void MemorySSAUpdater::wireOldPredecessorsToNewImmediatePredecessor(
BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds) {
assert(!MSSA->getWritableBlockAccesses(New) &&
"Access list should be null for a new block.");
MemoryPhi *Phi = MSSA->getMemoryAccess(Old);
if (!Phi)
return;
if (pred_size(Old) == 1) {
assert(pred_size(New) == Preds.size() &&
"Should have moved all predecessors.");
MSSA->moveTo(Phi, New, MemorySSA::Beginning);
} else {
assert(!Preds.empty() && "Must be moving at least one predecessor to the "
"new immediate predecessor.");
MemoryPhi *NewPhi = MSSA->createMemoryPhi(New);
SmallPtrSet<BasicBlock *, 16> PredsSet(Preds.begin(), Preds.end());
Phi->unorderedDeleteIncomingIf([&](MemoryAccess *MA, BasicBlock *B) {
if (PredsSet.count(B)) {
NewPhi->addIncoming(MA, B);
return true;
}
return false;
});
Phi->addIncoming(NewPhi, New);
if (onlySingleValue(NewPhi))
removeMemoryAccess(NewPhi);
}
}
// This is the marker algorithm from "Simple and Efficient Construction of
// Static Single Assignment Form"
// The simple, non-marker algorithm places phi nodes at any join
// Here, we place markers, and only place phi nodes if they end up necessary.
// They are only necessary if they break a cycle (IE we recursively visit
// ourselves again), or we discover, while getting the value of the operands,
// that there are two or more definitions needing to be merged.
// This still will leave non-minimal form in the case of irreducible control
// flow, where phi nodes may be in cycles with themselves, but unnecessary.
MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(BasicBlock *BB) {
// Single predecessor case, just recurse, we can only have one definition.
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
return getPreviousDefFromEnd(Pred);
} else if (VisitedBlocks.count(BB)) {
// We hit our node again, meaning we had a cycle, we must insert a phi
// node to break it so we have an operand. The only case this will
// insert useless phis is if we have irreducible control flow.
return MSSA->createMemoryPhi(BB);
} else if (VisitedBlocks.insert(BB).second) {
// Mark us visited so we can detect a cycle
SmallVector<MemoryAccess *, 8> PhiOps;
// Recurse to get the values in our predecessors for placement of a
// potential phi node. This will insert phi nodes if we cycle in order to
// break the cycle and have an operand.
for (auto *Pred : predecessors(BB))
PhiOps.push_back(getPreviousDefFromEnd(Pred));
// Now try to simplify the ops to avoid placing a phi.
// This may return null if we never created a phi yet, that's okay
MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MSSA->getMemoryAccess(BB));
bool PHIExistsButNeedsUpdate = false;
// See if the existing phi operands match what we need.
// Unlike normal SSA, we only allow one phi node per block, so we can't just
// create a new one.
if (Phi && Phi->getNumOperands() != 0)
if (!std::equal(Phi->op_begin(), Phi->op_end(), PhiOps.begin())) {
PHIExistsButNeedsUpdate = true;
}
// See if we can avoid the phi by simplifying it.
auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
// If we couldn't simplify, we may have to create a phi
if (Result == Phi) {
if (!Phi)
Phi = MSSA->createMemoryPhi(BB);
// These will have been filled in by the recursive read we did above.
if (PHIExistsButNeedsUpdate) {
std::copy(PhiOps.begin(), PhiOps.end(), Phi->op_begin());
std::copy(pred_begin(BB), pred_end(BB), Phi->block_begin());
} else {
unsigned i = 0;
for (auto *Pred : predecessors(BB))
Phi->addIncoming(PhiOps[i++], Pred);
}
Result = Phi;
}
if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Result))
InsertedPHIs.push_back(MP);
// Set ourselves up for the next variable by resetting visited state.
VisitedBlocks.erase(BB);
return Result;
}
llvm_unreachable("Should have hit one of the three cases above");
}
bool mssa::runOnFunction(Function &F) {
MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
//MemorySSAWalker MAW = new MemorySSAWalker(MSSA);
errs()<<"\n";
for (Function::iterator BB = F.begin(); BB != F.end(); BB++){
errs() << "Basic block (name=" << BB->getName() << ")\n";
//Get MemoryPhi and print it out
MemoryPhi* MP = MSSA->getMemoryAccess(dyn_cast<BasicBlock>(BB));
if (MP != NULL)
MP->dump();
for (BasicBlock::iterator itrIns = (*BB).begin(); itrIns != (*BB).end(); itrIns++) {
//MemoryAccess* MA = MAW.getClobberingMemoryAccess(itrIns);
//MemoryLocation Location;
//MemoryAccess* MAR = MAW.getClobberingMemoryAccess(MA,&Location);
//MAR->dump();
errs()<<"Instruction: "<< *itrIns <<"\n";
//Get MemoryDef or MemoryUse and print it out
MemoryAccess *MA = MSSA->getMemoryAccess(dyn_cast<Value>(itrIns));
if (MA != NULL) {
MA->dump();
//if(MSSA->isLiveOnEntryDef(MA))
//Get immediate MemoryDef of the instruction annotated MemoryDef/MemoryUse
for (memoryaccess_def_iterator MAitr = MA->defs_begin();
MAitr != MA->defs_end();
MAitr++)
{
errs()<<"Def: "<<**MAitr<<"\n";
//Get the instruction the immediate Memory Def annotation represent
Instruction* u = cast<MemoryUseOrDef>(*MAitr)->getMemoryInst();
if (u != NULL)
errs()<<" Def Inst: "<<*u<<"\n";
}
}
}
}
return 0;
}
// This is the marker algorithm from "Simple and Efficient Construction of
// Static Single Assignment Form"
// The simple, non-marker algorithm places phi nodes at any join
// Here, we place markers, and only place phi nodes if they end up necessary.
// They are only necessary if they break a cycle (IE we recursively visit
// ourselves again), or we discover, while getting the value of the operands,
// that there are two or more definitions needing to be merged.
// This still will leave non-minimal form in the case of irreducible control
// flow, where phi nodes may be in cycles with themselves, but unnecessary.
MemoryAccess *MemorySSAUpdater::getPreviousDefRecursive(
BasicBlock *BB,
DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &CachedPreviousDef) {
// First, do a cache lookup. Without this cache, certain CFG structures
// (like a series of if statements) take exponential time to visit.
auto Cached = CachedPreviousDef.find(BB);
if (Cached != CachedPreviousDef.end()) {
return Cached->second;
}
if (BasicBlock *Pred = BB->getSinglePredecessor()) {
// Single predecessor case, just recurse, we can only have one definition.
MemoryAccess *Result = getPreviousDefFromEnd(Pred, CachedPreviousDef);
CachedPreviousDef.insert({BB, Result});
return Result;
}
if (VisitedBlocks.count(BB)) {
// We hit our node again, meaning we had a cycle, we must insert a phi
// node to break it so we have an operand. The only case this will
// insert useless phis is if we have irreducible control flow.
MemoryAccess *Result = MSSA->createMemoryPhi(BB);
CachedPreviousDef.insert({BB, Result});
return Result;
}
if (VisitedBlocks.insert(BB).second) {
// Mark us visited so we can detect a cycle
SmallVector<TrackingVH<MemoryAccess>, 8> PhiOps;
// Recurse to get the values in our predecessors for placement of a
// potential phi node. This will insert phi nodes if we cycle in order to
// break the cycle and have an operand.
for (auto *Pred : predecessors(BB))
PhiOps.push_back(getPreviousDefFromEnd(Pred, CachedPreviousDef));
// Now try to simplify the ops to avoid placing a phi.
// This may return null if we never created a phi yet, that's okay
MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MSSA->getMemoryAccess(BB));
// See if we can avoid the phi by simplifying it.
auto *Result = tryRemoveTrivialPhi(Phi, PhiOps);
// If we couldn't simplify, we may have to create a phi
if (Result == Phi) {
if (!Phi)
Phi = MSSA->createMemoryPhi(BB);
// See if the existing phi operands match what we need.
// Unlike normal SSA, we only allow one phi node per block, so we can't just
// create a new one.
if (Phi->getNumOperands() != 0) {
// FIXME: Figure out whether this is dead code and if so remove it.
if (!std::equal(Phi->op_begin(), Phi->op_end(), PhiOps.begin())) {
// These will have been filled in by the recursive read we did above.
std::copy(PhiOps.begin(), PhiOps.end(), Phi->op_begin());
std::copy(pred_begin(BB), pred_end(BB), Phi->block_begin());
}
} else {
unsigned i = 0;
for (auto *Pred : predecessors(BB))
Phi->addIncoming(&*PhiOps[i++], Pred);
InsertedPHIs.push_back(Phi);
}
Result = Phi;
}
// Set ourselves up for the next variable by resetting visited state.
VisitedBlocks.erase(BB);
CachedPreviousDef.insert({BB, Result});
return Result;
}
llvm_unreachable("Should have hit one of the three cases above");
}
// A brief description of the algorithm:
// First, we compute what should define the new def, using the SSA
// construction algorithm.
// Then, we update the defs below us (and any new phi nodes) in the graph to
// point to the correct new defs, to ensure we only have one variable, and no
// disconnected stores.
void MemorySSAUpdater::insertDef(MemoryDef *MD, bool RenameUses) {
InsertedPHIs.clear();
// See if we had a local def, and if not, go hunting.
MemoryAccess *DefBefore = getPreviousDef(MD);
bool DefBeforeSameBlock = DefBefore->getBlock() == MD->getBlock();
// There is a def before us, which means we can replace any store/phi uses
// of that thing with us, since we are in the way of whatever was there
// before.
// We now define that def's memorydefs and memoryphis
if (DefBeforeSameBlock) {
for (auto UI = DefBefore->use_begin(), UE = DefBefore->use_end();
UI != UE;) {
Use &U = *UI++;
// Leave the uses alone
if (isa<MemoryUse>(U.getUser()))
continue;
U.set(MD);
}
}
// and that def is now our defining access.
// We change them in this order otherwise we will appear in the use list
// above and reset ourselves.
MD->setDefiningAccess(DefBefore);
SmallVector<WeakVH, 8> FixupList(InsertedPHIs.begin(), InsertedPHIs.end());
if (!DefBeforeSameBlock) {
// If there was a local def before us, we must have the same effect it
// did. Because every may-def is the same, any phis/etc we would create, it
// would also have created. If there was no local def before us, we
// performed a global update, and have to search all successors and make
// sure we update the first def in each of them (following all paths until
// we hit the first def along each path). This may also insert phi nodes.
// TODO: There are other cases we can skip this work, such as when we have a
// single successor, and only used a straight line of single pred blocks
// backwards to find the def. To make that work, we'd have to track whether
// getDefRecursive only ever used the single predecessor case. These types
// of paths also only exist in between CFG simplifications.
FixupList.push_back(MD);
}
while (!FixupList.empty()) {
unsigned StartingPHISize = InsertedPHIs.size();
fixupDefs(FixupList);
FixupList.clear();
// Put any new phis on the fixup list, and process them
FixupList.append(InsertedPHIs.begin() + StartingPHISize, InsertedPHIs.end());
}
// Now that all fixups are done, rename all uses if we are asked.
if (RenameUses) {
SmallPtrSet<BasicBlock *, 16> Visited;
BasicBlock *StartBlock = MD->getBlock();
// We are guaranteed there is a def in the block, because we just got it
// handed to us in this function.
MemoryAccess *FirstDef = &*MSSA->getWritableBlockDefs(StartBlock)->begin();
// Convert to incoming value if it's a memorydef. A phi *is* already an
// incoming value.
if (auto *MD = dyn_cast<MemoryDef>(FirstDef))
FirstDef = MD->getDefiningAccess();
MSSA->renamePass(MD->getBlock(), FirstDef, Visited);
// We just inserted a phi into this block, so the incoming value will become
// the phi anyway, so it does not matter what we pass.
for (auto &MP : InsertedPHIs) {
MemoryPhi *Phi = dyn_cast_or_null<MemoryPhi>(MP);
if (Phi)
MSSA->renamePass(Phi->getBlock(), nullptr, Visited);
}
}
}
