#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/CaptureTracking.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"
+#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumFastStores, "Number of stores deleted");
struct DSE : public FunctionPass {
AliasAnalysis *AA;
MemoryDependenceAnalysis *MD;
+ DominatorTree *DT;
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass(ID), AA(0), MD(0) {
+ DSE() : FunctionPass(ID), AA(0), MD(0), DT(0) {
initializeDSEPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F) {
AA = &getAnalysis<AliasAnalysis>();
MD = &getAnalysis<MemoryDependenceAnalysis>();
- DominatorTree &DT = getAnalysis<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))
+ if (DT->isReachableFromEntry(I))
Changed |= runOnBasicBlock(*I);
-
- AA = 0; MD = 0;
+
+ AA = 0; MD = 0; DT = 0;
return Changed;
}
-
+
bool runOnBasicBlock(BasicBlock &BB);
bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
void RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
SmallPtrSet<Value*, 16> &DeadStackObjects);
-
- // getAnalysisUsage - We require post dominance frontiers (aka Control
- // Dependence Graph)
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<DominatorTree>();
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());
}
}
/// getLocForWrite - Return a Location stored to by the specified instruction.
+/// If isRemovable returns true, this function and getLocForRead completely
+/// describe the memory operations for this instruction.
static AliasAnalysis::Location
getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
return AA.getLocation(SI);
-
+
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(Inst)) {
// memcpy/memmove/memset.
AliasAnalysis::Location Loc = AA.getLocationForDest(MI);
return AliasAnalysis::Location();
return Loc;
}
-
+
IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst);
if (II == 0) return AliasAnalysis::Location();
-
+
switch (II->getIntrinsicID()) {
default: return AliasAnalysis::Location(); // Unhandled intrinsic.
case Intrinsic::init_trampoline:
// that we should use the size of the pointee type. This isn't valid for
// init.trampoline, which writes more than an i8.
if (AA.getTargetData() == 0) return AliasAnalysis::Location();
-
+
// FIXME: We don't know the size of the trampoline, so we can't really
// handle it here.
return AliasAnalysis::Location(II->getArgOperand(0));
}
}
+/// 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) {
- // Don't remove volatile stores.
+ // Don't remove volatile/atomic stores.
if (StoreInst *SI = dyn_cast<StoreInst>(I))
- return !SI->isVolatile();
-
+ return SI->isUnordered();
+
IntrinsicInst *II = cast<IntrinsicInst>(I);
switch (II->getIntrinsicID()) {
default: assert(0 && "doesn't pass 'hasMemoryWrite' predicate");
case Intrinsic::init_trampoline:
// Always safe to remove init_trampoline.
return true;
-
+
case Intrinsic::memset:
case Intrinsic::memmove:
case Intrinsic::memcpy:
}
}
+
+/// isShortenable - Returns true if this instruction can be safely shortened in
+/// length.
+static bool isShortenable(Instruction *I) {
+ // Don't shorten stores for now
+ if (isa<StoreInst>(I))
+ return false;
+
+ IntrinsicInst *II = cast<IntrinsicInst>(I);
+ switch (II->getIntrinsicID()) {
+ default: return false;
+ case Intrinsic::memset:
+ case Intrinsic::memcpy:
+ // Do shorten memory intrinsics.
+ return true;
+ }
+}
+
/// getStoredPointerOperand - Return the pointer that is being written to.
static Value *getStoredPointerOperand(Instruction *I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
static uint64_t getPointerSize(Value *V, AliasAnalysis &AA) {
const TargetData *TD = AA.getTargetData();
+
+ if (CallInst *CI = dyn_cast<CallInst>(V)) {
+ assert(isMalloc(CI) && "Expected Malloc call!");
+ if (ConstantInt *C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
+ return C->getZExtValue();
+ return AliasAnalysis::UnknownSize;
+ }
+
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());
+
+ assert(isa<Argument>(V) && "Expected AllocaInst, malloc call or Argument!");
+ 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();
+ if (isMalloc(V))
+ return true;
+ return false;
+}
+
+namespace {
+ enum OverwriteResult
+ {
+ OverwriteComplete,
+ OverwriteEnd,
+ OverwriteUnknown
+ };
+}
-/// isCompleteOverwrite - Return true if a store to the 'Later' location
+/// isOverwrite - Return 'OverwriteComplete' 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) {
+/// 'OverwriteEnd' if the end of the 'Earlier' location is completely
+/// overwritten by 'Later', or 'OverwriteUnknown' if nothing can be determined
+static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
+ const AliasAnalysis::Location &Earlier,
+ AliasAnalysis &AA,
+ int64_t& EarlierOff,
+ int64_t& LaterOff) {
const Value *P1 = Earlier.Ptr->stripPointerCasts();
const Value *P2 = Later.Ptr->stripPointerCasts();
-
+
// 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 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;
+ if (AA.getTargetData() == 0 &&
+ Later.Ptr->getType() == Earlier.Ptr->getType())
+ return OverwriteComplete;
+
+ return OverwriteUnknown;
}
-
+
// Make sure that the Later size is >= the Earlier size.
- if (Later.Size < Earlier.Size)
- return false;
- return true;
+ if (Later.Size >= Earlier.Size)
+ return OverwriteComplete;
}
-
+
// 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;
-
+ return OverwriteUnknown;
+
+ // 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, &TD),
+ *UO2 = GetUnderlyingObject(P2, &TD);
+
+ // If we can't resolve the same pointers to the same object, then we can't
+ // analyze them at all.
+ if (UO1 != UO2)
+ return OverwriteUnknown;
+
+ // 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 OverwriteComplete;
+ }
+
// 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);
-
+ EarlierOff = 0;
+ LaterOff = 0;
+ const Value *BP1 = GetPointerBaseWithConstantOffset(P1, EarlierOff, TD);
+ const Value *BP2 = GetPointerBaseWithConstantOffset(P2, LaterOff, TD);
+
// If the base pointers still differ, we have two completely different stores.
if (BP1 != BP2)
- return false;
+ return OverwriteUnknown;
+
+ // The later store completely overlaps the earlier store if:
+ //
+ // 1. Both start at the same offset and the later one's size is greater than
+ // or equal to the earlier one's, or
+ //
+ // |--earlier--|
+ // |-- later --|
+ //
+ // 2. The earlier store has an offset greater than the later offset, but which
+ // still lies completely within the later store.
+ //
+ // |--earlier--|
+ // |----- later ------|
+ //
+ // We have to be careful here as *Off is signed while *.Size is unsigned.
+ if (EarlierOff >= LaterOff &&
+ Later.Size > Earlier.Size &&
+ uint64_t(EarlierOff - LaterOff) + Earlier.Size <= Later.Size)
+ return OverwriteComplete;
- // 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.
+ // The other interesting case is if the later store overwrites the end of
+ // the earlier store
+ //
+ // |--earlier--|
+ // |-- later --|
+ //
+ // In this case we may want to trim the size of earlier to avoid generating
+ // writes to addresses which will definitely be overwritten later
+ if (LaterOff > EarlierOff &&
+ LaterOff < int64_t(EarlierOff + Earlier.Size) &&
+ LaterOff + Later.Size >= EarlierOff + Earlier.Size)
+ return OverwriteEnd;
+
+ // Otherwise, they don't completely overlap.
+ return OverwriteUnknown;
+}
+
+/// 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);
+
+ if (DepReadLoc.Ptr && AA.isMustAlias(InstReadLoc.Ptr, DepReadLoc.Ptr))
return false;
- // Otherwise, we have complete overlap.
+
+ // 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) {
bool MadeChange = false;
-
+
// Do a top-down walk on the BB.
for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
Instruction *Inst = BBI++;
-
+
// Handle 'free' calls specially.
if (CallInst *F = isFreeCall(Inst)) {
MadeChange |= HandleFree(F);
continue;
}
-
+
// If we find something that writes memory, get its memory dependence.
if (!hasMemoryWrite(Inst))
continue;
MemDepResult InstDep = MD->getDependency(Inst);
-
- // Ignore non-local store liveness.
+
+ // Ignore any store where we can't find a local dependence.
// FIXME: cross-block DSE would be fun. :)
- if (InstDep.isNonLocal() ||
- // Ignore self dependence, which happens in the entry block of the
- // function.
- InstDep.getInst() == Inst)
+ if (!InstDep.isDef() && !InstDep.isClobber())
continue;
-
+
// If we're storing the same value back to a pointer that we just
// loaded from, then the store can be removed.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
- SI->getOperand(0) == DepLoad && !SI->isVolatile()) {
+ SI->getOperand(0) == DepLoad && isRemovable(SI)) {
+ 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, *MD);
-
+
if (NextInst == 0) // Next instruction deleted.
BBI = BB.begin();
else if (BBI != BB.begin()) // Revisit this instruction if possible.
}
}
}
-
+
// Figure out what location is being stored to.
AliasAnalysis::Location Loc = getLocForWrite(Inst, *AA);
// If we didn't get a useful location, fail.
if (Loc.Ptr == 0)
continue;
-
- while (!InstDep.isNonLocal()) {
+
+ while (InstDep.isDef() || InstDep.isClobber()) {
// Get the memory clobbered by the instruction we depend on. MemDep will
// skip any instructions that 'Loc' clearly doesn't interact with. If we
// end up depending on a may- or must-aliased load, then we can't optimize
// away the store and we bail out. However, if we depend on on something
// that overwrites the memory location we *can* potentially optimize it.
//
- // Find out what memory location the dependant instruction stores.
+ // Find out what memory location the dependent instruction stores.
Instruction *DepWrite = InstDep.getInst();
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)) {
- // Delete the store and now-dead instructions that feed it.
- DeleteDeadInstruction(DepWrite, *MD);
- ++NumFastStores;
- MadeChange = true;
-
- // DeleteDeadInstruction can delete the current instruction in loop
- // cases, reset BBI.
- BBI = Inst;
- if (BBI != BB.begin())
- --BBI;
- break;
+ // 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) &&
+ !isPossibleSelfRead(Inst, Loc, DepWrite, *AA)) {
+ int64_t InstWriteOffset, DepWriteOffset;
+ OverwriteResult OR = isOverwrite(Loc, DepLoc, *AA,
+ DepWriteOffset, InstWriteOffset);
+ if (OR == OverwriteComplete) {
+ 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, *MD);
+ ++NumFastStores;
+ MadeChange = true;
+
+ // DeleteDeadInstruction can delete the current instruction in loop
+ // cases, reset BBI.
+ BBI = Inst;
+ if (BBI != BB.begin())
+ --BBI;
+ break;
+ } else if (OR == OverwriteEnd && isShortenable(DepWrite)) {
+ // TODO: base this on the target vector size so that if the earlier
+ // store was too small to get vector writes anyway then its likely
+ // a good idea to shorten it
+ // Power of 2 vector writes are probably always a bad idea to optimize
+ // as any store/memset/memcpy is likely using vector instructions so
+ // shortening it to not vector size is likely to be slower
+ MemIntrinsic* DepIntrinsic = cast<MemIntrinsic>(DepWrite);
+ unsigned DepWriteAlign = DepIntrinsic->getAlignment();
+ if (llvm::isPowerOf2_64(InstWriteOffset) ||
+ ((DepWriteAlign != 0) && InstWriteOffset % DepWriteAlign == 0)) {
+
+ DEBUG(dbgs() << "DSE: Remove Dead Store:\n OW END: "
+ << *DepWrite << "\n KILLER (offset "
+ << InstWriteOffset << ", "
+ << DepLoc.Size << ")"
+ << *Inst << '\n');
+
+ Value* DepWriteLength = DepIntrinsic->getLength();
+ Value* TrimmedLength = ConstantInt::get(DepWriteLength->getType(),
+ InstWriteOffset -
+ DepWriteOffset);
+ DepIntrinsic->setLength(TrimmedLength);
+ MadeChange = true;
+ }
+ }
}
-
+
// If this is a may-aliased store that is clobbering the store value, we
// can keep searching past it for another must-aliased pointer that stores
// to the same location. For example, in:
// we can remove the first store to P even though we don't know if P and Q
// alias.
if (DepWrite == &BB.front()) break;
-
+
// Can't look past this instruction if it might read 'Loc'.
if (AA->getModRefInfo(DepWrite, Loc) & AliasAnalysis::Ref)
break;
-
+
InstDep = MD->getPointerDependencyFrom(Loc, false, DepWrite, &BB);
}
}
-
+
// If this block ends in a return, unwind, or unreachable, all allocas are
// dead at its end, which means stores to them are also dead.
if (BB.getTerminator()->getNumSuccessors() == 0)
MadeChange |= handleEndBlock(BB);
-
+
return MadeChange;
}
+/// Find all blocks that will unconditionally lead to the block BB and append
+/// them to F.
+static void FindUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
+ BasicBlock *BB, DominatorTree *DT) {
+ for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
+ BasicBlock *Pred = *I;
+ TerminatorInst *PredTI = Pred->getTerminator();
+ if (PredTI->getNumSuccessors() != 1)
+ continue;
+
+ if (DT->isReachableFromEntry(Pred))
+ Blocks.push_back(Pred);
+ }
+}
+
/// HandleFree - Handle frees of entire structures whose dependency is a store
/// to a field of that structure.
bool DSE::HandleFree(CallInst *F) {
- MemDepResult Dep = MD->getDependency(F);
- do {
- if (Dep.isNonLocal()) return false;
-
- Instruction *Dependency = Dep.getInst();
- if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
- return false;
-
- Value *DepPointer =
- getStoredPointerOperand(Dependency)->getUnderlyingObject();
+ bool MadeChange = false;
- // Check for aliasing.
- if (AA->alias(F->getArgOperand(0), 1, DepPointer, 1) !=
- AliasAnalysis::MustAlias)
- return false;
-
- // DCE instructions only used to calculate that store
- DeleteDeadInstruction(Dependency, *MD);
- ++NumFastStores;
-
- // Inst's old Dependency is now deleted. Compute the next dependency,
- // which may also be dead, as in
- // s[0] = 0;
- // s[1] = 0; // This has just been deleted.
- // free(s);
- Dep = MD->getDependency(F);
- } while (!Dep.isNonLocal());
-
- return true;
+ AliasAnalysis::Location Loc = AliasAnalysis::Location(F->getOperand(0));
+ SmallVector<BasicBlock *, 16> Blocks;
+ Blocks.push_back(F->getParent());
+
+ while (!Blocks.empty()) {
+ BasicBlock *BB = Blocks.pop_back_val();
+ Instruction *InstPt = BB->getTerminator();
+ if (BB == F->getParent()) InstPt = F;
+
+ MemDepResult Dep = MD->getPointerDependencyFrom(Loc, false, InstPt, BB);
+ while (Dep.isDef() || Dep.isClobber()) {
+ Instruction *Dependency = Dep.getInst();
+ if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
+ break;
+
+ Value *DepPointer =
+ GetUnderlyingObject(getStoredPointerOperand(Dependency));
+
+ // Check for aliasing.
+ if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
+ break;
+
+ Instruction *Next = llvm::next(BasicBlock::iterator(Dependency));
+
+ // DCE instructions only used to calculate that store
+ DeleteDeadInstruction(Dependency, *MD);
+ ++NumFastStores;
+ MadeChange = true;
+
+ // Inst's old Dependency is now deleted. Compute the next dependency,
+ // which may also be dead, as in
+ // s[0] = 0;
+ // s[1] = 0; // This has just been deleted.
+ // free(s);
+ Dep = MD->getPointerDependencyFrom(Loc, false, Next, BB);
+ }
+
+ if (Dep.isNonLocal())
+ FindUnconditionalPreds(Blocks, BB, DT);
+ }
+
+ return MadeChange;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
bool MadeChange = false;
-
+
// 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)
+ for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
DeadStackObjects.insert(AI);
-
+
+ // Okay, so these are dead heap objects, but if the pointer never escapes
+ // then it's leaked by this function anyways.
+ if (CallInst *CI = extractMallocCall(I))
+ if (!PointerMayBeCaptured(CI, true, true))
+ DeadStackObjects.insert(CI);
+ }
+
// 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())
DeadStackObjects.insert(AI);
-
+
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--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 = getStoredPointerOperand(BBI)->getUnderlyingObject();
+ Value *Pointer = GetUnderlyingObject(getStoredPointerOperand(BBI));
// Stores to stack values are valid candidates for removal.
if (DeadStackObjects.count(Pointer)) {
- // DCE instructions only used to calculate that store.
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;
}
}
-
+
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(BBI)) {
Instruction *Inst = BBI++;
MadeChange = true;
continue;
}
-
+
if (AllocaInst *A = dyn_cast<AllocaInst>(BBI)) {
DeadStackObjects.erase(A);
continue;
}
-
+
+ if (CallInst *CI = extractMallocCall(BBI)) {
+ DeadStackObjects.erase(CI);
+ continue;
+ }
+
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 NumModRef = 0, NumOther = 0;
-
+
// 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 =
+ AliasAnalysis::ModRefResult A =
AA->getModRefInfo(CS, *I, getPointerSize(*I, *AA));
-
- if (A == AliasAnalysis::ModRef)
- ++NumModRef;
- else
- ++NumOther;
-
+
if (A == AliasAnalysis::ModRef || A == AliasAnalysis::Ref)
LiveAllocas.push_back(*I);
}
-
+
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;
}
-
+
AliasAnalysis::Location LoadedLoc;
-
+
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
+ if (!L->isUnordered()) // Be conservative with atomic/volatile load
+ break;
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.
+ } else if (!BBI->mayReadFromMemory()) {
+ // Instruction doesn't read memory. Note that stores that weren't removed
+ // above will hit this case.
continue;
+ } else {
+ // Unknown inst; assume it clobbers everything.
+ break;
}
// Remove any allocas from the DeadPointer set that are loaded, as this
if (DeadStackObjects.empty())
break;
}
-
+
return MadeChange;
}
/// because the location is being loaded.
void DSE::RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
SmallPtrSet<Value*, 16> &DeadStackObjects) {
- const Value *UnderlyingPointer = LoadedLoc.Ptr->getUnderlyingObject();
+ const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr);
// A constant can't be in the dead pointer set.
if (isa<Constant>(UnderlyingPointer))
return;
-
+
// 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;
}
-
+
SmallVector<Value*, 16> NowLive;
for (SmallPtrSet<Value*, 16>::iterator I = DeadStackObjects.begin(),
E = DeadStackObjects.end(); I != E; ++I) {
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