/// remove - Remove the specified (potentially non-empty) alias set from the
/// tracker.
void AliasSetTracker::remove(AliasSet &AS) {
// Drop all call sites.
AS.UnknownInsts.clear();
// Clear the alias set.
unsigned NumRefs = 0;
while (!AS.empty()) {
AliasSet::PointerRec *P = AS.PtrList;
Value *ValToRemove = P->getValue();
// Unlink and delete entry from the list of values.
P->eraseFromList();
// Remember how many references need to be dropped.
++NumRefs;
// Finally, remove the entry.
PointerMap.erase(ValToRemove);
}
// Stop using the alias set, removing it.
AS.RefCount -= NumRefs;
if (AS.RefCount == 0)
AS.removeFromTracker(*this);
}
// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely. It should be used when an instruction is deleted
// from the program to update the AST. If you don't use this, you would have
// dangling pointers to deleted instructions.
//
void AliasSetTracker::deleteValue(Value *PtrVal) {
// Notify the alias analysis implementation that this value is gone.
AA.deleteValue(PtrVal);
// If this is a call instruction, remove the callsite from the appropriate
// AliasSet.
CallSite CS = CallSite::get(PtrVal);
if (CS.getInstruction()) {
Function *F = CS.getCalledFunction();
if (!F || !AA.doesNotAccessMemory(F)) {
if (AliasSet *AS = findAliasSetForCallSite(CS))
AS->removeCallSite(CS);
}
}
// First, look up the PointerRec for this pointer.
hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(PtrVal);
if (I == PointerMap.end()) return; // Noop
// If we found one, remove the pointer from the alias set it is in.
AliasSet::HashNodePair &PtrValEnt = *I;
AliasSet *AS = PtrValEnt.second.getAliasSet(*this);
// Unlink from the list of values...
PtrValEnt.second.removeFromList();
// Stop using the alias set
AS->dropRef(*this);
PointerMap.erase(I);
}
// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely. It should be used when an instruction is deleted
// from the program to update the AST. If you don't use this, you would have
// dangling pointers to deleted instructions.
//
void AliasSetTracker::deleteValue(Value *PtrVal) {
// Notify the alias analysis implementation that this value is gone.
AA.deleteValue(PtrVal);
// If this is a call instruction, remove the callsite from the appropriate
// AliasSet (if present).
if (Instruction *Inst = dyn_cast<Instruction>(PtrVal)) {
if (Inst->mayReadOrWriteMemory()) {
// Scan all the alias sets to see if this call site is contained.
for (iterator I = begin(), E = end(); I != E; ++I) {
if (I->Forward) continue;
I->removeUnknownInst(Inst);
}
}
}
// First, look up the PointerRec for this pointer.
PointerMapType::iterator I = PointerMap.find(PtrVal);
if (I == PointerMap.end()) return; // Noop
// If we found one, remove the pointer from the alias set it is in.
AliasSet::PointerRec *PtrValEnt = I->second;
AliasSet *AS = PtrValEnt->getAliasSet(*this);
// Unlink and delete from the list of values.
PtrValEnt->eraseFromList();
// Stop using the alias set.
AS->dropRef(*this);
PointerMap.erase(I);
}
/// mergeSetIn - Merge the specified alias set into this alias set.
///
void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
assert(!AS.Forward && "Alias set is already forwarding!");
assert(!Forward && "This set is a forwarding set!!");
bool WasMustAlias = (Alias == SetMustAlias);
// Update the alias and access types of this set...
Access |= AS.Access;
Alias |= AS.Alias;
if (Alias == SetMustAlias) {
// Check that these two merged sets really are must aliases. Since both
// used to be must-alias sets, we can just check any pointer from each set
// for aliasing.
AliasAnalysis &AA = AST.getAliasAnalysis();
PointerRec *L = getSomePointer();
PointerRec *R = AS.getSomePointer();
// If the pointers are not a must-alias pair, this set becomes a may alias.
if (AA.alias(MemoryLocation(L->getValue(), L->getSize(), L->getAAInfo()),
MemoryLocation(R->getValue(), R->getSize(), R->getAAInfo())) !=
MustAlias)
Alias = SetMayAlias;
}
if (Alias == SetMayAlias) {
if (WasMustAlias)
AST.TotalMayAliasSetSize += size();
if (AS.Alias == SetMustAlias)
AST.TotalMayAliasSetSize += AS.size();
}
bool ASHadUnknownInsts = !AS.UnknownInsts.empty();
if (UnknownInsts.empty()) { // Merge call sites...
if (ASHadUnknownInsts) {
std::swap(UnknownInsts, AS.UnknownInsts);
addRef();
}
} else if (ASHadUnknownInsts) {
UnknownInsts.insert(UnknownInsts.end(), AS.UnknownInsts.begin(), AS.UnknownInsts.end());
AS.UnknownInsts.clear();
}
AS.Forward = this; // Forward across AS now...
addRef(); // AS is now pointing to us...
// Merge the list of constituent pointers...
if (AS.PtrList) {
SetSize += AS.size();
AS.SetSize = 0;
*PtrListEnd = AS.PtrList;
AS.PtrList->setPrevInList(PtrListEnd);
PtrListEnd = AS.PtrListEnd;
AS.PtrList = nullptr;
AS.PtrListEnd = &AS.PtrList;
assert(*AS.PtrListEnd == nullptr && "End of list is not null?");
}
if (ASHadUnknownInsts)
AS.dropRef(AST);
}
// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely. It should be used when an instruction is deleted
// from the program to update the AST. If you don't use this, you would have
// dangling pointers to deleted instructions.
//
void AliasSetTracker::deleteValue(Value *PtrVal) {
// Notify the alias analysis implementation that this value is gone.
AA.deleteValue(PtrVal);
// If this is a call instruction, remove the callsite from the appropriate
// AliasSet.
CallSite CS = CallSite::get(PtrVal);
if (CS.getInstruction())
if (!AA.doesNotAccessMemory(CS))
if (AliasSet *AS = findAliasSetForCallSite(CS))
AS->removeCallSite(CS);
// First, look up the PointerRec for this pointer.
PointerMapType::iterator I = PointerMap.find(PtrVal);
if (I == PointerMap.end()) return; // Noop
// If we found one, remove the pointer from the alias set it is in.
AliasSet::PointerRec *PtrValEnt = I->second;
AliasSet *AS = PtrValEnt->getAliasSet(*this);
// Unlink and delete from the list of values.
PtrValEnt->eraseFromList();
// Stop using the alias set.
AS->dropRef(*this);
PointerMap.erase(I);
}
/// remove - Remove the specified (potentially non-empty) alias set from the
/// tracker.
void AliasSetTracker::remove(AliasSet &AS) {
// Drop all call sites.
AS.CallSites.clear();
// Clear the alias set.
unsigned NumRefs = 0;
while (!AS.empty()) {
AliasSet::HashNodePair *P = AS.PtrList;
// Unlink from the list of values.
P->second.removeFromList();
// Remember how many references need to be dropped.
++NumRefs;
// Finally, remove the entry.
Value *Remove = P->first; // Take a copy because it is invalid to pass
PointerMap.erase(Remove); // a reference to the data being erased.
}
// Stop using the alias set, removing it.
AS.RefCount -= NumRefs;
if (AS.RefCount == 0)
AS.removeFromTracker(*this);
}
/// mergeAliasSetsForPointer - Given a pointer, merge all alias sets that may
/// alias the pointer. Return the unified set, or nullptr if no set that aliases
/// the pointer was found. MustAliasAll is updated to true/false if the pointer
/// is found to MustAlias all the sets it merged.
AliasSet *AliasSetTracker::mergeAliasSetsForPointer(const Value *Ptr,
LocationSize Size,
const AAMDNodes &AAInfo,
bool &MustAliasAll) {
AliasSet *FoundSet = nullptr;
AliasResult AllAR = MustAlias;
for (iterator I = begin(), E = end(); I != E;) {
iterator Cur = I++;
if (Cur->Forward)
continue;
AliasResult AR = Cur->aliasesPointer(Ptr, Size, AAInfo, AA);
if (AR == NoAlias)
continue;
AllAR =
AliasResult(AllAR & AR); // Possible downgrade to May/Partial, even No
if (!FoundSet) {
// If this is the first alias set ptr can go into, remember it.
FoundSet = &*Cur;
} else {
// Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*Cur, *this);
}
}
MustAliasAll = (AllAR == MustAlias);
return FoundSet;
}
void AliasSetTracker::addUnknown(Instruction *Inst) {
if (isa<DbgInfoIntrinsic>(Inst))
return; // Ignore DbgInfo Intrinsics.
if (auto *II = dyn_cast<IntrinsicInst>(Inst)) {
// These intrinsics will show up as affecting memory, but they are just
// markers.
switch (II->getIntrinsicID()) {
default:
break;
// FIXME: Add lifetime/invariant intrinsics (See: PR30807).
case Intrinsic::assume:
case Intrinsic::sideeffect:
return;
}
}
if (!Inst->mayReadOrWriteMemory())
return; // doesn't alias anything
AliasSet *AS = findAliasSetForUnknownInst(Inst);
if (AS) {
AS->addUnknownInst(Inst, AA);
return;
}
AliasSets.push_back(new AliasSet());
AS = &AliasSets.back();
AS->addUnknownInst(Inst, AA);
}
AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
AliasSet *FoundSet = nullptr;
for (iterator I = begin(), E = end(); I != E;) {
iterator Cur = I++;
if (Cur->Forward || !Cur->aliasesUnknownInst(Inst, AA))
continue;
if (!FoundSet) // If this is the first alias set ptr can go into.
FoundSet = &*Cur; // Remember it.
else // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*Cur, *this); // Merge in contents.
}
return FoundSet;
}
AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
AliasSet *FoundSet = 0;
for (iterator I = begin(), E = end(); I != E; ++I) {
if (I->Forward || !I->aliasesUnknownInst(Inst, AA))
continue;
if (FoundSet == 0) // If this is the first alias set ptr can go into.
FoundSet = I; // Remember it.
else if (!I->Forward) // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*I, *this); // Merge in contents.
}
return FoundSet;
}
AliasSet *AliasSetTracker::findAliasSetForCallSite(CallSite CS) {
AliasSet *FoundSet = 0;
for (iterator I = begin(), E = end(); I != E; ++I)
if (!I->Forward && I->aliasesCallSite(CS, AA)) {
if (FoundSet == 0) { // If this is the first alias set ptr can go into.
FoundSet = I; // Remember it.
} else if (!I->Forward) { // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*I, *this); // Merge in contents.
}
}
return FoundSet;
}
/// findAliasSetForPointer - Given a pointer, find the one alias set to put the
/// instruction referring to the pointer into. If there are multiple alias sets
/// that may alias the pointer, merge them together and return the unified set.
///
AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
unsigned Size) {
AliasSet *FoundSet = 0;
for (iterator I = begin(), E = end(); I != E; ++I)
if (!I->Forward && I->aliasesPointer(Ptr, Size, AA)) {
if (FoundSet == 0) { // If this is the first alias set ptr can go into.
FoundSet = I; // Remember it.
} else { // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*I, *this); // Merge in contents.
}
}
return FoundSet;
}
/// findAliasSetForPointer - Given a pointer, find the one alias set to put the
/// instruction referring to the pointer into. If there are multiple alias sets
/// that may alias the pointer, merge them together and return the unified set.
///
AliasSet *AliasSetTracker::findAliasSetForPointer(const Value *Ptr,
uint64_t Size,
const MDNode *TBAAInfo) {
AliasSet *FoundSet = 0;
for (iterator I = begin(), E = end(); I != E; ++I) {
if (I->Forward || !I->aliasesPointer(Ptr, Size, TBAAInfo, AA)) continue;
if (FoundSet == 0) { // If this is the first alias set ptr can go into.
FoundSet = I; // Remember it.
} else { // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*I, *this); // Merge in contents.
}
}
return FoundSet;
}
// copyValue - This method should be used whenever a preexisting value in the
// program is copied or cloned, introducing a new value. Note that it is ok for
// clients that use this method to introduce the same value multiple times: if
// the tracker already knows about a value, it will ignore the request.
//
void AliasSetTracker::copyValue(Value *From, Value *To) {
// Notify the alias analysis implementation that this value is copied.
AA.copyValue(From, To);
// First, look up the PointerRec for this pointer.
hash_map<Value*, AliasSet::PointerRec>::iterator I = PointerMap.find(From);
if (I == PointerMap.end() || !I->second.hasAliasSet())
return; // Noop
AliasSet::HashNodePair &Entry = getEntryFor(To);
if (Entry.second.hasAliasSet()) return; // Already in the tracker!
// Add it to the alias set it aliases...
AliasSet *AS = I->second.getAliasSet(*this);
AS->addPointer(*this, Entry, I->second.getSize(), true);
}
bool AliasSetTracker::add(CallSite CS) {
if (Function *F = CS.getCalledFunction())
if (AA.doesNotAccessMemory(F))
return true; // doesn't alias anything
AliasSet *AS = findAliasSetForCallSite(CS);
if (!AS) {
AliasSets.push_back(new AliasSet());
AS = &AliasSets.back();
AS->addCallSite(CS, AA);
return true;
} else {
AS->addCallSite(CS, AA);
return false;
}
}
bool AliasSetTracker::add(CallSite CS) {
if (isa<DbgInfoIntrinsic>(CS.getInstruction()))
return true; // Ignore DbgInfo Intrinsics.
if (AA.doesNotAccessMemory(CS))
return true; // doesn't alias anything
AliasSet *AS = findAliasSetForCallSite(CS);
if (AS) {
AS->addCallSite(CS, AA);
return false;
}
AliasSets.push_back(new AliasSet());
AS = &AliasSets.back();
AS->addCallSite(CS, AA);
return true;
}
bool AliasSetTracker::addUnknown(Instruction *Inst) {
if (isa<DbgInfoIntrinsic>(Inst))
return true; // Ignore DbgInfo Intrinsics.
if (!Inst->mayReadOrWriteMemory())
return true; // doesn't alias anything
AliasSet *AS = findAliasSetForUnknownInst(Inst);
if (AS) {
AS->addUnknownInst(Inst, AA);
return false;
}
AliasSets.push_back(new AliasSet());
AS = &AliasSets.back();
AS->addUnknownInst(Inst, AA);
return true;
}
/// mergeAliasSetsForPointer - Given a pointer, merge all alias sets that may
/// alias the pointer. Return the unified set, or nullptr if no set that aliases
/// the pointer was found.
AliasSet *AliasSetTracker::mergeAliasSetsForPointer(const Value *Ptr,
LocationSize Size,
const AAMDNodes &AAInfo) {
AliasSet *FoundSet = nullptr;
for (iterator I = begin(), E = end(); I != E;) {
iterator Cur = I++;
if (Cur->Forward || !Cur->aliasesPointer(Ptr, Size, AAInfo, AA)) continue;
if (!FoundSet) { // If this is the first alias set ptr can go into.
FoundSet = &*Cur; // Remember it.
} else { // Otherwise, we must merge the sets.
FoundSet->mergeSetIn(*Cur, *this); // Merge in contents.
}
}
return FoundSet;
}
// copyValue - This method should be used whenever a preexisting value in the
// program is copied or cloned, introducing a new value. Note that it is ok for
// clients that use this method to introduce the same value multiple times: if
// the tracker already knows about a value, it will ignore the request.
//
void AliasSetTracker::copyValue(Value *From, Value *To) {
// First, look up the PointerRec for this pointer.
PointerMapType::iterator I = PointerMap.find_as(From);
if (I == PointerMap.end())
return; // Noop
assert(I->second->hasAliasSet() && "Dead entry?");
AliasSet::PointerRec &Entry = getEntryFor(To);
if (Entry.hasAliasSet()) return; // Already in the tracker!
// getEntryFor above may invalidate iterator \c I, so reinitialize it.
I = PointerMap.find_as(From);
// Add it to the alias set it aliases...
AliasSet *AS = I->second->getAliasSet(*this);
AS->addPointer(*this, Entry, I->second->getSize(), I->second->getAAInfo(),
true, true);
}
AliasSetIterator(AliasSet set)
: flags(set.flags()), pos(0)
{
while (flags && (flags & 1) == 0) {
flags >>= 1;
pos++;
}
}
// copyValue - This method should be used whenever a preexisting value in the
// program is copied or cloned, introducing a new value. Note that it is ok for
// clients that use this method to introduce the same value multiple times: if
// the tracker already knows about a value, it will ignore the request.
//
void AliasSetTracker::copyValue(Value *From, Value *To) {
// Notify the alias analysis implementation that this value is copied.
AA.copyValue(From, To);
// First, look up the PointerRec for this pointer.
PointerMapType::iterator I = PointerMap.find(From);
if (I == PointerMap.end())
return; // Noop
assert(I->second->hasAliasSet() && "Dead entry?");
AliasSet::PointerRec &Entry = getEntryFor(To);
if (Entry.hasAliasSet()) return; // Already in the tracker!
// Add it to the alias set it aliases...
I = PointerMap.find(From);
AliasSet *AS = I->second->getAliasSet(*this);
AS->addPointer(*this, Entry, I->second->getSize(), true);
}
// deleteValue method - This method is used to remove a pointer value from the
// AliasSetTracker entirely. It should be used when an instruction is deleted
// from the program to update the AST. If you don't use this, you would have
// dangling pointers to deleted instructions.
//
void AliasSetTracker::deleteValue(Value *PtrVal) {
// First, look up the PointerRec for this pointer.
PointerMapType::iterator I = PointerMap.find_as(PtrVal);
if (I == PointerMap.end()) return; // Noop
// If we found one, remove the pointer from the alias set it is in.
AliasSet::PointerRec *PtrValEnt = I->second;
AliasSet *AS = PtrValEnt->getAliasSet(*this);
// Unlink and delete from the list of values.
PtrValEnt->eraseFromList();
if (AS->Alias == AliasSet::SetMayAlias) {
AS->SetSize--;
TotalMayAliasSetSize--;
}
// Stop using the alias set.
AS->dropRef(*this);
PointerMap.erase(I);
}
/// mergeSetIn - Merge the specified alias set into this alias set.
///
void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST) {
assert(!AS.Forward && "Alias set is already forwarding!");
assert(!Forward && "This set is a forwarding set!!");
// Update the alias and access types of this set...
AccessTy |= AS.AccessTy;
AliasTy |= AS.AliasTy;
Volatile |= AS.Volatile;
if (AliasTy == MustAlias) {
// Check that these two merged sets really are must aliases. Since both
// used to be must-alias sets, we can just check any pointer from each set
// for aliasing.
AliasAnalysis &AA = AST.getAliasAnalysis();
PointerRec *L = getSomePointer();
PointerRec *R = AS.getSomePointer();
// If the pointers are not a must-alias pair, this set becomes a may alias.
if (AA.alias(AliasAnalysis::Location(L->getValue(),
L->getSize(),
L->getTBAAInfo()),
AliasAnalysis::Location(R->getValue(),
R->getSize(),
R->getTBAAInfo()))
!= AliasAnalysis::MustAlias)
AliasTy = MayAlias;
}
if (CallSites.empty()) { // Merge call sites...
if (!AS.CallSites.empty())
std::swap(CallSites, AS.CallSites);
} else if (!AS.CallSites.empty()) {
CallSites.insert(CallSites.end(), AS.CallSites.begin(), AS.CallSites.end());
AS.CallSites.clear();
}
AS.Forward = this; // Forward across AS now...
addRef(); // AS is now pointing to us...
// Merge the list of constituent pointers...
if (AS.PtrList) {
*PtrListEnd = AS.PtrList;
AS.PtrList->setPrevInList(PtrListEnd);
PtrListEnd = AS.PtrListEnd;
AS.PtrList = 0;
AS.PtrListEnd = &AS.PtrList;
assert(*AS.PtrListEnd == 0 && "End of list is not null?");
}
}
AliasSet &AliasSetTracker::mergeAllAliasSets() {
assert(!AliasAnyAS && (TotalMayAliasSetSize > SaturationThreshold) &&
"Full merge should happen once, when the saturation threshold is "
"reached");
// Collect all alias sets, so that we can drop references with impunity
// without worrying about iterator invalidation.
std::vector<AliasSet *> ASVector;
ASVector.reserve(SaturationThreshold);
for (iterator I = begin(), E = end(); I != E; I++)
ASVector.push_back(&*I);
// Copy all instructions and pointers into a new set, and forward all other
// sets to it.
AliasSets.push_back(new AliasSet());
AliasAnyAS = &AliasSets.back();
AliasAnyAS->Alias = AliasSet::SetMayAlias;
AliasAnyAS->Access = AliasSet::ModRefAccess;
AliasAnyAS->AliasAny = true;
for (auto Cur : ASVector) {
// If Cur was already forwarding, just forward to the new AS instead.
AliasSet *FwdTo = Cur->Forward;
if (FwdTo) {
Cur->Forward = AliasAnyAS;
AliasAnyAS->addRef();
FwdTo->dropRef(*this);
continue;
}
// Otherwise, perform the actual merge.
AliasAnyAS->mergeSetIn(*Cur, *this);
}
return *AliasAnyAS;
}
DeadMemOpElimination::instr_iterator
DeadMemOpElimination::handleMemOp(instr_iterator I, DefMapTy &Defs,
AliasSetTracker &AST) {
MachineInstr *MI = I;
MachineMemOperand *MO = *MI->memoperands_begin();
// AliasAnalysis cannot handle offset right now, so we pretend to write a
// a big enough size to the location pointed by the base pointer.
uint64_t Size = MO->getSize() + MO->getOffset();
AliasSet *ASet = &AST.getAliasSetForPointer(const_cast<Value*>(MO->getValue()),
Size, 0);
MachineInstr *&LastMI = Defs[ASet];
bool canHandleLastStore = LastMI && ASet->isMustAlias()
&& LastMI->getOpcode() != VTM::VOpInternalCall
// FIXME: We may need to remember the last
// definition for all predicates.
&& isPredIdentical(LastMI, MI);
if (canHandleLastStore) {
MachineMemOperand *LastMO = *LastMI->memoperands_begin();
// We can only handle last store if and only if their memory operand have
// the must-alias address and the same size.
canHandleLastStore = LastMO->getSize() == MO->getSize()
&& !LastMO->isVolatile()
&& MachineMemOperandAlias(MO, LastMO, AA, SE)
== AliasAnalysis::MustAlias;
}
// FIXME: These elimination is only valid if we are in single-thread mode!
if (VInstrInfo::mayStore(MI)) {
if (canHandleLastStore) {
// Dead store find, remove it.
LastMI->eraseFromParent();
++DeadStoreEliminated;
}
// Update the definition.
LastMI = MI;
return I;
}
// Now MI is a load.
if (!canHandleLastStore) return I;
// Loading the value that just be stored, the load is not necessary.
MachineOperand LoadedMO = MI->getOperand(0);
MachineOperand StoredMO = LastMI->getOperand(2);
// Simply replace the load by a copy.
DebugLoc dl = MI->getDebugLoc();
I = *BuildMI(*MI->getParent(), I, dl, VInstrInfo::getDesc(VTM::VOpMove))
.addOperand(LoadedMO).addOperand(StoredMO).
addOperand(*VInstrInfo::getPredOperand(MI)).
addOperand(*VInstrInfo::getTraceOperand(MI));
MI->eraseFromParent();
++DeadLoadEliminated;
return I;
}
/// PromoteAliasSet - Try to promote memory values to scalars by sinking
/// stores out of the loop and moving loads to before the loop. We do this by
/// looping over the stores in the loop, looking for stores to Must pointers
/// which are loop invariant.
///
void LICM::PromoteAliasSet(AliasSet &AS) {
// We can promote this alias set if it has a store, if it is a "Must" alias
// set, if the pointer is loop invariant, and if we are not eliminating any
// volatile loads or stores.
if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue()))
return;
assert(!AS.empty() &&
"Must alias set should have at least one pointer element in it!");
Value *SomePtr = AS.begin()->getValue();
// It isn't safe to promote a load/store from the loop if the load/store is
// conditional. For example, turning:
//
// for () { if (c) *P += 1; }
//
// into:
//
// tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
//
// is not safe, because *P may only be valid to access if 'c' is true.
//
// It is safe to promote P if all uses are direct load/stores and if at
// least one is guaranteed to be executed.
bool GuaranteedToExecute = false;
SmallVector<Instruction*, 64> LoopUses;
SmallPtrSet<Value*, 4> PointerMustAliases;
// Check that all of the pointers in the alias set have the same type. We
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) {
Value *ASIV = ASI->getValue();
PointerMustAliases.insert(ASIV);
// Check that all of the pointers in the alias set have the same type. We
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
if (SomePtr->getType() != ASIV->getType())
return;
for (Value::use_iterator UI = ASIV->use_begin(), UE = ASIV->use_end();
UI != UE; ++UI) {
// Ignore instructions that are outside the loop.
Instruction *Use = dyn_cast<Instruction>(*UI);
if (!Use || !CurLoop->contains(Use))
continue;
// If there is an non-load/store instruction in the loop, we can't promote
// it.
if (isa<LoadInst>(Use))
assert(!cast<LoadInst>(Use)->isVolatile() && "AST broken");
else if (isa<StoreInst>(Use)) {
assert(!cast<StoreInst>(Use)->isVolatile() && "AST broken");
if (Use->getOperand(0) == ASIV) return;
} else
return; // Not a load or store.
if (!GuaranteedToExecute)
GuaranteedToExecute = isSafeToExecuteUnconditionally(*Use);
LoopUses.push_back(Use);
}
}
// If there isn't a guaranteed-to-execute instruction, we can't promote.
if (!GuaranteedToExecute)
return;
// Otherwise, this is safe to promote, lets do it!
DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n');
Changed = true;
++NumPromoted;
// We use the SSAUpdater interface to insert phi nodes as required.
SmallVector<PHINode*, 16> NewPHIs;
SSAUpdater SSA(&NewPHIs);
// It wants to know some value of the same type as what we'll be inserting.
Value *SomeValue;
if (isa<LoadInst>(LoopUses[0]))
SomeValue = LoopUses[0];
else
SomeValue = cast<StoreInst>(LoopUses[0])->getOperand(0);
SSA.Initialize(SomeValue->getType(), SomeValue->getName());
// First step: bucket up uses of the pointers by the block they occur in.
// This is important because we have to handle multiple defs/uses in a block
// ourselves: SSAUpdater is purely for cross-block references.
// FIXME: Want a TinyVector<Instruction*> since there is usually 0/1 element.
DenseMap<BasicBlock*, std::vector<Instruction*> > UsesByBlock;
for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
Instruction *User = LoopUses[i];
UsesByBlock[User->getParent()].push_back(User);
}
// Okay, now we can iterate over all the blocks in the loop with uses,
// processing them. Keep track of which loads are loading a live-in value.
SmallVector<LoadInst*, 32> LiveInLoads;
DenseMap<Value*, Value*> ReplacedLoads;
for (unsigned LoopUse = 0, e = LoopUses.size(); LoopUse != e; ++LoopUse) {
Instruction *User = LoopUses[LoopUse];
std::vector<Instruction*> &BlockUses = UsesByBlock[User->getParent()];
// If this block has already been processed, ignore this repeat use.
if (BlockUses.empty()) continue;
// Okay, this is the first use in the block. If this block just has a
// single user in it, we can rewrite it trivially.
if (BlockUses.size() == 1) {
// If it is a store, it is a trivial def of the value in the block.
if (isa<StoreInst>(User)) {
SSA.AddAvailableValue(User->getParent(),
cast<StoreInst>(User)->getOperand(0));
} else {
// Otherwise it is a load, queue it to rewrite as a live-in load.
LiveInLoads.push_back(cast<LoadInst>(User));
}
BlockUses.clear();
continue;
}
// Otherwise, check to see if this block is all loads. If so, we can queue
// them all as live in loads.
bool HasStore = false;
for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
if (isa<StoreInst>(BlockUses[i])) {
HasStore = true;
break;
}
}
if (!HasStore) {
for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
BlockUses.clear();
continue;
}
// Otherwise, we have mixed loads and stores (or just a bunch of stores).
// Since SSAUpdater is purely for cross-block values, we need to determine
// the order of these instructions in the block. If the first use in the
// block is a load, then it uses the live in value. The last store defines
// the live out value. We handle this by doing a linear scan of the block.
BasicBlock *BB = User->getParent();
Value *StoredValue = 0;
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
if (LoadInst *L = dyn_cast<LoadInst>(II)) {
// If this is a load from an unrelated pointer, ignore it.
if (!PointerMustAliases.count(L->getOperand(0))) continue;
// If we haven't seen a store yet, this is a live in use, otherwise
// use the stored value.
if (StoredValue) {
L->replaceAllUsesWith(StoredValue);
ReplacedLoads[L] = StoredValue;
} else {
LiveInLoads.push_back(L);
}
continue;
}
if (StoreInst *S = dyn_cast<StoreInst>(II)) {
// If this is a store to an unrelated pointer, ignore it.
if (!PointerMustAliases.count(S->getOperand(1))) continue;
// Remember that this is the active value in the block.
StoredValue = S->getOperand(0);
}
}
// The last stored value that happened is the live-out for the block.
assert(StoredValue && "Already checked that there is a store in block");
SSA.AddAvailableValue(BB, StoredValue);
BlockUses.clear();
}
// Now that all the intra-loop values are classified, set up the preheader.
// It gets a load of the pointer we're promoting, and it is the live-out value
// from the preheader.
LoadInst *PreheaderLoad = new LoadInst(SomePtr,SomePtr->getName()+".promoted",
Preheader->getTerminator());
SSA.AddAvailableValue(Preheader, PreheaderLoad);
// Now that the preheader is good to go, set up the exit blocks. Each exit
// block gets a store of the live-out values that feed them. Since we've
// already told the SSA updater about the defs in the loop and the preheader
// definition, it is all set and we can start using it.
SmallVector<BasicBlock*, 8> ExitBlocks;
CurLoop->getUniqueExitBlocks(ExitBlocks);
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBlock = ExitBlocks[i];
Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
Instruction *InsertPos = ExitBlock->getFirstNonPHI();
new StoreInst(LiveInValue, SomePtr, InsertPos);
}
// Okay, now we rewrite all loads that use live-in values in the loop,
// inserting PHI nodes as necessary.
for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
LoadInst *ALoad = LiveInLoads[i];
Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
ALoad->replaceAllUsesWith(NewVal);
CurAST->copyValue(ALoad, NewVal);
ReplacedLoads[ALoad] = NewVal;
}
// If the preheader load is itself a pointer, we need to tell alias analysis
// about the new pointer we created in the preheader block and about any PHI
// nodes that just got inserted.
if (PreheaderLoad->getType()->isPointerTy()) {
// Copy any value stored to or loaded from a must-alias of the pointer.
CurAST->copyValue(SomeValue, PreheaderLoad);
for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
CurAST->copyValue(SomeValue, NewPHIs[i]);
}
// Now that everything is rewritten, delete the old instructions from the body
// of the loop. They should all be dead now.
for (unsigned i = 0, e = LoopUses.size(); i != e; ++i) {
Instruction *User = LoopUses[i];
// If this is a load that still has uses, then the load must have been added
// as a live value in the SSAUpdate data structure for a block (e.g. because
// the loaded value was stored later). In this case, we need to recursively
// propagate the updates until we get to the real value.
if (!User->use_empty()) {
Value *NewVal = ReplacedLoads[User];
assert(NewVal && "not a replaced load?");
// Propagate down to the ultimate replacee. The intermediately loads
// could theoretically already have been deleted, so we don't want to
// dereference the Value*'s.
DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
while (RLI != ReplacedLoads.end()) {
NewVal = RLI->second;
RLI = ReplacedLoads.find(NewVal);
}
User->replaceAllUsesWith(NewVal);
CurAST->copyValue(User, NewVal);
}
CurAST->deleteValue(User);
User->eraseFromParent();
}
// fwew, we're done!
}
/// PromoteAliasSet - Try to promote memory values to scalars by sinking
/// stores out of the loop and moving loads to before the loop. We do this by
/// looping over the stores in the loop, looking for stores to Must pointers
/// which are loop invariant.
///
void LICM::PromoteAliasSet(AliasSet &AS) {
// We can promote this alias set if it has a store, if it is a "Must" alias
// set, if the pointer is loop invariant, and if we are not eliminating any
// volatile loads or stores.
if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue()))
return;
assert(!AS.empty() &&
"Must alias set should have at least one pointer element in it!");
Value *SomePtr = AS.begin()->getValue();
// It isn't safe to promote a load/store from the loop if the load/store is
// conditional. For example, turning:
//
// for () { if (c) *P += 1; }
//
// into:
//
// tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
//
// is not safe, because *P may only be valid to access if 'c' is true.
//
// It is safe to promote P if all uses are direct load/stores and if at
// least one is guaranteed to be executed.
bool GuaranteedToExecute = false;
SmallVector<Instruction*, 64> LoopUses;
SmallPtrSet<Value*, 4> PointerMustAliases;
// We start with an alignment of one and try to find instructions that allow
// us to prove better alignment.
unsigned Alignment = 1;
// Check that all of the pointers in the alias set have the same type. We
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) {
Value *ASIV = ASI->getValue();
PointerMustAliases.insert(ASIV);
// Check that all of the pointers in the alias set have the same type. We
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
if (SomePtr->getType() != ASIV->getType())
return;
for (Value::use_iterator UI = ASIV->use_begin(), UE = ASIV->use_end();
UI != UE; ++UI) {
// Ignore instructions that are outside the loop.
Instruction *Use = dyn_cast<Instruction>(*UI);
if (!Use || !CurLoop->contains(Use))
continue;
// If there is an non-load/store instruction in the loop, we can't promote
// it.
if (LoadInst *load = dyn_cast<LoadInst>(Use)) {
assert(!load->isVolatile() && "AST broken");
if (!load->isSimple())
return;
} else if (StoreInst *store = dyn_cast<StoreInst>(Use)) {
// Stores *of* the pointer are not interesting, only stores *to* the
// pointer.
if (Use->getOperand(1) != ASIV)
continue;
assert(!store->isVolatile() && "AST broken");
if (!store->isSimple())
return;
// Note that we only check GuaranteedToExecute inside the store case
// so that we do not introduce stores where they did not exist before
// (which would break the LLVM concurrency model).
// If the alignment of this instruction allows us to specify a more
// restrictive (and performant) alignment and if we are sure this
// instruction will be executed, update the alignment.
// Larger is better, with the exception of 0 being the best alignment.
unsigned InstAlignment = store->getAlignment();
if ((InstAlignment > Alignment || InstAlignment == 0)
&& (Alignment != 0))
if (isGuaranteedToExecute(*Use)) {
GuaranteedToExecute = true;
Alignment = InstAlignment;
}
if (!GuaranteedToExecute)
GuaranteedToExecute = isGuaranteedToExecute(*Use);
} else
return; // Not a load or store.
LoopUses.push_back(Use);
}
}
// If there isn't a guaranteed-to-execute instruction, we can't promote.
if (!GuaranteedToExecute)
return;
// Otherwise, this is safe to promote, lets do it!
DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n');
Changed = true;
++NumPromoted;
// Grab a debug location for the inserted loads/stores; given that the
// inserted loads/stores have little relation to the original loads/stores,
// this code just arbitrarily picks a location from one, since any debug
// location is better than none.
DebugLoc DL = LoopUses[0]->getDebugLoc();
SmallVector<BasicBlock*, 8> ExitBlocks;
CurLoop->getUniqueExitBlocks(ExitBlocks);
// We use the SSAUpdater interface to insert phi nodes as required.
SmallVector<PHINode*, 16> NewPHIs;
SSAUpdater SSA(&NewPHIs);
LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
*CurAST, DL, Alignment);
// Set up the preheader to have a definition of the value. It is the live-out
// value from the preheader that uses in the loop will use.
LoadInst *PreheaderLoad =
new LoadInst(SomePtr, SomePtr->getName()+".promoted",
Preheader->getTerminator());
PreheaderLoad->setAlignment(Alignment);
PreheaderLoad->setDebugLoc(DL);
SSA.AddAvailableValue(Preheader, PreheaderLoad);
// Rewrite all the loads in the loop and remember all the definitions from
// stores in the loop.
Promoter.run(LoopUses);
// If the SSAUpdater didn't use the load in the preheader, just zap it now.
if (PreheaderLoad->use_empty())
PreheaderLoad->eraseFromParent();
}
// This pass annotates every load instruction with the last store instruction
// on which it depends. The algorithm is optimistic in that it ignores explicit
// dependencies and only considers loads and stores.
//
// Loads inside loops only have an implicit dependency on a store before the
// loop header if no instruction inside the loop body aliases it. To calculate
// this efficiently, we maintain a list of maybe-invariant loads and the combined
// alias set for all stores inside the loop. When we see the loop's backedge, this
// information is used to mark every load we wrongly assumed to be loop invariant as
// having an implicit dependency on the last instruction of the loop header, so that
// it's never moved before the loop header.
//
// The algorithm depends on the invariant that both control instructions and effectful
// instructions (stores) are never hoisted.
bool
AliasAnalysis::analyze()
{
Vector<MInstructionVector, AliasSet::NumCategories, JitAllocPolicy> stores(alloc());
// Initialize to the first instruction.
MInstruction* firstIns = *graph_.entryBlock()->begin();
for (unsigned i = 0; i < AliasSet::NumCategories; i++) {
MInstructionVector defs(alloc());
if (!defs.append(firstIns))
return false;
if (!stores.append(Move(defs)))
return false;
}
// Type analysis may have inserted new instructions. Since this pass depends
// on the instruction number ordering, all instructions are renumbered.
uint32_t newId = 0;
for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
if (mir->shouldCancel("Alias Analysis (main loop)"))
return false;
if (block->isLoopHeader()) {
JitSpew(JitSpew_Alias, "Processing loop header %d", block->id());
loop_ = new(alloc()) LoopAliasInfo(alloc(), loop_, *block);
}
for (MPhiIterator def(block->phisBegin()), end(block->phisEnd()); def != end; ++def)
def->setId(newId++);
for (MInstructionIterator def(block->begin()), end(block->begin(block->lastIns()));
def != end;
++def)
{
def->setId(newId++);
AliasSet set = def->getAliasSet();
if (set.isNone())
continue;
// For the purposes of alias analysis, all recoverable operations
// are treated as effect free as the memory represented by these
// operations cannot be aliased by others.
if (def->canRecoverOnBailout())
continue;
if (set.isStore()) {
for (AliasSetIterator iter(set); iter; iter++) {
if (!stores[*iter].append(*def))
return false;
}
if (JitSpewEnabled(JitSpew_Alias)) {
Fprinter& out = JitSpewPrinter();
out.printf("Processing store ");
def->printName(out);
out.printf(" (flags %x)\n", set.flags());
}
} else {
// Find the most recent store on which this instruction depends.
MInstruction* lastStore = firstIns;
for (AliasSetIterator iter(set); iter; iter++) {
MInstructionVector& aliasedStores = stores[*iter];
for (int i = aliasedStores.length() - 1; i >= 0; i--) {
MInstruction* store = aliasedStores[i];
if (genericMightAlias(*def, store) != MDefinition::AliasType::NoAlias &&
def->mightAlias(store) != MDefinition::AliasType::NoAlias &&
BlockMightReach(store->block(), *block))
{
if (lastStore->id() < store->id())
lastStore = store;
break;
}
}
}
def->setDependency(lastStore);
IonSpewDependency(*def, lastStore, "depends", "");
// If the last store was before the current loop, we assume this load
// is loop invariant. If a later instruction writes to the same location,
// we will fix this at the end of the loop.
if (loop_ && lastStore->id() < loop_->firstInstruction()->id()) {
if (!loop_->addInvariantLoad(*def))
return false;
}
}
}
// Renumber the last instruction, as the analysis depends on this and the order.
block->lastIns()->setId(newId++);
if (block->isLoopBackedge()) {
MOZ_ASSERT(loop_->loopHeader() == block->loopHeaderOfBackedge());
JitSpew(JitSpew_Alias, "Processing loop backedge %d (header %d)", block->id(),
loop_->loopHeader()->id());
LoopAliasInfo* outerLoop = loop_->outer();
MInstruction* firstLoopIns = *loop_->loopHeader()->begin();
const MInstructionVector& invariant = loop_->invariantLoads();
for (unsigned i = 0; i < invariant.length(); i++) {
MInstruction* ins = invariant[i];
AliasSet set = ins->getAliasSet();
MOZ_ASSERT(set.isLoad());
bool hasAlias = false;
for (AliasSetIterator iter(set); iter; iter++) {
MInstructionVector& aliasedStores = stores[*iter];
for (int i = aliasedStores.length() - 1;; i--) {
MInstruction* store = aliasedStores[i];
if (store->id() < firstLoopIns->id())
break;
if (genericMightAlias(ins, store) != MDefinition::AliasType::NoAlias &&
ins->mightAlias(store) != MDefinition::AliasType::NoAlias)
{
hasAlias = true;
IonSpewDependency(ins, store, "aliases", "store in loop body");
break;
}
}
if (hasAlias)
break;
}
if (hasAlias) {
// This instruction depends on stores inside the loop body. Mark it as having a
// dependency on the last instruction of the loop header. The last instruction is a
// control instruction and these are never hoisted.
MControlInstruction* controlIns = loop_->loopHeader()->lastIns();
IonSpewDependency(ins, controlIns, "depends", "due to stores in loop body");
ins->setDependency(controlIns);
} else {
IonSpewAliasInfo("Load", ins, "does not depend on any stores in this loop");
if (outerLoop && ins->dependency()->id() < outerLoop->firstInstruction()->id()) {
IonSpewAliasInfo("Load", ins, "may be invariant in outer loop");
if (!outerLoop->addInvariantLoad(ins))
return false;
}
}
}
loop_ = loop_->outer();
}
}
spewDependencyList();
MOZ_ASSERT(loop_ == nullptr);
return true;
}
