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llvm-mirror/lib/CodeGen/AtomicExpandPass.cpp
Brendon Cahoon 4b5fd94277 Align store conditional address 
In cases where the alignment of the datatype is smaller than
expected by the instruction, the address is aligned. The aligned
address is used for the load, but wasn't used for the store
conditional, which resulted in a run-time alignment exception.
2020-07-30 10:42:00 -05:00

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//===- AtomicExpandPass.cpp - Expand atomic instructions ------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/ADT/ArrayRef.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/AtomicExpandUtils.h"
#include "llvm/CodeGen/RuntimeLibcalls.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/AtomicOrdering.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <cassert>
#include <cstdint>
#include <iterator>
using namespace llvm;
#define DEBUG_TYPE "atomic-expand"
namespace {
class AtomicExpand: public FunctionPass {
const TargetLowering *TLI = nullptr;
public:
static char ID; // Pass identification, replacement for typeid
AtomicExpand() : FunctionPass(ID) {
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);
AtomicRMWInst *widenPartwordAtomicRMW(AtomicRMWInst *AI);
bool expandPartwordCmpXchg(AtomicCmpXchgInst *I);
void expandAtomicRMWToMaskedIntrinsic(AtomicRMWInst *AI);
void expandAtomicCmpXchgToMaskedIntrinsic(AtomicCmpXchgInst *CI);
AtomicCmpXchgInst *convertCmpXchgToIntegerType(AtomicCmpXchgInst *CI);
static Value *insertRMWCmpXchgLoop(
IRBuilder<> &Builder, Type *ResultType, Value *Addr,
AtomicOrdering MemOpOrder,
function_ref<Value *(IRBuilder<> &, Value *)> PerformOp,
CreateCmpXchgInstFun CreateCmpXchg);
bool tryExpandAtomicCmpXchg(AtomicCmpXchgInst *CI);
bool expandAtomicCmpXchg(AtomicCmpXchgInst *CI);
bool isIdempotentRMW(AtomicRMWInst *RMWI);
bool simplifyIdempotentRMW(AtomicRMWInst *RMWI);
bool expandAtomicOpToLibcall(Instruction *I, unsigned Size, Align Alignment,
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);
};
} // end anonymous namespace
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(); }
// Helper functions to retrieve the size of atomic instructions.
static unsigned getAtomicOpSize(LoadInst *LI) {
const DataLayout &DL = LI->getModule()->getDataLayout();
return DL.getTypeStoreSize(LI->getType());
}
static unsigned getAtomicOpSize(StoreInst *SI) {
const DataLayout &DL = SI->getModule()->getDataLayout();
return DL.getTypeStoreSize(SI->getValueOperand()->getType());
}
static unsigned getAtomicOpSize(AtomicRMWInst *RMWI) {
const DataLayout &DL = RMWI->getModule()->getDataLayout();
return DL.getTypeStoreSize(RMWI->getValOperand()->getType());
}
static unsigned getAtomicOpSize(AtomicCmpXchgInst *CASI) {
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>
static bool atomicSizeSupported(const TargetLowering *TLI, Inst *I) {
unsigned Size = getAtomicOpSize(I);
Align Alignment = I->getAlign();
return Alignment >= Size &&
Size <= TLI->getMaxAtomicSizeInBitsSupported() / 8;
}
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) ==
TargetLoweringBase::AtomicExpansionKind::None &&
(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 {
unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
unsigned ValueSize = getAtomicOpSize(RMWI);
AtomicRMWInst::BinOp Op = RMWI->getOperation();
if (ValueSize < MinCASSize &&
(Op == AtomicRMWInst::Or || Op == AtomicRMWInst::Xor ||
Op == AtomicRMWInst::And)) {
RMWI = widenPartwordAtomicRMW(RMWI);
MadeChange = true;
}
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;
}
MadeChange |= tryExpandAtomicCmpXchg(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);
// We have a guard here because not every atomic operation generates a
// trailing fence.
if (TrailingFence)
TrailingFence->moveAfter(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->getMemValueType(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(NewTy, NewAddr);
NewLI->setAlignment(LI->getAlign());
NewLI->setVolatile(LI->isVolatile());
NewLI->setAtomic(LI->getOrdering(), LI->getSyncScopeID());
LLVM_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);
default:
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();
if (Order == AtomicOrdering::Unordered)
Order = AtomicOrdering::Monotonic;
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->getAlign());
NewSI->setVolatile(SI->isVolatile());
NewSI->setAtomic(SI->getOrdering(), SI->getSyncScopeID());
LLVM_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) {
Type *OrigTy = NewVal->getType();
// This code can go away when cmpxchg supports FP types.
bool NeedBitcast = OrigTy->isFloatingPointTy();
if (NeedBitcast) {
IntegerType *IntTy = Builder.getIntNTy(OrigTy->getPrimitiveSizeInBits());
unsigned AS = Addr->getType()->getPointerAddressSpace();
Addr = Builder.CreateBitCast(Addr, IntTy->getPointerTo(AS));
NewVal = Builder.CreateBitCast(NewVal, IntTy);
Loaded = Builder.CreateBitCast(Loaded, IntTy);
}
Value* Pair = Builder.CreateAtomicCmpXchg(
Addr, Loaded, NewVal, MemOpOrder,
AtomicCmpXchgInst::getStrongestFailureOrdering(MemOpOrder));
Success = Builder.CreateExtractValue(Pair, 1, "success");
NewLoaded = Builder.CreateExtractValue(Pair, 0, "newloaded");
if (NeedBitcast)
NewLoaded = Builder.CreateBitCast(NewLoaded, OrigTy);
}
/// 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");
case AtomicRMWInst::FAdd:
return Builder.CreateFAdd(Loaded, Inc, "new");
case AtomicRMWInst::FSub:
return Builder.CreateFSub(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) {
expandPartwordAtomicRMW(AI,
TargetLoweringBase::AtomicExpansionKind::LLSC);
} 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) {
// TODO: Handle atomicrmw fadd/fsub
if (AI->getType()->isFloatingPointTy())
return false;
expandPartwordAtomicRMW(AI,
TargetLoweringBase::AtomicExpansionKind::CmpXChg);
} else {
expandAtomicRMWToCmpXchg(AI, createCmpXchgInstFun);
}
return true;
}
case TargetLoweringBase::AtomicExpansionKind::MaskedIntrinsic: {
expandAtomicRMWToMaskedIntrinsic(AI);
return true;
}
default:
llvm_unreachable("Unhandled case in tryExpandAtomicRMW");
}
}
namespace {
struct PartwordMaskValues {
// These three fields are guaranteed to be set by createMaskInstrs.
Type *WordType = nullptr;
Type *ValueType = nullptr;
Value *AlignedAddr = nullptr;
// The remaining fields can be null.
Value *ShiftAmt = nullptr;
Value *Mask = nullptr;
Value *Inv_Mask = nullptr;
};
LLVM_ATTRIBUTE_UNUSED
raw_ostream &operator<<(raw_ostream &O, const PartwordMaskValues &PMV) {
auto PrintObj = [&O](auto *V) {
if (V)
O << *V;
else
O << "nullptr";
O << '\n';
};
O << "PartwordMaskValues {\n";
O << " WordType: ";
PrintObj(PMV.WordType);
O << " ValueType: ";
PrintObj(PMV.ValueType);
O << " AlignedAddr: ";
PrintObj(PMV.AlignedAddr);
O << " ShiftAmt: ";
PrintObj(PMV.ShiftAmt);
O << " Mask: ";
PrintObj(PMV.Mask);
O << " Inv_Mask: ";
PrintObj(PMV.Inv_Mask);
O << "}\n";
return O;
}
} // 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 MinWordSize) {
PartwordMaskValues PMV;
Module *M = I->getModule();
LLVMContext &Ctx = M->getContext();
const DataLayout &DL = M->getDataLayout();
unsigned ValueSize = DL.getTypeStoreSize(ValueType);
PMV.ValueType = ValueType;
PMV.WordType = MinWordSize > ValueSize ? Type::getIntNTy(Ctx, MinWordSize * 8)
: ValueType;
if (PMV.ValueType == PMV.WordType) {
PMV.AlignedAddr = Addr;
return PMV;
}
assert(ValueSize < MinWordSize);
Type *WordPtrType =
PMV.WordType->getPointerTo(Addr->getType()->getPointerAddressSpace());
Value *AddrInt = Builder.CreatePtrToInt(Addr, DL.getIntPtrType(Ctx));
PMV.AlignedAddr = Builder.CreateIntToPtr(
Builder.CreateAnd(AddrInt, ~(uint64_t)(MinWordSize - 1)), WordPtrType,
"AlignedAddr");
Value *PtrLSB = Builder.CreateAnd(AddrInt, MinWordSize - 1, "PtrLSB");
if (DL.isLittleEndian()) {
// turn bytes into bits
PMV.ShiftAmt = Builder.CreateShl(PtrLSB, 3);
} else {
// turn bytes into bits, and count from the other side.
PMV.ShiftAmt = Builder.CreateShl(
Builder.CreateXor(PtrLSB, MinWordSize - ValueSize), 3);
}
PMV.ShiftAmt = Builder.CreateTrunc(PMV.ShiftAmt, PMV.WordType, "ShiftAmt");
PMV.Mask = Builder.CreateShl(
ConstantInt::get(PMV.WordType, (1 << (ValueSize * 8)) - 1), PMV.ShiftAmt,
"Mask");
PMV.Inv_Mask = Builder.CreateNot(PMV.Mask, "Inv_Mask");
return PMV;
}
static Value *extractMaskedValue(IRBuilder<> &Builder, Value *WideWord,
const PartwordMaskValues &PMV) {
assert(WideWord->getType() == PMV.WordType && "Widened type mismatch");
if (PMV.WordType == PMV.ValueType)
return WideWord;
Value *Shift = Builder.CreateLShr(WideWord, PMV.ShiftAmt, "shifted");
Value *Trunc = Builder.CreateTrunc(Shift, PMV.ValueType, "extracted");
return Trunc;
}
static Value *insertMaskedValue(IRBuilder<> &Builder, Value *WideWord,
Value *Updated, const PartwordMaskValues &PMV) {
assert(WideWord->getType() == PMV.WordType && "Widened type mismatch");
assert(Updated->getType() == PMV.ValueType && "Value type mismatch");
if (PMV.WordType == PMV.ValueType)
return Updated;
Value *ZExt = Builder.CreateZExt(Updated, PMV.WordType, "extended");
Value *Shift =
Builder.CreateShl(ZExt, PMV.ShiftAmt, "shifted", /*HasNUW*/ true);
Value *And = Builder.CreateAnd(WideWord, PMV.Inv_Mask, "unmasked");
Value *Or = Builder.CreateOr(And, Shift, "inserted");
return Or;
}
/// 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) {
// TODO: update to use
// https://graphics.stanford.edu/~seander/bithacks.html#MaskedMerge in order
// to merge bits from two values without requiring PMV.Inv_Mask.
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:
case AtomicRMWInst::And:
llvm_unreachable("Or/Xor/And handled by widenPartwordAtomicRMW");
case AtomicRMWInst::Add:
case AtomicRMWInst::Sub:
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_Extract = extractMaskedValue(Builder, Loaded, PMV);
Value *NewVal = performAtomicOp(Op, Builder, Loaded_Extract, Inc);
Value *FinalVal = insertMaskedValue(Builder, Loaded, NewVal, PMV);
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 may operate upon only a
/// part of the value.
void AtomicExpand::expandPartwordAtomicRMW(
AtomicRMWInst *AI, TargetLoweringBase::AtomicExpansionKind ExpansionKind) {
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);
};
Value *OldResult;
if (ExpansionKind == TargetLoweringBase::AtomicExpansionKind::CmpXChg) {
OldResult =
insertRMWCmpXchgLoop(Builder, PMV.WordType, PMV.AlignedAddr, MemOpOrder,
PerformPartwordOp, createCmpXchgInstFun);
} else {
assert(ExpansionKind == TargetLoweringBase::AtomicExpansionKind::LLSC);
OldResult = insertRMWLLSCLoop(Builder, PMV.WordType, PMV.AlignedAddr,
MemOpOrder, PerformPartwordOp);
}
Value *FinalOldResult = extractMaskedValue(Builder, OldResult, PMV);
AI->replaceAllUsesWith(FinalOldResult);
AI->eraseFromParent();
}
// Widen the bitwise atomicrmw (or/xor/and) to the minimum supported width.
AtomicRMWInst *AtomicExpand::widenPartwordAtomicRMW(AtomicRMWInst *AI) {
IRBuilder<> Builder(AI);
AtomicRMWInst::BinOp Op = AI->getOperation();
assert((Op == AtomicRMWInst::Or || Op == AtomicRMWInst::Xor ||
Op == AtomicRMWInst::And) &&
"Unable to widen operation");
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");
Value *NewOperand;
if (Op == AtomicRMWInst::And)
NewOperand =
Builder.CreateOr(PMV.Inv_Mask, ValOperand_Shifted, "AndOperand");
else
NewOperand = ValOperand_Shifted;
AtomicRMWInst *NewAI = Builder.CreateAtomicRMW(Op, PMV.AlignedAddr,
NewOperand, AI->getOrdering());
Value *FinalOldResult = extractMaskedValue(Builder, NewAI, PMV);
AI->replaceAllUsesWith(FinalOldResult);
AI->eraseFromParent();
return NewAI;
}
bool 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->getSyncScopeID());
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 = extractMaskedValue(Builder, OldVal, PMV);
Value *Res = UndefValue::get(CI->getType());
Res = Builder.CreateInsertValue(Res, FinalOldVal, 0);
Res = Builder.CreateInsertValue(Res, Success, 1);
CI->replaceAllUsesWith(Res);
CI->eraseFromParent();
return true;
}
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();
}
void AtomicExpand::expandAtomicRMWToMaskedIntrinsic(AtomicRMWInst *AI) {
IRBuilder<> Builder(AI);
PartwordMaskValues PMV =
createMaskInstrs(Builder, AI, AI->getType(), AI->getPointerOperand(),
TLI->getMinCmpXchgSizeInBits() / 8);
// The value operand must be sign-extended for signed min/max so that the
// target's signed comparison instructions can be used. Otherwise, just
// zero-ext.
Instruction::CastOps CastOp = Instruction::ZExt;
AtomicRMWInst::BinOp RMWOp = AI->getOperation();
if (RMWOp == AtomicRMWInst::Max || RMWOp == AtomicRMWInst::Min)
CastOp = Instruction::SExt;
Value *ValOperand_Shifted = Builder.CreateShl(
Builder.CreateCast(CastOp, AI->getValOperand(), PMV.WordType),
PMV.ShiftAmt, "ValOperand_Shifted");
Value *OldResult = TLI->emitMaskedAtomicRMWIntrinsic(
Builder, AI, PMV.AlignedAddr, ValOperand_Shifted, PMV.Mask, PMV.ShiftAmt,
AI->getOrdering());
Value *FinalOldResult = extractMaskedValue(Builder, OldResult, PMV);
AI->replaceAllUsesWith(FinalOldResult);
AI->eraseFromParent();
}
void AtomicExpand::expandAtomicCmpXchgToMaskedIntrinsic(AtomicCmpXchgInst *CI) {
IRBuilder<> Builder(CI);
PartwordMaskValues PMV = createMaskInstrs(
Builder, CI, CI->getCompareOperand()->getType(), CI->getPointerOperand(),
TLI->getMinCmpXchgSizeInBits() / 8);
Value *CmpVal_Shifted = Builder.CreateShl(
Builder.CreateZExt(CI->getCompareOperand(), PMV.WordType), PMV.ShiftAmt,
"CmpVal_Shifted");
Value *NewVal_Shifted = Builder.CreateShl(
Builder.CreateZExt(CI->getNewValOperand(), PMV.WordType), PMV.ShiftAmt,
"NewVal_Shifted");
Value *OldVal = TLI->emitMaskedAtomicCmpXchgIntrinsic(
Builder, CI, PMV.AlignedAddr, CmpVal_Shifted, NewVal_Shifted, PMV.Mask,
CI->getSuccessOrdering());
Value *FinalOldVal = extractMaskedValue(Builder, OldVal, PMV);
Value *Res = UndefValue::get(CI->getType());
Res = Builder.CreateInsertValue(Res, FinalOldVal, 0);
Value *Success = Builder.CreateICmpEQ(
CmpVal_Shifted, Builder.CreateAnd(OldVal, PMV.Mask), "Success");
Res = Builder.CreateInsertValue(Res, Success, 1);
CI->replaceAllUsesWith(Res);
CI->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->getSyncScopeID());
NewCI->setVolatile(CI->isVolatile());
NewCI->setWeak(CI->isWeak());
LLVM_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->hasMinSize();
// There's no overhead for sinking the release barrier in a weak cmpxchg, so
// do it even on minsize.
bool UseUnconditionalReleaseBarrier = F->hasMinSize() && !CI->isWeak();
// Given: cmpxchg some_op iN* %addr, iN %desired, iN %new success_ord fail_ord
//
// The full expansion we produce is:
// [...]
// %aligned.addr = ...
// cmpxchg.start:
// %unreleasedload = @load.linked(%aligned.addr)
// %unreleasedload.extract = extract value from %unreleasedload
// %should_store = icmp eq %unreleasedload.extract, %desired
// br i1 %should_store, label %cmpxchg.releasingstore,
// label %cmpxchg.nostore
// cmpxchg.releasingstore:
// fence?
// br label cmpxchg.trystore
// cmpxchg.trystore:
// %loaded.trystore = phi [%unreleasedload, %cmpxchg.releasingstore],
// [%releasedload, %cmpxchg.releasedload]
// %updated.new = insert %new into %loaded.trystore
// %stored = @store_conditional(%updated.new, %aligned.addr)
// %success = icmp eq i32 %stored, 0
// br i1 %success, label %cmpxchg.success,
// label %cmpxchg.releasedload/%cmpxchg.failure
// cmpxchg.releasedload:
// %releasedload = @load.linked(%aligned.addr)
// %releasedload.extract = extract value from %releasedload
// %should_store = icmp eq %releasedload.extract, %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.exit = phi [%loaded.nostore, %cmpxchg.failure],
// [%loaded.trystore, %cmpxchg.trystore]
// %success = phi i1 [true, %cmpxchg.success], [false, %cmpxchg.failure]
// %loaded = extract value from %loaded.exit
// %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);
PartwordMaskValues PMV =
createMaskInstrs(Builder, CI, CI->getCompareOperand()->getType(), Addr,
TLI->getMinCmpXchgSizeInBits() / 8);
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, PMV.AlignedAddr, MemOpOrder);
Value *UnreleasedLoadExtract =
extractMaskedValue(Builder, UnreleasedLoad, PMV);
Value *ShouldStore = Builder.CreateICmpEQ(
UnreleasedLoadExtract, 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);
PHINode *LoadedTryStore =
Builder.CreatePHI(PMV.WordType, 2, "loaded.trystore");
LoadedTryStore->addIncoming(UnreleasedLoad, ReleasingStoreBB);
Value *NewValueInsert =
insertMaskedValue(Builder, LoadedTryStore, CI->getNewValOperand(), PMV);
Value *StoreSuccess =
TLI->emitStoreConditional(Builder, NewValueInsert, PMV.AlignedAddr,
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, PMV.AlignedAddr, MemOpOrder);
Value *SecondLoadExtract = extractMaskedValue(Builder, SecondLoad, PMV);
ShouldStore = Builder.CreateICmpEQ(SecondLoadExtract,
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);
// Update PHI node in TryStoreBB.
LoadedTryStore->addIncoming(SecondLoad, ReleasedLoadBB);
} 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);
PHINode *LoadedNoStore =
Builder.CreatePHI(UnreleasedLoad->getType(), 2, "loaded.nostore");
LoadedNoStore->addIncoming(UnreleasedLoad, StartBB);
if (HasReleasedLoadBB)
LoadedNoStore->addIncoming(SecondLoad, ReleasedLoadBB);
// 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);
PHINode *LoadedFailure =
Builder.CreatePHI(UnreleasedLoad->getType(), 2, "loaded.failure");
LoadedFailure->addIncoming(LoadedNoStore, NoStoreBB);
if (CI->isWeak())
LoadedFailure->addIncoming(LoadedTryStore, TryStoreBB);
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 *LoadedExit =
Builder.CreatePHI(UnreleasedLoad->getType(), 2, "loaded.exit");
LoadedExit->addIncoming(LoadedTryStore, SuccessBB);
LoadedExit->addIncoming(LoadedFailure, FailureBB);
PHINode *Success = Builder.CreatePHI(Type::getInt1Ty(Ctx), 2, "success");
Success->addIncoming(ConstantInt::getTrue(Ctx), SuccessBB);
Success->addIncoming(ConstantInt::getFalse(Ctx), FailureBB);
// This is the "exit value" from the cmpxchg expansion. It may be of
// a type wider than the one in the cmpxchg instruction.
Value *LoadedFull = LoadedExit;
Builder.SetInsertPoint(ExitBB, std::next(Success->getIterator()));
Value *Loaded = extractMaskedValue(Builder, LoadedFull, PMV);
// 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(Align(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;
}
bool AtomicExpand::tryExpandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
unsigned MinCASSize = TLI->getMinCmpXchgSizeInBits() / 8;
unsigned ValueSize = getAtomicOpSize(CI);
switch (TLI->shouldExpandAtomicCmpXchgInIR(CI)) {
default:
llvm_unreachable("Unhandled case in tryExpandAtomicCmpXchg");
case TargetLoweringBase::AtomicExpansionKind::None:
if (ValueSize < MinCASSize)
return expandPartwordCmpXchg(CI);
return false;
case TargetLoweringBase::AtomicExpansionKind::LLSC: {
return expandAtomicCmpXchg(CI);
}
case TargetLoweringBase::AtomicExpansionKind::MaskedIntrinsic:
expandAtomicCmpXchgToMaskedIntrinsic(CI);
return true;
}
}
// 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, Align Alignment,
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 Alignment >= 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);
bool expanded = expandAtomicOpToLibcall(
I, Size, I->getAlign(), 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);
bool expanded = expandAtomicOpToLibcall(
I, Size, I->getAlign(), 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);
bool expanded = expandAtomicOpToLibcall(
I, Size, I->getAlign(), 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:
case AtomicRMWInst::FAdd:
case AtomicRMWInst::FSub:
// 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);
bool Success = false;
if (!Libcalls.empty())
Success = expandAtomicOpToLibcall(
I, Size, I->getAlign(), 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, Align Alignment, 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, Alignment, DL);
Type *SizedIntTy = Type::getIntNTy(Ctx, Size * 8);
const Align AllocaAlignment = DL.getPrefTypeAlign(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.
// note: This assumes all address spaces share a common libfunc
// implementation and that addresses are convertable. For systems without
// that property, we'd need to extend this mechanism to support AS-specific
// families of atomic intrinsics.
auto PtrTypeAS = PointerOperand->getType()->getPointerAddressSpace();
Value *PtrVal = Builder.CreateBitCast(PointerOperand,
Type::getInt8PtrTy(Ctx, PtrTypeAS));
PtrVal = Builder.CreateAddrSpaceCast(PtrVal, Type::getInt8PtrTy(Ctx));
Args.push_back(PtrVal);
// 'expected' argument, if present.
if (CASExpected) {
AllocaCASExpected = AllocaBuilder.CreateAlloca(CASExpected->getType());
AllocaCASExpected->setAlignment(AllocaAlignment);
unsigned AllocaAS = AllocaCASExpected->getType()->getPointerAddressSpace();
AllocaCASExpected_i8 =
Builder.CreateBitCast(AllocaCASExpected,
Type::getInt8PtrTy(Ctx, AllocaAS));
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);
unsigned AllocaAS = AllocaResult->getType()->getPointerAddressSpace();
AllocaResult_i8 =
Builder.CreateBitCast(AllocaResult, Type::getInt8PtrTy(Ctx, AllocaAS));
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);
FunctionCallee 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(
CASExpected->getType(), 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(I->getType(), AllocaResult,
AllocaAlignment);
Builder.CreateLifetimeEnd(AllocaResult_i8, SizeVal64);
}
I->replaceAllUsesWith(V);
}
I->eraseFromParent();
return true;
}
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