//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
-// This file promote memory references to be register references. It promotes
+// This file promotes memory references to be register references. It promotes
// alloca instructions which only have loads and stores as uses. An alloca is
// transformed by using dominator frontiers to place PHI nodes, then traversing
// the function in depth-first order to rewrite loads and stores as appropriate.
STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
+STATISTIC(NumPHIInsert, "Number of PHI nodes inserted");
-// Provide DenseMapKeyInfo for all pointers.
+// Provide DenseMapInfo for all pointers.
namespace llvm {
template<>
-struct DenseMapKeyInfo<std::pair<BasicBlock*, unsigned> > {
- static inline std::pair<BasicBlock*, unsigned> getEmptyKey() {
- return std::make_pair((BasicBlock*)-1, ~0U);
+struct DenseMapInfo<std::pair<BasicBlock*, unsigned> > {
+ typedef std::pair<BasicBlock*, unsigned> EltTy;
+ static inline EltTy getEmptyKey() {
+ return EltTy(reinterpret_cast<BasicBlock*>(-1), ~0U);
}
- static inline std::pair<BasicBlock*, unsigned> getTombstoneKey() {
- return std::make_pair((BasicBlock*)-2, 0U);
+ static inline EltTy getTombstoneKey() {
+ return EltTy(reinterpret_cast<BasicBlock*>(-2), 0U);
}
static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) {
- return DenseMapKeyInfo<void*>::getHashValue(Val.first) + Val.second*2;
+ return DenseMapInfo<void*>::getHashValue(Val.first) + Val.second*2;
+ }
+ static bool isEqual(const EltTy &LHS, const EltTy &RHS) {
+ return LHS == RHS;
}
static bool isPod() { return true; }
};
// FIXME: If the memory unit is of pointer or integer type, we can permit
// assignments to subsections of the memory unit.
- // Only allow direct loads and stores...
+ // Only allow direct and non-volatile loads and stores...
for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) // Loop over all of the uses of the alloca
- if (isa<LoadInst>(*UI)) {
- // noop
+ if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
+ if (LI->isVolatile())
+ return false;
} else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == AI)
return false; // Don't allow a store OF the AI, only INTO the AI.
+ if (SI->isVolatile())
+ return false;
} else {
return false; // Not a load or store.
}
return NP-1;
}
+ void DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
+ AllocaInfo &Info);
+ void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
+ const SmallPtrSet<BasicBlock*, 32> &DefBlocks,
+ SmallPtrSet<BasicBlock*, 32> &LiveInBlocks);
void RewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info);
- void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
- SmallPtrSet<PHINode*, 16> &DeadPHINodes);
bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
void PromoteLocallyUsedAllocas(BasicBlock *BB,
const std::vector<AllocaInst*> &AIs);
continue;
}
- if (AST)
- PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
-
// If we haven't computed a numbering for the BB's in the function, do so
// now.
if (BBNumbers.empty()) {
BBNumbers[I] = ID++;
}
- // Compute the locations where PhiNodes need to be inserted. Look at the
- // dominance frontier of EACH basic-block we have a write in.
- //
- unsigned CurrentVersion = 0;
- SmallPtrSet<PHINode*, 16> InsertedPHINodes;
- std::vector<std::pair<unsigned, BasicBlock*> > DFBlocks;
- while (!Info.DefiningBlocks.empty()) {
- BasicBlock *BB = Info.DefiningBlocks.back();
- Info.DefiningBlocks.pop_back();
-
- // Look up the DF for this write, add it to PhiNodes
- DominanceFrontier::const_iterator it = DF.find(BB);
- if (it != DF.end()) {
- const DominanceFrontier::DomSetType &S = it->second;
-
- // In theory we don't need the indirection through the DFBlocks vector.
- // In practice, the order of calling QueuePhiNode would depend on the
- // (unspecified) ordering of basic blocks in the dominance frontier,
- // which would give PHI nodes non-determinstic subscripts. Fix this by
- // processing blocks in order of the occurance in the function.
- for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
- PE = S.end(); P != PE; ++P)
- DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P));
-
- // Sort by which the block ordering in the function.
- std::sort(DFBlocks.begin(), DFBlocks.end());
-
- for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
- BasicBlock *BB = DFBlocks[i].second;
- if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
- Info.DefiningBlocks.push_back(BB);
- }
- DFBlocks.clear();
- }
- }
-
- // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
- // of the writes to the variable, scan through the reads of the variable,
- // marking PHI nodes which are actually necessary as alive (by removing them
- // from the InsertedPHINodes set). This is not perfect: there may PHI
- // marked alive because of loads which are dominated by stores, but there
- // will be no unmarked PHI nodes which are actually used.
- //
- for (unsigned i = 0, e = Info.UsingBlocks.size(); i != e; ++i)
- MarkDominatingPHILive(Info.UsingBlocks[i], AllocaNum, InsertedPHINodes);
- Info.UsingBlocks.clear();
-
- // If there are any PHI nodes which are now known to be dead, remove them!
- for (SmallPtrSet<PHINode*, 16>::iterator I = InsertedPHINodes.begin(),
- E = InsertedPHINodes.end(); I != E; ++I) {
- PHINode *PN = *I;
- bool Erased=NewPhiNodes.erase(std::make_pair(PN->getParent(), AllocaNum));
- Erased=Erased;
- assert(Erased && "PHI already removed?");
-
- if (AST && isa<PointerType>(PN->getType()))
- AST->deleteValue(PN);
- PN->eraseFromParent();
- PhiToAllocaMap.erase(PN);
- }
-
- // Keep the reverse mapping of the 'Allocas' array.
+ // If we have an AST to keep updated, remember some pointer value that is
+ // stored into the alloca.
+ if (AST)
+ PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
+
+ // Keep the reverse mapping of the 'Allocas' array for the rename pass.
AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
+
+ // At this point, we're committed to promoting the alloca using IDF's, and
+ // the standard SSA construction algorithm. Determine which blocks need phi
+ // nodes and see if we can optimize out some work by avoiding insertion of
+ // dead phi nodes.
+ DetermineInsertionPoint(AI, AllocaNum, Info);
}
// Process all allocas which are only used in a single basic block.
if (&BB->front() != SomePHI)
continue;
- // Count the number of preds for BB.
- SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
-
// Only do work here if there the PHI nodes are missing incoming values. We
// know that all PHI nodes that were inserted in a block will have the same
// number of incoming values, so we can just check any of them.
- if (SomePHI->getNumIncomingValues() == Preds.size())
+ if (SomePHI->getNumIncomingValues() == getNumPreds(BB))
continue;
+
+ // Get the preds for BB.
+ SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
// Ok, now we know that all of the PHI nodes are missing entries for some
// basic blocks. Start by sorting the incoming predecessors for efficient
}
+/// ComputeLiveInBlocks - Determine which blocks the value is live in. These
+/// are blocks which lead to uses. Knowing this allows us to avoid inserting
+/// PHI nodes into blocks which don't lead to uses (thus, the inserted phi nodes
+/// would be dead).
+void PromoteMem2Reg::
+ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
+ const SmallPtrSet<BasicBlock*, 32> &DefBlocks,
+ SmallPtrSet<BasicBlock*, 32> &LiveInBlocks) {
+
+ // To determine liveness, we must iterate through the predecessors of blocks
+ // where the def is live. Blocks are added to the worklist if we need to
+ // check their predecessors. Start with all the using blocks.
+ SmallVector<BasicBlock*, 64> LiveInBlockWorklist;
+ LiveInBlockWorklist.insert(LiveInBlockWorklist.end(),
+ Info.UsingBlocks.begin(), Info.UsingBlocks.end());
+
+ // If any of the using blocks is also a definition block, check to see if the
+ // definition occurs before or after the use. If it happens before the use,
+ // the value isn't really live-in.
+ for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) {
+ BasicBlock *BB = LiveInBlockWorklist[i];
+ if (!DefBlocks.count(BB)) continue;
+
+ // Okay, this is a block that both uses and defines the value. If the first
+ // reference to the alloca is a def (store), then we know it isn't live-in.
+ for (BasicBlock::iterator I = BB->begin(); ; ++I) {
+ if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
+ if (SI->getOperand(1) != AI) continue;
+
+ // We found a store to the alloca before a load. The alloca is not
+ // actually live-in here.
+ LiveInBlockWorklist[i] = LiveInBlockWorklist.back();
+ LiveInBlockWorklist.pop_back();
+ --i, --e;
+ break;
+ } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+ if (LI->getOperand(0) != AI) continue;
+
+ // Okay, we found a load before a store to the alloca. It is actually
+ // live into this block.
+ break;
+ }
+ }
+ }
+
+ // Now that we have a set of blocks where the phi is live-in, recursively add
+ // their predecessors until we find the full region the value is live.
+ while (!LiveInBlockWorklist.empty()) {
+ BasicBlock *BB = LiveInBlockWorklist.back();
+ LiveInBlockWorklist.pop_back();
+
+ // The block really is live in here, insert it into the set. If already in
+ // the set, then it has already been processed.
+ if (!LiveInBlocks.insert(BB))
+ continue;
+
+ // Since the value is live into BB, it is either defined in a predecessor or
+ // live into it to. Add the preds to the worklist unless they are a
+ // defining block.
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *P = *PI;
+
+ // The value is not live into a predecessor if it defines the value.
+ if (DefBlocks.count(P))
+ continue;
+
+ // Otherwise it is, add to the worklist.
+ LiveInBlockWorklist.push_back(P);
+ }
+ }
+}
+
+/// DetermineInsertionPoint - At this point, we're committed to promoting the
+/// alloca using IDF's, and the standard SSA construction algorithm. Determine
+/// which blocks need phi nodes and see if we can optimize out some work by
+/// avoiding insertion of dead phi nodes.
+void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
+ AllocaInfo &Info) {
+
+ // Unique the set of defining blocks for efficient lookup.
+ SmallPtrSet<BasicBlock*, 32> DefBlocks;
+ DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
+
+ // Determine which blocks the value is live in. These are blocks which lead
+ // to uses.
+ SmallPtrSet<BasicBlock*, 32> LiveInBlocks;
+ ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
+
+ // Compute the locations where PhiNodes need to be inserted. Look at the
+ // dominance frontier of EACH basic-block we have a write in.
+ unsigned CurrentVersion = 0;
+ SmallPtrSet<PHINode*, 16> InsertedPHINodes;
+ std::vector<std::pair<unsigned, BasicBlock*> > DFBlocks;
+ while (!Info.DefiningBlocks.empty()) {
+ BasicBlock *BB = Info.DefiningBlocks.back();
+ Info.DefiningBlocks.pop_back();
+
+ // Look up the DF for this write, add it to defining blocks.
+ DominanceFrontier::const_iterator it = DF.find(BB);
+ if (it == DF.end()) continue;
+
+ const DominanceFrontier::DomSetType &S = it->second;
+
+ // In theory we don't need the indirection through the DFBlocks vector.
+ // In practice, the order of calling QueuePhiNode would depend on the
+ // (unspecified) ordering of basic blocks in the dominance frontier,
+ // which would give PHI nodes non-determinstic subscripts. Fix this by
+ // processing blocks in order of the occurance in the function.
+ for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
+ PE = S.end(); P != PE; ++P) {
+ // If the frontier block is not in the live-in set for the alloca, don't
+ // bother processing it.
+ if (!LiveInBlocks.count(*P))
+ continue;
+
+ DFBlocks.push_back(std::make_pair(BBNumbers[*P], *P));
+ }
+
+ // Sort by which the block ordering in the function.
+ if (DFBlocks.size() > 1)
+ std::sort(DFBlocks.begin(), DFBlocks.end());
+
+ for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
+ BasicBlock *BB = DFBlocks[i].second;
+ if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
+ Info.DefiningBlocks.push_back(BB);
+ }
+ DFBlocks.clear();
+ }
+}
+
+
/// RewriteSingleStoreAlloca - If there is only a single store to this value,
/// replace any loads of it that are directly dominated by the definition with
/// the value stored.
}
-// MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
-// "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
-// as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
-// each read of the variable. For each block that reads the variable, this
-// function is called, which removes used PHI nodes from the DeadPHINodes set.
-// After all of the reads have been processed, any PHI nodes left in the
-// DeadPHINodes set are removed.
-//
-void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
- SmallPtrSet<PHINode*, 16> &DeadPHINodes) {
- // Scan the immediate dominators of this block looking for a block which has a
- // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
- DomTreeNode *IDomNode = DT.getNode(BB);
- for (DomTreeNode *IDom = IDomNode; IDom; IDom = IDom->getIDom()) {
- BasicBlock *DomBB = IDom->getBlock();
- DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator
- I = NewPhiNodes.find(std::make_pair(DomBB, AllocaNum));
- if (I == NewPhiNodes.end()) continue;
-
- // Ok, we found an inserted PHI node which dominates this value.
- PHINode *DominatingPHI = I->second;
-
- // Find out if we previously thought it was dead. If so, mark it as being
- // live by removing it from the DeadPHINodes set.
- if (!DeadPHINodes.erase(DominatingPHI))
- continue;
-
- // Now that we have marked the PHI node alive, also mark any PHI nodes
- // which it might use as being alive as well.
- for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
- PI != PE; ++PI)
- MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
- }
-}
-
/// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
/// block. If this is the case, avoid traversing the CFG and inserting a lot of
/// potentially useless PHI nodes by just performing a single linear pass over
// Create a PhiNode using the dereferenced type... and add the phi-node to the
// BasicBlock.
- PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
- Allocas[AllocaNo]->getName() + "." +
- utostr(Version++), BB->begin());
+ PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(),
+ Allocas[AllocaNo]->getName() + "." +
+ utostr(Version++), BB->begin());
+ ++NumPHIInsert;
PhiToAllocaMap[PN] = AllocaNo;
PN->reserveOperandSpace(getNumPreds(BB));
return true;
}
-
// RenamePass - Recursively traverse the CFG of the function, renaming loads and
// stores to the allocas which we are promoting. IncomingVals indicates what
// value each Alloca contains on exit from the predecessor block Pred.
// If we have PHI nodes to update, compute the number of edges from Pred to
// BB.
if (!HasPredEntries) {
- TerminatorInst *PredTerm = Pred->getTerminator();
+ // We want to be able to distinguish between PHI nodes being inserted by
+ // this invocation of mem2reg from those phi nodes that already existed in
+ // the IR before mem2reg was run. We determine that APN is being inserted
+ // because it is missing incoming edges. All other PHI nodes being
+ // inserted by this pass of mem2reg will have the same number of incoming
+ // operands so far. Remember this count.
+ unsigned NewPHINumOperands = APN->getNumOperands();
+
unsigned NumEdges = 0;
- for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) {
- if (PredTerm->getSuccessor(i) == BB)
+ for (succ_iterator I = succ_begin(Pred), E = succ_end(Pred); I != E; ++I)
+ if (*I == BB)
++NumEdges;
- }
assert(NumEdges && "Must be at least one edge from Pred to BB!");
// Add entries for all the phis.
APN = dyn_cast<PHINode>(PNI);
if (APN == 0) break;
- // Verify it doesn't already have entries for Pred. If it does, it is
- // not being inserted by this mem2reg invocation.
- HasPredEntries = false;
- for (unsigned i = 0, e = APN->getNumIncomingValues(); i != e; ++i) {
- if (APN->getIncomingBlock(i) == Pred) {
- HasPredEntries = true;
- break;
- }
- }
- } while (!HasPredEntries);
+ // Verify that it is missing entries. If not, it is not being inserted
+ // by this mem2reg invocation so we want to ignore it.
+ } while (APN->getNumOperands() == NewPHINumOperands);
}
}
}
// 'Recurse' to our successors.
- TerminatorInst *TI = BB->getTerminator();
- unsigned NumSuccs = TI->getNumSuccessors();
- if (NumSuccs == 0) return;
-
- // Add all-but-one successor to the worklist.
- for (unsigned i = 0; i != NumSuccs-1; i++)
- Worklist.push_back(RenamePassData(TI->getSuccessor(i), BB, IncomingVals));
-
+ succ_iterator I = succ_begin(BB), E = succ_end(BB);
+ if (I == E) return;
+
// Handle the last successor without using the worklist. This allows us to
// handle unconditional branches directly, for example.
+ --E;
+ for (; I != E; ++I)
+ Worklist.push_back(RenamePassData(*I, BB, IncomingVals));
+
Pred = BB;
- BB = TI->getSuccessor(NumSuccs-1);
+ BB = *I;
goto NextIteration;
}
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