#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
-#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
Changed |= runOnBasicBlock(*I);
return Changed;
}
-
+
bool runOnBasicBlock(BasicBlock &BB);
- bool handleFreeWithNonTrivialDependency(FreeInst* F,
- Instruction* dependency,
- SetVector<Instruction*>& possiblyDead);
- bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
- bool RemoveUndeadPointers(Value* pointer, uint64_t killPointerSize,
+ bool handleFreeWithNonTrivialDependency(FreeInst *F, MemDepResult Dep);
+ bool handleEndBlock(BasicBlock &BB);
+ bool RemoveUndeadPointers(Value* Ptr, uint64_t killPointerSize,
BasicBlock::iterator& BBI,
- SmallPtrSet<Value*, 64>& deadPointers,
- SetVector<Instruction*>& possiblyDead);
- void DeleteDeadInstructionChains(Instruction *I,
- SetVector<Instruction*> &DeadInsts);
-
+ SmallPtrSet<Value*, 64>& deadPointers);
+ void DeleteDeadInstruction(Instruction *I,
+ SmallPtrSet<Value*, 64> *deadPointers = 0);
+
// getAnalysisUsage - We require post dominance frontiers (aka Control
// Dependence Graph)
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
TargetData &TD = getAnalysis<TargetData>();
- // Record the last-seen store to this pointer
- DenseMap<Value*, StoreInst*> lastStore;
- // Record instructions possibly made dead by deleting a store
- SetVector<Instruction*> possiblyDead;
-
bool MadeChange = false;
// Do a top-down walk on the BB
- for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end();
- BBI != BBE; ++BBI) {
- // If we find a store or a free...
- if (!isa<StoreInst>(BBI) && !isa<FreeInst>(BBI))
+ for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
+ Instruction *Inst = BBI++;
+
+ // If we find a store or a free, get it's memory dependence.
+ if (!isa<StoreInst>(Inst) && !isa<FreeInst>(Inst))
continue;
-
- Value* pointer = 0;
- if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
- if (S->isVolatile())
+
+ // Don't molest volatile stores or do queries that will return "clobber".
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
+ if (SI->isVolatile())
continue;
- pointer = S->getPointerOperand();
- } else {
- pointer = cast<FreeInst>(BBI)->getPointerOperand();
- }
-
- pointer = pointer->stripPointerCasts();
- StoreInst*& last = lastStore[pointer];
- bool deletedStore = false;
- // ... to a pointer that has been stored to before...
- if (last) {
- Instruction* dep = MD.getDependency(BBI);
-
- // ... and no other memory dependencies are between them....
- while (dep != MemoryDependenceAnalysis::None &&
- dep != MemoryDependenceAnalysis::NonLocal &&
- isa<StoreInst>(dep)) {
- if (dep != last ||
- TD.getTypeStoreSize(last->getOperand(0)->getType()) >
- TD.getTypeStoreSize(BBI->getOperand(0)->getType())) {
- dep = MD.getDependency(BBI, dep);
- continue;
- }
-
- // Remove it!
- MD.removeInstruction(last);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
- possiblyDead.insert(D);
-
- last->eraseFromParent();
+ MemDepResult InstDep = MD.getDependency(Inst);
+
+ // Ignore non-local stores.
+ // FIXME: cross-block DSE would be fun. :)
+ if (InstDep.isNonLocal()) continue;
+
+ // Handle frees whose dependencies are non-trivial.
+ if (FreeInst *FI = dyn_cast<FreeInst>(Inst)) {
+ MadeChange |= handleFreeWithNonTrivialDependency(FI, InstDep);
+ continue;
+ }
+
+ StoreInst *SI = cast<StoreInst>(Inst);
+
+ // If not a definite must-alias dependency, ignore it.
+ if (!InstDep.isDef())
+ continue;
+
+ // If this is a store-store dependence, then the previous store is dead so
+ // long as this store is at least as big as it.
+ if (StoreInst *DepStore = dyn_cast<StoreInst>(InstDep.getInst()))
+ if (TD.getTypeStoreSize(DepStore->getOperand(0)->getType()) <=
+ TD.getTypeStoreSize(SI->getOperand(0)->getType())) {
+ // Delete the store and now-dead instructions that feed it.
+ DeleteDeadInstruction(DepStore);
NumFastStores++;
- deletedStore = true;
MadeChange = true;
-
- break;
+
+ if (BBI != BB.begin())
+ --BBI;
+ continue;
}
- }
- // Handle frees whose dependencies are non-trivial.
- if (FreeInst* F = dyn_cast<FreeInst>(BBI)) {
- if (!deletedStore)
- MadeChange |= handleFreeWithNonTrivialDependency(F,
- MD.getDependency(F),
- possiblyDead);
- // No known stores after the free
- last = 0;
- } else {
- StoreInst* S = cast<StoreInst>(BBI);
-
- // If we're storing the same value back to a pointer that we just
- // loaded from, then the store can be removed;
- if (LoadInst* L = dyn_cast<LoadInst>(S->getOperand(0))) {
- Instruction* dep = MD.getDependency(S);
- DominatorTree& DT = getAnalysis<DominatorTree>();
-
- if (!S->isVolatile() && S->getParent() == L->getParent() &&
- S->getPointerOperand() == L->getPointerOperand() &&
- ( dep == MemoryDependenceAnalysis::None ||
- dep == MemoryDependenceAnalysis::NonLocal ||
- DT.dominates(dep, L))) {
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
- possiblyDead.insert(D);
-
- // Avoid iterator invalidation.
- BBI--;
-
- MD.removeInstruction(S);
- S->eraseFromParent();
- NumFastStores++;
- MadeChange = true;
- } else
- // Update our most-recent-store map.
- last = S;
- } else
- // Update our most-recent-store map.
- last = S;
+ // If we're storing the same value back to a pointer that we just
+ // loaded from, then the store can be removed.
+ if (LoadInst *DepLoad = dyn_cast<LoadInst>(InstDep.getInst())) {
+ if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
+ SI->getOperand(0) == DepLoad) {
+ DeleteDeadInstruction(SI);
+ if (BBI != BB.begin())
+ --BBI;
+ NumFastStores++;
+ MadeChange = true;
+ continue;
+ }
}
}
- // If this block ends in a return, unwind, unreachable, and eventually
- // tailcall, then all allocas are dead at its end.
+ // 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, possiblyDead);
-
- // Do a trivial DCE
- while (!possiblyDead.empty()) {
- Instruction *I = possiblyDead.back();
- possiblyDead.pop_back();
- DeleteDeadInstructionChains(I, possiblyDead);
- }
+ MadeChange |= handleEndBlock(BB);
return MadeChange;
}
/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
-/// dependency is a store to a field of that structure
-bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
- SetVector<Instruction*>& possiblyDead) {
- TargetData &TD = getAnalysis<TargetData>();
+/// dependency is a store to a field of that structure.
+bool DSE::handleFreeWithNonTrivialDependency(FreeInst *F, MemDepResult Dep) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
- if (dep == MemoryDependenceAnalysis::None ||
- dep == MemoryDependenceAnalysis::NonLocal)
+ StoreInst *Dependency = dyn_cast_or_null<StoreInst>(Dep.getInst());
+ if (!Dependency || Dependency->isVolatile())
return false;
- StoreInst* dependency = dyn_cast<StoreInst>(dep);
- if (!dependency)
- return false;
- else if (dependency->isVolatile())
- return false;
-
- Value* depPointer = dependency->getPointerOperand();
- const Type* depType = dependency->getOperand(0)->getType();
- unsigned depPointerSize = TD.getTypeStoreSize(depType);
-
- // Check for aliasing
- AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0U,
- depPointer, depPointerSize);
+ Value *DepPointer = Dependency->getPointerOperand()->getUnderlyingObject();
- if (A == AliasAnalysis::MustAlias) {
- // Remove it!
- MD.removeInstruction(dependency);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(1)))
- possiblyDead.insert(D);
-
- dependency->eraseFromParent();
- NumFastStores++;
- return true;
- }
+ // Check for aliasing.
+ if (AA.alias(F->getPointerOperand(), 1, DepPointer, 1) !=
+ AliasAnalysis::MustAlias)
+ return false;
- return false;
+ // DCE instructions only used to calculate that store
+ DeleteDeadInstruction(Dependency);
+ NumFastStores++;
+ return true;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// ...
/// store i32 1, i32* %A
/// ret void
-bool DSE::handleEndBlock(BasicBlock& BB,
- SetVector<Instruction*>& possiblyDead) {
+bool DSE::handleEndBlock(BasicBlock &BB) {
TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block
SmallPtrSet<Value*, 64> deadPointers;
- // Find all of the alloca'd pointers in the entry block
+ // 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);
+
+ // 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())
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
- // If we find a store whose pointer is dead...
+ // If we find a store whose pointer is dead.
if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
if (!S->isVolatile()) {
// See through pointer-to-pointer bitcasts
// Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal.
if (deadPointers.count(pointerOperand)) {
- // Remove it!
- MD.removeInstruction(S);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
- possiblyDead.insert(D);
-
+ // DCE instructions only used to calculate that store.
BBI++;
- MD.removeInstruction(S);
- S->eraseFromParent();
+ DeleteDeadInstruction(S, &deadPointers);
NumFastStores++;
MadeChange = true;
}
}
continue;
+ }
- // We can also remove memcpy's to local variables at the end of a function
- } else if (MemCpyInst* M = dyn_cast<MemCpyInst>(BBI)) {
- Value* dest = M->getDest()->getUnderlyingObject();
+ // We can also remove memcpy's to local variables at the end of a function.
+ if (MemCpyInst *M = dyn_cast<MemCpyInst>(BBI)) {
+ Value *dest = M->getDest()->getUnderlyingObject();
if (deadPointers.count(dest)) {
- MD.removeInstruction(M);
-
- // DCE instructions only used to calculate that memcpy
- if (Instruction* D = dyn_cast<Instruction>(M->getRawSource()))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(M->getLength()))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(M->getRawDest()))
- possiblyDead.insert(D);
-
BBI++;
- M->eraseFromParent();
+ DeleteDeadInstruction(M, &deadPointers);
NumFastOther++;
MadeChange = true;
-
continue;
}
- // Because a memcpy is also a load, we can't skip it if we didn't remove it
+ // Because a memcpy is also a load, we can't skip it if we didn't remove
+ // it.
}
Value* killPointer = 0;
uint64_t killPointerSize = ~0UL;
// If we encounter a use of the pointer, it is no longer considered dead
- if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
+ 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()) {
- MD.removeInstruction(L);
-
- // DCE instructions only used to calculate that load
- if (Instruction* D = dyn_cast<Instruction>(L->getPointerOperand()))
- possiblyDead.insert(D);
-
BBI++;
- L->eraseFromParent();
+ DeleteDeadInstruction(L, &deadPointers);
NumFastOther++;
MadeChange = true;
- possiblyDead.remove(L);
-
continue;
}
// Dead alloca's can be DCE'd when we reach them
if (A->use_empty()) {
- MD.removeInstruction(A);
-
- // DCE instructions only used to calculate that load
- if (Instruction* D = dyn_cast<Instruction>(A->getArraySize()))
- possiblyDead.insert(D);
-
BBI++;
- A->eraseFromParent();
+ DeleteDeadInstruction(A, &deadPointers);
NumFastOther++;
MadeChange = true;
- possiblyDead.remove(A);
}
continue;
unsigned pointerSize = ~0U;
if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getABITypeSize(A->getAllocatedType());
+ pointerSize = C->getZExtValue() *
+ TD.getTypeAllocSize(A->getAllocatedType());
} else {
const PointerType* PT = cast<PointerType>(
cast<Argument>(*I)->getType());
- pointerSize = TD.getABITypeSize(PT->getElementType());
+ pointerSize = TD.getTypeAllocSize(PT->getElementType());
}
// See if the call site touches it
deadPointers.erase(*I);
continue;
- } else {
+ } else if (isInstructionTriviallyDead(BBI)) {
// For any non-memory-affecting non-terminators, DCE them as we reach them
- Instruction *CI = BBI;
- if (!CI->isTerminator() && CI->use_empty() && !isa<FreeInst>(CI)) {
-
- // DCE instructions only used to calculate that load
- for (Instruction::op_iterator OI = CI->op_begin(), OE = CI->op_end();
- OI != OE; ++OI)
- if (Instruction* D = dyn_cast<Instruction>(OI))
- possiblyDead.insert(D);
-
- BBI++;
- CI->eraseFromParent();
- NumFastOther++;
- MadeChange = true;
- possiblyDead.remove(CI);
-
- continue;
- }
+ Instruction *Inst = BBI;
+ BBI++;
+ DeleteDeadInstruction(Inst, &deadPointers);
+ NumFastOther++;
+ MadeChange = true;
+ continue;
}
if (!killPointer)
// Deal with undead pointers
MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
- deadPointers, possiblyDead);
+ deadPointers);
}
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,
- SetVector<Instruction*>& possiblyDead) {
+ BasicBlock::iterator &BBI,
+ SmallPtrSet<Value*, 64>& deadPointers) {
TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
- MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// If the kill pointer can be easily reduced to an alloca,
- // don't bother doing extraneous AA queries
+ // don't bother doing extraneous AA queries.
if (deadPointers.count(killPointer)) {
deadPointers.erase(killPointer);
return false;
- } else if (isa<GlobalValue>(killPointer)) {
- // A global can't be in the dead pointer set
- return false;
}
+ // A global can't be in the dead pointer set.
+ if (isa<GlobalValue>(killPointer))
+ return false;
+
bool MadeChange = false;
- std::vector<Value*> undead;
+ SmallVector<Value*, 16> undead;
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
E = deadPointers.end(); I != E; ++I) {
- // Get size information for the alloca
+ // Get size information for the alloca.
unsigned pointerSize = ~0U;
if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
- pointerSize = C->getZExtValue() * \
- TD.getABITypeSize(A->getAllocatedType());
+ pointerSize = C->getZExtValue() *
+ TD.getTypeAllocSize(A->getAllocatedType());
} else {
- const PointerType* PT = cast<PointerType>(
- cast<Argument>(*I)->getType());
- pointerSize = TD.getABITypeSize(PT->getElementType());
+ const PointerType* PT = cast<PointerType>(cast<Argument>(*I)->getType());
+ pointerSize = TD.getTypeAllocSize(PT->getElementType());
}
// See if this pointer could alias it
StoreInst* S = cast<StoreInst>(BBI);
// Remove it!
- MD.removeInstruction(S);
-
- // DCE instructions only used to calculate that store
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
- possiblyDead.insert(D);
- if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
- possiblyDead.insert(D);
-
BBI++;
- S->eraseFromParent();
+ DeleteDeadInstruction(S, &deadPointers);
NumFastStores++;
MadeChange = true;
continue;
// Otherwise, it is undead
- } else if (A != AliasAnalysis::NoAlias)
- undead.push_back(*I);
+ } else if (A != AliasAnalysis::NoAlias)
+ undead.push_back(*I);
}
- for (std::vector<Value*>::iterator I = undead.begin(), E = undead.end();
+ for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
I != E; ++I)
deadPointers.erase(*I);
return MadeChange;
}
-/// DeleteDeadInstructionChains - takes an instruction and a setvector of
-/// dead instructions. If I is dead, it is erased, and its operands are
-/// checked for deadness. If they are dead, they are added to the dead
-/// setvector.
-void DSE::DeleteDeadInstructionChains(Instruction *I,
- SetVector<Instruction*> &DeadInsts) {
- // Instruction must be dead.
- if (!I->use_empty() || !isInstructionTriviallyDead(I)) return;
-
- // Let the memory dependence know
- getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I);
-
- // See if this made any operands dead. We do it this way in case the
- // instruction uses the same operand twice. We don't want to delete a
- // value then reference it.
- for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
- if (I->getOperand(i)->hasOneUse())
- if (Instruction* Op = dyn_cast<Instruction>(I->getOperand(i)))
- DeadInsts.insert(Op); // Attempt to nuke it later.
+/// 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>();
+ while (!NowDeadInsts.empty()) {
+ Instruction *DeadInst = NowDeadInsts.back();
+ NowDeadInsts.pop_back();
- I->setOperand(i, 0); // Drop from the operand list.
+ ++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);
}
-
- I->eraseFromParent();
- ++NumFastOther;
}