AtomicExpandLoadLinkedPass.cpp [plain text]
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "arm-atomic-expand"
namespace {
class AtomicExpandLoadLinked : public FunctionPass {
const TargetMachine *TM;
public:
static char ID; explicit AtomicExpandLoadLinked(const TargetMachine *TM = nullptr)
: FunctionPass(ID), TM(TM) {
initializeAtomicExpandLoadLinkedPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
bool expandAtomicInsts(Function &F);
bool expandAtomicLoad(LoadInst *LI);
bool expandAtomicStore(StoreInst *LI);
bool expandAtomicRMW(AtomicRMWInst *AI);
bool expandAtomicCmpXchg(AtomicCmpXchgInst *CI);
AtomicOrdering insertLeadingFence(IRBuilder<> &Builder, AtomicOrdering Ord);
void insertTrailingFence(IRBuilder<> &Builder, AtomicOrdering Ord);
};
}
char AtomicExpandLoadLinked::ID = 0;
char &llvm::AtomicExpandLoadLinkedID = AtomicExpandLoadLinked::ID;
INITIALIZE_TM_PASS(AtomicExpandLoadLinked, "atomic-ll-sc",
"Expand Atomic calls in terms of load-linked & store-conditional",
false, false)
FunctionPass *llvm::createAtomicExpandLoadLinkedPass(const TargetMachine *TM) {
return new AtomicExpandLoadLinked(TM);
}
bool AtomicExpandLoadLinked::runOnFunction(Function &F) {
if (!TM || !TM->getSubtargetImpl()->enableAtomicExpandLoadLinked())
return false;
SmallVector<Instruction *, 1> AtomicInsts;
for (BasicBlock &BB : F)
for (Instruction &Inst : BB) {
if (isa<AtomicRMWInst>(&Inst) || isa<AtomicCmpXchgInst>(&Inst) ||
(isa<LoadInst>(&Inst) && cast<LoadInst>(&Inst)->isAtomic()) ||
(isa<StoreInst>(&Inst) && cast<StoreInst>(&Inst)->isAtomic()))
AtomicInsts.push_back(&Inst);
}
bool MadeChange = false;
for (Instruction *Inst : AtomicInsts) {
if (!TM->getSubtargetImpl()->getTargetLowering()->shouldExpandAtomicInIR(
Inst))
continue;
if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(Inst))
MadeChange |= expandAtomicRMW(AI);
else if (AtomicCmpXchgInst *CI = dyn_cast<AtomicCmpXchgInst>(Inst))
MadeChange |= expandAtomicCmpXchg(CI);
else if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
MadeChange |= expandAtomicLoad(LI);
else if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
MadeChange |= expandAtomicStore(SI);
else
llvm_unreachable("Unknown atomic instruction");
}
return MadeChange;
}
bool AtomicExpandLoadLinked::expandAtomicLoad(LoadInst *LI) {
AtomicOrdering MemOpOrder =
TM->getSubtargetImpl()->getTargetLowering()->getInsertFencesForAtomic()
? Monotonic
: LI->getOrdering();
IRBuilder<> Builder(LI);
Value *Val = TM->getSubtargetImpl()->getTargetLowering()->emitLoadLinked(
Builder, LI->getPointerOperand(), MemOpOrder);
insertTrailingFence(Builder, LI->getOrdering());
LI->replaceAllUsesWith(Val);
LI->eraseFromParent();
return true;
}
bool AtomicExpandLoadLinked::expandAtomicStore(StoreInst *SI) {
IRBuilder<> Builder(SI);
AtomicRMWInst *AI =
Builder.CreateAtomicRMW(AtomicRMWInst::Xchg, SI->getPointerOperand(),
SI->getValueOperand(), SI->getOrdering());
SI->eraseFromParent();
return expandAtomicRMW(AI);
}
bool AtomicExpandLoadLinked::expandAtomicRMW(AtomicRMWInst *AI) {
AtomicOrdering Order = AI->getOrdering();
Value *Addr = AI->getPointerOperand();
BasicBlock *BB = AI->getParent();
Function *F = BB->getParent();
LLVMContext &Ctx = F->getContext();
BasicBlock *ExitBB = BB->splitBasicBlock(AI, "atomicrmw.end");
BasicBlock *LoopBB = BasicBlock::Create(Ctx, "atomicrmw.start", F, ExitBB);
IRBuilder<> Builder(AI);
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
AtomicOrdering MemOpOrder = insertLeadingFence(Builder, Order);
Builder.CreateBr(LoopBB);
Builder.SetInsertPoint(LoopBB);
Value *Loaded = TM->getSubtargetImpl()->getTargetLowering()->emitLoadLinked(
Builder, Addr, MemOpOrder);
Value *NewVal;
switch (AI->getOperation()) {
case AtomicRMWInst::Xchg:
NewVal = AI->getValOperand();
break;
case AtomicRMWInst::Add:
NewVal = Builder.CreateAdd(Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::Sub:
NewVal = Builder.CreateSub(Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::And:
NewVal = Builder.CreateAnd(Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::Nand:
NewVal = Builder.CreateNot(Builder.CreateAnd(Loaded, AI->getValOperand()),
"new");
break;
case AtomicRMWInst::Or:
NewVal = Builder.CreateOr(Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::Xor:
NewVal = Builder.CreateXor(Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::Max:
NewVal = Builder.CreateICmpSGT(Loaded, AI->getValOperand());
NewVal = Builder.CreateSelect(NewVal, Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::Min:
NewVal = Builder.CreateICmpSLE(Loaded, AI->getValOperand());
NewVal = Builder.CreateSelect(NewVal, Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::UMax:
NewVal = Builder.CreateICmpUGT(Loaded, AI->getValOperand());
NewVal = Builder.CreateSelect(NewVal, Loaded, AI->getValOperand(), "new");
break;
case AtomicRMWInst::UMin:
NewVal = Builder.CreateICmpULE(Loaded, AI->getValOperand());
NewVal = Builder.CreateSelect(NewVal, Loaded, AI->getValOperand(), "new");
break;
default:
llvm_unreachable("Unknown atomic op");
}
Value *StoreSuccess =
TM->getSubtargetImpl()->getTargetLowering()->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());
insertTrailingFence(Builder, Order);
AI->replaceAllUsesWith(Loaded);
AI->eraseFromParent();
return true;
}
bool AtomicExpandLoadLinked::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();
BasicBlock *ExitBB = BB->splitBasicBlock(CI, "cmpxchg.end");
auto FailureBB = BasicBlock::Create(Ctx, "cmpxchg.failure", F, ExitBB);
auto SuccessBB = BasicBlock::Create(Ctx, "cmpxchg.success", F, FailureBB);
auto TryStoreBB = BasicBlock::Create(Ctx, "cmpxchg.trystore", F, SuccessBB);
auto LoopBB = BasicBlock::Create(Ctx, "cmpxchg.start", F, TryStoreBB);
IRBuilder<> Builder(CI);
std::prev(BB->end())->eraseFromParent();
Builder.SetInsertPoint(BB);
AtomicOrdering MemOpOrder = insertLeadingFence(Builder, SuccessOrder);
Builder.CreateBr(LoopBB);
Builder.SetInsertPoint(LoopBB);
Value *Loaded = TM->getSubtargetImpl()->getTargetLowering()->emitLoadLinked(
Builder, Addr, MemOpOrder);
Value *ShouldStore =
Builder.CreateICmpEQ(Loaded, CI->getCompareOperand(), "should_store");
Builder.CreateCondBr(ShouldStore, TryStoreBB, FailureBB);
Builder.SetInsertPoint(TryStoreBB);
Value *StoreSuccess =
TM->getSubtargetImpl()->getTargetLowering()->emitStoreConditional(
Builder, CI->getNewValOperand(), Addr, MemOpOrder);
StoreSuccess = Builder.CreateICmpEQ(
StoreSuccess, ConstantInt::get(Type::getInt32Ty(Ctx), 0), "success");
Builder.CreateCondBr(StoreSuccess, SuccessBB,
CI->isWeak() ? FailureBB : LoopBB);
Builder.SetInsertPoint(SuccessBB);
insertTrailingFence(Builder, SuccessOrder);
Builder.CreateBr(ExitBB);
Builder.SetInsertPoint(FailureBB);
insertTrailingFence(Builder, FailureOrder);
Builder.CreateBr(ExitBB);
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);
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);
}
for (auto EV : PrunedInsts)
EV->eraseFromParent();
if (!CI->use_empty()) {
Value *Res;
Res = Builder.CreateInsertValue(UndefValue::get(CI->getType()), Loaded, 0);
Res = Builder.CreateInsertValue(Res, Success, 1);
CI->replaceAllUsesWith(Res);
}
CI->eraseFromParent();
return true;
}
AtomicOrdering AtomicExpandLoadLinked::insertLeadingFence(IRBuilder<> &Builder,
AtomicOrdering Ord) {
if (!TM->getSubtargetImpl()->getTargetLowering()->getInsertFencesForAtomic())
return Ord;
if (Ord == Release || Ord == AcquireRelease || Ord == SequentiallyConsistent)
Builder.CreateFence(Release);
return Monotonic;
}
void AtomicExpandLoadLinked::insertTrailingFence(IRBuilder<> &Builder,
AtomicOrdering Ord) {
if (!TM->getSubtargetImpl()->getTargetLowering()->getInsertFencesForAtomic())
return;
if (Ord == Acquire || Ord == AcquireRelease)
Builder.CreateFence(Acquire);
else if (Ord == SequentiallyConsistent)
Builder.CreateFence(SequentiallyConsistent);
}