//
// 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.
-// This is just the standard SSA construction algorithm to construct "pruned"
-// SSA form.
+// transformed by using iterated dominator frontiers to place PHI nodes, then
+// traversing the function in depth-first order to rewrite loads and stores as
+// appropriate.
+//
+// The algorithm used here is based on:
+//
+// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
+// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
+// Programming Languages
+// POPL '95. ACM, New York, NY, 62-73.
+//
+// It has been modified to not explicitly use the DJ graph data structure and to
+// directly compute pruned SSA using per-variable liveness information.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "mem2reg"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
-#include "llvm/Constants.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Metadata.h"
-#include "llvm/Analysis/AliasSetTracker.h"
-#include "llvm/Analysis/DebugInfo.h"
-#include "llvm/Analysis/DominanceFrontier.h"
-#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/AliasSetTracker.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/DIBuilder.h"
+#include "llvm/DebugInfo.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Metadata.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Transforms/Utils/Local.h"
#include <algorithm>
+#include <queue>
using namespace llvm;
STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
STATISTIC(NumPHIInsert, "Number of PHI nodes inserted");
-namespace llvm {
-template<>
-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 EltTy getTombstoneKey() {
- return EltTy(reinterpret_cast<BasicBlock*>(-2), 0U);
- }
- static unsigned getHashValue(const std::pair<BasicBlock*, unsigned> &Val) {
- return DenseMapInfo<void*>::getHashValue(Val.first) + Val.second*2;
- }
- static bool isEqual(const EltTy &LHS, const EltTy &RHS) {
- return LHS == RHS;
- }
-};
-}
-
-/// isAllocaPromotable - Return true if this alloca is legal for promotion.
-/// This is true if there are only loads and stores to the alloca.
-///
bool llvm::isAllocaPromotable(const AllocaInst *AI) {
// FIXME: If the memory unit is of pointer or integer type, we can permit
// assignments to subsections of the memory unit.
// Only allow direct and non-volatile loads and stores...
for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
- UI != UE; ++UI) { // Loop over all of the uses of the alloca
+ UI != UE; ++UI) { // Loop over all of the uses of the alloca
const User *U = *UI;
if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
+ // Note that atomic loads can be transformed; atomic semantics do
+ // not have any meaning for a local alloca.
if (LI->isVolatile())
return false;
} else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
if (SI->getOperand(0) == AI)
- return false; // Don't allow a store OF the AI, only INTO the AI.
+ return false; // Don't allow a store OF the AI, only INTO the AI.
+ // Note that atomic stores can be transformed; atomic semantics do
+ // not have any meaning for a local alloca.
if (SI->isVolatile())
return false;
+ } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
+ if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
+ II->getIntrinsicID() != Intrinsic::lifetime_end)
+ return false;
+ } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
+ if (BCI->getType() != Type::getInt8PtrTy(U->getContext()))
+ return false;
+ if (!onlyUsedByLifetimeMarkers(BCI))
+ return false;
+ } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
+ if (GEPI->getType() != Type::getInt8PtrTy(U->getContext()))
+ return false;
+ if (!GEPI->hasAllZeroIndices())
+ return false;
+ if (!onlyUsedByLifetimeMarkers(GEPI))
+ return false;
} else {
return false;
}
return true;
}
-/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
-/// alloca 'V', if any.
-static DbgDeclareInst *FindAllocaDbgDeclare(Value *V) {
- if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), &V, 1))
- for (Value::use_iterator UI = DebugNode->use_begin(),
- E = DebugNode->use_end(); UI != E; ++UI)
- if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))
- return DDI;
+namespace {
- return 0;
-}
+struct AllocaInfo {
+ SmallVector<BasicBlock *, 32> DefiningBlocks;
+ SmallVector<BasicBlock *, 32> UsingBlocks;
+
+ StoreInst *OnlyStore;
+ BasicBlock *OnlyBlock;
+ bool OnlyUsedInOneBlock;
+
+ Value *AllocaPointerVal;
+ DbgDeclareInst *DbgDeclare;
+
+ void clear() {
+ DefiningBlocks.clear();
+ UsingBlocks.clear();
+ OnlyStore = 0;
+ OnlyBlock = 0;
+ OnlyUsedInOneBlock = true;
+ AllocaPointerVal = 0;
+ DbgDeclare = 0;
+ }
-namespace {
- struct AllocaInfo;
-
- // Data package used by RenamePass()
- class RenamePassData {
- public:
- typedef std::vector<Value *> ValVector;
-
- RenamePassData() : BB(NULL), Pred(NULL), Values() {}
- RenamePassData(BasicBlock *B, BasicBlock *P,
- const ValVector &V) : BB(B), Pred(P), Values(V) {}
- BasicBlock *BB;
- BasicBlock *Pred;
- ValVector Values;
-
- void swap(RenamePassData &RHS) {
- std::swap(BB, RHS.BB);
- std::swap(Pred, RHS.Pred);
- Values.swap(RHS.Values);
+ /// Scan the uses of the specified alloca, filling in the AllocaInfo used
+ /// by the rest of the pass to reason about the uses of this alloca.
+ void AnalyzeAlloca(AllocaInst *AI) {
+ clear();
+
+ // As we scan the uses of the alloca instruction, keep track of stores,
+ // and decide whether all of the loads and stores to the alloca are within
+ // the same basic block.
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
+ UI != E;) {
+ Instruction *User = cast<Instruction>(*UI++);
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+ // Remember the basic blocks which define new values for the alloca
+ DefiningBlocks.push_back(SI->getParent());
+ AllocaPointerVal = SI->getOperand(0);
+ OnlyStore = SI;
+ } else {
+ LoadInst *LI = cast<LoadInst>(User);
+ // Otherwise it must be a load instruction, keep track of variable
+ // reads.
+ UsingBlocks.push_back(LI->getParent());
+ AllocaPointerVal = LI;
+ }
+
+ if (OnlyUsedInOneBlock) {
+ if (OnlyBlock == 0)
+ OnlyBlock = User->getParent();
+ else if (OnlyBlock != User->getParent())
+ OnlyUsedInOneBlock = false;
+ }
}
- };
-
- /// LargeBlockInfo - This assigns and keeps a per-bb relative ordering of
- /// load/store instructions in the block that directly load or store an alloca.
+
+ DbgDeclare = FindAllocaDbgDeclare(AI);
+ }
+};
+
+// Data package used by RenamePass()
+class RenamePassData {
+public:
+ typedef std::vector<Value *> ValVector;
+
+ RenamePassData() : BB(NULL), Pred(NULL), Values() {}
+ RenamePassData(BasicBlock *B, BasicBlock *P, const ValVector &V)
+ : BB(B), Pred(P), Values(V) {}
+ BasicBlock *BB;
+ BasicBlock *Pred;
+ ValVector Values;
+
+ void swap(RenamePassData &RHS) {
+ std::swap(BB, RHS.BB);
+ std::swap(Pred, RHS.Pred);
+ Values.swap(RHS.Values);
+ }
+};
+
+/// \brief This assigns and keeps a per-bb relative ordering of load/store
+/// instructions in the block that directly load or store an alloca.
+///
+/// This functionality is important because it avoids scanning large basic
+/// blocks multiple times when promoting many allocas in the same block.
+class LargeBlockInfo {
+ /// \brief For each instruction that we track, keep the index of the
+ /// instruction.
///
- /// This functionality is important because it avoids scanning large basic
- /// blocks multiple times when promoting many allocas in the same block.
- class LargeBlockInfo {
- /// InstNumbers - For each instruction that we track, keep the index of the
- /// instruction. The index starts out as the number of the instruction from
- /// the start of the block.
- DenseMap<const Instruction *, unsigned> InstNumbers;
- public:
-
- /// isInterestingInstruction - This code only looks at accesses to allocas.
- static bool isInterestingInstruction(const Instruction *I) {
- return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
- (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
- }
-
- /// getInstructionIndex - Get or calculate the index of the specified
- /// instruction.
- unsigned getInstructionIndex(const Instruction *I) {
- assert(isInterestingInstruction(I) &&
- "Not a load/store to/from an alloca?");
-
- // If we already have this instruction number, return it.
- DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I);
- if (It != InstNumbers.end()) return It->second;
-
- // Scan the whole block to get the instruction. This accumulates
- // information for every interesting instruction in the block, in order to
- // avoid gratuitus rescans.
- const BasicBlock *BB = I->getParent();
- unsigned InstNo = 0;
- for (BasicBlock::const_iterator BBI = BB->begin(), E = BB->end();
- BBI != E; ++BBI)
- if (isInterestingInstruction(BBI))
- InstNumbers[BBI] = InstNo++;
- It = InstNumbers.find(I);
-
- assert(It != InstNumbers.end() && "Didn't insert instruction?");
+ /// The index starts out as the number of the instruction from the start of
+ /// the block.
+ DenseMap<const Instruction *, unsigned> InstNumbers;
+
+public:
+
+ /// This code only looks at accesses to allocas.
+ static bool isInterestingInstruction(const Instruction *I) {
+ return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
+ (isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
+ }
+
+ /// Get or calculate the index of the specified instruction.
+ unsigned getInstructionIndex(const Instruction *I) {
+ assert(isInterestingInstruction(I) &&
+ "Not a load/store to/from an alloca?");
+
+ // If we already have this instruction number, return it.
+ DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I);
+ if (It != InstNumbers.end())
return It->second;
- }
-
- void deleteValue(const Instruction *I) {
- InstNumbers.erase(I);
- }
-
- void clear() {
- InstNumbers.clear();
- }
- };
-
- struct PromoteMem2Reg {
- /// Allocas - The alloca instructions being promoted.
- ///
- std::vector<AllocaInst*> Allocas;
- DominatorTree &DT;
- DominanceFrontier &DF;
- DIFactory *DIF;
-
- /// AST - An AliasSetTracker object to update. If null, don't update it.
- ///
- AliasSetTracker *AST;
-
- /// AllocaLookup - Reverse mapping of Allocas.
- ///
- std::map<AllocaInst*, unsigned> AllocaLookup;
-
- /// NewPhiNodes - The PhiNodes we're adding.
- ///
- DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*> NewPhiNodes;
-
- /// PhiToAllocaMap - For each PHI node, keep track of which entry in Allocas
- /// it corresponds to.
- DenseMap<PHINode*, unsigned> PhiToAllocaMap;
-
- /// PointerAllocaValues - If we are updating an AliasSetTracker, then for
- /// each alloca that is of pointer type, we keep track of what to copyValue
- /// to the inserted PHI nodes here.
- ///
- std::vector<Value*> PointerAllocaValues;
-
- /// AllocaDbgDeclares - For each alloca, we keep track of the dbg.declare
- /// intrinsic that describes it, if any, so that we can convert it to a
- /// dbg.value intrinsic if the alloca gets promoted.
- SmallVector<DbgDeclareInst*, 8> AllocaDbgDeclares;
-
- /// Visited - The set of basic blocks the renamer has already visited.
- ///
- SmallPtrSet<BasicBlock*, 16> Visited;
-
- /// BBNumbers - Contains a stable numbering of basic blocks to avoid
- /// non-determinstic behavior.
- DenseMap<BasicBlock*, unsigned> BBNumbers;
-
- /// BBNumPreds - Lazily compute the number of predecessors a block has.
- DenseMap<const BasicBlock*, unsigned> BBNumPreds;
- public:
- PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
- DominanceFrontier &df, AliasSetTracker *ast)
- : Allocas(A), DT(dt), DF(df), DIF(0), AST(ast) {}
- ~PromoteMem2Reg() {
- delete DIF;
- }
- void run();
+ // Scan the whole block to get the instruction. This accumulates
+ // information for every interesting instruction in the block, in order to
+ // avoid gratuitus rescans.
+ const BasicBlock *BB = I->getParent();
+ unsigned InstNo = 0;
+ for (BasicBlock::const_iterator BBI = BB->begin(), E = BB->end(); BBI != E;
+ ++BBI)
+ if (isInterestingInstruction(BBI))
+ InstNumbers[BBI] = InstNo++;
+ It = InstNumbers.find(I);
+
+ assert(It != InstNumbers.end() && "Didn't insert instruction?");
+ return It->second;
+ }
- /// dominates - Return true if BB1 dominates BB2 using the DominatorTree.
- ///
- bool dominates(BasicBlock *BB1, BasicBlock *BB2) const {
- return DT.dominates(BB1, BB2);
- }
+ void deleteValue(const Instruction *I) { InstNumbers.erase(I); }
- private:
- void RemoveFromAllocasList(unsigned &AllocaIdx) {
- Allocas[AllocaIdx] = Allocas.back();
- Allocas.pop_back();
- --AllocaIdx;
- }
+ void clear() { InstNumbers.clear(); }
+};
+
+struct PromoteMem2Reg {
+ /// The alloca instructions being promoted.
+ std::vector<AllocaInst *> Allocas;
+ DominatorTree &DT;
+ DIBuilder DIB;
+
+ /// An AliasSetTracker object to update. If null, don't update it.
+ AliasSetTracker *AST;
+
+ /// Reverse mapping of Allocas.
+ DenseMap<AllocaInst *, unsigned> AllocaLookup;
+
+ /// \brief The PhiNodes we're adding.
+ ///
+ /// That map is used to simplify some Phi nodes as we iterate over it, so
+ /// it should have deterministic iterators. We could use a MapVector, but
+ /// since we already maintain a map from BasicBlock* to a stable numbering
+ /// (BBNumbers), the DenseMap is more efficient (also supports removal).
+ DenseMap<std::pair<unsigned, unsigned>, PHINode *> NewPhiNodes;
+
+ /// For each PHI node, keep track of which entry in Allocas it corresponds
+ /// to.
+ DenseMap<PHINode *, unsigned> PhiToAllocaMap;
+
+ /// If we are updating an AliasSetTracker, then for each alloca that is of
+ /// pointer type, we keep track of what to copyValue to the inserted PHI
+ /// nodes here.
+ std::vector<Value *> PointerAllocaValues;
+
+ /// For each alloca, we keep track of the dbg.declare intrinsic that
+ /// describes it, if any, so that we can convert it to a dbg.value
+ /// intrinsic if the alloca gets promoted.
+ SmallVector<DbgDeclareInst *, 8> AllocaDbgDeclares;
+
+ /// The set of basic blocks the renamer has already visited.
+ ///
+ SmallPtrSet<BasicBlock *, 16> Visited;
+
+ /// Contains a stable numbering of basic blocks to avoid non-determinstic
+ /// behavior.
+ DenseMap<BasicBlock *, unsigned> BBNumbers;
+
+ /// Maps DomTreeNodes to their level in the dominator tree.
+ DenseMap<DomTreeNode *, unsigned> DomLevels;
+
+ /// Lazily compute the number of predecessors a block has.
+ DenseMap<const BasicBlock *, unsigned> BBNumPreds;
+
+public:
+ PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
+ AliasSetTracker *AST)
+ : Allocas(Allocas.begin(), Allocas.end()), DT(DT),
+ DIB(*DT.getRoot()->getParent()->getParent()), AST(AST) {}
+
+ void run();
+
+private:
+ void RemoveFromAllocasList(unsigned &AllocaIdx) {
+ Allocas[AllocaIdx] = Allocas.back();
+ Allocas.pop_back();
+ --AllocaIdx;
+ }
+
+ unsigned getNumPreds(const BasicBlock *BB) {
+ unsigned &NP = BBNumPreds[BB];
+ if (NP == 0)
+ NP = std::distance(pred_begin(BB), pred_end(BB)) + 1;
+ 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 RenamePass(BasicBlock *BB, BasicBlock *Pred,
+ RenamePassData::ValVector &IncVals,
+ std::vector<RenamePassData> &Worklist);
+ bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
+};
+
+} // end of anonymous namespace
- unsigned getNumPreds(const BasicBlock *BB) {
- unsigned &NP = BBNumPreds[BB];
- if (NP == 0)
- NP = std::distance(pred_begin(BB), pred_end(BB))+1;
- return NP-1;
+static void removeLifetimeIntrinsicUsers(AllocaInst *AI) {
+ // Knowing that this alloca is promotable, we know that it's safe to kill all
+ // instructions except for load and store.
+
+ for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE;) {
+ Instruction *I = cast<Instruction>(*UI);
+ ++UI;
+ if (isa<LoadInst>(I) || isa<StoreInst>(I))
+ continue;
+
+ if (!I->getType()->isVoidTy()) {
+ // The only users of this bitcast/GEP instruction are lifetime intrinsics.
+ // Follow the use/def chain to erase them now instead of leaving it for
+ // dead code elimination later.
+ for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE;) {
+ Instruction *Inst = cast<Instruction>(*UI);
+ ++UI;
+ Inst->eraseFromParent();
+ }
}
+ I->eraseFromParent();
+ }
+}
+
+/// \brief Rewrite as many loads as possible given a single store.
+///
+/// When there is only a single store, we can use the domtree to trivially
+/// replace all of the dominated loads with the stored value. Do so, and return
+/// true if this has successfully promoted the alloca entirely. If this returns
+/// false there were some loads which were not dominated by the single store
+/// and thus must be phi-ed with undef. We fall back to the standard alloca
+/// promotion algorithm in that case.
+static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
+ LargeBlockInfo &LBI,
+ DominatorTree &DT,
+ AliasSetTracker *AST) {
+ StoreInst *OnlyStore = Info.OnlyStore;
+ bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
+ BasicBlock *StoreBB = OnlyStore->getParent();
+ int StoreIndex = -1;
+
+ // Clear out UsingBlocks. We will reconstruct it here if needed.
+ Info.UsingBlocks.clear();
- 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,
- LargeBlockInfo &LBI);
- void PromoteSingleBlockAlloca(AllocaInst *AI, AllocaInfo &Info,
- LargeBlockInfo &LBI);
- void ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, StoreInst *SI);
-
-
- void RenamePass(BasicBlock *BB, BasicBlock *Pred,
- RenamePassData::ValVector &IncVals,
- std::vector<RenamePassData> &Worklist);
- bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
- };
-
- struct AllocaInfo {
- std::vector<BasicBlock*> DefiningBlocks;
- std::vector<BasicBlock*> UsingBlocks;
-
- StoreInst *OnlyStore;
- BasicBlock *OnlyBlock;
- bool OnlyUsedInOneBlock;
-
- Value *AllocaPointerVal;
- DbgDeclareInst *DbgDeclare;
-
- void clear() {
- DefiningBlocks.clear();
- UsingBlocks.clear();
- OnlyStore = 0;
- OnlyBlock = 0;
- OnlyUsedInOneBlock = true;
- AllocaPointerVal = 0;
- DbgDeclare = 0;
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) {
+ Instruction *UserInst = cast<Instruction>(*UI++);
+ if (!isa<LoadInst>(UserInst)) {
+ assert(UserInst == OnlyStore && "Should only have load/stores");
+ continue;
}
-
- /// AnalyzeAlloca - Scan the uses of the specified alloca, filling in our
- /// ivars.
- void AnalyzeAlloca(AllocaInst *AI) {
- clear();
-
- // As we scan the uses of the alloca instruction, keep track of stores,
- // and decide whether all of the loads and stores to the alloca are within
- // the same basic block.
- for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
- UI != E;) {
- Instruction *User = cast<Instruction>(*UI++);
-
- if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
- // Remember the basic blocks which define new values for the alloca
- DefiningBlocks.push_back(SI->getParent());
- AllocaPointerVal = SI->getOperand(0);
- OnlyStore = SI;
- } else {
- LoadInst *LI = cast<LoadInst>(User);
- // Otherwise it must be a load instruction, keep track of variable
- // reads.
- UsingBlocks.push_back(LI->getParent());
- AllocaPointerVal = LI;
- }
-
- if (OnlyUsedInOneBlock) {
- if (OnlyBlock == 0)
- OnlyBlock = User->getParent();
- else if (OnlyBlock != User->getParent())
- OnlyUsedInOneBlock = false;
+ LoadInst *LI = cast<LoadInst>(UserInst);
+
+ // Okay, if we have a load from the alloca, we want to replace it with the
+ // only value stored to the alloca. We can do this if the value is
+ // dominated by the store. If not, we use the rest of the mem2reg machinery
+ // to insert the phi nodes as needed.
+ if (!StoringGlobalVal) { // Non-instructions are always dominated.
+ if (LI->getParent() == StoreBB) {
+ // If we have a use that is in the same block as the store, compare the
+ // indices of the two instructions to see which one came first. If the
+ // load came before the store, we can't handle it.
+ if (StoreIndex == -1)
+ StoreIndex = LBI.getInstructionIndex(OnlyStore);
+
+ if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
+ // Can't handle this load, bail out.
+ Info.UsingBlocks.push_back(StoreBB);
+ continue;
}
+
+ } else if (LI->getParent() != StoreBB &&
+ !DT.dominates(StoreBB, LI->getParent())) {
+ // If the load and store are in different blocks, use BB dominance to
+ // check their relationships. If the store doesn't dom the use, bail
+ // out.
+ Info.UsingBlocks.push_back(LI->getParent());
+ continue;
}
-
- DbgDeclare = FindAllocaDbgDeclare(AI);
}
- };
-} // end of anonymous namespace
+ // Otherwise, we *can* safely rewrite this load.
+ Value *ReplVal = OnlyStore->getOperand(0);
+ // If the replacement value is the load, this must occur in unreachable
+ // code.
+ if (ReplVal == LI)
+ ReplVal = UndefValue::get(LI->getType());
+ LI->replaceAllUsesWith(ReplVal);
+ if (AST && LI->getType()->isPointerTy())
+ AST->deleteValue(LI);
+ LI->eraseFromParent();
+ LBI.deleteValue(LI);
+ }
+
+ // Finally, after the scan, check to see if the store is all that is left.
+ if (!Info.UsingBlocks.empty())
+ return false; // If not, we'll have to fall back for the remainder.
+
+ // Record debuginfo for the store and remove the declaration's
+ // debuginfo.
+ if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+ DIBuilder DIB(*AI->getParent()->getParent()->getParent());
+ ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
+ DDI->eraseFromParent();
+ LBI.deleteValue(DDI);
+ }
+ // Remove the (now dead) store and alloca.
+ Info.OnlyStore->eraseFromParent();
+ LBI.deleteValue(Info.OnlyStore);
+
+ if (AST)
+ AST->deleteValue(AI);
+ AI->eraseFromParent();
+ LBI.deleteValue(AI);
+ return true;
+}
+
+/// 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 the basic block
+/// using the Alloca.
+///
+/// If we cannot promote this alloca (because it is read before it is written),
+/// return true. This is necessary in cases where, due to control flow, the
+/// alloca is potentially undefined on some control flow paths. e.g. code like
+/// this is potentially correct:
+///
+/// for (...) { if (c) { A = undef; undef = B; } }
+///
+/// ... so long as A is not used before undef is set.
+static void promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
+ LargeBlockInfo &LBI,
+ AliasSetTracker *AST) {
+ // The trickiest case to handle is when we have large blocks. Because of this,
+ // this code is optimized assuming that large blocks happen. This does not
+ // significantly pessimize the small block case. This uses LargeBlockInfo to
+ // make it efficient to get the index of various operations in the block.
+
+ // Walk the use-def list of the alloca, getting the locations of all stores.
+ typedef SmallVector<std::pair<unsigned, StoreInst *>, 64> StoresByIndexTy;
+ StoresByIndexTy StoresByIndex;
+
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;
+ ++UI)
+ if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
+ StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
+
+ // Sort the stores by their index, making it efficient to do a lookup with a
+ // binary search.
+ std::sort(StoresByIndex.begin(), StoresByIndex.end(), less_first());
+
+ // Walk all of the loads from this alloca, replacing them with the nearest
+ // store above them, if any.
+ for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) {
+ LoadInst *LI = dyn_cast<LoadInst>(*UI++);
+ if (!LI)
+ continue;
+
+ unsigned LoadIdx = LBI.getInstructionIndex(LI);
+
+ // Find the nearest store that has a lower index than this load.
+ StoresByIndexTy::iterator I =
+ std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(),
+ std::make_pair(LoadIdx, static_cast<StoreInst *>(0)),
+ less_first());
+
+ if (I == StoresByIndex.begin())
+ // If there is no store before this load, the load takes the undef value.
+ LI->replaceAllUsesWith(UndefValue::get(LI->getType()));
+ else
+ // Otherwise, there was a store before this load, the load takes its value.
+ LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0));
+
+ if (AST && LI->getType()->isPointerTy())
+ AST->deleteValue(LI);
+ LI->eraseFromParent();
+ LBI.deleteValue(LI);
+ }
+
+ // Remove the (now dead) stores and alloca.
+ while (!AI->use_empty()) {
+ StoreInst *SI = cast<StoreInst>(AI->use_back());
+ // Record debuginfo for the store before removing it.
+ if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+ DIBuilder DIB(*AI->getParent()->getParent()->getParent());
+ ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+ }
+ SI->eraseFromParent();
+ LBI.deleteValue(SI);
+ }
+
+ if (AST)
+ AST->deleteValue(AI);
+ AI->eraseFromParent();
+ LBI.deleteValue(AI);
+
+ // The alloca's debuginfo can be removed as well.
+ if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+ DDI->eraseFromParent();
+ LBI.deleteValue(DDI);
+ }
+
+ ++NumLocalPromoted;
+}
void PromoteMem2Reg::run() {
- Function &F = *DF.getRoot()->getParent();
+ Function &F = *DT.getRoot()->getParent();
- if (AST) PointerAllocaValues.resize(Allocas.size());
+ if (AST)
+ PointerAllocaValues.resize(Allocas.size());
AllocaDbgDeclares.resize(Allocas.size());
AllocaInfo Info;
for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
AllocaInst *AI = Allocas[AllocaNum];
- assert(isAllocaPromotable(AI) &&
- "Cannot promote non-promotable alloca!");
+ assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!");
assert(AI->getParent()->getParent() == &F &&
"All allocas should be in the same function, which is same as DF!");
+ removeLifetimeIntrinsicUsers(AI);
+
if (AI->use_empty()) {
// If there are no uses of the alloca, just delete it now.
- if (AST) AST->deleteValue(AI);
+ if (AST)
+ AST->deleteValue(AI);
AI->eraseFromParent();
// Remove the alloca from the Allocas list, since it has been processed
++NumDeadAlloca;
continue;
}
-
+
// Calculate the set of read and write-locations for each alloca. This is
// analogous to finding the 'uses' and 'definitions' of each variable.
Info.AnalyzeAlloca(AI);
// 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.
if (Info.DefiningBlocks.size() == 1) {
- RewriteSingleStoreAlloca(AI, Info, LBI);
-
- // Finally, after the scan, check to see if the store is all that is left.
- if (Info.UsingBlocks.empty()) {
- // Record debuginfo for the store and remove the declaration's debuginfo.
- if (DbgDeclareInst *DDI = Info.DbgDeclare) {
- ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore);
- DDI->eraseFromParent();
- }
- // Remove the (now dead) store and alloca.
- Info.OnlyStore->eraseFromParent();
- LBI.deleteValue(Info.OnlyStore);
-
- if (AST) AST->deleteValue(AI);
- AI->eraseFromParent();
- LBI.deleteValue(AI);
-
+ if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) {
// The alloca has been processed, move on.
RemoveFromAllocasList(AllocaNum);
-
++NumSingleStore;
continue;
}
}
-
+
// If the alloca is only read and written in one basic block, just perform a
// linear sweep over the block to eliminate it.
if (Info.OnlyUsedInOneBlock) {
- PromoteSingleBlockAlloca(AI, Info, LBI);
-
- // Finally, after the scan, check to see if the stores are all that is
- // left.
- if (Info.UsingBlocks.empty()) {
-
- // Remove the (now dead) stores and alloca.
- while (!AI->use_empty()) {
- StoreInst *SI = cast<StoreInst>(AI->use_back());
- // Record debuginfo for the store before removing it.
- if (DbgDeclareInst *DDI = Info.DbgDeclare)
- ConvertDebugDeclareToDebugValue(DDI, SI);
- SI->eraseFromParent();
- LBI.deleteValue(SI);
- }
-
- if (AST) AST->deleteValue(AI);
- AI->eraseFromParent();
- LBI.deleteValue(AI);
-
- // The alloca has been processed, move on.
- RemoveFromAllocasList(AllocaNum);
-
- // The alloca's debuginfo can be removed as well.
- if (DbgDeclareInst *DDI = Info.DbgDeclare)
- DDI->eraseFromParent();
+ promoteSingleBlockAlloca(AI, Info, LBI, AST);
- ++NumLocalPromoted;
- continue;
+ // The alloca has been processed, move on.
+ RemoveFromAllocasList(AllocaNum);
+ continue;
+ }
+
+ // If we haven't computed dominator tree levels, do so now.
+ if (DomLevels.empty()) {
+ SmallVector<DomTreeNode *, 32> Worklist;
+
+ DomTreeNode *Root = DT.getRootNode();
+ DomLevels[Root] = 0;
+ Worklist.push_back(Root);
+
+ while (!Worklist.empty()) {
+ DomTreeNode *Node = Worklist.pop_back_val();
+ unsigned ChildLevel = DomLevels[Node] + 1;
+ for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end();
+ CI != CE; ++CI) {
+ DomLevels[*CI] = ChildLevel;
+ Worklist.push_back(*CI);
+ }
}
}
-
+
// If we haven't computed a numbering for the BB's in the function, do so
// now.
if (BBNumbers.empty()) {
// stored into the alloca.
if (AST)
PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
-
+
// Remember the dbg.declare intrinsic describing this alloca, if any.
- if (Info.DbgDeclare) AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
-
+ if (Info.DbgDeclare)
+ AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
+
// Keep the reverse mapping of the 'Allocas' array for the rename pass.
AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
return; // All of the allocas must have been trivial!
LBI.clear();
-
-
+
// Set the incoming values for the basic block to be null values for all of
// the alloca's. We do this in case there is a load of a value that has not
// been stored yet. In this case, it will get this null value.
// RenamePass may add new worklist entries.
RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
} while (!RenamePassWorkList.empty());
-
+
// The renamer uses the Visited set to avoid infinite loops. Clear it now.
Visited.clear();
Instruction *A = Allocas[i];
// If there are any uses of the alloca instructions left, they must be in
- // sections of dead code that were not processed on the dominance frontier.
- // Just delete the users now.
- //
+ // unreachable basic blocks that were not processed by walking the dominator
+ // tree. Just delete the users now.
if (!A->use_empty())
A->replaceAllUsesWith(UndefValue::get(A->getType()));
- if (AST) AST->deleteValue(A);
+ if (AST)
+ AST->deleteValue(A);
A->eraseFromParent();
}
bool EliminatedAPHI = true;
while (EliminatedAPHI) {
EliminatedAPHI = false;
-
- for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
- NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) {
+
+ // Iterating over NewPhiNodes is deterministic, so it is safe to try to
+ // simplify and RAUW them as we go. If it was not, we could add uses to
+ // the values we replace with in a non-deterministic order, thus creating
+ // non-deterministic def->use chains.
+ for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
+ I = NewPhiNodes.begin(),
+ E = NewPhiNodes.end();
+ I != E;) {
PHINode *PN = I->second;
// If this PHI node merges one value and/or undefs, get the value.
- if (Value *V = SimplifyInstruction(PN, 0, &DT)) {
+ if (Value *V = SimplifyInstruction(PN, 0, 0, &DT)) {
if (AST && PN->getType()->isPointerTy())
AST->deleteValue(PN);
PN->replaceAllUsesWith(V);
++I;
}
}
-
+
// At this point, the renamer has added entries to PHI nodes for all reachable
// code. Unfortunately, there may be unreachable blocks which the renamer
// hasn't traversed. If this is the case, the PHI nodes may not
// have incoming values for all predecessors. Loop over all PHI nodes we have
// created, inserting undef values if they are missing any incoming values.
//
- for (DenseMap<std::pair<BasicBlock*, unsigned>, PHINode*>::iterator I =
- NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
+ for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
+ I = NewPhiNodes.begin(),
+ E = NewPhiNodes.end();
+ I != E; ++I) {
// We want to do this once per basic block. As such, only process a block
// when we find the PHI that is the first entry in the block.
PHINode *SomePHI = I->second;
continue;
// Get the preds for BB.
- SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(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
// access.
std::sort(Preds.begin(), Preds.end());
-
+
// Now we loop through all BB's which have entries in SomePHI and remove
// them from the Preds list.
for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
// Do a log(n) search of the Preds list for the entry we want.
- SmallVector<BasicBlock*, 16>::iterator EntIt =
- std::lower_bound(Preds.begin(), Preds.end(),
- SomePHI->getIncomingBlock(i));
- assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i)&&
+ SmallVectorImpl<BasicBlock *>::iterator EntIt = std::lower_bound(
+ Preds.begin(), Preds.end(), SomePHI->getIncomingBlock(i));
+ assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) &&
"PHI node has entry for a block which is not a predecessor!");
// Remove the entry
SomePHI->addIncoming(UndefVal, Preds[pred]);
}
}
-
+
NewPhiNodes.clear();
}
+/// \brief 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) {
-/// 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(Info.UsingBlocks.begin(),
- Info.UsingBlocks.end());
-
+ SmallVector<BasicBlock *, 64> LiveInBlockWorklist(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;
-
+ 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) {
+ for (BasicBlock::iterator I = BB->begin();; ++I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
- if (SI->getOperand(1) != AI) continue;
-
+ 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();
--i, --e;
break;
}
-
+
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
- if (LI->getOperand(0) != AI) continue;
-
+ 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.pop_back_val();
-
+
// 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.
+/// 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;
+ 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;
+ 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;
- 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))
- Info.DefiningBlocks.push_back(BB);
- }
- DFBlocks.clear();
+ // Use a priority queue keyed on dominator tree level so that inserted nodes
+ // are handled from the bottom of the dominator tree upwards.
+ typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
+ typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
+ less_second> IDFPriorityQueue;
+ IDFPriorityQueue PQ;
+
+ for (SmallPtrSet<BasicBlock *, 32>::const_iterator I = DefBlocks.begin(),
+ E = DefBlocks.end();
+ I != E; ++I) {
+ if (DomTreeNode *Node = DT.getNode(*I))
+ PQ.push(std::make_pair(Node, DomLevels[Node]));
}
-}
-
-/// 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.
-void PromoteMem2Reg::RewriteSingleStoreAlloca(AllocaInst *AI,
- AllocaInfo &Info,
- LargeBlockInfo &LBI) {
- StoreInst *OnlyStore = Info.OnlyStore;
- bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
- BasicBlock *StoreBB = OnlyStore->getParent();
- int StoreIndex = -1;
-
- // Clear out UsingBlocks. We will reconstruct it here if needed.
- Info.UsingBlocks.clear();
-
- for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E; ) {
- Instruction *UserInst = cast<Instruction>(*UI++);
- if (!isa<LoadInst>(UserInst)) {
- assert(UserInst == OnlyStore && "Should only have load/stores");
- continue;
- }
- LoadInst *LI = cast<LoadInst>(UserInst);
-
- // Okay, if we have a load from the alloca, we want to replace it with the
- // only value stored to the alloca. We can do this if the value is
- // dominated by the store. If not, we use the rest of the mem2reg machinery
- // to insert the phi nodes as needed.
- if (!StoringGlobalVal) { // Non-instructions are always dominated.
- if (LI->getParent() == StoreBB) {
- // If we have a use that is in the same block as the store, compare the
- // indices of the two instructions to see which one came first. If the
- // load came before the store, we can't handle it.
- if (StoreIndex == -1)
- StoreIndex = LBI.getInstructionIndex(OnlyStore);
- if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
- // Can't handle this load, bail out.
- Info.UsingBlocks.push_back(StoreBB);
+ SmallVector<std::pair<unsigned, BasicBlock *>, 32> DFBlocks;
+ SmallPtrSet<DomTreeNode *, 32> Visited;
+ SmallVector<DomTreeNode *, 32> Worklist;
+ while (!PQ.empty()) {
+ DomTreeNodePair RootPair = PQ.top();
+ PQ.pop();
+ DomTreeNode *Root = RootPair.first;
+ unsigned RootLevel = RootPair.second;
+
+ // Walk all dominator tree children of Root, inspecting their CFG edges with
+ // targets elsewhere on the dominator tree. Only targets whose level is at
+ // most Root's level are added to the iterated dominance frontier of the
+ // definition set.
+
+ Worklist.clear();
+ Worklist.push_back(Root);
+
+ while (!Worklist.empty()) {
+ DomTreeNode *Node = Worklist.pop_back_val();
+ BasicBlock *BB = Node->getBlock();
+
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
+ ++SI) {
+ DomTreeNode *SuccNode = DT.getNode(*SI);
+
+ // Quickly skip all CFG edges that are also dominator tree edges instead
+ // of catching them below.
+ if (SuccNode->getIDom() == Node)
continue;
- }
-
- } else if (LI->getParent() != StoreBB &&
- !dominates(StoreBB, LI->getParent())) {
- // If the load and store are in different blocks, use BB dominance to
- // check their relationships. If the store doesn't dom the use, bail
- // out.
- Info.UsingBlocks.push_back(LI->getParent());
- continue;
- }
- }
-
- // Otherwise, we *can* safely rewrite this load.
- Value *ReplVal = OnlyStore->getOperand(0);
- // If the replacement value is the load, this must occur in unreachable
- // code.
- if (ReplVal == LI)
- ReplVal = UndefValue::get(LI->getType());
- LI->replaceAllUsesWith(ReplVal);
- if (AST && LI->getType()->isPointerTy())
- AST->deleteValue(LI);
- LI->eraseFromParent();
- LBI.deleteValue(LI);
- }
-}
-namespace {
+ unsigned SuccLevel = DomLevels[SuccNode];
+ if (SuccLevel > RootLevel)
+ continue;
-/// StoreIndexSearchPredicate - This is a helper predicate used to search by the
-/// first element of a pair.
-struct StoreIndexSearchPredicate {
- bool operator()(const std::pair<unsigned, StoreInst*> &LHS,
- const std::pair<unsigned, StoreInst*> &RHS) {
- return LHS.first < RHS.first;
- }
-};
+ if (!Visited.insert(SuccNode))
+ continue;
-}
+ BasicBlock *SuccBB = SuccNode->getBlock();
+ if (!LiveInBlocks.count(SuccBB))
+ continue;
-/// PromoteSingleBlockAlloca - 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
-/// the basic block using the Alloca.
-///
-/// If we cannot promote this alloca (because it is read before it is written),
-/// return true. This is necessary in cases where, due to control flow, the
-/// alloca is potentially undefined on some control flow paths. e.g. code like
-/// this is potentially correct:
-///
-/// for (...) { if (c) { A = undef; undef = B; } }
-///
-/// ... so long as A is not used before undef is set.
-///
-void PromoteMem2Reg::PromoteSingleBlockAlloca(AllocaInst *AI, AllocaInfo &Info,
- LargeBlockInfo &LBI) {
- // The trickiest case to handle is when we have large blocks. Because of this,
- // this code is optimized assuming that large blocks happen. This does not
- // significantly pessimize the small block case. This uses LargeBlockInfo to
- // make it efficient to get the index of various operations in the block.
-
- // Clear out UsingBlocks. We will reconstruct it here if needed.
- Info.UsingBlocks.clear();
-
- // Walk the use-def list of the alloca, getting the locations of all stores.
- typedef SmallVector<std::pair<unsigned, StoreInst*>, 64> StoresByIndexTy;
- StoresByIndexTy StoresByIndex;
-
- for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
- UI != E; ++UI)
- if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
- StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
+ DFBlocks.push_back(std::make_pair(BBNumbers[SuccBB], SuccBB));
+ if (!DefBlocks.count(SuccBB))
+ PQ.push(std::make_pair(SuccNode, SuccLevel));
+ }
- // If there are no stores to the alloca, just replace any loads with undef.
- if (StoresByIndex.empty()) {
- for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;)
- if (LoadInst *LI = dyn_cast<LoadInst>(*UI++)) {
- LI->replaceAllUsesWith(UndefValue::get(LI->getType()));
- if (AST && LI->getType()->isPointerTy())
- AST->deleteValue(LI);
- LBI.deleteValue(LI);
- LI->eraseFromParent();
+ for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end(); CI != CE;
+ ++CI) {
+ if (!Visited.count(*CI))
+ Worklist.push_back(*CI);
}
- return;
- }
-
- // Sort the stores by their index, making it efficient to do a lookup with a
- // binary search.
- std::sort(StoresByIndex.begin(), StoresByIndex.end());
-
- // Walk all of the loads from this alloca, replacing them with the nearest
- // store above them, if any.
- for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) {
- LoadInst *LI = dyn_cast<LoadInst>(*UI++);
- if (!LI) continue;
-
- unsigned LoadIdx = LBI.getInstructionIndex(LI);
-
- // Find the nearest store that has a lower than this load.
- StoresByIndexTy::iterator I =
- std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(),
- std::pair<unsigned, StoreInst*>(LoadIdx, static_cast<StoreInst*>(0)),
- StoreIndexSearchPredicate());
-
- // If there is no store before this load, then we can't promote this load.
- if (I == StoresByIndex.begin()) {
- // Can't handle this load, bail out.
- Info.UsingBlocks.push_back(LI->getParent());
- continue;
}
-
- // Otherwise, there was a store before this load, the load takes its value.
- --I;
- LI->replaceAllUsesWith(I->second->getOperand(0));
- if (AST && LI->getType()->isPointerTy())
- AST->deleteValue(LI);
- LI->eraseFromParent();
- LBI.deleteValue(LI);
}
-}
-// Inserts a llvm.dbg.value instrinsic before the stores to an alloca'd value
-// that has an associated llvm.dbg.decl intrinsic.
-void PromoteMem2Reg::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
- StoreInst *SI) {
- DIVariable DIVar(DDI->getVariable());
- if (!DIVar.Verify())
- return;
+ if (DFBlocks.size() > 1)
+ std::sort(DFBlocks.begin(), DFBlocks.end());
- if (!DIF)
- DIF = new DIFactory(*SI->getParent()->getParent()->getParent());
- Instruction *DbgVal = DIF->InsertDbgValueIntrinsic(SI->getOperand(0), 0,
- DIVar, SI);
-
- // Propagate any debug metadata from the store onto the dbg.value.
- DebugLoc SIDL = SI->getDebugLoc();
- if (!SIDL.isUnknown())
- DbgVal->setDebugLoc(SIDL);
- // Otherwise propagate debug metadata from dbg.declare.
- else
- DbgVal->setDebugLoc(DDI->getDebugLoc());
+ unsigned CurrentVersion = 0;
+ for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i)
+ QueuePhiNode(DFBlocks[i].second, AllocaNum, CurrentVersion);
}
-// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
-// Alloca returns true if there wasn't already a phi-node for that variable
-//
+/// \brief Queue a phi-node to be added to a basic-block for a specific Alloca.
+///
+/// Returns true if there wasn't already a phi-node for that variable
bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
unsigned &Version) {
// Look up the basic-block in question.
- PHINode *&PN = NewPhiNodes[std::make_pair(BB, AllocaNo)];
+ PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)];
// If the BB already has a phi node added for the i'th alloca then we're done!
- if (PN) return false;
+ if (PN)
+ return false;
// Create a PhiNode using the dereferenced type... and add the phi-node to the
// BasicBlock.
- PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(),
- Allocas[AllocaNo]->getName() + "." + Twine(Version++),
+ PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB),
+ Allocas[AllocaNo]->getName() + "." + Twine(Version++),
BB->begin());
++NumPHIInsert;
PhiToAllocaMap[PN] = AllocaNo;
- PN->reserveOperandSpace(getNumPreds(BB));
if (AST && PN->getType()->isPointerTy())
AST->copyValue(PointerAllocaValues[AllocaNo], PN);
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.
-//
+/// \brief 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.
void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
RenamePassData::ValVector &IncomingVals,
std::vector<RenamePassData> &Worklist) {
// 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 (succ_iterator I = succ_begin(Pred), E = succ_end(Pred); I != E; ++I)
- if (*I == BB)
- ++NumEdges;
+
+ unsigned NumEdges = std::count(succ_begin(Pred), succ_end(Pred), BB);
assert(NumEdges && "Must be at least one edge from Pred to BB!");
-
+
// Add entries for all the phis.
BasicBlock::iterator PNI = BB->begin();
do {
unsigned AllocaNo = PhiToAllocaMap[APN];
-
+
// Add N incoming values to the PHI node.
for (unsigned i = 0; i != NumEdges; ++i)
APN->addIncoming(IncomingVals[AllocaNo], Pred);
-
+
// The currently active variable for this block is now the PHI.
IncomingVals[AllocaNo] = APN;
-
+
// Get the next phi node.
++PNI;
APN = dyn_cast<PHINode>(PNI);
- if (APN == 0) break;
-
+ if (APN == 0)
+ break;
+
// 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);
}
}
-
+
// Don't revisit blocks.
- if (!Visited.insert(BB)) return;
+ if (!Visited.insert(BB))
+ return;
- for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
+ for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II);) {
Instruction *I = II++; // get the instruction, increment iterator
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand());
- if (!Src) continue;
-
- std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
- if (AI == AllocaLookup.end()) continue;
+ if (!Src)
+ continue;
+
+ DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src);
+ if (AI == AllocaLookup.end())
+ continue;
Value *V = IncomingVals[AI->second];
// Delete this instruction and mark the name as the current holder of the
// value
AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand());
- if (!Dest) continue;
-
- std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
+ if (!Dest)
+ continue;
+
+ DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
if (ai == AllocaLookup.end())
continue;
-
+
// what value were we writing?
IncomingVals[ai->second] = SI->getOperand(0);
// Record debuginfo for the store before removing it.
if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second])
- ConvertDebugDeclareToDebugValue(DDI, SI);
+ ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
BB->getInstList().erase(SI);
}
}
// 'Recurse' to our successors.
succ_iterator I = succ_begin(BB), E = succ_end(BB);
- if (I == E) return;
+ if (I == E)
+ return;
// Keep track of the successors so we don't visit the same successor twice
- SmallPtrSet<BasicBlock*, 8> VisitedSuccs;
+ SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
// Handle the first successor without using the worklist.
VisitedSuccs.insert(*I);
goto NextIteration;
}
-/// PromoteMemToReg - Promote the specified list of alloca instructions into
-/// scalar registers, inserting PHI nodes as appropriate. This function makes
-/// use of DominanceFrontier information. This function does not modify the CFG
-/// of the function at all. All allocas must be from the same function.
-///
-/// If AST is specified, the specified tracker is updated to reflect changes
-/// made to the IR.
-///
-void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
- DominatorTree &DT, DominanceFrontier &DF,
+void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
AliasSetTracker *AST) {
// If there is nothing to do, bail out...
- if (Allocas.empty()) return;
+ if (Allocas.empty())
+ return;
- PromoteMem2Reg(Allocas, DT, DF, AST).run();
+ PromoteMem2Reg(Allocas, DT, AST).run();
}
projects / oota-llvm.git / blobdiff