#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;
}
IntrinsicInst *II = cast<IntrinsicInst>(I);
switch (II->getIntrinsicID()) {
- default: assert(0 && "doesn't pass 'hasMemoryWrite' predicate");
+ default: llvm_unreachable("doesn't pass 'hasMemoryWrite' predicate");
case Intrinsic::lifetime_end:
// Never remove dead lifetime_end's, e.g. because it is followed by a
// free.
IntrinsicInst *II = cast<IntrinsicInst>(I);
switch (II->getIntrinsicID()) {
- default: assert(false && "Unexpected intrinsic!");
+ default: llvm_unreachable("Unexpected intrinsic!");
case Intrinsic::init_trampoline:
return II->getArgOperand(0);
}
}
-static uint64_t getPointerSize(Value *V, AliasAnalysis &AA) {
+static uint64_t getPointerSize(const 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)))
+ if (const CallInst *CI = extractMallocCall(V)) {
+ if (const 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)) {
+ if (
const AllocaInst *A = dyn_cast<AllocaInst>(V)) {
// Get size information for the alloca
- if (ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
+ if (const ConstantInt *C = dyn_cast<ConstantInt>(A->getArraySize()))
return C->getZExtValue() * TD->getTypeAllocSize(A->getAllocatedType());
- return AliasAnalysis::UnknownSize;
}
- assert(isa<Argument>(V) && "Expected AllocaInst, malloc call or Argument!");
- PointerType *PT = cast<PointerType>(V->getType());
- return TD->getTypeAllocSize(PT->getElementType());
-}
+ if (const Argument *A = dyn_cast<Argument>(V)) {
+ if (A->hasByValAttr())
+ if (PointerType *PT = dyn_cast<PointerType>(A->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;
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
+ if (!GV->mayBeOverridden())
+ return TD->getTypeAllocSize(GV->getType()->getElementType());
+ }
+
+ return AliasAnalysis::UnknownSize;
}
namespace {
static OverwriteResult isOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA,
- int64_t& EarlierOff,
- int64_t& LaterOff) {
+ int64_t &EarlierOff,
+ int64_t &LaterOff) {
const Value *P1 = Earlier.Ptr->stripPointerCasts();
const Value *P2 = Later.Ptr->stripPointerCasts();
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)
+ uint64_t ObjectSize = getPointerSize(UO2, AA);
+ if (ObjectSize != AliasAnalysis::UnknownSize)
+ if (ObjectSize == Later.Size && ObjectSize >= Earlier.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
// 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 + Later.Size >= EarlierOff + Earlier.Size)
+ LaterOff < int64_t(EarlierOff + Earlier.Size) &&
+ int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
return OverwriteEnd;
// Otherwise, they don't completely overlap.
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;
+ if (Pred == BB) continue;
+ 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) {
bool MadeChange = false;
- MemDepResult Dep = MD->getDependency(F);
+ 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;
- while (Dep.isDef() || Dep.isClobber()) {
- Instruction *Dependency = Dep.getInst();
- if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
- return MadeChange;
+ 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));
+ Value *DepPointer =
+ GetUnderlyingObject(getStoredPointerOperand(Dependency));
- // Check for aliasing.
- if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
- return MadeChange;
+ // Check for aliasing.
+ if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
+ break;
- // DCE instructions only used to calculate that store
- DeleteDeadInstruction(Dependency, *MD);
- ++NumFastStores;
- MadeChange = true;
+ Instruction *Next = llvm::next(BasicBlock::iterator(Dependency));
- // 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);
- };
+ // 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;
}
I != E; ++I)
DeadStackObjects.erase(*I);
}
-
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