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Add support for walking up memory def chains, which enables finding many more

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dead stores on 400.perlbench.

llvm-svn: 39929
This commit is contained in:
Owen Anderson 2007-07-16 21:52:50 +00:00
parent f01c29815d
commit efc00e35cf
3 changed files with 65 additions and 34 deletions
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8
include/llvm/Analysis/MemoryDependenceAnalysis.h
View File

@ -35,7 +35,8 @@ class MemoryDependenceAnalysis : public FunctionPass {
DenseMap<Instruction*, std::pair<Instruction*, bool> > depGraphLocal;
std::multimap<Instruction*, Instruction*> reverseDep;
Instruction* getCallSiteDependency(CallSite C, bool local = true);
Instruction* getCallSiteDependency(CallSite C, Instruction* start,
bool local = true);
public:
static Instruction* NonLocal;
@ -60,8 +61,9 @@ class MemoryDependenceAnalysis : public FunctionPass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
/// getDependency - Return the instruction on which a memory operation
/// depends.
Instruction* getDependency(Instruction* query, bool local = true);
/// depends, starting with start.
Instruction* getDependency(Instruction* query, Instruction* start = 0,
bool local = true);
/// removeInstruction - Remove an instruction from the dependence analysis,
/// updating the dependence of instructions that previously depended on it.

55
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -41,7 +41,8 @@ void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
}
// Find the dependency of a CallSite
Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C, bool local) {
Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C, Instruction* start,
bool local) {
assert(local && "Non-local memory dependence analysis not yet implemented");
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
@ -103,6 +104,7 @@ Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C, bool lo
/// depends. The local paramter indicates if the query should only
/// evaluate dependencies within the same basic block.
Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
Instruction* start,
bool local) {
if (!local)
assert(0 && "Non-local memory dependence is not yet supported.");
@ -119,6 +121,9 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
// If we have an unconfirmed cached entry, we can start our search from there
QI = cachedResult.first;
if (start)
QI = start;
AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
TargetData& TD = getAnalysis<TargetData>();
@ -126,24 +131,24 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
Value* dependee = 0;
uint64_t dependeeSize = 0;
bool queryIsVolatile = false;
if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
if (StoreInst* S = dyn_cast<StoreInst>(query)) {
dependee = S->getPointerOperand();
dependeeSize = TD.getTypeSize(S->getOperand(0)->getType());
queryIsVolatile = S->isVolatile();
} else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
} else if (LoadInst* L = dyn_cast<LoadInst>(query)) {
dependee = L->getPointerOperand();
dependeeSize = TD.getTypeSize(L->getType());
queryIsVolatile = L->isVolatile();
} else if (VAArgInst* V = dyn_cast<VAArgInst>(QI)) {
} else if (VAArgInst* V = dyn_cast<VAArgInst>(query)) {
dependee = V->getOperand(0);
dependeeSize = TD.getTypeSize(V->getType());
} else if (FreeInst* F = dyn_cast<FreeInst>(QI)) {
} 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);
else if (isa<AllocationInst>(query))
return None;
else
@ -160,8 +165,11 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
// All volatile loads/stores depend on each other
if (queryIsVolatile && S->isVolatile()) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(S, true)));
reverseDep.insert(std::make_pair(S, query));
if (!start) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(S, true)));
reverseDep.insert(std::make_pair(S, query));
}
return S;
}
@ -170,8 +178,11 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
} else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
// All volatile loads/stores depend on each other
if (queryIsVolatile && L->isVolatile()) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(L, true)));
reverseDep.insert(std::make_pair(L, query));
if (!start) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(L, true)));
reverseDep.insert(std::make_pair(L, query));
}
return L;
}
@ -195,8 +206,11 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
// 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));
if (!start) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));
}
return QI;
} else {
continue;
@ -209,17 +223,22 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
dependee, dependeeSize);
if (R != AliasAnalysis::NoAlias) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, query));
if (!start) {
depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
reverseDep.insert(std::make_pair(QI, 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) {
depGraphLocal.insert(std::make_pair(query,
std::make_pair(NonLocal, true)));
reverseDep.insert(std::make_pair(NonLocal, query));
}
return NonLocal;
}

36
lib/Transforms/Scalar/FastDSE.cpp
View File

@ -119,22 +119,32 @@ bool FDSE::runOnBasicBlock(BasicBlock &BB) {
// ... to a pointer that has been stored to before...
if (last) {
Instruction* dep = MD.getDependency(BBI);
// ... and no other memory dependencies are between them....
if (MD.getDependency(BBI) == last) {
while (dep != MemoryDependenceAnalysis::None &&
dep != MemoryDependenceAnalysis::NonLocal &&
isa<StoreInst>(dep)) {
if (dep == last) {
// Remove it!
MD.removeInstruction(last);
// Remove it!
MD.removeInstruction(last);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
possiblyDead.insert(D);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
possiblyDead.insert(D);
last->eraseFromParent();
NumFastStores++;
deletedStore = true;
MadeChange = true;
last->eraseFromParent();
NumFastStores++;
deletedStore = true;
MadeChange = true;
break;
} else {
dep = MD.getDependency(BBI, dep);
}
}
}