#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"
using namespace llvm;
bool runOnBasicBlock(BasicBlock &BB);
bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
- void RemoveAccessedObjects(Value *Ptr, uint64_t killPointerSize,
- SmallPtrSet<Value*, 16> &deadPointers);
- void DeleteDeadInstruction(Instruction *I,
- SmallPtrSet<Value*, 16> *deadPointers = 0);
+ void RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
+ SmallPtrSet<Value*, 16> &DeadStackObjects);
// getAnalysisUsage - We require post dominance frontiers (aka Control
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) {
}
}
-/// 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 bool isCompleteOverwrite(const AliasAnalysis::Location &Later,
const AliasAnalysis::Location &Earlier,
AliasAnalysis &AA) {
- const Value *P1 = Later.Ptr->stripPointerCasts();
- const Value *P2 = Earlier.Ptr->stripPointerCasts();
+ const Value *P1 = Earlier.Ptr->stripPointerCasts();
+ const Value *P2 = Later.Ptr->stripPointerCasts();
- // Make sure that the start pointers are the same.
- if (P1 != P2)
- return false;
-
- // If we don't know the sizes of either access, then we can't do a comparison.
+ // 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) {
- // 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();
+ Earlier.Size == AliasAnalysis::UnknownSize ||
+ Later.Size <= Earlier.Size ||
+ AA.getTargetData() == 0)
return false;
- }
- // Make sure that the Later size is >= the Earlier size.
- if (Later.Size < Earlier.Size)
+ const TargetData &TD = *AA.getTargetData();
+
+ // 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;
}
+
+//===----------------------------------------------------------------------===//
+// DSE Pass
+//===----------------------------------------------------------------------===//
+
bool DSE::runOnBasicBlock(BasicBlock &BB) {
bool MadeChange = false;
// in case we need it.
WeakVH NextInst(BBI);
- DeleteDeadInstruction(SI);
+ DeleteDeadInstruction(SI, *MD);
if (NextInst == 0) // Next instruction deleted.
BBI = BB.begin();
// 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);
+ DeleteDeadInstruction(DepWrite, *MD);
++NumFastStores;
MadeChange = true;
if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
return false;
- Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
+ Value *DepPointer =
+ getStoredPointerOperand(Dependency)->getUnderlyingObject();
// Check for aliasing.
if (AA->alias(F->getArgOperand(0), 1, DepPointer, 1) !=
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,
// 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 = getPointerOperand(BBI)->getUnderlyingObject();
+ Value *Pointer = getStoredPointerOperand(BBI)->getUnderlyingObject();
- // Alloca'd pointers or byval arguments (which are functionally like
- // alloca's) are valid candidates for removal.
+ // Stores to stack values are valid candidates for removal.
if (DeadStackObjects.count(Pointer)) {
// DCE instructions only used to calculate that store.
Instruction *Dead = BBI++;
- DeleteDeadInstruction(Dead, &DeadStackObjects);
+ DeleteDeadInstruction(Dead, *MD, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
continue;
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(BBI)) {
Instruction *Inst = BBI++;
- DeleteDeadInstruction(Inst, &DeadStackObjects);
+ DeleteDeadInstruction(Inst, *MD, &DeadStackObjects);
++NumFastOther;
MadeChange = true;
continue;
continue;
}
- Value *KillPointer = 0;
- uint64_t KillPointerSize = AliasAnalysis::UnknownSize;
+ AliasAnalysis::Location LoadedLoc;
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
- KillPointer = L->getPointerOperand();
+ LoadedLoc = AA->getLocation(L);
} else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
- KillPointer = V->getOperand(0);
+ LoadedLoc = AA->getLocation(V);
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
- KillPointer = cast<MemTransferInst>(BBI)->getSource();
- if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
- KillPointerSize = Len->getZExtValue();
+ LoadedLoc = AA->getLocationForSource(MTI);
} else {
// Not a loading instruction.
continue;
// Remove any allocas from the DeadPointer set that are loaded, as this
// makes any stores above the access live.
- RemoveAccessedObjects(KillPointer, KillPointerSize, DeadStackObjects);
+ RemoveAccessedObjects(LoadedLoc, DeadStackObjects);
// If all of the allocas were clobbered by the access then we're not going
// to find anything else to process.
/// 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(Value *KillPointer, uint64_t KillPointerSize,
+void DSE::RemoveAccessedObjects(const AliasAnalysis::Location &LoadedLoc,
SmallPtrSet<Value*, 16> &DeadStackObjects) {
- Value *UnderlyingPointer = KillPointer->getUnderlyingObject();
+ const Value *UnderlyingPointer = LoadedLoc.Ptr->getUnderlyingObject();
// A constant can't be in the dead pointer set.
if (isa<Constant>(UnderlyingPointer))
// 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(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) {
- // See if this pointer could alias it
- AliasAnalysis::AliasResult A = AA->alias(*I, getPointerSize(*I, *AA),
- KillPointer, KillPointerSize);
- if (A != AliasAnalysis::NoAlias)
+ // 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);
}
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*, 16> *ValueSet) {
- 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());
-}
-
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