }
+
pointer = S->getPointerOperand();
pointerSize = TD.getTypeSize(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) {
+ depGraphLocal.insert(std::make_pair(query, std::make_pair(L, true)));
+ reverseDep[L].insert(query);
+ }
+
+ return L;
+ }
+
pointer = L->getPointerOperand();
pointerSize = TD.getTypeSize(L->getType());
} else if (AllocationInst* AI = dyn_cast<AllocationInst>(QI)) {
pointer = AI;
if (ConstantInt* C = dyn_cast<ConstantInt>(AI->getArraySize()))
- pointerSize = C->getZExtValue();
+ pointerSize = C->getZExtValue() * \
+ TD.getTypeSize(AI->getAllocatedType());
else
pointerSize = ~0UL;
+ } else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
+ pointer = V->getOperand(0);
+ pointerSize = TD.getTypeSize(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 is they can modify our pointer
- if (AA.getModRefInfo(CallSite::get(QI), dependee, dependeeSize) !=
- AliasAnalysis::NoModRef) {
- depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
- reverseDep.insert(std::make_pair(QI, query));
+ // 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) {
+ depGraphLocal.insert(std::make_pair(query,
+ std::make_pair(QI, true)));
+ reverseDep[QI].insert(query);
+ }
+
return QI;
} else {
continue;
dependee, dependeeSize);
if (R != AliasAnalysis::NoAlias) {
- depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
- reverseDep.insert(std::make_pair(QI, query));
+ // May-alias loads don't depend on each other
+ if (isa<LoadInst>(query) && isa<LoadInst>(QI) &&
+ R == AliasAnalysis::MayAlias)
+ continue;
+
+ if (!start && !block) {
+ depGraphLocal.insert(std::make_pair(query,
+ std::make_pair(QI, true)));
+ reverseDep[QI].insert(query);
+ }
+
return QI;
}
}
}
// If we found nothing, return the non-local flag
- depGraphLocal.insert(std::make_pair(query,
- std::make_pair(NonLocal, true)));
- reverseDep.insert(std::make_pair(NonLocal, query));
+ if (!start && !block) {
+ depGraphLocal.insert(std::make_pair(query,
+ std::make_pair(NonLocal, true)));
+ reverseDep[NonLocal].insert(query);
+ }
return NonLocal;
}
/// 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;
- if (depGraphLocal[rem].first != NonLocal) {
- // If we have dep info for rem, set them to it
- BasicBlock::iterator RI = depGraphLocal[rem].first;
- RI++;
- newDep = RI;
- } else if (depGraphLocal[rem].first == NonLocal &&
- depGraphLocal[rem].second ) {
- // If we have a confirmed non-local flag, use it
- newDep = NonLocal;
- } 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;
- }
- std::multimap<Instruction*, Instruction*>::iterator I = reverseDep.find(rem);
- while (I->first == rem) {
- // Insert the new dependencies
- // Mark it as unconfirmed as long as it is not the non-local flag
- depGraphLocal[I->second] = std::make_pair(newDep, !newDep);
- reverseDep.erase(I);
- I = reverseDep.find(rem);
+ depMapType::iterator depGraphEntry = depGraphLocal.find(rem);
+
+ if (depGraphEntry != depGraphLocal.end()) {
+ if (depGraphEntry->second.first != NonLocal &&
+ depGraphEntry->second.second) {
+ // If we have dep info for rem, set them to it
+ BasicBlock::iterator RI = depGraphEntry->second.first;
+ RI++;
+ newDep = RI;
+ } else if (depGraphEntry->second.first == NonLocal &&
+ depGraphEntry->second.second ) {
+ // If we have a confirmed non-local flag, use it
+ newDep = NonLocal;
+ } 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);
+ }
+
+ 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);
+ }
+
+ getAnalysis<AliasAnalysis>().deleteValue(rem);
}
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