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llvm/lib/CodeGen/AtomicExpandPass.cpp
Matthias Braun 94c4904dc5 CodeGen: Rename DEBUG_TYPE to match passnames 
Rename the DEBUG_TYPE to match the names of corresponding passes where
it makes sense. Also establish the pattern of simply referencing
DEBUG_TYPE instead of repeating the passname where possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303921 91177308-0d34-0410-b5e6-96231b3b80d8
2017-05-25 21:26:32 +00:00

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//===-- AtomicExpandPass.cpp - Expand atomic instructions -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a pass (at IR level) to replace atomic instructions with
// __atomic_* library calls, or target specific instruction which implement the
// same semantics in a way which better fits the target backend. This can
// include the use of (intrinsic-based) load-linked/store-conditional loops,
// AtomicCmpXchg, or type coercions.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/AtomicExpandUtils.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "atomic-expand"
namespace {
class AtomicExpand: public FunctionPass {
const TargetLowering *TLI;
public:
static char ID; // Pass identification, replacement for typeid
AtomicExpand() : FunctionPass(ID), TLI(nullptr) {
initializeAtomicExpandPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
private:
bool bracketInstWithFences(Instruction *I, AtomicOrdering Order);
IntegerType *getCorrespondingIntegerType(Type *T, const DataLayout &DL);
LoadInst *convertAtomicLoadToIntegerType(LoadInst *LI);
bool tryExpandAtomicLoad(LoadInst *LI);
bool expandAtomicLoadToLL(LoadInst *LI);
bool expandAtomicLoadToCmpXchg(LoadInst *LI);
StoreInst *convertAtomicStoreToIntegerType(StoreInst *SI);
bool expandAtomicStore(StoreInst *SI);
bool tryExpandAtomicRMW(AtomicRMWInst *AI);
Value *
insertRMWLLSCLoop(IRBuilder<> &Builder, Type *ResultTy, Value *Addr,
AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp);
void expandAtomicOpToLLSC(
Instruction *I, Type *ResultTy, Value *Addr, AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp);
void expandPartwordAtomicRMW(
AtomicRMWInst *I,
TargetLoweringBase::AtomicExpansionKind ExpansionKind);
void expandPartwordCmpXchg(AtomicCmpXchgInst *I);
AtomicCmpXchgInst *convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI);
static Value *insertRMWCmpXchgLoop(
IRBuilder<> &Builder, Type *ResultType, Value *Addr,
AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp,
CreateCmpXchgInstFun CreateCmpXchg);
bool expandAtomicCmpXchg(AtomicCmpXchgInst *CI);
bool isIdempotentRMW(AtomicRMWInst *AI);
bool simplifyIdempotentRMW(AtomicRMWInst *AI);
bool expandAtomicOpToLibcall(Instruction *I, unsigned Size, unsigned Align,
Value *PointerOperand, Value *ValueOperand,
Value *CASExpected, AtomicOrdering Ordering,
AtomicOrdering Ordering2,
ArrayRef<RTLIB::Libcall> Libcalls);
void expandAtomicLoadToLibcall(LoadInst *LI);
void expandAtomicStoreToLibcall(StoreInst *LI);
void expandAtomicRMWToLibcall(AtomicRMWInst *I);
void expandAtomicCASToLibcall(AtomicCmpXchgInst *I);
friend bool
llvm::expandAtomicRMWToCmpXchg(AtomicRMWInst *AI,
CreateCmpXchgInstFun CreateCmpXchg);
};
}
char AtomicExpand::ID = 0;
char &llvm::AtomicExpandID = AtomicExpand::ID;
INITIALIZE_PASS(AtomicExpand, DEBUG_TYPE, "Expand Atomic instructions",
false, false)
FunctionPass *llvm::createAtomicExpandPass() { return new AtomicExpand(); }
namespace {
// Helper functions to retrieve the size of atomic instructions.
unsigned getAtomicOpSize(LoadInst *LI) {
const DataLayout &DL = LI->getModule()->getDataLayout();
return DL.getTypeStoreSize(LI->getType());
}
unsigned getAtomicOpSize(StoreInst *SI) {
const DataLayout &DL = SI->getModule()->getDataLayout();
return DL.getTypeStoreSize(SI->getValueOperand()->getType());
}
unsigned getAtomicOpSize(AtomicRMWInst *RMWI) {
const DataLayout &DL = RMWI->getModule()->getDataLayout();
return DL.getTypeStoreSize(RMWI->getValOperand()->getType());
}
unsigned getAtomicOpSize(AtomicCmpXchgInst *CASI) {
const DataLayout &DL = CASI->getModule()->getDataLayout();
return DL.getTypeStoreSize(CASI->getCompareOperand()->getType());
}
// Helper functions to retrieve the alignment of atomic instructions.
unsigned getAtomicOpAlign(LoadInst *LI) {
unsigned Align = LI->getAlignment();
// In the future, if this IR restriction is relaxed, we should
// return DataLayout::getABITypeAlignment when there's no align
// value.
assert(Align != 0 && "An atomic LoadInst always has an explicit alignment");
return Align;
}
unsigned getAtomicOpAlign(StoreInst *SI) {
unsigned Align = SI->getAlignment();
// In the future, if this IR restriction is relaxed, we should
// return DataLayout::getABITypeAlignment when there's no align
// value.
assert(Align != 0 && "An atomic StoreInst always has an explicit alignment");
return Align;
}
unsigned getAtomicOpAlign(AtomicRMWInst *RMWI) {
// TODO(PR27168): This instruction has no alignment attribute, but unlike the
// default alignment for load/store, the default here is to assume
// it has NATURAL alignment, not DataLayout-specified alignment.
const DataLayout &DL = RMWI->getModule()->getDataLayout();
return DL.getTypeStoreSize(RMWI->getValOperand()->getType());
}
unsigned getAtomicOpAlign(AtomicCmpXchgInst *CASI) {
// TODO(PR27168): same comment as above.
const DataLayout &DL = CASI->getModule()->getDataLayout();
return DL.getTypeStoreSize(CASI->getCompareOperand()->getType());
}
// Determine if a particular atomic operation has a supported size,
// and is of appropriate alignment, to be passed through for target
// lowering. (Versus turning into a __atomic libcall)
template <typename Inst>
bool atomicSizeSupported(const TargetLowering *TLI, Inst *I) {
unsigned Size = getAtomicOpSize(I);
unsigned Align = getAtomicOpAlign(I);
return Align >= Size && Size <= TLI->getMaxAtomicSizeInBitsSupported() / 8;
}
} // end anonymous namespace
bool AtomicExpand::runOnFunction(Function &F) {
auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
if (!TPC)
return false;
auto &TM = TPC->getTM<TargetMachine>();
if (!TM.getSubtargetImpl(F)->enableAtomicExpand())
return false;
TLI = TM.getSubtargetImpl(F)->getTargetLowering();
SmallVector<Instruction *, 1> AtomicInsts;
// Changing control-flow while iterating through it is a bad idea, so gather a
// list of all atomic instructions before we start.
for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
Instruction *I = &*II;
if (I->isAtomic() && !isa<FenceInst>(I))
AtomicInsts.push_back(I);
}
bool MadeChange = false;
for (auto I : AtomicInsts) {
auto LI = dyn_cast<LoadInst>(I);
auto SI = dyn_cast<StoreInst>(I);
auto RMWI = dyn_cast<AtomicRMWInst>(I);
auto CASI = dyn_cast<AtomicCmpXchgInst>(I);
assert((LI || SI || RMWI || CASI) && "Unknown atomic instruction");
// If the Size/Alignment is not supported, replace with a libcall.
if (LI) {
if (!atomicSizeSupported(TLI, LI)) {
expandAtomicLoadToLibcall(LI);
MadeChange = true;
continue;
}
} else if (SI) {
if (!atomicSizeSupported(TLI, SI)) {
expandAtomicStoreToLibcall(SI);
MadeChange = true;
continue;
}
} else if (RMWI) {
if (!atomicSizeSupported(TLI, RMWI)) {
expandAtomicRMWToLibcall(RMWI);
MadeChange = true;
continue;
}
} else if (CASI) {
if (!atomicSizeSupported(TLI, CASI)) {
expandAtomicCASToLibcall(CASI);
MadeChange = true;
continue;
}
}
if (TLI->shouldInsertFencesForAtomic(I)) {
auto FenceOrdering = AtomicOrdering::Monotonic;
if (LI && isAcquireOrStronger(LI->getOrdering())) {
FenceOrdering = LI->getOrdering();
LI->setOrdering(AtomicOrdering::Monotonic);
} else if (SI && isReleaseOrStronger(SI->getOrdering())) {
FenceOrdering = SI->getOrdering();
SI->setOrdering(AtomicOrdering::Monotonic);
} else if (RMWI && (isReleaseOrStronger(RMWI->getOrdering()) ||
isAcquireOrStronger(RMWI->getOrdering()))) {
FenceOrdering = RMWI->getOrdering();
RMWI->setOrdering(AtomicOrdering::Monotonic);
} else if (CASI && !TLI->shouldExpandAtomicCmpXchgInIR(CASI) &&
(isReleaseOrStronger(CASI->getSuccessOrdering()) ||
isAcquireOrStronger(CASI->getSuccessOrdering()))) {
// If a compare and swap is lowered to LL/SC, we can do smarter fence
// insertion, with a stronger one on the success path than on the
// failure path. As a result, fence insertion is directly done by
// expandAtomicCmpXchg in that case.
FenceOrdering = CASI->getSuccessOrdering();
CASI->setSuccessOrdering(AtomicOrdering::Monotonic);
CASI->setFailureOrdering(AtomicOrdering::Monotonic);
}
if (FenceOrdering != AtomicOrdering::Monotonic) {
MadeChange |= bracketInstWithFences(I, FenceOrdering);
}
}
if (LI) {
if (LI->getType()->isFloatingPointTy()) {
// TODO: add a TLI hook to control this so that each target can
// convert to lowering the original type one at a time.
LI = convertAtomicLoadToIntegerType(LI);
assert(LI->getType()->isIntegerTy() && "invariant broken");
MadeChange = true;
}
MadeChange |= tryExpandAtomicLoad(LI);
} else if (SI) {
if (SI->getValueOperand()->getType()->isFloatingPointTy()) {
// TODO: add a TLI hook to control this so that each target can
// convert to lowering the original type one at a time.
SI = convertAtomicStoreToIntegerType(SI);
assert(SI->getValueOperand()->getType()->isIntegerTy() &&
"invariant broken");
MadeChange = true;
}
if (TLI->shouldExpandAtomicStoreInIR(SI))
MadeChange |= expandAtomicStore(SI);
} else if (RMWI) {
// There are two different ways of expanding RMW instructions:
// - into a load if it is idempotent
// - into a Cmpxchg/LL-SC loop otherwise
// we try them in that order.
if (isIdempotentRMW(RMWI) && simplifyIdempotentRMW(RMWI)) {
MadeChange = true;
} else {
MadeChange |= tryExpandAtomicRMW(RMWI);
}
} else if (CASI) {
// TODO: when we're ready to make the change at the IR level, we can
// extend convertCmpXchgToInteger for floating point too.
assert(!CASI->getCompareOperand()->getType()->isFloatingPointTy() &&
"unimplemented - floating point not legal at IR level");
if (CASI->getCompareOperand()->getType()->isPointerTy() ) {
// TODO: add a TLI hook to control this so that each target can
// convert to lowering the original type one at a time.
CASI = convertCmpXchgToIntegerType(CASI);
assert(CASI->getCompareOperand()->getType()->isIntegerTy() &&
"invariant broken");
MadeChange = true;
}
unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
unsigned ValueSize = getAtomicOpSize(CASI);
if (ValueSize < MinCASSize) {
assert(!TLI->shouldExpandAtomicCmpXchgInIR(CASI) &&
"MinCmpXchgSizeInBits not yet supported for LL/SC expansions.");
expandPartwordCmpXchg(CASI);
} else {
if (TLI->shouldExpandAtomicCmpXchgInIR(CASI))
MadeChange |= expandAtomicCmpXchg(CASI);
}
}
}
return MadeChange;
}
bool AtomicExpand::bracketInstWithFences(Instruction *I, AtomicOrdering Order) {
IRBuilder<> Builder(I);
auto LeadingFence = TLI->emitLeadingFence(Builder, I, Order);
auto TrailingFence = TLI->emitTrailingFence(Builder, I, Order);
// The trailing fence is emitted before the instruction instead of after
// because there is no easy way of setting Builder insertion point after
// an instruction. So we must erase it from the BB, and insert it back
// in the right place.
// We have a guard here because not every atomic operation generates a
// trailing fence.
if (TrailingFence) {
TrailingFence->removeFromParent();
TrailingFence->insertAfter(I);
}
return (LeadingFence || TrailingFence);
}
/// Get the iX type with the same bitwidth as T.
IntegerType *AtomicExpand::getCorrespondingIntegerType(Type *T,
const DataLayout &DL) {
EVT VT = TLI->getValueType(DL, T);
unsigned BitWidth = VT.getStoreSizeInBits();
assert(BitWidth == VT.getSizeInBits() && "must be a power of two");
return IntegerType::get(T->getContext(), BitWidth);
}
/// Convert an atomic load of a non-integral type to an integer load of the
/// equivalent bitwidth. See the function comment on
/// convertAtomicStoreToIntegerType for background.
LoadInst *AtomicExpand::convertAtomicLoadToIntegerType(LoadInst *LI) {
auto *M = LI->getModule();
Type *NewTy = getCorrespondingIntegerType(LI->getType(),
M->getDataLayout());
IRBuilder<> Builder(LI);
Value *Addr = LI->getPointerOperand();
Type *PT = PointerType::get(NewTy,
Addr->getType()->getPointerAddressSpace());
Value *NewAddr = Builder.CreateBitCast(Addr, PT);
auto *NewLI = Builder.CreateLoad(NewAddr);
NewLI->setAlignment(LI->getAlignment());
NewLI->setVolatile(LI->isVolatile());
NewLI->setAtomic(LI->getOrdering(), LI->getSynchScope());
DEBUG(dbgs() << "Replaced " << *LI << " with " << *NewLI << "\n");
Value *NewVal = Builder.CreateBitCast(NewLI, LI->getType());
LI->replaceAllUsesWith(NewVal);
LI->eraseFromParent();
return NewLI;
}
bool AtomicExpand::tryExpandAtomicLoad(LoadInst *LI) {
switch (TLI->shouldExpandAtomicLoadInIR(LI)) {
case TargetLoweringBase::AtomicExpansionKind::None:
return false;
case TargetLoweringBase::AtomicExpansionKind::LLSC:
expandAtomicOpToLLSC(
LI, LI->getType(), LI->getPointerOperand(), LI->getOrdering(),
[](IRBuilder<> &Builder, Value *Loaded) { return Loaded; });
return true;
case TargetLoweringBase::AtomicExpansionKind::LLOnly:
return expandAtomicLoadToLL(LI);
case TargetLoweringBase::AtomicExpansionKind::CmpXChg:
return expandAtomicLoadToCmpXchg(LI);
}
llvm_unreachable("Unhandled case in tryExpandAtomicLoad");
}
bool AtomicExpand::expandAtomicLoadToLL(LoadInst *LI) {
IRBuilder<> Builder(LI);
// On some architectures, load-linked instructions are atomic for larger
// sizes than normal loads. For example, the only 64-bit load guaranteed
// to be single-copy atomic by ARM is an ldrexd (A3.5.3).
Value *Val =
TLI->emitLoadLinked(Builder, LI->getPointerOperand(), LI->getOrdering());
TLI->emitAtomicCmpXchgNoStoreLLBalance(Builder);
LI->replaceAllUsesWith(Val);
LI->eraseFromParent();
return true;
}
bool AtomicExpand::expandAtomicLoadToCmpXchg(LoadInst *LI) {
IRBuilder<> Builder(LI);
AtomicOrdering Order = LI->getOrdering();
Value *Addr = LI->getPointerOperand();
Type *Ty = cast<PointerType>(Addr->getType())->getElementType();
Constant *DummyVal = Constant::getNullValue(Ty);
Value *Pair = Builder.CreateAtomicCmpXchg(
Addr, DummyVal, DummyVal, Order,
AtomicCmpXchgInst::getStrongestFailureOrdering(Order));
Value *Loaded = Builder.CreateExtractValue(Pair, 0, "loaded");
LI->replaceAllUsesWith(Loaded);
LI->eraseFromParent();
return true;
}
/// Convert an atomic store of a non-integral type to an integer store of the
/// equivalent bitwidth. We used to not support floating point or vector
/// atomics in the IR at all. The backends learned to deal with the bitcast
/// idiom because that was the only way of expressing the notion of a atomic
/// float or vector store. The long term plan is to teach each backend to
/// instruction select from the original atomic store, but as a migration
/// mechanism, we convert back to the old format which the backends understand.
/// Each backend will need individual work to recognize the new format.
StoreInst *AtomicExpand::convertAtomicStoreToIntegerType(StoreInst *SI) {
IRBuilder<> Builder(SI);
auto *M = SI->getModule();
Type *NewTy = getCorrespondingIntegerType(SI->getValueOperand()->getType(),
M->getDataLayout());
Value *NewVal = Builder.CreateBitCast(SI->getValueOperand(), NewTy);
Value *Addr = SI->getPointerOperand();
Type *PT = PointerType::get(NewTy,
Addr->getType()->getPointerAddressSpace());
Value *NewAddr = Builder.CreateBitCast(Addr, PT);
StoreInst *NewSI = Builder.CreateStore(NewVal, NewAddr);
NewSI->setAlignment(SI->getAlignment());
NewSI->setVolatile(SI->isVolatile());
NewSI->setAtomic(SI->getOrdering(), SI->getSynchScope());
DEBUG(dbgs() << "Replaced " << *SI << " with " << *NewSI << "\n");
SI->eraseFromParent();
return NewSI;
}
bool AtomicExpand::expandAtomicStore(StoreInst *SI) {
// This function is only called on atomic stores that are too large to be
// atomic if implemented as a native store. So we replace them by an
// atomic swap, that can be implemented for example as a ldrex/strex on ARM
// or lock cmpxchg8/16b on X86, as these are atomic for larger sizes.
// It is the responsibility of the target to only signal expansion via
// shouldExpandAtomicRMW in cases where this is required and possible.
IRBuilder<> Builder(SI);
AtomicRMWInst *AI =
Builder.CreateAtomicRMW(AtomicRMWInst::Xchg, SI->getPointerOperand(),
SI->getValueOperand(), SI->getOrdering());
SI->eraseFromParent();
// Now we have an appropriate swap instruction, lower it as usual.
return tryExpandAtomicRMW(AI);
}
static void createCmpXchgInstFun(IRBuilder<> &Builder, Value *Addr,
Value *Loaded, Value *NewVal,
AtomicOrdering MemOpOrder,
Value *&Success, Value *&NewLoaded) {
Value* Pair = Builder.CreateAtomicCmpXchg(
Addr, Loaded, NewVal, MemOpOrder,
AtomicCmpXchgInst::getStrongestFailureOrdering(MemOpOrder));
Success = Builder.CreateExtractValue(Pair, 1, "success");
NewLoaded = Builder.CreateExtractValue(Pair, 0, "newloaded");
}
/// Emit IR to implement the given atomicrmw operation on values in registers,
/// returning the new value.
static Value *performAtomicOp(AtomicRMWInst::BinOp Op, IRBuilder<> &Builder,
Value *Loaded, Value *Inc) {
Value *NewVal;
switch (Op) {
case AtomicRMWInst::Xchg:
return Inc;
case AtomicRMWInst::Add:
return Builder.CreateAdd(Loaded, Inc, "new");
case AtomicRMWInst::Sub:
return Builder.CreateSub(Loaded, Inc, "new");
case AtomicRMWInst::And:
return Builder.CreateAnd(Loaded, Inc, "new");
case AtomicRMWInst::Nand:
return Builder.CreateNot(Builder.CreateAnd(Loaded, Inc), "new");
case AtomicRMWInst::Or:
return Builder.CreateOr(Loaded, Inc, "new");
case AtomicRMWInst::Xor:
return Builder.CreateXor(Loaded, Inc, "new");
case AtomicRMWInst::Max:
NewVal = Builder.CreateICmpSGT(Loaded, Inc);
return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
case AtomicRMWInst::Min:
NewVal = Builder.CreateICmpSLE(Loaded, Inc);
return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
case AtomicRMWInst::UMax:
NewVal = Builder.CreateICmpUGT(Loaded, Inc);
return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
case AtomicRMWInst::UMin:
NewVal = Builder.CreateICmpULE(Loaded, Inc);
return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
default:
llvm_unreachable("Unknown atomic op");
}
}
bool AtomicExpand::tryExpandAtomicRMW(AtomicRMWInst *AI) {
switch (TLI->shouldExpandAtomicRMWInIR(AI)) {
case TargetLoweringBase::AtomicExpansionKind::None:
return false;
case TargetLoweringBase::AtomicExpansionKind::LLSC: {
unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
unsigned ValueSize = getAtomicOpSize(AI);
if (ValueSize < MinCASSize) {
llvm_unreachable(
"MinCmpXchgSizeInBits not yet supported for LL/SC architectures.");
} else {
auto PerformOp = [&](IRBuilder<> &Builder, Value *Loaded) {
return performAtomicOp(AI->getOperation(), Builder, Loaded,
AI->getValOperand());
};
expandAtomicOpToLLSC(AI, AI->getType(), AI->getPointerOperand(),
AI->getOrdering(), PerformOp);
}
return true;
}
case TargetLoweringBase::AtomicExpansionKind::CmpXChg: {
unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
unsigned ValueSize = getAtomicOpSize(AI);
if (ValueSize < MinCASSize) {
expandPartwordAtomicRMW(AI,
TargetLoweringBase::AtomicExpansionKind::CmpXChg);
} else {
expandAtomicRMWToCmpXchg(AI, createCmpXchgInstFun);
}
return true;
}
default:
llvm_unreachable("Unhandled case in tryExpandAtomicRMW");
}
}
namespace {
/// Result values from createMaskInstrs helper.
struct PartwordMaskValues {
Type *WordType;
Type *ValueType;
Value *AlignedAddr;
Value *ShiftAmt;
Value *Mask;
Value *Inv_Mask;
};
} // end anonymous namespace
/// This is a helper function which builds instructions to provide
/// values necessary for partword atomic operations. It takes an
/// incoming address, Addr, and ValueType, and constructs the address,
/// shift-amounts and masks needed to work with a larger value of size
/// WordSize.
///
/// AlignedAddr: Addr rounded down to a multiple of WordSize
///
/// ShiftAmt: Number of bits to right-shift a WordSize value loaded
/// from AlignAddr for it to have the same value as if
/// ValueType was loaded from Addr.
///
/// Mask: Value to mask with the value loaded from AlignAddr to
/// include only the part that would've been loaded from Addr.
///
/// Inv_Mask: The inverse of Mask.
static PartwordMaskValues createMaskInstrs(IRBuilder<> &Builder, Instruction *I,
Type *ValueType, Value *Addr,
unsigned WordSize) {
PartwordMaskValues Ret;
BasicBlock *BB = I->getParent();
Function *F = BB->getParent();
Module *M = I->getModule();
LLVMContext &Ctx = F->getContext();
const DataLayout &DL = M->getDataLayout();
unsigned ValueSize = DL.getTypeStoreSize(ValueType);
assert(ValueSize < WordSize);
Ret.ValueType = ValueType;
Ret.WordType = Type::getIntNTy(Ctx, WordSize * 8);
Type *WordPtrType =
Ret.WordType->getPointerTo(Addr->getType()->getPointerAddressSpace());
Value *AddrInt = Builder.CreatePtrToInt(Addr, DL.getIntPtrType(Ctx));
Ret.AlignedAddr = Builder.CreateIntToPtr(
Builder.CreateAnd(AddrInt, ~(uint64_t)(WordSize - 1)), WordPtrType,
"AlignedAddr");
Value *PtrLSB = Builder.CreateAnd(AddrInt, WordSize - 1, "PtrLSB");
if (DL.isLittleEndian()) {
// turn bytes into bits
Ret.ShiftAmt = Builder.CreateShl(PtrLSB, 3);
} else {
// turn bytes into bits, and count from the other side.
Ret.ShiftAmt =
Builder.CreateShl(Builder.CreateXor(PtrLSB, WordSize - ValueSize), 3);
}
Ret.ShiftAmt = Builder.CreateTrunc(Ret.ShiftAmt, Ret.WordType, "ShiftAmt");
Ret.Mask = Builder.CreateShl(
ConstantInt::get(Ret.WordType, (1 << ValueSize * 8) - 1), Ret.ShiftAmt,
"Mask");
Ret.Inv_Mask = Builder.CreateNot(Ret.Mask, "Inv_Mask");
return Ret;
}
/// Emit IR to implement a masked version of a given atomicrmw
/// operation. (That is, only the bits under the Mask should be
/// affected by the operation)
static Value *performMaskedAtomicOp(AtomicRMWInst::BinOp Op,
IRBuilder<> &Builder, Value *Loaded,
Value *Shifted_Inc, Value *Inc,
const PartwordMaskValues &PMV) {
switch (Op) {
case AtomicRMWInst::Xchg: {
Value *Loaded_MaskOut = Builder.CreateAnd(Loaded, PMV.Inv_Mask);
Value *FinalVal = Builder.CreateOr(Loaded_MaskOut, Shifted_Inc);
return FinalVal;
}
case AtomicRMWInst::Or:
case AtomicRMWInst::Xor:
// Or/Xor won't affect any other bits, so can just be done
// directly.
return performAtomicOp(Op, Builder, Loaded, Shifted_Inc);
case AtomicRMWInst::Add:
case AtomicRMWInst::Sub:
case AtomicRMWInst::And:
case AtomicRMWInst::Nand: {
// The other arithmetic ops need to be masked into place.
Value *NewVal = performAtomicOp(Op, Builder, Loaded, Shifted_Inc);
Value *NewVal_Masked = Builder.CreateAnd(NewVal, PMV.Mask);
Value *Loaded_MaskOut = Builder.CreateAnd(Loaded, PMV.Inv_Mask);
Value *FinalVal = Builder.CreateOr(Loaded_MaskOut, NewVal_Masked);
return FinalVal;
}
case AtomicRMWInst::Max:
case AtomicRMWInst::Min:
case AtomicRMWInst::UMax:
case AtomicRMWInst::UMin: {
// Finally, comparison ops will operate on the full value, so
// truncate down to the original size, and expand out again after
// doing the operation.
Value *Loaded_Shiftdown = Builder.CreateTrunc(
Builder.CreateLShr(Loaded, PMV.ShiftAmt), PMV.ValueType);
Value *NewVal = performAtomicOp(Op, Builder, Loaded_Shiftdown, Inc);
Value *NewVal_Shiftup = Builder.CreateShl(
Builder.CreateZExt(NewVal, PMV.WordType), PMV.ShiftAmt);
Value *Loaded_MaskOut = Builder.CreateAnd(Loaded, PMV.Inv_Mask);
Value *FinalVal = Builder.CreateOr(Loaded_MaskOut, NewVal_Shiftup);
return FinalVal;
}
default:
llvm_unreachable("Unknown atomic op");
}
}
/// Expand a sub-word atomicrmw operation into an appropriate
/// word-sized operation.
///
/// It will create an LL/SC or cmpxchg loop, as appropriate, the same
/// way as a typical atomicrmw expansion. The only difference here is
/// that the operation inside of the loop must operate only upon a
/// part of the value.
void AtomicExpand::expandPartwordAtomicRMW(
AtomicRMWInst *AI, TargetLoweringBase::AtomicExpansionKind ExpansionKind) {
assert(ExpansionKind == TargetLoweringBase::AtomicExpansionKind::CmpXChg);
AtomicOrdering MemOpOrder = AI->getOrdering();
IRBuilder<> Builder(AI);
PartwordMaskValues PMV =
createMaskInstrs(Builder, AI, AI->getType(), AI->getPointerOperand(),
TLI->getMinCmpXchgSizeInBits() / 8);
Value *ValOperand_Shifted =
Builder.CreateShl(Builder.CreateZExt(AI->getValOperand(), PMV.WordType),
PMV.ShiftAmt, "ValOperand_Shifted");
auto PerformPartwordOp = [&](IRBuilder<> &Builder, Value *Loaded) {
return performMaskedAtomicOp(AI->getOperation(), Builder, Loaded,
ValOperand_Shifted, AI->getValOperand(), PMV);
};
// TODO: When we're ready to support LLSC conversions too, use
// insertRMWLLSCLoop here for ExpansionKind==LLSC.
Value *OldResult =
insertRMWCmpXchgLoop(Builder, PMV.WordType, PMV.AlignedAddr, MemOpOrder,
PerformPartwordOp, createCmpXchgInstFun);
Value *FinalOldResult = Builder.CreateTrunc(
Builder.CreateLShr(OldResult, PMV.ShiftAmt), PMV.ValueType);
AI->replaceAllUsesWith(FinalOldResult);
AI->eraseFromParent();
}
void AtomicExpand::expandPartwordCmpXchg(AtomicCmpXchgInst *CI) {
// The basic idea here is that we're expanding a cmpxchg of a
// smaller memory size up to a word-sized cmpxchg. To do this, we
// need to add a retry-loop for strong cmpxchg, so that
// modifications to other parts of the word don't cause a spurious
// failure.
// This generates code like the following:
// [[Setup mask values PMV.*]]
// %NewVal_Shifted = shl i32 %NewVal, %PMV.ShiftAmt
// %Cmp_Shifted = shl i32 %Cmp, %PMV.ShiftAmt
// %InitLoaded = load i32* %addr
// %InitLoaded_MaskOut = and i32 %InitLoaded, %PMV.Inv_Mask
// br partword.cmpxchg.loop
// partword.cmpxchg.loop:
// %Loaded_MaskOut = phi i32 [ %InitLoaded_MaskOut, %entry ],
// [ %OldVal_MaskOut, %partword.cmpxchg.failure ]
// %FullWord_NewVal = or i32 %Loaded_MaskOut, %NewVal_Shifted
// %FullWord_Cmp = or i32 %Loaded_MaskOut, %Cmp_Shifted
// %NewCI = cmpxchg i32* %PMV.AlignedAddr, i32 %FullWord_Cmp,
// i32 %FullWord_NewVal success_ordering failure_ordering
// %OldVal = extractvalue { i32, i1 } %NewCI, 0
// %Success = extractvalue { i32, i1 } %NewCI, 1
// br i1 %Success, label %partword.cmpxchg.end,
// label %partword.cmpxchg.failure
// partword.cmpxchg.failure:
// %OldVal_MaskOut = and i32 %OldVal, %PMV.Inv_Mask
// %ShouldContinue = icmp ne i32 %Loaded_MaskOut, %OldVal_MaskOut
// br i1 %ShouldContinue, label %partword.cmpxchg.loop,
// label %partword.cmpxchg.end
// partword.cmpxchg.end:
// %tmp1 = lshr i32 %OldVal, %PMV.ShiftAmt
// %FinalOldVal = trunc i32 %tmp1 to i8
// %tmp2 = insertvalue { i8, i1 } undef, i8 %FinalOldVal, 0
// %Res = insertvalue { i8, i1 } %25, i1 %Success, 1
Value *Addr = CI->getPointerOperand();
Value *Cmp = CI->getCompareOperand();
Value *NewVal = CI->getNewValOperand();
BasicBlock *BB = CI->getParent();
Function *F = BB->getParent();
IRBuilder<> Builder(CI);
LLVMContext &Ctx = Builder.getContext();
const int WordSize = TLI->getMinCmpXchgSizeInBits() / 8;
BasicBlock *EndBB =
BB->splitBasicBlock(CI->getIterator(), "partword.cmpxchg.end");
auto FailureBB =
BasicBlock::Create(Ctx, "partword.cmpxchg.failure", F, EndBB);
auto LoopBB = BasicBlock::Create(Ctx, "partword.cmpxchg.loop", F, FailureBB);
// The split call above "helpfully" added a branch at the end of BB
// (to the wrong place).
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
PartwordMaskValues PMV = createMaskInstrs(
Builder, CI, CI->getCompareOperand()->getType(), Addr, WordSize);
// Shift the incoming values over, into the right location in the word.
Value *NewVal_Shifted =
Builder.CreateShl(Builder.CreateZExt(NewVal, PMV.WordType), PMV.ShiftAmt);
Value *Cmp_Shifted =
Builder.CreateShl(Builder.CreateZExt(Cmp, PMV.WordType), PMV.ShiftAmt);
// Load the entire current word, and mask into place the expected and new
// values
LoadInst *InitLoaded = Builder.CreateLoad(PMV.WordType, PMV.AlignedAddr);
InitLoaded->setVolatile(CI->isVolatile());
Value *InitLoaded_MaskOut = Builder.CreateAnd(InitLoaded, PMV.Inv_Mask);
Builder.CreateBr(LoopBB);
// partword.cmpxchg.loop:
Builder.SetInsertPoint(LoopBB);
PHINode *Loaded_MaskOut = Builder.CreatePHI(PMV.WordType, 2);
Loaded_MaskOut->addIncoming(InitLoaded_MaskOut, BB);
// Mask/Or the expected and new values into place in the loaded word.
Value *FullWord_NewVal = Builder.CreateOr(Loaded_MaskOut, NewVal_Shifted);
Value *FullWord_Cmp = Builder.CreateOr(Loaded_MaskOut, Cmp_Shifted);
AtomicCmpXchgInst *NewCI = Builder.CreateAtomicCmpXchg(
PMV.AlignedAddr, FullWord_Cmp, FullWord_NewVal, CI->getSuccessOrdering(),
CI->getFailureOrdering(), CI->getSynchScope());
NewCI->setVolatile(CI->isVolatile());
// When we're building a strong cmpxchg, we need a loop, so you
// might think we could use a weak cmpxchg inside. But, using strong
// allows the below comparison for ShouldContinue, and we're
// expecting the underlying cmpxchg to be a machine instruction,
// which is strong anyways.
NewCI->setWeak(CI->isWeak());
Value *OldVal = Builder.CreateExtractValue(NewCI, 0);
Value *Success = Builder.CreateExtractValue(NewCI, 1);
if (CI->isWeak())
Builder.CreateBr(EndBB);
else
Builder.CreateCondBr(Success, EndBB, FailureBB);
// partword.cmpxchg.failure:
Builder.SetInsertPoint(FailureBB);
// Upon failure, verify that the masked-out part of the loaded value
// has been modified. If it didn't, abort the cmpxchg, since the
// masked-in part must've.
Value *OldVal_MaskOut = Builder.CreateAnd(OldVal, PMV.Inv_Mask);
Value *ShouldContinue = Builder.CreateICmpNE(Loaded_MaskOut, OldVal_MaskOut);
Builder.CreateCondBr(ShouldContinue, LoopBB, EndBB);
// Add the second value to the phi from above
Loaded_MaskOut->addIncoming(OldVal_MaskOut, FailureBB);
// partword.cmpxchg.end:
Builder.SetInsertPoint(CI);
Value *FinalOldVal = Builder.CreateTrunc(
Builder.CreateLShr(OldVal, PMV.ShiftAmt), PMV.ValueType);
Value *Res = UndefValue::get(CI->getType());
Res = Builder.CreateInsertValue(Res, FinalOldVal, 0);
Res = Builder.CreateInsertValue(Res, Success, 1);
CI->replaceAllUsesWith(Res);
CI->eraseFromParent();
}
void AtomicExpand::expandAtomicOpToLLSC(
Instruction *I, Type *ResultType, Value *Addr, AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp) {
IRBuilder<> Builder(I);
Value *Loaded =
insertRMWLLSCLoop(Builder, ResultType, Addr, MemOpOrder, PerformOp);
I->replaceAllUsesWith(Loaded);
I->eraseFromParent();
}
Value *AtomicExpand::insertRMWLLSCLoop(
IRBuilder<> &Builder, Type *ResultTy, Value *Addr,
AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp) {
LLVMContext &Ctx = Builder.getContext();
BasicBlock *BB = Builder.GetInsertBlock();
Function *F = BB->getParent();
// Given: atomicrmw some_op iN* %addr, iN %incr ordering
//
// The standard expansion we produce is:
// [...]
// atomicrmw.start:
// %loaded = @load.linked(%addr)
// %new = some_op iN %loaded, %incr
// %stored = @store_conditional(%new, %addr)
// %try_again = icmp i32 ne %stored, 0
// br i1 %try_again, label %loop, label %atomicrmw.end
// atomicrmw.end:
// [...]
BasicBlock *ExitBB =
BB->splitBasicBlock(Builder.GetInsertPoint(), "atomicrmw.end");
BasicBlock *LoopBB = BasicBlock::Create(Ctx, "atomicrmw.start", F, ExitBB);
// The split call above "helpfully" added a branch at the end of BB (to the
// wrong place).
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
Builder.CreateBr(LoopBB);
// Start the main loop block now that we've taken care of the preliminaries.
Builder.SetInsertPoint(LoopBB);
Value *Loaded = TLI->emitLoadLinked(Builder, Addr, MemOpOrder);
Value *NewVal = PerformOp(Builder, Loaded);
Value *StoreSuccess =
TLI->emitStoreConditional(Builder, NewVal, Addr, MemOpOrder);
Value *TryAgain = Builder.CreateICmpNE(
StoreSuccess, ConstantInt::get(IntegerType::get(Ctx, 32), 0), "tryagain");
Builder.CreateCondBr(TryAgain, LoopBB, ExitBB);
Builder.SetInsertPoint(ExitBB, ExitBB->begin());
return Loaded;
}
/// Convert an atomic cmpxchg of a non-integral type to an integer cmpxchg of
/// the equivalent bitwidth. We used to not support pointer cmpxchg in the
/// IR. As a migration step, we convert back to what use to be the standard
/// way to represent a pointer cmpxchg so that we can update backends one by
/// one.
AtomicCmpXchgInst *AtomicExpand::convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI) {
auto *M = CI->getModule();
Type *NewTy = getCorrespondingIntegerType(CI->getCompareOperand()->getType(),
M->getDataLayout());
IRBuilder<> Builder(CI);
Value *Addr = CI->getPointerOperand();
Type *PT = PointerType::get(NewTy,
Addr->getType()->getPointerAddressSpace());
Value *NewAddr = Builder.CreateBitCast(Addr, PT);
Value *NewCmp = Builder.CreatePtrToInt(CI->getCompareOperand(), NewTy);
Value *NewNewVal = Builder.CreatePtrToInt(CI->getNewValOperand(), NewTy);
auto *NewCI = Builder.CreateAtomicCmpXchg(NewAddr, NewCmp, NewNewVal,
CI->getSuccessOrdering(),
CI->getFailureOrdering(),
CI->getSynchScope());
NewCI->setVolatile(CI->isVolatile());
NewCI->setWeak(CI->isWeak());
DEBUG(dbgs() << "Replaced " << *CI << " with " << *NewCI << "\n");
Value *OldVal = Builder.CreateExtractValue(NewCI, 0);
Value *Succ = Builder.CreateExtractValue(NewCI, 1);
OldVal = Builder.CreateIntToPtr(OldVal, CI->getCompareOperand()->getType());
Value *Res = UndefValue::get(CI->getType());
Res = Builder.CreateInsertValue(Res, OldVal, 0);
Res = Builder.CreateInsertValue(Res, Succ, 1);
CI->replaceAllUsesWith(Res);
CI->eraseFromParent();
return NewCI;
}
bool AtomicExpand::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
AtomicOrdering SuccessOrder = CI->getSuccessOrdering();
AtomicOrdering FailureOrder = CI->getFailureOrdering();
Value *Addr = CI->getPointerOperand();
BasicBlock *BB = CI->getParent();
Function *F = BB->getParent();
LLVMContext &Ctx = F->getContext();
// If shouldInsertFencesForAtomic() returns true, then the target does not
// want to deal with memory orders, and emitLeading/TrailingFence should take
// care of everything. Otherwise, emitLeading/TrailingFence are no-op and we
// should preserve the ordering.
bool ShouldInsertFencesForAtomic = TLI->shouldInsertFencesForAtomic(CI);
AtomicOrdering MemOpOrder =
ShouldInsertFencesForAtomic ? AtomicOrdering::Monotonic : SuccessOrder;
// In implementations which use a barrier to achieve release semantics, we can
// delay emitting this barrier until we know a store is actually going to be
// attempted. The cost of this delay is that we need 2 copies of the block
// emitting the load-linked, affecting code size.
//
// Ideally, this logic would be unconditional except for the minsize check
// since in other cases the extra blocks naturally collapse down to the
// minimal loop. Unfortunately, this puts too much stress on later
// optimisations so we avoid emitting the extra logic in those cases too.
bool HasReleasedLoadBB = !CI->isWeak() && ShouldInsertFencesForAtomic &&
SuccessOrder != AtomicOrdering::Monotonic &&
SuccessOrder != AtomicOrdering::Acquire &&
!F->optForMinSize();
// There's no overhead for sinking the release barrier in a weak cmpxchg, so
// do it even on minsize.
bool UseUnconditionalReleaseBarrier = F->optForMinSize() && !CI->isWeak();
// Given: cmpxchg some_op iN* %addr, iN %desired, iN %new success_ord fail_ord
//
// The full expansion we produce is:
// [...]
// cmpxchg.start:
// %unreleasedload = @load.linked(%addr)
// %should_store = icmp eq %unreleasedload, %desired
// br i1 %should_store, label %cmpxchg.fencedstore,
// label %cmpxchg.nostore
// cmpxchg.releasingstore:
// fence?
// br label cmpxchg.trystore
// cmpxchg.trystore:
// %loaded.trystore = phi [%unreleasedload, %releasingstore],
// [%releasedload, %cmpxchg.releasedload]
// %stored = @store_conditional(%new, %addr)
// %success = icmp eq i32 %stored, 0
// br i1 %success, label %cmpxchg.success,
// label %cmpxchg.releasedload/%cmpxchg.failure
// cmpxchg.releasedload:
// %releasedload = @load.linked(%addr)
// %should_store = icmp eq %releasedload, %desired
// br i1 %should_store, label %cmpxchg.trystore,
// label %cmpxchg.failure
// cmpxchg.success:
// fence?
// br label %cmpxchg.end
// cmpxchg.nostore:
// %loaded.nostore = phi [%unreleasedload, %cmpxchg.start],
// [%releasedload,
// %cmpxchg.releasedload/%cmpxchg.trystore]
// @load_linked_fail_balance()?
// br label %cmpxchg.failure
// cmpxchg.failure:
// fence?
// br label %cmpxchg.end
// cmpxchg.end:
// %loaded = phi [%loaded.nostore, %cmpxchg.failure],
// [%loaded.trystore, %cmpxchg.trystore]
// %success = phi i1 [true, %cmpxchg.success], [false, %cmpxchg.failure]
// %restmp = insertvalue { iN, i1 } undef, iN %loaded, 0
// %res = insertvalue { iN, i1 } %restmp, i1 %success, 1
// [...]
BasicBlock *ExitBB = BB->splitBasicBlock(CI->getIterator(), "cmpxchg.end");
auto FailureBB = BasicBlock::Create(Ctx, "cmpxchg.failure", F, ExitBB);
auto NoStoreBB = BasicBlock::Create(Ctx, "cmpxchg.nostore", F, FailureBB);
auto SuccessBB = BasicBlock::Create(Ctx, "cmpxchg.success", F, NoStoreBB);
auto ReleasedLoadBB =
BasicBlock::Create(Ctx, "cmpxchg.releasedload", F, SuccessBB);
auto TryStoreBB =
BasicBlock::Create(Ctx, "cmpxchg.trystore", F, ReleasedLoadBB);
auto ReleasingStoreBB =
BasicBlock::Create(Ctx, "cmpxchg.fencedstore", F, TryStoreBB);
auto StartBB = BasicBlock::Create(Ctx, "cmpxchg.start", F, ReleasingStoreBB);
// This grabs the DebugLoc from CI
IRBuilder<> Builder(CI);
// The split call above "helpfully" added a branch at the end of BB (to the
// wrong place), but we might want a fence too. It's easiest to just remove
// the branch entirely.
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
if (ShouldInsertFencesForAtomic && UseUnconditionalReleaseBarrier)
TLI->emitLeadingFence(Builder, CI, SuccessOrder);
Builder.CreateBr(StartBB);
// Start the main loop block now that we've taken care of the preliminaries.
Builder.SetInsertPoint(StartBB);
Value *UnreleasedLoad = TLI->emitLoadLinked(Builder, Addr, MemOpOrder);
Value *ShouldStore = Builder.CreateICmpEQ(
UnreleasedLoad, CI->getCompareOperand(), "should_store");
// If the cmpxchg doesn't actually need any ordering when it fails, we can
// jump straight past that fence instruction (if it exists).
Builder.CreateCondBr(ShouldStore, ReleasingStoreBB, NoStoreBB);
Builder.SetInsertPoint(ReleasingStoreBB);
if (ShouldInsertFencesForAtomic && !UseUnconditionalReleaseBarrier)
TLI->emitLeadingFence(Builder, CI, SuccessOrder);
Builder.CreateBr(TryStoreBB);
Builder.SetInsertPoint(TryStoreBB);
Value *StoreSuccess = TLI->emitStoreConditional(
Builder, CI->getNewValOperand(), Addr, MemOpOrder);
StoreSuccess = Builder.CreateICmpEQ(
StoreSuccess, ConstantInt::get(Type::getInt32Ty(Ctx), 0), "success");
BasicBlock *RetryBB = HasReleasedLoadBB ? ReleasedLoadBB : StartBB;
Builder.CreateCondBr(StoreSuccess, SuccessBB,
CI->isWeak() ? FailureBB : RetryBB);
Builder.SetInsertPoint(ReleasedLoadBB);
Value *SecondLoad;
if (HasReleasedLoadBB) {
SecondLoad = TLI->emitLoadLinked(Builder, Addr, MemOpOrder);
ShouldStore = Builder.CreateICmpEQ(SecondLoad, CI->getCompareOperand(),
"should_store");
// If the cmpxchg doesn't actually need any ordering when it fails, we can
// jump straight past that fence instruction (if it exists).
Builder.CreateCondBr(ShouldStore, TryStoreBB, NoStoreBB);
} else
Builder.CreateUnreachable();
// Make sure later instructions don't get reordered with a fence if
// necessary.
Builder.SetInsertPoint(SuccessBB);
if (ShouldInsertFencesForAtomic)
TLI->emitTrailingFence(Builder, CI, SuccessOrder);
Builder.CreateBr(ExitBB);
Builder.SetInsertPoint(NoStoreBB);
// In the failing case, where we don't execute the store-conditional, the
// target might want to balance out the load-linked with a dedicated
// instruction (e.g., on ARM, clearing the exclusive monitor).
TLI->emitAtomicCmpXchgNoStoreLLBalance(Builder);
Builder.CreateBr(FailureBB);
Builder.SetInsertPoint(FailureBB);
if (ShouldInsertFencesForAtomic)
TLI->emitTrailingFence(Builder, CI, FailureOrder);
Builder.CreateBr(ExitBB);
// Finally, we have control-flow based knowledge of whether the cmpxchg
// succeeded or not. We expose this to later passes by converting any
// subsequent "icmp eq/ne %loaded, %oldval" into a use of an appropriate
// PHI.
Builder.SetInsertPoint(ExitBB, ExitBB->begin());
PHINode *Success = Builder.CreatePHI(Type::getInt1Ty(Ctx), 2);
Success->addIncoming(ConstantInt::getTrue(Ctx), SuccessBB);
Success->addIncoming(ConstantInt::getFalse(Ctx), FailureBB);
// Setup the builder so we can create any PHIs we need.
Value *Loaded;
if (!HasReleasedLoadBB)
Loaded = UnreleasedLoad;
else {
Builder.SetInsertPoint(TryStoreBB, TryStoreBB->begin());
PHINode *TryStoreLoaded = Builder.CreatePHI(UnreleasedLoad->getType(), 2);
TryStoreLoaded->addIncoming(UnreleasedLoad, ReleasingStoreBB);
TryStoreLoaded->addIncoming(SecondLoad, ReleasedLoadBB);
Builder.SetInsertPoint(NoStoreBB, NoStoreBB->begin());
PHINode *NoStoreLoaded = Builder.CreatePHI(UnreleasedLoad->getType(), 2);
NoStoreLoaded->addIncoming(UnreleasedLoad, StartBB);
NoStoreLoaded->addIncoming(SecondLoad, ReleasedLoadBB);
Builder.SetInsertPoint(ExitBB, ++ExitBB->begin());
PHINode *ExitLoaded = Builder.CreatePHI(UnreleasedLoad->getType(), 2);
ExitLoaded->addIncoming(TryStoreLoaded, SuccessBB);
ExitLoaded->addIncoming(NoStoreLoaded, FailureBB);
Loaded = ExitLoaded;
}
// Look for any users of the cmpxchg that are just comparing the loaded value
// against the desired one, and replace them with the CFG-derived version.
SmallVector<ExtractValueInst *, 2> PrunedInsts;
for (auto User : CI->users()) {
ExtractValueInst *EV = dyn_cast<ExtractValueInst>(User);
if (!EV)
continue;
assert(EV->getNumIndices() == 1 && EV->getIndices()[0] <= 1 &&
"weird extraction from { iN, i1 }");
if (EV->getIndices()[0] == 0)
EV->replaceAllUsesWith(Loaded);
else
EV->replaceAllUsesWith(Success);
PrunedInsts.push_back(EV);
}
// We can remove the instructions now we're no longer iterating through them.
for (auto EV : PrunedInsts)
EV->eraseFromParent();
if (!CI->use_empty()) {
// Some use of the full struct return that we don't understand has happened,
// so we've got to reconstruct it properly.
Value *Res;
Res = Builder.CreateInsertValue(UndefValue::get(CI->getType()), Loaded, 0);
Res = Builder.CreateInsertValue(Res, Success, 1);
CI->replaceAllUsesWith(Res);
}
CI->eraseFromParent();
return true;
}
bool AtomicExpand::isIdempotentRMW(AtomicRMWInst* RMWI) {
auto C = dyn_cast<ConstantInt>(RMWI->getValOperand());
if(!C)
return false;
AtomicRMWInst::BinOp Op = RMWI->getOperation();
switch(Op) {
case AtomicRMWInst::Add:
case AtomicRMWInst::Sub:
case AtomicRMWInst::Or:
case AtomicRMWInst::Xor:
return C->isZero();
case AtomicRMWInst::And:
return C->isMinusOne();
// FIXME: we could also treat Min/Max/UMin/UMax by the INT_MIN/INT_MAX/...
default:
return false;
}
}
bool AtomicExpand::simplifyIdempotentRMW(AtomicRMWInst* RMWI) {
if (auto ResultingLoad = TLI->lowerIdempotentRMWIntoFencedLoad(RMWI)) {
tryExpandAtomicLoad(ResultingLoad);
return true;
}
return false;
}
Value *AtomicExpand::insertRMWCmpXchgLoop(
IRBuilder<> &Builder, Type *ResultTy, Value *Addr,
AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp,
CreateCmpXchgInstFun CreateCmpXchg) {
LLVMContext &Ctx = Builder.getContext();
BasicBlock *BB = Builder.GetInsertBlock();
Function *F = BB->getParent();
// Given: atomicrmw some_op iN* %addr, iN %incr ordering
//
// The standard expansion we produce is:
// [...]
// %init_loaded = load atomic iN* %addr
// br label %loop
// loop:
// %loaded = phi iN [ %init_loaded, %entry ], [ %new_loaded, %loop ]
// %new = some_op iN %loaded, %incr
// %pair = cmpxchg iN* %addr, iN %loaded, iN %new
// %new_loaded = extractvalue { iN, i1 } %pair, 0
// %success = extractvalue { iN, i1 } %pair, 1
// br i1 %success, label %atomicrmw.end, label %loop
// atomicrmw.end:
// [...]
BasicBlock *ExitBB =
BB->splitBasicBlock(Builder.GetInsertPoint(), "atomicrmw.end");
BasicBlock *LoopBB = BasicBlock::Create(Ctx, "atomicrmw.start", F, ExitBB);
// The split call above "helpfully" added a branch at the end of BB (to the
// wrong place), but we want a load. It's easiest to just remove
// the branch entirely.
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
LoadInst *InitLoaded = Builder.CreateLoad(ResultTy, Addr);
// Atomics require at least natural alignment.
InitLoaded->setAlignment(ResultTy->getPrimitiveSizeInBits() / 8);
Builder.CreateBr(LoopBB);
// Start the main loop block now that we've taken care of the preliminaries.
Builder.SetInsertPoint(LoopBB);
PHINode *Loaded = Builder.CreatePHI(ResultTy, 2, "loaded");
Loaded->addIncoming(InitLoaded, BB);
Value *NewVal = PerformOp(Builder, Loaded);
Value *NewLoaded = nullptr;
Value *Success = nullptr;
CreateCmpXchg(Builder, Addr, Loaded, NewVal,
MemOpOrder == AtomicOrdering::Unordered
? AtomicOrdering::Monotonic
: MemOpOrder,
Success, NewLoaded);
assert(Success && NewLoaded);
Loaded->addIncoming(NewLoaded, LoopBB);
Builder.CreateCondBr(Success, ExitBB, LoopBB);
Builder.SetInsertPoint(ExitBB, ExitBB->begin());
return NewLoaded;
}
// Note: This function is exposed externally by AtomicExpandUtils.h
bool llvm::expandAtomicRMWToCmpXchg(AtomicRMWInst *AI,
CreateCmpXchgInstFun CreateCmpXchg) {
IRBuilder<> Builder(AI);
Value *Loaded = AtomicExpand::insertRMWCmpXchgLoop(
Builder, AI->getType(), AI->getPointerOperand(), AI->getOrdering(),
[&](IRBuilder<> &Builder, Value *Loaded) {
return performAtomicOp(AI->getOperation(), Builder, Loaded,
AI->getValOperand());
},
CreateCmpXchg);
AI->replaceAllUsesWith(Loaded);
AI->eraseFromParent();
return true;
}
// In order to use one of the sized library calls such as
// __atomic_fetch_add_4, the alignment must be sufficient, the size
// must be one of the potentially-specialized sizes, and the value
// type must actually exist in C on the target (otherwise, the
// function wouldn't actually be defined.)
static bool canUseSizedAtomicCall(unsigned Size, unsigned Align,
const DataLayout &DL) {
// TODO: "LargestSize" is an approximation for "largest type that
// you can express in C". It seems to be the case that int128 is
// supported on all 64-bit platforms, otherwise only up to 64-bit
// integers are supported. If we get this wrong, then we'll try to
// call a sized libcall that doesn't actually exist. There should
// really be some more reliable way in LLVM of determining integer
// sizes which are valid in the target's C ABI...
unsigned LargestSize = DL.getLargestLegalIntTypeSizeInBits() >= 64 ? 16 : 8;
return Align >= Size &&
(Size == 1 || Size == 2 || Size == 4 || Size == 8 || Size == 16) &&
Size <= LargestSize;
}
void AtomicExpand::expandAtomicLoadToLibcall(LoadInst *I) {
static const RTLIB::Libcall Libcalls[6] = {
RTLIB::ATOMIC_LOAD, RTLIB::ATOMIC_LOAD_1, RTLIB::ATOMIC_LOAD_2,
RTLIB::ATOMIC_LOAD_4, RTLIB::ATOMIC_LOAD_8, RTLIB::ATOMIC_LOAD_16};
unsigned Size = getAtomicOpSize(I);
unsigned Align = getAtomicOpAlign(I);
bool expanded = expandAtomicOpToLibcall(
I, Size, Align, I->getPointerOperand(), nullptr, nullptr,
I->getOrdering(), AtomicOrdering::NotAtomic, Libcalls);
(void)expanded;
assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor Load");
}
void AtomicExpand::expandAtomicStoreToLibcall(StoreInst *I) {
static const RTLIB::Libcall Libcalls[6] = {
RTLIB::ATOMIC_STORE, RTLIB::ATOMIC_STORE_1, RTLIB::ATOMIC_STORE_2,
RTLIB::ATOMIC_STORE_4, RTLIB::ATOMIC_STORE_8, RTLIB::ATOMIC_STORE_16};
unsigned Size = getAtomicOpSize(I);
unsigned Align = getAtomicOpAlign(I);
bool expanded = expandAtomicOpToLibcall(
I, Size, Align, I->getPointerOperand(), I->getValueOperand(), nullptr,
I->getOrdering(), AtomicOrdering::NotAtomic, Libcalls);
(void)expanded;
assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor Store");
}
void AtomicExpand::expandAtomicCASToLibcall(AtomicCmpXchgInst *I) {
static const RTLIB::Libcall Libcalls[6] = {
RTLIB::ATOMIC_COMPARE_EXCHANGE, RTLIB::ATOMIC_COMPARE_EXCHANGE_1,
RTLIB::ATOMIC_COMPARE_EXCHANGE_2, RTLIB::ATOMIC_COMPARE_EXCHANGE_4,
RTLIB::ATOMIC_COMPARE_EXCHANGE_8, RTLIB::ATOMIC_COMPARE_EXCHANGE_16};
unsigned Size = getAtomicOpSize(I);
unsigned Align = getAtomicOpAlign(I);
bool expanded = expandAtomicOpToLibcall(
I, Size, Align, I->getPointerOperand(), I->getNewValOperand(),
I->getCompareOperand(), I->getSuccessOrdering(), I->getFailureOrdering(),
Libcalls);
(void)expanded;
assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor CAS");
}
static ArrayRef<RTLIB::Libcall> GetRMWLibcall(AtomicRMWInst::BinOp Op) {
static const RTLIB::Libcall LibcallsXchg[6] = {
RTLIB::ATOMIC_EXCHANGE, RTLIB::ATOMIC_EXCHANGE_1,
RTLIB::ATOMIC_EXCHANGE_2, RTLIB::ATOMIC_EXCHANGE_4,
RTLIB::ATOMIC_EXCHANGE_8, RTLIB::ATOMIC_EXCHANGE_16};
static const RTLIB::Libcall LibcallsAdd[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_ADD_1,
RTLIB::ATOMIC_FETCH_ADD_2, RTLIB::ATOMIC_FETCH_ADD_4,
RTLIB::ATOMIC_FETCH_ADD_8, RTLIB::ATOMIC_FETCH_ADD_16};
static const RTLIB::Libcall LibcallsSub[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_SUB_1,
RTLIB::ATOMIC_FETCH_SUB_2, RTLIB::ATOMIC_FETCH_SUB_4,
RTLIB::ATOMIC_FETCH_SUB_8, RTLIB::ATOMIC_FETCH_SUB_16};
static const RTLIB::Libcall LibcallsAnd[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_AND_1,
RTLIB::ATOMIC_FETCH_AND_2, RTLIB::ATOMIC_FETCH_AND_4,
RTLIB::ATOMIC_FETCH_AND_8, RTLIB::ATOMIC_FETCH_AND_16};
static const RTLIB::Libcall LibcallsOr[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_OR_1,
RTLIB::ATOMIC_FETCH_OR_2, RTLIB::ATOMIC_FETCH_OR_4,
RTLIB::ATOMIC_FETCH_OR_8, RTLIB::ATOMIC_FETCH_OR_16};
static const RTLIB::Libcall LibcallsXor[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_XOR_1,
RTLIB::ATOMIC_FETCH_XOR_2, RTLIB::ATOMIC_FETCH_XOR_4,
RTLIB::ATOMIC_FETCH_XOR_8, RTLIB::ATOMIC_FETCH_XOR_16};
static const RTLIB::Libcall LibcallsNand[6] = {
RTLIB::UNKNOWN_LIBCALL, RTLIB::ATOMIC_FETCH_NAND_1,
RTLIB::ATOMIC_FETCH_NAND_2, RTLIB::ATOMIC_FETCH_NAND_4,
RTLIB::ATOMIC_FETCH_NAND_8, RTLIB::ATOMIC_FETCH_NAND_16};
switch (Op) {
case AtomicRMWInst::BAD_BINOP:
llvm_unreachable("Should not have BAD_BINOP.");
case AtomicRMWInst::Xchg:
return makeArrayRef(LibcallsXchg);
case AtomicRMWInst::Add:
return makeArrayRef(LibcallsAdd);
case AtomicRMWInst::Sub:
return makeArrayRef(LibcallsSub);
case AtomicRMWInst::And:
return makeArrayRef(LibcallsAnd);
case AtomicRMWInst::Or:
return makeArrayRef(LibcallsOr);
case AtomicRMWInst::Xor:
return makeArrayRef(LibcallsXor);
case AtomicRMWInst::Nand:
return makeArrayRef(LibcallsNand);
case AtomicRMWInst::Max:
case AtomicRMWInst::Min:
case AtomicRMWInst::UMax:
case AtomicRMWInst::UMin:
// No atomic libcalls are available for max/min/umax/umin.
return {};
}
llvm_unreachable("Unexpected AtomicRMW operation.");
}
void AtomicExpand::expandAtomicRMWToLibcall(AtomicRMWInst *I) {
ArrayRef<RTLIB::Libcall> Libcalls = GetRMWLibcall(I->getOperation());
unsigned Size = getAtomicOpSize(I);
unsigned Align = getAtomicOpAlign(I);
bool Success = false;
if (!Libcalls.empty())
Success = expandAtomicOpToLibcall(
I, Size, Align, I->getPointerOperand(), I->getValOperand(), nullptr,
I->getOrdering(), AtomicOrdering::NotAtomic, Libcalls);
// The expansion failed: either there were no libcalls at all for
// the operation (min/max), or there were only size-specialized
// libcalls (add/sub/etc) and we needed a generic. So, expand to a
// CAS libcall, via a CAS loop, instead.
if (!Success) {
expandAtomicRMWToCmpXchg(I, [this](IRBuilder<> &Builder, Value *Addr,
Value *Loaded, Value *NewVal,
AtomicOrdering MemOpOrder,
Value *&Success, Value *&NewLoaded) {
// Create the CAS instruction normally...
AtomicCmpXchgInst *Pair = Builder.CreateAtomicCmpXchg(
Addr, Loaded, NewVal, MemOpOrder,
AtomicCmpXchgInst::getStrongestFailureOrdering(MemOpOrder));
Success = Builder.CreateExtractValue(Pair, 1, "success");
NewLoaded = Builder.CreateExtractValue(Pair, 0, "newloaded");
// ...and then expand the CAS into a libcall.
expandAtomicCASToLibcall(Pair);
});
}
}
// A helper routine for the above expandAtomic*ToLibcall functions.
//
// 'Libcalls' contains an array of enum values for the particular
// ATOMIC libcalls to be emitted. All of the other arguments besides
// 'I' are extracted from the Instruction subclass by the
// caller. Depending on the particular call, some will be null.
bool AtomicExpand::expandAtomicOpToLibcall(
Instruction *I, unsigned Size, unsigned Align, Value *PointerOperand,
Value *ValueOperand, Value *CASExpected, AtomicOrdering Ordering,
AtomicOrdering Ordering2, ArrayRef<RTLIB::Libcall> Libcalls) {
assert(Libcalls.size() == 6);
LLVMContext &Ctx = I->getContext();
Module *M = I->getModule();
const DataLayout &DL = M->getDataLayout();
IRBuilder<> Builder(I);
IRBuilder<> AllocaBuilder(&I->getFunction()->getEntryBlock().front());
bool UseSizedLibcall = canUseSizedAtomicCall(Size, Align, DL);
Type *SizedIntTy = Type::getIntNTy(Ctx, Size * 8);
unsigned AllocaAlignment = DL.getPrefTypeAlignment(SizedIntTy);
// TODO: the "order" argument type is "int", not int32. So
// getInt32Ty may be wrong if the arch uses e.g. 16-bit ints.
ConstantInt *SizeVal64 = ConstantInt::get(Type::getInt64Ty(Ctx), Size);
assert(Ordering != AtomicOrdering::NotAtomic && "expect atomic MO");
Constant *OrderingVal =
ConstantInt::get(Type::getInt32Ty(Ctx), (int)toCABI(Ordering));
Constant *Ordering2Val = nullptr;
if (CASExpected) {
assert(Ordering2 != AtomicOrdering::NotAtomic && "expect atomic MO");
Ordering2Val =
ConstantInt::get(Type::getInt32Ty(Ctx), (int)toCABI(Ordering2));
}
bool HasResult = I->getType() != Type::getVoidTy(Ctx);
RTLIB::Libcall RTLibType;
if (UseSizedLibcall) {
switch (Size) {
case 1: RTLibType = Libcalls[1]; break;
case 2: RTLibType = Libcalls[2]; break;
case 4: RTLibType = Libcalls[3]; break;
case 8: RTLibType = Libcalls[4]; break;
case 16: RTLibType = Libcalls[5]; break;
}
} else if (Libcalls[0] != RTLIB::UNKNOWN_LIBCALL) {
RTLibType = Libcalls[0];
} else {
// Can't use sized function, and there's no generic for this
// operation, so give up.
return false;
}
// Build up the function call. There's two kinds. First, the sized
// variants. These calls are going to be one of the following (with
// N=1,2,4,8,16):
// iN __atomic_load_N(iN *ptr, int ordering)
// void __atomic_store_N(iN *ptr, iN val, int ordering)
// iN __atomic_{exchange|fetch_*}_N(iN *ptr, iN val, int ordering)
// bool __atomic_compare_exchange_N(iN *ptr, iN *expected, iN desired,
// int success_order, int failure_order)
//
// Note that these functions can be used for non-integer atomic
// operations, the values just need to be bitcast to integers on the
// way in and out.
//
// And, then, the generic variants. They look like the following:
// void __atomic_load(size_t size, void *ptr, void *ret, int ordering)
// void __atomic_store(size_t size, void *ptr, void *val, int ordering)
// void __atomic_exchange(size_t size, void *ptr, void *val, void *ret,
// int ordering)
// bool __atomic_compare_exchange(size_t size, void *ptr, void *expected,
// void *desired, int success_order,
// int failure_order)
//
// The different signatures are built up depending on the
// 'UseSizedLibcall', 'CASExpected', 'ValueOperand', and 'HasResult'
// variables.
AllocaInst *AllocaCASExpected = nullptr;
Value *AllocaCASExpected_i8 = nullptr;
AllocaInst *AllocaValue = nullptr;
Value *AllocaValue_i8 = nullptr;
AllocaInst *AllocaResult = nullptr;
Value *AllocaResult_i8 = nullptr;
Type *ResultTy;
SmallVector<Value *, 6> Args;
AttributeList Attr;
// 'size' argument.
if (!UseSizedLibcall) {
// Note, getIntPtrType is assumed equivalent to size_t.
Args.push_back(ConstantInt::get(DL.getIntPtrType(Ctx), Size));
}
// 'ptr' argument.
Value *PtrVal =
Builder.CreateBitCast(PointerOperand, Type::getInt8PtrTy(Ctx));
Args.push_back(PtrVal);
// 'expected' argument, if present.
if (CASExpected) {
AllocaCASExpected = AllocaBuilder.CreateAlloca(CASExpected->getType());
AllocaCASExpected->setAlignment(AllocaAlignment);
AllocaCASExpected_i8 =
Builder.CreateBitCast(AllocaCASExpected, Type::getInt8PtrTy(Ctx));
Builder.CreateLifetimeStart(AllocaCASExpected_i8, SizeVal64);
Builder.CreateAlignedStore(CASExpected, AllocaCASExpected, AllocaAlignment);
Args.push_back(AllocaCASExpected_i8);
}
// 'val' argument ('desired' for cas), if present.
if (ValueOperand) {
if (UseSizedLibcall) {
Value *IntValue =
Builder.CreateBitOrPointerCast(ValueOperand, SizedIntTy);
Args.push_back(IntValue);
} else {
AllocaValue = AllocaBuilder.CreateAlloca(ValueOperand->getType());
AllocaValue->setAlignment(AllocaAlignment);
AllocaValue_i8 =
Builder.CreateBitCast(AllocaValue, Type::getInt8PtrTy(Ctx));
Builder.CreateLifetimeStart(AllocaValue_i8, SizeVal64);
Builder.CreateAlignedStore(ValueOperand, AllocaValue, AllocaAlignment);
Args.push_back(AllocaValue_i8);
}
}
// 'ret' argument.
if (!CASExpected && HasResult && !UseSizedLibcall) {
AllocaResult = AllocaBuilder.CreateAlloca(I->getType());
AllocaResult->setAlignment(AllocaAlignment);
AllocaResult_i8 =
Builder.CreateBitCast(AllocaResult, Type::getInt8PtrTy(Ctx));
Builder.CreateLifetimeStart(AllocaResult_i8, SizeVal64);
Args.push_back(AllocaResult_i8);
}
// 'ordering' ('success_order' for cas) argument.
Args.push_back(OrderingVal);
// 'failure_order' argument, if present.
if (Ordering2Val)
Args.push_back(Ordering2Val);
// Now, the return type.
if (CASExpected) {
ResultTy = Type::getInt1Ty(Ctx);
Attr = Attr.addAttribute(Ctx, AttributeList::ReturnIndex, Attribute::ZExt);
} else if (HasResult && UseSizedLibcall)
ResultTy = SizedIntTy;
else
ResultTy = Type::getVoidTy(Ctx);
// Done with setting up arguments and return types, create the call:
SmallVector<Type *, 6> ArgTys;
for (Value *Arg : Args)
ArgTys.push_back(Arg->getType());
FunctionType *FnType = FunctionType::get(ResultTy, ArgTys, false);
Constant *LibcallFn =
M->getOrInsertFunction(TLI->getLibcallName(RTLibType), FnType, Attr);
CallInst *Call = Builder.CreateCall(LibcallFn, Args);
Call->setAttributes(Attr);
Value *Result = Call;
// And then, extract the results...
if (ValueOperand && !UseSizedLibcall)
Builder.CreateLifetimeEnd(AllocaValue_i8, SizeVal64);
if (CASExpected) {
// The final result from the CAS is {load of 'expected' alloca, bool result
// from call}
Type *FinalResultTy = I->getType();
Value *V = UndefValue::get(FinalResultTy);
Value *ExpectedOut =
Builder.CreateAlignedLoad(AllocaCASExpected, AllocaAlignment);
Builder.CreateLifetimeEnd(AllocaCASExpected_i8, SizeVal64);
V = Builder.CreateInsertValue(V, ExpectedOut, 0);
V = Builder.CreateInsertValue(V, Result, 1);
I->replaceAllUsesWith(V);
} else if (HasResult) {
Value *V;
if (UseSizedLibcall)
V = Builder.CreateBitOrPointerCast(Result, I->getType());
else {
V = Builder.CreateAlignedLoad(AllocaResult, AllocaAlignment);
Builder.CreateLifetimeEnd(AllocaResult_i8, SizeVal64);
}
I->replaceAllUsesWith(V);
}
I->eraseFromParent();
return true;
}
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