#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Instructions.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/Support/AlignOf.h"
+#include "llvm/Support/Allocator.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
-typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy;
-typedef std::vector<std::pair<BasicBlock*, TrackingVH<Value> > >
- IncomingPredInfoTy;
+/// BBInfo - Per-basic block information used internally by SSAUpdater.
+/// The predecessors of each block are cached here since pred_iterator is
+/// slow and we need to iterate over the blocks at least a few times.
+class SSAUpdater::BBInfo {
+public:
+ Value *AvailableVal; // Value to use in this block.
+ BasicBlock *DefBB; // Block that defines the available value.
+ unsigned NumPreds; // Number of predecessor blocks.
+ BasicBlock **Preds; // Array[NumPreds] of predecessor blocks.
+ unsigned Counter; // Marker to identify blocks already visited.
+ PHINode *PHITag; // Marker for existing PHIs that match.
+
+ BBInfo(BasicBlock *BB, Value *V, BumpPtrAllocator *Allocator);
+};
+typedef DenseMap<BasicBlock*, SSAUpdater::BBInfo*> BBMapTy;
+
+SSAUpdater::BBInfo::BBInfo(BasicBlock *BB, Value *V,
+ BumpPtrAllocator *Allocator)
+ : AvailableVal(V), DefBB(0), NumPreds(0), Preds(0), Counter(0), PHITag(0) {
+ // If this block has a known value, don't bother finding its predecessors.
+ if (V) {
+ DefBB = BB;
+ return;
+ }
+
+ // We can get our predecessor info by walking the pred_iterator list, but it
+ // is relatively slow. If we already have PHI nodes in this block, walk one
+ // of them to get the predecessor list instead.
+ if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
+ NumPreds = SomePhi->getNumIncomingValues();
+ Preds = static_cast<BasicBlock**>
+ (Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
+ AlignOf<BasicBlock*>::Alignment));
+ for (unsigned pi = 0; pi != NumPreds; ++pi)
+ Preds[pi] = SomePhi->getIncomingBlock(pi);
+ return;
+ }
+
+ // Stash the predecessors in a temporary vector until we know how much space
+ // to allocate for them.
+ SmallVector<BasicBlock*, 10> TmpPreds;
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ TmpPreds.push_back(*PI);
+ ++NumPreds;
+ }
+ Preds = static_cast<BasicBlock**>
+ (Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
+ AlignOf<BasicBlock*>::Alignment));
+ memcpy(Preds, TmpPreds.data(), NumPreds * sizeof(BasicBlock*));
+}
+typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
-static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
- return *static_cast<IncomingPredInfoTy*>(IPI);
+static BBMapTy *getBBMap(void *BM) {
+ return static_cast<BBMapTy*>(BM);
}
+static BumpPtrAllocator *getAllocator(void *BPA) {
+ return static_cast<BumpPtrAllocator*>(BPA);
+}
SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
- : AV(0), PrototypeValue(0), IPI(0), InsertedPHIs(NewPHI) {}
+ : AV(0), PrototypeValue(0), BM(0), BPA(0), InsertedPHIs(NewPHI) {}
SSAUpdater::~SSAUpdater() {
delete &getAvailableVals(AV);
- delete &getIncomingPredInfo(IPI);
}
/// Initialize - Reset this object to get ready for a new set of SSA
AV = new AvailableValsTy();
else
getAvailableVals(AV).clear();
-
- if (IPI == 0)
- IPI = new IncomingPredInfoTy();
- else
- getIncomingPredInfo(IPI).clear();
PrototypeValue = ProtoValue;
}
getAvailableVals(AV)[BB] = V;
}
+/// IsEquivalentPHI - Check if PHI has the same incoming value as specified
+/// in ValueMapping for each predecessor block.
+static bool IsEquivalentPHI(PHINode *PHI,
+ DenseMap<BasicBlock*, Value*> &ValueMapping) {
+ unsigned PHINumValues = PHI->getNumIncomingValues();
+ if (PHINumValues != ValueMapping.size())
+ return false;
+
+ // Scan the phi to see if it matches.
+ for (unsigned i = 0, e = PHINumValues; i != e; ++i)
+ if (ValueMapping[PHI->getIncomingBlock(i)] !=
+ PHI->getIncomingValue(i)) {
+ return false;
+ }
+
+ return true;
+}
+
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
- assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
+ assert(BM == 0 && BPA == 0 && "Unexpected Internal State");
Value *Res = GetValueAtEndOfBlockInternal(BB);
- assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
+ assert(BM == 0 && BPA == 0 && "Unexpected Internal State");
return Res;
}
Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
// If there is no definition of the renamed variable in this block, just use
// GetValueAtEndOfBlock to do our work.
- if (!getAvailableVals(AV).count(BB))
+ if (!HasValueForBlock(BB))
return GetValueAtEndOfBlock(BB);
// Otherwise, we have the hard case. Get the live-in values for each
PHINode *SomePHI;
for (BasicBlock::iterator It = BB->begin();
(SomePHI = dyn_cast<PHINode>(It)); ++It) {
- // Scan this phi to see if it is what we need.
- bool Equal = true;
- for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i)
- if (ValueMapping[SomePHI->getIncomingBlock(i)] !=
- SomePHI->getIncomingValue(i)) {
- Equal = false;
- break;
- }
-
- if (Equal)
+ if (IsEquivalentPHI(SomePHI, ValueMapping))
return SomePHI;
}
}
-
+
// Ok, we have no way out, insert a new one now.
PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
PrototypeValue->getName(),
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
- DEBUG(errs() << " Inserted PHI: " << *InsertedPHI << "\n");
+ DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
return InsertedPHI;
}
/// which use their value in the corresponding predecessor.
void SSAUpdater::RewriteUse(Use &U) {
Instruction *User = cast<Instruction>(U.getUser());
-
+
Value *V;
if (PHINode *UserPN = dyn_cast<PHINode>(User))
V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
U.set(V);
}
-
/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
/// for the specified BB and if so, return it. If not, construct SSA form by
-/// walking predecessors inserting PHI nodes as needed until we get to a block
-/// where the value is available.
-///
+/// first calculating the required placement of PHIs and then inserting new
+/// PHIs where needed.
Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
+ if (Value *V = AvailableVals[BB])
+ return V;
+
+ // Pool allocation used internally by GetValueAtEndOfBlock.
+ BumpPtrAllocator AllocatorObj;
+ BBMapTy BBMapObj;
+ BPA = &AllocatorObj;
+ BM = &BBMapObj;
+
+ BBInfo *Info = new (AllocatorObj) BBInfo(BB, 0, &AllocatorObj);
+ BBMapObj[BB] = Info;
+
+ bool Changed;
+ unsigned Counter = 1;
+ do {
+ Changed = false;
+ FindPHIPlacement(BB, Info, Changed, Counter);
+ ++Counter;
+ } while (Changed);
+
+ FindAvailableVal(BB, Info, Counter);
+
+ BPA = 0;
+ BM = 0;
+ return Info->AvailableVal;
+}
- // Query AvailableVals by doing an insertion of null.
- std::pair<AvailableValsTy::iterator, bool> InsertRes =
- AvailableVals.insert(std::make_pair(BB, WeakVH()));
-
- // Handle the case when the insertion fails because we have already seen BB.
- if (!InsertRes.second) {
- // If the insertion failed, there are two cases. The first case is that the
- // value is already available for the specified block. If we get this, just
- // return the value.
- if (InsertRes.first->second != 0)
- return InsertRes.first->second;
-
- // Otherwise, if the value we find is null, then this is the value is not
- // known but it is being computed elsewhere in our recursion. This means
- // that we have a cycle. Handle this by inserting a PHI node and returning
- // it. When we get back to the first instance of the recursion we will fill
- // in the PHI node.
- return InsertRes.first->second =
- PHINode::Create(PrototypeValue->getType(), PrototypeValue->getName(),
- &BB->front());
+/// FindPHIPlacement - Recursively visit the predecessors of a block to find
+/// the reaching definition for each predecessor and then determine whether
+/// a PHI is needed in this block.
+void SSAUpdater::FindPHIPlacement(BasicBlock *BB, BBInfo *Info, bool &Changed,
+ unsigned Counter) {
+ AvailableValsTy &AvailableVals = getAvailableVals(AV);
+ BBMapTy *BBMap = getBBMap(BM);
+ BumpPtrAllocator *Allocator = getAllocator(BPA);
+ bool BBNeedsPHI = false;
+ BasicBlock *SamePredDefBB = 0;
+
+ // If there are no predecessors, then we must have found an unreachable
+ // block. Treat it as a definition with 'undef'.
+ if (Info->NumPreds == 0) {
+ Info->AvailableVal = UndefValue::get(PrototypeValue->getType());
+ Info->DefBB = BB;
+ return;
}
- // Okay, the value isn't in the map and we just inserted a null in the entry
- // to indicate that we're processing the block. Since we have no idea what
- // value is in this block, we have to recurse through our predecessors.
- //
- // While we're walking our predecessors, we keep track of them in a vector,
- // then insert a PHI node in the end if we actually need one. We could use a
- // smallvector here, but that would take a lot of stack space for every level
- // of the recursion, just use IncomingPredInfo as an explicit stack.
- IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
- unsigned FirstPredInfoEntry = IncomingPredInfo.size();
-
- // As we're walking the predecessors, keep track of whether they are all
- // producing the same value. If so, this value will capture it, if not, it
- // will get reset to null. We distinguish the no-predecessor case explicitly
- // below.
- TrackingVH<Value> SingularValue;
-
- // We can get our predecessor info by walking the pred_iterator list, but it
- // is relatively slow. If we already have PHI nodes in this block, walk one
- // of them to get the predecessor list instead.
- if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
- for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
- BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
- Value *PredVal = GetValueAtEndOfBlockInternal(PredBB);
- IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
-
- // Compute SingularValue.
- if (i == 0)
- SingularValue = PredVal;
- else if (PredVal != SingularValue)
- SingularValue = 0;
+ Info->Counter = Counter;
+ for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
+ BasicBlock *Pred = Info->Preds[pi];
+ BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
+ if (!BBMapBucket.second) {
+ Value *PredVal = AvailableVals.lookup(Pred);
+ BBMapBucket.second = new (*Allocator) BBInfo(Pred, PredVal, Allocator);
}
- } else {
- bool isFirstPred = true;
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
- BasicBlock *PredBB = *PI;
- Value *PredVal = GetValueAtEndOfBlockInternal(PredBB);
- IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
-
- // Compute SingularValue.
- if (isFirstPred) {
- SingularValue = PredVal;
- isFirstPred = false;
- } else if (PredVal != SingularValue)
- SingularValue = 0;
+ BBInfo *PredInfo = BBMapBucket.second;
+ BasicBlock *DefBB = 0;
+ if (!PredInfo->AvailableVal) {
+ if (PredInfo->Counter != Counter)
+ FindPHIPlacement(Pred, PredInfo, Changed, Counter);
+
+ // Ignore back edges where the value is not yet known.
+ if (!PredInfo->DefBB)
+ continue;
}
+ DefBB = PredInfo->DefBB;
+
+ if (!SamePredDefBB)
+ SamePredDefBB = DefBB;
+ else if (DefBB != SamePredDefBB)
+ BBNeedsPHI = true;
}
- // If there are no predecessors, then we must have found an unreachable block
- // just return 'undef'. Since there are no predecessors, InsertRes must not
- // be invalidated.
- if (IncomingPredInfo.size() == FirstPredInfoEntry)
- return InsertRes.first->second = UndefValue::get(PrototypeValue->getType());
-
- /// Look up BB's entry in AvailableVals. 'InsertRes' may be invalidated. If
- /// this block is involved in a loop, a no-entry PHI node will have been
- /// inserted as InsertedVal. Otherwise, we'll still have the null we inserted
- /// above.
- TrackingVH<Value> &InsertedVal = AvailableVals[BB];
-
- // If all the predecessor values are the same then we don't need to insert a
- // PHI. This is the simple and common case.
- if (SingularValue) {
- // If a PHI node got inserted, replace it with the singlar value and delete
- // it.
- if (InsertedVal) {
- PHINode *OldVal = cast<PHINode>(InsertedVal);
- // Be careful about dead loops. These RAUW's also update InsertedVal.
- if (InsertedVal != SingularValue)
- OldVal->replaceAllUsesWith(SingularValue);
- else
- OldVal->replaceAllUsesWith(UndefValue::get(InsertedVal->getType()));
- OldVal->eraseFromParent();
- } else {
- InsertedVal = SingularValue;
- }
+ BasicBlock *NewDefBB = (BBNeedsPHI ? BB : SamePredDefBB);
+ if (Info->DefBB != NewDefBB) {
+ Changed = true;
+ Info->DefBB = NewDefBB;
+ }
+}
- // Either path through the 'if' should have set insertedVal -> SingularVal.
- assert((InsertedVal == SingularValue || isa<UndefValue>(InsertedVal)) &&
- "RAUW didn't change InsertedVal to be SingularVal");
+/// FindAvailableVal - If this block requires a PHI, first check if an existing
+/// PHI matches the PHI placement and reaching definitions computed earlier,
+/// and if not, create a new PHI. Visit all the block's predecessors to
+/// calculate the available value for each one and fill in the incoming values
+/// for a new PHI.
+void SSAUpdater::FindAvailableVal(BasicBlock *BB, BBInfo *Info,
+ unsigned Counter) {
+ if (Info->AvailableVal || Info->Counter == Counter)
+ return;
- // Drop the entries we added in IncomingPredInfo to restore the stack.
- IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
- IncomingPredInfo.end());
- return SingularValue;
+ AvailableValsTy &AvailableVals = getAvailableVals(AV);
+ BBMapTy *BBMap = getBBMap(BM);
+
+ // Check if there needs to be a PHI in BB.
+ PHINode *NewPHI = 0;
+ if (Info->DefBB == BB) {
+ // Look for an existing PHI.
+ FindExistingPHI(BB);
+ if (!Info->AvailableVal) {
+ NewPHI = PHINode::Create(PrototypeValue->getType(),
+ PrototypeValue->getName(), &BB->front());
+ NewPHI->reserveOperandSpace(Info->NumPreds);
+ Info->AvailableVal = NewPHI;
+ AvailableVals[BB] = NewPHI;
+ }
}
- // Otherwise, we do need a PHI: insert one now if we don't already have one.
- if (InsertedVal == 0)
- InsertedVal = PHINode::Create(PrototypeValue->getType(),
- PrototypeValue->getName(), &BB->front());
+ // Iterate through the block's predecessors.
+ Info->Counter = Counter;
+ for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
+ BasicBlock *Pred = Info->Preds[pi];
+ BBInfo *PredInfo = (*BBMap)[Pred];
+ FindAvailableVal(Pred, PredInfo, Counter);
+ if (NewPHI) {
+ // Skip to the nearest preceding definition.
+ if (PredInfo->DefBB != Pred)
+ PredInfo = (*BBMap)[PredInfo->DefBB];
+ NewPHI->addIncoming(PredInfo->AvailableVal, Pred);
+ } else if (!Info->AvailableVal)
+ Info->AvailableVal = PredInfo->AvailableVal;
+ }
- PHINode *InsertedPHI = cast<PHINode>(InsertedVal);
- InsertedPHI->reserveOperandSpace(IncomingPredInfo.size()-FirstPredInfoEntry);
+ if (NewPHI) {
+ DEBUG(dbgs() << " Inserted PHI: " << *NewPHI << "\n");
- // Fill in all the predecessors of the PHI.
- for (IncomingPredInfoTy::iterator I =
- IncomingPredInfo.begin()+FirstPredInfoEntry,
- E = IncomingPredInfo.end(); I != E; ++I)
- InsertedPHI->addIncoming(I->second, I->first);
+ // If the client wants to know about all new instructions, tell it.
+ if (InsertedPHIs) InsertedPHIs->push_back(NewPHI);
+ }
+}
- // Drop the entries we added in IncomingPredInfo to restore the stack.
- IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
- IncomingPredInfo.end());
+/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
+/// them match what is needed.
+void SSAUpdater::FindExistingPHI(BasicBlock *BB) {
+ PHINode *SomePHI;
+ for (BasicBlock::iterator It = BB->begin();
+ (SomePHI = dyn_cast<PHINode>(It)); ++It) {
+ if (CheckIfPHIMatches(SomePHI)) {
+ RecordMatchingPHI(SomePHI);
+ break;
+ }
+ ClearPHITags(SomePHI);
+ }
+}
- // See if the PHI node can be merged to a single value. This can happen in
- // loop cases when we get a PHI of itself and one other value.
- if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
- InsertedPHI->replaceAllUsesWith(ConstVal);
- InsertedPHI->eraseFromParent();
- InsertedVal = ConstVal;
- } else {
- DEBUG(errs() << " Inserted PHI: " << *InsertedPHI << "\n");
+/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
+/// in the BBMap.
+bool SSAUpdater::CheckIfPHIMatches(PHINode *PHI) {
+ BBMapTy *BBMap = getBBMap(BM);
+ SmallVector<PHINode*, 20> WorkList;
+ WorkList.push_back(PHI);
+
+ // Mark that the block containing this PHI has been visited.
+ (*BBMap)[PHI->getParent()]->PHITag = PHI;
+
+ while (!WorkList.empty()) {
+ PHI = WorkList.pop_back_val();
+
+ // Iterate through the PHI's incoming values.
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
+ Value *IncomingVal = PHI->getIncomingValue(i);
+ BasicBlock *Pred = PHI->getIncomingBlock(i);
+ BBInfo *PredInfo = (*BBMap)[Pred];
+ // Skip to the nearest preceding definition.
+ if (PredInfo->DefBB != Pred) {
+ Pred = PredInfo->DefBB;
+ PredInfo = (*BBMap)[Pred];
+ }
+
+ // Check if it matches the expected value.
+ if (PredInfo->AvailableVal) {
+ if (IncomingVal == PredInfo->AvailableVal)
+ continue;
+ return false;
+ }
+
+ // Check if the value is a PHI in the correct block.
+ PHINode *IncomingPHIVal = dyn_cast<PHINode>(IncomingVal);
+ if (!IncomingPHIVal || IncomingPHIVal->getParent() != Pred)
+ return false;
+
+ // If this block has already been visited, check if this PHI matches.
+ if (PredInfo->PHITag) {
+ if (IncomingPHIVal == PredInfo->PHITag)
+ continue;
+ return false;
+ }
+ PredInfo->PHITag = IncomingPHIVal;
+
+ WorkList.push_back(IncomingPHIVal);
+ }
+ }
+ return true;
+}
- // If the client wants to know about all new instructions, tell it.
- if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
+/// RecordMatchingPHI - For a PHI node that matches, record it and its input
+/// PHIs in both the BBMap and the AvailableVals mapping.
+void SSAUpdater::RecordMatchingPHI(PHINode *PHI) {
+ BBMapTy *BBMap = getBBMap(BM);
+ AvailableValsTy &AvailableVals = getAvailableVals(AV);
+ SmallVector<PHINode*, 20> WorkList;
+ WorkList.push_back(PHI);
+
+ while (!WorkList.empty()) {
+ PHI = WorkList.pop_back_val();
+ BasicBlock *BB = PHI->getParent();
+ BBInfo *Info = (*BBMap)[BB];
+ if (!Info || Info->AvailableVal)
+ return;
+
+ // Record the PHI.
+ AvailableVals[BB] = PHI;
+ Info->AvailableVal = PHI;
+
+ // Iterate through the PHI's incoming values.
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
+ PHINode *IncomingVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
+ if (!IncomingVal) continue;
+ WorkList.push_back(IncomingVal);
+ }
}
+}
- return InsertedVal;
+/// ClearPHITags - When one of the existing PHI nodes fails to match, clear
+/// the PHITag values that were stored in the BBMap when checking to see if
+/// it matched.
+void SSAUpdater::ClearPHITags(PHINode *PHI) {
+ BBMapTy *BBMap = getBBMap(BM);
+ SmallVector<PHINode*, 20> WorkList;
+ WorkList.push_back(PHI);
+
+ while (!WorkList.empty()) {
+ PHI = WorkList.pop_back_val();
+ BasicBlock *BB = PHI->getParent();
+ BBInfo *Info = (*BBMap)[BB];
+ if (!Info || Info->AvailableVal || !Info->PHITag)
+ continue;
+
+ // Clear the tag.
+ Info->PHITag = 0;
+
+ // Iterate through the PHI's incoming values.
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
+ PHINode *IncomingVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
+ if (!IncomingVal) continue;
+ WorkList.push_back(IncomingVal);
+ }
+ }
}
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