#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
+#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumFastStores, "Number of stores deleted");
namespace {
struct DSE : public FunctionPass {
- TargetData *TD;
+ AliasAnalysis *AA;
+ MemoryDependenceAnalysis *MD;
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass(ID) {
+ DSE() : FunctionPass(ID), AA(0), MD(0) {
initializeDSEPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F) {
- bool Changed = false;
-
+ AA = &getAnalysis<AliasAnalysis>();
+ MD = &getAnalysis<MemoryDependenceAnalysis>();
DominatorTree &DT = getAnalysis<DominatorTree>();
+ bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
// Only check non-dead blocks. Dead blocks may have strange pointer
// cycles that will confuse alias analysis.
if (DT.isReachableFromEntry(I))
Changed |= runOnBasicBlock(*I);
+
+ AA = 0; MD = 0;
return Changed;
}
bool runOnBasicBlock(BasicBlock &BB);
bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
- bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
- BasicBlock::iterator &BBI,
- SmallPtrSet<Value*, 64> &deadPointers);
- void DeleteDeadInstruction(Instruction *I,
- SmallPtrSet<Value*, 64> *deadPointers = 0);
+ void RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
+ SmallPtrSet<Value*, 16> &DeadStackObjects);
// getAnalysisUsage - We require post dominance frontiers (aka Control
AU.addRequired<DominatorTree>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<MemoryDependenceAnalysis>();
+ AU.addPreserved<AliasAnalysis>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<MemoryDependenceAnalysis>();
}
-
- uint64_t getPointerSize(Value *V) const;
};
}
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
+//===----------------------------------------------------------------------===//
+// Helper functions
+//===----------------------------------------------------------------------===//
+
+/// DeleteDeadInstruction - Delete this instruction. Before we do, go through
+/// and zero out all the operands of this instruction. If any of them become
+/// dead, delete them and the computation tree that feeds them.
+///
+/// If ValueSet is non-null, remove any deleted instructions from it as well.
+///
+static void DeleteDeadInstruction(Instruction *I,
+ MemoryDependenceAnalysis &MD,
+ SmallPtrSet<Value*, 16> *ValueSet = 0) {
+ SmallVector<Instruction*, 32> NowDeadInsts;
+
+ NowDeadInsts.push_back(I);
+ --NumFastOther;
+
+ // Before we touch this instruction, remove it from memdep!
+ do {
+ Instruction *DeadInst = NowDeadInsts.pop_back_val();
+ ++NumFastOther;
+
+ // This instruction is dead, zap it, in stages. Start by removing it from
+ // MemDep, which needs to know the operands and needs it to be in the
+ // function.
+ MD.removeInstruction(DeadInst);
+
+ for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
+ Value *Op = DeadInst->getOperand(op);
+ DeadInst->setOperand(op, 0);
+
+ // If this operand just became dead, add it to the NowDeadInsts list.
+ if (!Op->use_empty()) continue;
+
+ if (Instruction *OpI = dyn_cast<Instruction>(Op))
+ if (isInstructionTriviallyDead(OpI))
+ NowDeadInsts.push_back(OpI);
+ }
+
+ DeadInst->eraseFromParent();
+
+ if (ValueSet) ValueSet->erase(DeadInst);
+ } while (!NowDeadInsts.empty());
+}
+
+
/// hasMemoryWrite - Does this instruction write some memory? This only returns
/// true for things that we can analyze with other helpers below.
static bool hasMemoryWrite(Instruction *I) {
}
}
+/// getLocForRead - Return the location read by the specified "hasMemoryWrite"
+/// instruction if any.
+static AliasAnalysis::Location
+getLocForRead(Instruction *Inst, AliasAnalysis &AA) {
+ assert(hasMemoryWrite(Inst) && "Unknown instruction case");
+
+ // The only instructions that both read and write are the mem transfer
+ // instructions (memcpy/memmove).
+ if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(Inst))
+ return AA.getLocationForSource(MTI);
+ return AliasAnalysis::Location();
+}
+
+
/// isRemovable - If the value of this instruction and the memory it writes to
/// is unused, may we delete this instruction?
static bool isRemovable(Instruction *I) {
- assert(hasMemoryWrite(I));
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
- return II->getIntrinsicID() != Intrinsic::lifetime_end;
+ // Don't remove volatile stores.
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return !SI->isVolatile();
- return true;
+
+ IntrinsicInst *II = cast<IntrinsicInst>(I);
+ switch (II->getIntrinsicID()) {
+ default: assert(0 && "doesn't pass 'hasMemoryWrite' predicate");
+ case Intrinsic::lifetime_end:
+ // Never remove dead lifetime_end's, e.g. because it is followed by a
+ // free.
+ return false;
+ case Intrinsic::init_trampoline:
+ // Always safe to remove init_trampoline.
+ return true;
+
+ case Intrinsic::memset:
+ case Intrinsic::memmove:
+ case Intrinsic::memcpy:
+ // Don't remove volatile memory intrinsics.
+ return !cast<MemIntrinsic>(II)->isVolatile();
+ }
}
-/// getPointerOperand - Return the pointer that is being written to.
-static Value *getPointerOperand(Instruction *I) {
- assert(hasMemoryWrite(I));
+/// getStoredPointerOperand - Return the pointer that is being written to.
+static Value *getStoredPointerOperand(Instruction *I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return SI->getPointerOperand();
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I))
- return MI->getArgOperand(0);
+ return MI->getDest();
IntrinsicInst *II = cast<IntrinsicInst>(I);
switch (II->getIntrinsicID()) {
default: assert(false && "Unexpected intrinsic!");
case Intrinsic::init_trampoline:
return II->getArgOperand(0);
- case Intrinsic::lifetime_end:
- return II->getArgOperand(1);
}
}
+static uint64_t getPointerSize(Value *V, AliasAnalysis &AA) {
+ const TargetData *TD = AA.getTargetData();
+ if (TD == 0)
+ return AliasAnalysis::UnknownSize;
+
+ if (AllocaInst *A = dyn_cast<AllocaInst>(V)) {
+ // Get size information for the alloca
+ if (ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
+ return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
+ return AliasAnalysis::UnknownSize;
+ }
+
+ assert(isa<Argument>(V) && "Expected AllocaInst or Argument!");
+ const PointerType *PT = cast<PointerType>(V->getType());
+ return TD->getTypeAllocSize(PT->getElementType());
+}
+
+/// isObjectPointerWithTrustworthySize - Return true if the specified Value* is
+/// pointing to an object with a pointer size we can trust.
+static bool isObjectPointerWithTrustworthySize(const Value *V) {
+ if (const AllocaInst *AI = dyn_cast<AllocaInst>(V))
+ return !AI->isArrayAllocation();
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
+ return !GV->mayBeOverridden();
+ if (const Argument *A = dyn_cast<Argument>(V))
+ return A->hasByValAttr();
+ return false;
+}
+
/// isCompleteOverwrite - Return true if a store to the 'Later' location
/// completely overwrites a store to the 'Earlier' location.
static bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
- AliasAnalysis &AA, const TargetData *TD) {
- const Value *P1 = Later.Ptr->stripPointerCasts();
- const Value *P2 = Earlier.Ptr->stripPointerCasts();
+ AliasAnalysis &AA) {
+ const Value *P1 = Earlier.Ptr->stripPointerCasts();
+ const Value *P2 = Later.Ptr->stripPointerCasts();
- // Make sure that the start pointers are the same.
- if (P1 != P2)
+ // If the start pointers are the same, we just have to compare sizes to see if
+ // the later store was larger than the earlier store.
+ if (P1 == P2) {
+ // If we don't know the sizes of either access, then we can't do a
+ // comparison.
+ if (Later.Size == AliasAnalysis::UnknownSize ||
+ Earlier.Size == AliasAnalysis::UnknownSize) {
+ // If we have no TargetData information around, then the size of the store
+ // is inferrable from the pointee type. If they are the same type, then
+ // we know that the store is safe.
+ if (AA.getTargetData() == 0)
+ return Later.Ptr->getType() == Earlier.Ptr->getType();
+ return false;
+ }
+
+ // Make sure that the Later size is >= the Earlier size.
+ if (Later.Size < Earlier.Size)
+ return false;
+ return true;
+ }
+
+ // Otherwise, we have to have size information, and the later store has to be
+ // larger than the earlier one.
+ if (Later.Size == AliasAnalysis::UnknownSize ||
+ Earlier.Size == AliasAnalysis::UnknownSize ||
+ Later.Size <= Earlier.Size || AA.getTargetData() == 0)
+ return false;
+
+ // Check to see if the later store is to the entire object (either a global,
+ // an alloca, or a byval argument). If so, then it clearly overwrites any
+ // other store to the same object.
+ const TargetData &TD = *AA.getTargetData();
+
+ const Value *UO1 = GetUnderlyingObject(P1), *UO2 = GetUnderlyingObject(P2);
+
+ // If we can't resolve the same pointers to the same object, then we can't
+ // analyze them at all.
+ if (UO1 != UO2)
+ return false;
+
+ // If the "Later" store is to a recognizable object, get its size.
+ if (isObjectPointerWithTrustworthySize(UO2)) {
+ uint64_t ObjectSize =
+ TD.getTypeAllocSize(cast<PointerType>(UO2->getType())->getElementType());
+ if (ObjectSize == Later.Size)
+ return true;
+ }
+
+ // Okay, we have stores to two completely different pointers. Try to
+ // decompose the pointer into a "base + constant_offset" form. If the base
+ // pointers are equal, then we can reason about the two stores.
+ int64_t Off1 = 0, Off2 = 0;
+ const Value *BP1 = GetPointerBaseWithConstantOffset(P1, Off1, TD);
+ const Value *BP2 = GetPointerBaseWithConstantOffset(P2, Off2, TD);
+
+ // If the base pointers still differ, we have two completely different stores.
+ if (BP1 != BP2)
+ return false;
+
+ // Otherwise, we might have a situation like:
+ // store i16 -> P + 1 Byte
+ // store i32 -> P
+ // In this case, we see if the later store completely overlaps all bytes
+ // stored by the previous store.
+ if (Off1 < Off2 || // Earlier starts before Later.
+ Off1+Earlier.Size > Off2+Later.Size) // Earlier goes beyond Later.
return false;
+ // Otherwise, we have complete overlap.
+ return true;
+}
- // If we have no TargetData information around, then the size of the store is
- // inferrable from the pointee type. If they are the same type, then we know
- // that the store is safe.
- if (TD == 0)
- return Later.Ptr->getType() == Earlier.Ptr->getType();
+/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
+/// memory region into an identical pointer) then it doesn't actually make its
+/// input dead in the traditional sense. Consider this case:
+///
+/// memcpy(A <- B)
+/// memcpy(A <- A)
+///
+/// In this case, the second store to A does not make the first store to A dead.
+/// The usual situation isn't an explicit A<-A store like this (which can be
+/// trivially removed) but a case where two pointers may alias.
+///
+/// This function detects when it is unsafe to remove a dependent instruction
+/// because the DSE inducing instruction may be a self-read.
+static bool isPossibleSelfRead(Instruction *Inst,
+ const AliasAnalysis::Location &InstStoreLoc,
+ Instruction *DepWrite, AliasAnalysis &AA) {
+ // Self reads can only happen for instructions that read memory. Get the
+ // location read.
+ AliasAnalysis::Location InstReadLoc = getLocForRead(Inst, AA);
+ if (InstReadLoc.Ptr == 0) return false; // Not a reading instruction.
+
+ // If the read and written loc obviously don't alias, it isn't a read.
+ if (AA.isNoAlias(InstReadLoc, InstStoreLoc)) return false;
+ // Okay, 'Inst' may copy over itself. However, we can still remove a the
+ // DepWrite instruction if we can prove that it reads from the same location
+ // as Inst. This handles useful cases like:
+ // memcpy(A <- B)
+ // memcpy(A <- B)
+ // Here we don't know if A/B may alias, but we do know that B/B are must
+ // aliases, so removing the first memcpy is safe (assuming it writes <= #
+ // bytes as the second one.
+ AliasAnalysis::Location DepReadLoc = getLocForRead(DepWrite, AA);
- // Make sure that the Later size is >= the Earlier size.
- if (Later.Size < Earlier.Size)
+ if (DepReadLoc.Ptr && AA.isMustAlias(InstReadLoc.Ptr, DepReadLoc.Ptr))
return false;
+ // If DepWrite doesn't read memory or if we can't prove it is a must alias,
+ // then it can't be considered dead.
return true;
}
-bool DSE::runOnBasicBlock(BasicBlock &BB) {
- MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- TD = getAnalysisIfAvailable<TargetData>();
+//===----------------------------------------------------------------------===//
+// DSE Pass
+//===----------------------------------------------------------------------===//
+
+bool DSE::runOnBasicBlock(BasicBlock &BB) {
bool MadeChange = false;
// Do a top-down walk on the BB.
if (!hasMemoryWrite(Inst))
continue;
- MemDepResult InstDep = MD.getDependency(Inst);
+ MemDepResult InstDep = MD->getDependency(Inst);
// Ignore non-local store liveness.
// FIXME: cross-block DSE would be fun. :)
if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
SI->getOperand(0) == DepLoad && !SI->isVolatile()) {
+ DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n "
+ << "LOAD: " << *DepLoad << "\n STORE: " << *SI << '\n');
+
// DeleteDeadInstruction can delete the current instruction. Save BBI
// in case we need it.
WeakVH NextInst(BBI);
- DeleteDeadInstruction(SI);
+ DeleteDeadInstruction(SI, *MD);
if (NextInst == 0) // Next instruction deleted.
BBI = BB.begin();
}
// Figure out what location is being stored to.
- AliasAnalysis::Location Loc = getLocForWrite(Inst, AA);
+ AliasAnalysis::Location Loc = getLocForWrite(Inst, *AA);
// If we didn't get a useful location, fail.
if (Loc.Ptr == 0)
//
// Find out what memory location the dependant instruction stores.
Instruction *DepWrite = InstDep.getInst();
- AliasAnalysis::Location DepLoc = getLocForWrite(DepWrite, AA);
+ AliasAnalysis::Location DepLoc = getLocForWrite(DepWrite, *AA);
// If we didn't get a useful location, or if it isn't a size, bail out.
if (DepLoc.Ptr == 0)
break;
- // If we find a removable write that is completely obliterated by the
- // store to 'Loc' then we can remove it.
- if (isRemovable(DepWrite) && isCompleteOverwrite(Loc, DepLoc, AA, TD)) {
+ // If we find a write that is a) removable (i.e., non-volatile), b) is
+ // completely obliterated by the store to 'Loc', and c) which we know that
+ // 'Inst' doesn't load from, then we can remove it.
+ if (isRemovable(DepWrite) && isCompleteOverwrite(Loc, DepLoc, *AA) &&
+ !isPossibleSelfRead(Inst, Loc, DepWrite, *AA)) {
+ DEBUG(dbgs() << "DSE: Remove Dead Store:\n DEAD: "
+ << *DepWrite << "\n KILLER: " << *Inst << '\n');
+
// Delete the store and now-dead instructions that feed it.
- DeleteDeadInstruction(DepWrite);
+ DeleteDeadInstruction(DepWrite, *MD);
++NumFastStores;
MadeChange = true;
if (DepWrite == &BB.front()) break;
// Can't look past this instruction if it might read 'Loc'.
- if (AA.getModRefInfo(DepWrite, Loc) & AliasAnalysis::Ref)
+ if (AA->getModRefInfo(DepWrite, Loc) & AliasAnalysis::Ref)
break;
- InstDep = MD.getPointerDependencyFrom(Loc, false, DepWrite, &BB);
+ InstDep = MD->getPointerDependencyFrom(Loc, false, DepWrite, &BB);
}
}
/// HandleFree - Handle frees of entire structures whose dependency is a store
/// to a field of that structure.
bool DSE::HandleFree(CallInst *F) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
-
- MemDepResult Dep = MD.getDependency(F);
+ MemDepResult Dep = MD->getDependency(F);
do {
if (Dep.isNonLocal()) return false;
if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
return false;
- Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
+ Value *DepPointer =
+ GetUnderlyingObject(getStoredPointerOperand(Dependency));
// Check for aliasing.
- if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
- AliasAnalysis::MustAlias)
+ if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
return false;
// DCE instructions only used to calculate that store
- DeleteDeadInstruction(Dependency);
+ DeleteDeadInstruction(Dependency, *MD);
++NumFastStores;
// Inst's old Dependency is now deleted. Compute the next dependency,
// s[0] = 0;
// s[1] = 0; // This has just been deleted.
// free(s);
- Dep = MD.getDependency(F);
+ Dep = MD->getDependency(F);
} while (!Dep.isNonLocal());
return true;
/// store i32 1, i32* %A
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
bool MadeChange = false;
- // Pointers alloca'd in this function are dead in the end block
- SmallPtrSet<Value*, 64> deadPointers;
+ // Keep track of all of the stack objects that are dead at the end of the
+ // function.
+ SmallPtrSet<Value*, 16> DeadStackObjects;
// Find all of the alloca'd pointers in the entry block.
BasicBlock *Entry = BB.getParent()->begin();
for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
- deadPointers.insert(AI);
+ DeadStackObjects.insert(AI);
// Treat byval arguments the same, stores to them are dead at the end of the
// function.
for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
AE = BB.getParent()->arg_end(); AI != AE; ++AI)
if (AI->hasByValAttr())
- deadPointers.insert(AI);
+ DeadStackObjects.insert(AI);
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
- // If we find a store whose pointer is dead.
- if (hasMemoryWrite(BBI)) {
- if (isRemovable(BBI)) {
- // See through pointer-to-pointer bitcasts
- Value *pointerOperand = getPointerOperand(BBI)->getUnderlyingObject();
-
- // Alloca'd pointers or byval arguments (which are functionally like
- // alloca's) are valid candidates for removal.
- if (deadPointers.count(pointerOperand)) {
- // DCE instructions only used to calculate that store.
- Instruction *Dead = BBI;
- ++BBI;
- DeleteDeadInstruction(Dead, &deadPointers);
- ++NumFastStores;
- MadeChange = true;
- continue;
- }
- }
-
- // Because a memcpy or memmove is also a load, we can't skip it if we
- // didn't remove it.
- if (!isa<MemTransferInst>(BBI))
+ // If we find a store, check to see if it points into a dead stack value.
+ if (hasMemoryWrite(BBI) && isRemovable(BBI)) {
+ // See through pointer-to-pointer bitcasts
+ Value *Pointer = GetUnderlyingObject(getStoredPointerOperand(BBI));
+
+ // Stores to stack values are valid candidates for removal.
+ if (DeadStackObjects.count(Pointer)) {
+ Instruction *Dead = BBI++;
+
+ DEBUG(dbgs() << "DSE: Dead Store at End of Block:\n DEAD: "
+ << *Dead << "\n Object: " << *Pointer << '\n');
+
+ // DCE instructions only used to calculate that store.
+ DeleteDeadInstruction(Dead, *MD, &DeadStackObjects);
+ ++NumFastStores;
+ MadeChange = true;
continue;
+ }
}
- Value *killPointer = 0;
- uint64_t killPointerSize = AliasAnalysis::UnknownSize;
+ // Remove any dead non-memory-mutating instructions.
+ if (isInstructionTriviallyDead(BBI)) {
+ Instruction *Inst = BBI++;
+ DeleteDeadInstruction(Inst, *MD, &DeadStackObjects);
+ ++NumFastOther;
+ MadeChange = true;
+ continue;
+ }
- // If we encounter a use of the pointer, it is no longer considered dead
- if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
- // However, if this load is unused and not volatile, we can go ahead and
- // remove it, and not have to worry about it making our pointer undead!
- if (L->use_empty() && !L->isVolatile()) {
- ++BBI;
- DeleteDeadInstruction(L, &deadPointers);
- ++NumFastOther;
- MadeChange = true;
- continue;
- }
-
- killPointer = L->getPointerOperand();
- } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
- killPointer = V->getOperand(0);
- } else if (isa<MemTransferInst>(BBI) &&
- isa<ConstantInt>(cast<MemTransferInst>(BBI)->getLength())) {
- killPointer = cast<MemTransferInst>(BBI)->getSource();
- killPointerSize = cast<ConstantInt>(
- cast<MemTransferInst>(BBI)->getLength())->getZExtValue();
- } else if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
- deadPointers.erase(A);
-
- // Dead alloca's can be DCE'd when we reach them
- if (A->use_empty()) {
- ++BBI;
- DeleteDeadInstruction(A, &deadPointers);
- ++NumFastOther;
- MadeChange = true;
- }
-
+ if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
+ DeadStackObjects.erase(A);
continue;
- } else if (CallSite CS = cast<Value>(BBI)) {
- // If this call does not access memory, it can't
- // be undeadifying any of our pointers.
- if (AA.doesNotAccessMemory(CS))
+ }
+
+ if (CallSite CS = cast<Value>(BBI)) {
+ // If this call does not access memory, it can't be loading any of our
+ // pointers.
+ if (AA->doesNotAccessMemory(CS))
continue;
- unsigned modRef = 0;
- unsigned other = 0;
+ unsigned NumModRef = 0, NumOther = 0;
- // Remove any pointers made undead by the call from the dead set
- std::vector<Value*> dead;
- for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // HACK: if we detect that our AA is imprecise, it's not
- // worth it to scan the rest of the deadPointers set. Just
- // assume that the AA will return ModRef for everything, and
- // go ahead and bail.
- if (modRef >= 16 && other == 0) {
- deadPointers.clear();
+ // If the call might load from any of our allocas, then any store above
+ // the call is live.
+ SmallVector<Value*, 8> LiveAllocas;
+ for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
+ E = DeadStackObjects.end(); I != E; ++I) {
+ // If we detect that our AA is imprecise, it's not worth it to scan the
+ // rest of the DeadPointers set. Just assume that the AA will return
+ // ModRef for everything, and go ahead and bail out.
+ if (NumModRef >= 16 && NumOther == 0)
return MadeChange;
- }
-
- // See if the call site touches it
- AliasAnalysis::ModRefResult A = AA.getModRefInfo(CS, *I,
- getPointerSize(*I));
+
+ // See if the call site touches it.
+ AliasAnalysis::ModRefResult A =
+ AA->getModRefInfo(CS, *I, getPointerSize(*I, *AA));
if (A == AliasAnalysis::ModRef)
- ++modRef;
+ ++NumModRef;
else
- ++other;
+ ++NumOther;
if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
- dead.push_back(*I);
+ LiveAllocas.push_back(*I);
}
-
- for (std::vector<Value*>::iterator I = dead.begin(), E = dead.end();
- I != E; ++I)
- deadPointers.erase(*I);
- continue;
- } else if (isInstructionTriviallyDead(BBI)) {
- // For any non-memory-affecting non-terminators, DCE them as we reach them
- Instruction *Inst = BBI;
- ++BBI;
- DeleteDeadInstruction(Inst, &deadPointers);
- ++NumFastOther;
- MadeChange = true;
+ for (SmallVector<Value*, 8>::iterator I = LiveAllocas.begin(),
+ E = LiveAllocas.end(); I != E; ++I)
+ DeadStackObjects.erase(*I);
+
+ // If all of the allocas were clobbered by the call then we're not going
+ // to find anything else to process.
+ if (DeadStackObjects.empty())
+ return MadeChange;
+
continue;
}
- if (!killPointer)
+ AliasAnalysis::Location LoadedLoc;
+
+ // If we encounter a use of the pointer, it is no longer considered dead
+ if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
+ LoadedLoc = AA->getLocation(L);
+ } else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
+ LoadedLoc = AA->getLocation(V);
+ } else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
+ LoadedLoc = AA->getLocationForSource(MTI);
+ } else {
+ // Not a loading instruction.
continue;
+ }
- killPointer = killPointer->getUnderlyingObject();
+ // Remove any allocas from the DeadPointer set that are loaded, as this
+ // makes any stores above the access live.
+ RemoveAccessedObjects(LoadedLoc, DeadStackObjects);
- // Deal with undead pointers
- MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
- deadPointers);
+ // If all of the allocas were clobbered by the access then we're not going
+ // to find anything else to process.
+ if (DeadStackObjects.empty())
+ break;
}
return MadeChange;
}
-/// RemoveUndeadPointers - check for uses of a pointer that make it
-/// undead when scanning for dead stores to alloca's.
-bool DSE::RemoveUndeadPointers(Value *killPointer, uint64_t killPointerSize,
- BasicBlock::iterator &BBI,
- SmallPtrSet<Value*, 64> &deadPointers) {
- AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-
- // If the kill pointer can be easily reduced to an alloca,
- // don't bother doing extraneous AA queries.
- if (deadPointers.count(killPointer)) {
- deadPointers.erase(killPointer);
- return false;
- }
-
- // A global can't be in the dead pointer set.
- if (isa<GlobalValue>(killPointer))
- return false;
-
- bool MadeChange = false;
+/// RemoveAccessedObjects - Check to see if the specified location may alias any
+/// of the stack objects in the DeadStackObjects set. If so, they become live
+/// because the location is being loaded.
+void DSE::RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
+ SmallPtrSet<Value*, 16> &DeadStackObjects) {
+ const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr);
+
+ // A constant can't be in the dead pointer set.
+ if (isa<Constant>(UnderlyingPointer))
+ return;
- SmallVector<Value*, 16> undead;
+ // If the kill pointer can be easily reduced to an alloca, don't bother doing
+ // extraneous AA queries.
+ if (isa<AllocaInst>(UnderlyingPointer) || isa<Argument>(UnderlyingPointer)) {
+ DeadStackObjects.erase(const_cast<Value*>(UnderlyingPointer));
+ return;
+ }
- for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
- E = deadPointers.end(); I != E; ++I) {
- // See if this pointer could alias it
- AliasAnalysis::AliasResult A = AA.alias(*I, getPointerSize(*I),
- killPointer, killPointerSize);
-
- // If it must-alias and a store, we can delete it
- if (isa<StoreInst>(BBI) && A == AliasAnalysis::MustAlias) {
- StoreInst *S = cast<StoreInst>(BBI);
-
- // Remove it!
- ++BBI;
- DeleteDeadInstruction(S, &deadPointers);
- ++NumFastStores;
- MadeChange = true;
-
- continue;
-
- // Otherwise, it is undead
- } else if (A != AliasAnalysis::NoAlias)
- undead.push_back(*I);
+ SmallVector<Value*, 16> NowLive;
+ for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
+ E = DeadStackObjects.end(); I != E; ++I) {
+ // See if the loaded location could alias the stack location.
+ AliasAnalysis::Location StackLoc(*I, getPointerSize(*I, *AA));
+ if (!AA->isNoAlias(StackLoc, LoadedLoc))
+ NowLive.push_back(*I);
}
- for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
+ for (SmallVector<Value*, 16>::iterator I = NowLive.begin(), E = NowLive.end();
I != E; ++I)
- deadPointers.erase(*I);
-
- return MadeChange;
+ DeadStackObjects.erase(*I);
}
-/// DeleteDeadInstruction - Delete this instruction. Before we do, go through
-/// and zero out all the operands of this instruction. If any of them become
-/// dead, delete them and the computation tree that feeds them.
-///
-/// If ValueSet is non-null, remove any deleted instructions from it as well.
-///
-void DSE::DeleteDeadInstruction(Instruction *I,
- SmallPtrSet<Value*, 64> *ValueSet) {
- SmallVector<Instruction*, 32> NowDeadInsts;
-
- NowDeadInsts.push_back(I);
- --NumFastOther;
-
- // Before we touch this instruction, remove it from memdep!
- MemoryDependenceAnalysis &MDA = getAnalysis<MemoryDependenceAnalysis>();
- do {
- Instruction *DeadInst = NowDeadInsts.pop_back_val();
-
- ++NumFastOther;
-
- // This instruction is dead, zap it, in stages. Start by removing it from
- // MemDep, which needs to know the operands and needs it to be in the
- // function.
- MDA.removeInstruction(DeadInst);
-
- for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
- Value *Op = DeadInst->getOperand(op);
- DeadInst->setOperand(op, 0);
-
- // If this operand just became dead, add it to the NowDeadInsts list.
- if (!Op->use_empty()) continue;
-
- if (Instruction *OpI = dyn_cast<Instruction>(Op))
- if (isInstructionTriviallyDead(OpI))
- NowDeadInsts.push_back(OpI);
- }
-
- DeadInst->eraseFromParent();
-
- if (ValueSet) ValueSet->erase(DeadInst);
- } while (!NowDeadInsts.empty());
-}
-
-uint64_t DSE::getPointerSize(Value *V) const {
- if (TD) {
- if (AllocaInst *A = dyn_cast<AllocaInst>(V)) {
- // Get size information for the alloca
- if (ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
- return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
- } else {
- assert(isa<Argument>(V) && "Expected AllocaInst or Argument!");
- const PointerType *PT = cast<PointerType>(V->getType());
- return TD->getTypeAllocSize(PT->getElementType());
- }
- }
- return AliasAnalysis::UnknownSize;
-}
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