bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
if (!SI->isSimple()) return false;
// Avoid merging nontemporal stores since the resulting
// memcpy/memset would not be able to preserve the nontemporal hint.
// In theory we could teach how to propagate the !nontemporal metadata to
// memset calls. However, that change would force the backend to
// conservatively expand !nontemporal memset calls back to sequences of
// store instructions (effectively undoing the merging).
if (SI->getMetadata(LLVMContext::MD_nontemporal))
return false;
const DataLayout &DL = SI->getModule()->getDataLayout();
// Detect cases where we're performing call slot forwarding, but
// happen to be using a load-store pair to implement it, rather than
// a memcpy.
if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
if (LI->isSimple() && LI->hasOneUse() &&
LI->getParent() == SI->getParent()) {
MemDepResult ldep = MD->getDependency(LI);
CallInst *C = nullptr;
if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
C = dyn_cast<CallInst>(ldep.getInst());
if (C) {
// Check that nothing touches the dest of the "copy" between
// the call and the store.
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
MemoryLocation StoreLoc = MemoryLocation::get(SI);
for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator();
I != E; --I) {
if (AA.getModRefInfo(&*I, StoreLoc) != MRI_NoModRef) {
C = nullptr;
break;
}
}
}
if (C) {
unsigned storeAlign = SI->getAlignment();
if (!storeAlign)
storeAlign = DL.getABITypeAlignment(SI->getOperand(0)->getType());
unsigned loadAlign = LI->getAlignment();
if (!loadAlign)
loadAlign = DL.getABITypeAlignment(LI->getType());
bool changed = performCallSlotOptzn(
LI, SI->getPointerOperand()->stripPointerCasts(),
LI->getPointerOperand()->stripPointerCasts(),
DL.getTypeStoreSize(SI->getOperand(0)->getType()),
std::min(storeAlign, loadAlign), C);
if (changed) {
MD->removeInstruction(SI);
SI->eraseFromParent();
MD->removeInstruction(LI);
LI->eraseFromParent();
++NumMemCpyInstr;
return true;
}
}
}
}
// There are two cases that are interesting for this code to handle: memcpy
// and memset. Right now we only handle memset.
// Ensure that the value being stored is something that can be memset'able a
// byte at a time like "0" or "-1" or any width, as well as things like
// 0xA0A0A0A0 and 0.0.
if (Value *ByteVal = isBytewiseValue(SI->getOperand(0)))
if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
ByteVal)) {
BBI = I->getIterator(); // Don't invalidate iterator.
return true;
}
return false;
}
/// performLocalReleaseMotion - Scan backwards from the specified release,
/// moving it earlier in the function if possible, over instructions that do not
/// access the released object. If we get to a retain or allocation of the
/// object, zap both.
static bool performLocalReleaseMotion(CallInst &Release, BasicBlock &BB,
SwiftRCIdentity *RC) {
// FIXME: Call classifier should identify the object for us. Too bad C++
// doesn't have nice Swift-style enums.
Value *ReleasedObject = RC->getSwiftRCIdentityRoot(Release.getArgOperand(0));
BasicBlock::iterator BBI = Release.getIterator();
// Scan until we get to the top of the block.
while (BBI != BB.begin()) {
--BBI;
// Don't analyze PHI nodes. We can't move retains before them and they
// aren't "interesting".
if (isa<PHINode>(BBI) ||
// If we found the instruction that defines the value we're releasing,
// don't push the release past it.
&*BBI == Release.getArgOperand(0)) {
++BBI;
goto OutOfLoop;
}
switch (classifyInstruction(*BBI)) {
// These instructions should not reach here based on the pass ordering.
// i.e. LLVMARCOpt -> LLVMContractOpt.
case RT_UnknownRetainN:
case RT_BridgeRetainN:
case RT_RetainN:
case RT_UnknownReleaseN:
case RT_BridgeReleaseN:
case RT_ReleaseN:
llvm_unreachable("These are only created by LLVMARCContract !");
case RT_NoMemoryAccessed:
// Skip over random instructions that don't touch memory. They don't need
// protection by retain/release.
continue;
case RT_UnknownRelease:
case RT_BridgeRelease:
case RT_ObjCRelease:
case RT_Release: {
// If we get to a release, we can generally ignore it and scan past it.
// However, if we get to a release of obviously the same object, we stop
// scanning here because it should have already be moved as early as
// possible, so there is no reason to move its friend to the same place.
//
// NOTE: If this occurs frequently, maybe we can have a release(Obj, N)
// API to drop multiple retain counts at once.
CallInst &ThisRelease = cast<CallInst>(*BBI);
Value *ThisReleasedObject = ThisRelease.getArgOperand(0);
ThisReleasedObject = RC->getSwiftRCIdentityRoot(ThisReleasedObject);
if (ThisReleasedObject == ReleasedObject) {
//Release.dump(); ThisRelease.dump(); BB.getParent()->dump();
++BBI;
goto OutOfLoop;
}
continue;
}
case RT_UnknownRetain:
case RT_BridgeRetain:
case RT_ObjCRetain:
case RT_Retain: { // swift_retain(obj)
CallInst &Retain = cast<CallInst>(*BBI);
Value *RetainedObject = Retain.getArgOperand(0);
RetainedObject = RC->getSwiftRCIdentityRoot(RetainedObject);
// Since we canonicalized earlier, we know that if our retain has any
// uses, they were replaced already. This assertion documents this
// assumption.
assert(Retain.use_empty() && "Retain should have been canonicalized to "
"have no uses.");
// If the retain and release are to obviously pointer-equal objects, then
// we can delete both of them. We have proven that they do not protect
// anything of value.
if (RetainedObject == ReleasedObject) {
Retain.eraseFromParent();
Release.eraseFromParent();
++NumRetainReleasePairs;
return true;
}
// Otherwise, this is a retain of an object that is not statically known
// to be the same object. It may still be dynamically the same object
// though. In this case, we can't move the release past it.
// TODO: Strengthen analysis.
//Release.dump(); ThisRelease.dump(); BB.getParent()->dump();
++BBI;
goto OutOfLoop;
}
case RT_AllocObject: { // %obj = swift_alloc(...)
CallInst &Allocation = cast<CallInst>(*BBI);
// If this is an allocation of an unrelated object, just ignore it.
// TODO: This is not safe without proving the object being released is not
// related to the allocated object. Consider something silly like this:
// A = allocate()
// B = bitcast A to object
// release(B)
if (ReleasedObject != &Allocation) {
// Release.dump(); BB.getParent()->dump();
++BBI;
goto OutOfLoop;
}
// If this is a release right after an allocation of the object, then we
// can zap both.
Allocation.replaceAllUsesWith(UndefValue::get(Allocation.getType()));
Allocation.eraseFromParent();
Release.eraseFromParent();
++NumAllocateReleasePairs;
return true;
}
case RT_FixLifetime:
case RT_RetainUnowned:
case RT_CheckUnowned:
case RT_Unknown:
// Otherwise, we have reached something that we do not understand. Do not
// attempt to shorten the lifetime of this object beyond this point so we
// are conservative.
++BBI;
goto OutOfLoop;
}
}
OutOfLoop:
// If we got to the top of the block, (and if the instruction didn't start
// there) move the release to the top of the block.
// TODO: This is where we'd plug in some global algorithms someday.
if (&*BBI != &Release) {
Release.moveBefore(&*BBI);
return true;
}
return false;
}
/// performLocalRetainMotion - Scan forward from the specified retain, moving it
/// later in the function if possible, over instructions that provably can't
/// release the object. If we get to a release of the object, zap both.
///
/// NOTE: this handles both objc_retain and swift_retain.
///
static bool performLocalRetainMotion(CallInst &Retain, BasicBlock &BB,
SwiftRCIdentity *RC) {
// FIXME: Call classifier should identify the object for us. Too bad C++
// doesn't have nice Swift-style enums.
Value *RetainedObject = RC->getSwiftRCIdentityRoot(Retain.getArgOperand(0));
BasicBlock::iterator BBI = Retain.getIterator(),
BBE = BB.getTerminator()->getIterator();
bool isObjCRetain = Retain.getCalledFunction()->getName() == "objc_retain";
bool MadeProgress = false;
// Scan until we get to the end of the block.
for (++BBI; BBI != BBE; ++BBI) {
Instruction &CurInst = *BBI;
// Classify the instruction. This switch does a "break" when the instruction
// can be skipped and is interesting, and a "continue" when it is a retain
// of the same pointer.
switch (classifyInstruction(CurInst)) {
// These instructions should not reach here based on the pass ordering.
// i.e. LLVMARCOpt -> LLVMContractOpt.
case RT_RetainN:
case RT_UnknownRetainN:
case RT_BridgeRetainN:
case RT_ReleaseN:
case RT_UnknownReleaseN:
case RT_BridgeReleaseN:
llvm_unreachable("These are only created by LLVMARCContract !");
case RT_NoMemoryAccessed:
case RT_AllocObject:
case RT_CheckUnowned:
// Skip over random instructions that don't touch memory. They don't need
// protection by retain/release.
break;
case RT_FixLifetime: // This only stops release motion. Retains can move over it.
break;
case RT_Retain:
case RT_UnknownRetain:
case RT_BridgeRetain:
case RT_RetainUnowned:
case RT_ObjCRetain: { // swift_retain(obj)
//CallInst &ThisRetain = cast<CallInst>(CurInst);
//Value *ThisRetainedObject = ThisRetain.getArgOperand(0);
// If we see a retain of the same object, we can skip over it, but we
// can't count it as progress. Just pushing a retain(x) past a retain(y)
// doesn't change the program.
continue;
}
case RT_UnknownRelease:
case RT_BridgeRelease:
case RT_ObjCRelease:
case RT_Release: {
// If we get to a release that is provably to this object, then we can zap
// it and the retain.
CallInst &ThisRelease = cast<CallInst>(CurInst);
Value *ThisReleasedObject = ThisRelease.getArgOperand(0);
ThisReleasedObject = RC->getSwiftRCIdentityRoot(ThisReleasedObject);
if (ThisReleasedObject == RetainedObject) {
Retain.eraseFromParent();
ThisRelease.eraseFromParent();
if (isObjCRetain) {
++NumObjCRetainReleasePairs;
} else {
++NumRetainReleasePairs;
}
return true;
}
// Otherwise, if this is some other pointer, we can only ignore it if we
// can prove that the two objects don't alias.
// Retain.dump(); ThisRelease.dump(); BB.getParent()->dump();
goto OutOfLoop;
}
case RT_Unknown:
// Loads cannot affect the retain.
if (isa<LoadInst>(CurInst))
continue;
// Load, store, memcpy etc can't do a release.
if (isa<LoadInst>(CurInst) || isa<StoreInst>(CurInst) ||
isa<MemIntrinsic>(CurInst))
break;
// CurInst->dump(); BBI->dump();
// Otherwise, we get to something unknown/unhandled. Bail out for now.
goto OutOfLoop;
}
// If the switch did a break, we made some progress moving this retain.
MadeProgress = true;
}
OutOfLoop:
// If we were able to move the retain down, move it now.
// TODO: This is where we'd plug in some global algorithms someday.
if (MadeProgress) {
Retain.moveBefore(&*BBI);
return true;
}
return false;
}
bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
if (!SI->isSimple()) return false;
// Avoid merging nontemporal stores since the resulting
// memcpy/memset would not be able to preserve the nontemporal hint.
// In theory we could teach how to propagate the !nontemporal metadata to
// memset calls. However, that change would force the backend to
// conservatively expand !nontemporal memset calls back to sequences of
// store instructions (effectively undoing the merging).
if (SI->getMetadata(LLVMContext::MD_nontemporal))
return false;
const DataLayout &DL = SI->getModule()->getDataLayout();
// Load to store forwarding can be interpreted as memcpy.
if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
if (LI->isSimple() && LI->hasOneUse() &&
LI->getParent() == SI->getParent()) {
auto *T = LI->getType();
if (T->isAggregateType()) {
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
MemoryLocation LoadLoc = MemoryLocation::get(LI);
// We use alias analysis to check if an instruction may store to
// the memory we load from in between the load and the store. If
// such an instruction is found, we store it in AI.
Instruction *AI = nullptr;
for (BasicBlock::iterator I = ++LI->getIterator(), E = SI->getIterator();
I != E; ++I) {
if (AA.getModRefInfo(&*I, LoadLoc) & MRI_Mod) {
AI = &*I;
break;
}
}
// If no aliasing instruction is found, then we can promote the
// load/store pair to a memcpy at the store loaction.
if (!AI) {
// If we load from memory that may alias the memory we store to,
// memmove must be used to preserve semantic. If not, memcpy can
// be used.
bool UseMemMove = false;
if (!AA.isNoAlias(MemoryLocation::get(SI), LoadLoc))
UseMemMove = true;
unsigned Align = findCommonAlignment(DL, SI, LI);
uint64_t Size = DL.getTypeStoreSize(T);
IRBuilder<> Builder(SI);
Instruction *M;
if (UseMemMove)
M = Builder.CreateMemMove(SI->getPointerOperand(),
LI->getPointerOperand(), Size,
Align, SI->isVolatile());
else
M = Builder.CreateMemCpy(SI->getPointerOperand(),
LI->getPointerOperand(), Size,
Align, SI->isVolatile());
DEBUG(dbgs() << "Promoting " << *LI << " to " << *SI
<< " => " << *M << "\n");
MD->removeInstruction(SI);
SI->eraseFromParent();
MD->removeInstruction(LI);
LI->eraseFromParent();
++NumMemCpyInstr;
// Make sure we do not invalidate the iterator.
BBI = M->getIterator();
return true;
}
}
// Detect cases where we're performing call slot forwarding, but
// happen to be using a load-store pair to implement it, rather than
// a memcpy.
MemDepResult ldep = MD->getDependency(LI);
CallInst *C = nullptr;
if (ldep.isClobber() && !isa<MemCpyInst>(ldep.getInst()))
C = dyn_cast<CallInst>(ldep.getInst());
if (C) {
// Check that nothing touches the dest of the "copy" between
// the call and the store.
AliasAnalysis &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
MemoryLocation StoreLoc = MemoryLocation::get(SI);
for (BasicBlock::iterator I = --SI->getIterator(), E = C->getIterator();
I != E; --I) {
if (AA.getModRefInfo(&*I, StoreLoc) != MRI_NoModRef) {
C = nullptr;
break;
}
}
}
if (C) {
bool changed = performCallSlotOptzn(
LI, SI->getPointerOperand()->stripPointerCasts(),
LI->getPointerOperand()->stripPointerCasts(),
DL.getTypeStoreSize(SI->getOperand(0)->getType()),
findCommonAlignment(DL, SI, LI), C);
if (changed) {
MD->removeInstruction(SI);
SI->eraseFromParent();
MD->removeInstruction(LI);
LI->eraseFromParent();
++NumMemCpyInstr;
return true;
}
}
}
}
// There are two cases that are interesting for this code to handle: memcpy
// and memset. Right now we only handle memset.
// Ensure that the value being stored is something that can be memset'able a
// byte at a time like "0" or "-1" or any width, as well as things like
// 0xA0A0A0A0 and 0.0.
if (Value *ByteVal = isBytewiseValue(SI->getOperand(0)))
if (Instruction *I = tryMergingIntoMemset(SI, SI->getPointerOperand(),
ByteVal)) {
BBI = I->getIterator(); // Don't invalidate iterator.
return true;
}
return false;
}
