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llvm-mirror/lib/Analysis/MemoryDependenceAnalysis.cpp
Duncan Sands 14f11d6836 Integrate the readonly/readnone logic more deeply 
into alias analysis.  This meant updating the API
which now has versions of the getModRefBehavior,
doesNotAccessMemory and onlyReadsMemory methods
which take a callsite parameter.  These should be
used unless the callsite is not known, since in
general they can do a better job than the versions
that take a function.  Also, users should no longer
call the version of getModRefBehavior that takes
both a function and a callsite.  To reduce the
chance of misuse it is now protected.

llvm-svn: 44487
2007-12-01 07:51:45 +00:00

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//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation --*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the Owen Anderson and 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/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* 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");
/// 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) {
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;
// 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 (isa<CallInst>(QI)) {
AliasAnalysis::ModRefBehavior result =
AA.getModRefBehavior(CallSite::get(QI));
if (result != AliasAnalysis::DoesNotAccessMemory &&
result != AliasAnalysis::OnlyReadsMemory) {
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) {
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[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,
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 (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) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(S, 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) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(L, 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) {
depGraphLocal.insert(std::make_pair(query,
std::make_pair(QI, 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) {
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
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;
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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