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//===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===//
//
// 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 pass lowers atomic intrinsics to non-atomic form for use in a known
// non-preemptible environment.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LowerAtomic.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
using namespace llvm;
#define DEBUG_TYPE "loweratomic"
static bool LowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
IRBuilder<> Builder(CXI);
Value *Ptr = CXI->getPointerOperand();
Value *Cmp = CXI->getCompareOperand();
Value *Val = CXI->getNewValOperand();
LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
Value *Res = Builder.CreateSelect(Equal, Val, Orig);
Builder.CreateStore(Res, Ptr);
Res = Builder.CreateInsertValue(UndefValue::get(CXI->getType()), Orig, 0);
Res = Builder.CreateInsertValue(Res, Equal, 1);
CXI->replaceAllUsesWith(Res);
CXI->eraseFromParent();
return true;
}
bool llvm::lowerAtomicRMWInst(AtomicRMWInst *RMWI) {
IRBuilder<> Builder(RMWI);
Value *Ptr = RMWI->getPointerOperand();
Value *Val = RMWI->getValOperand();
LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
Value *Res = nullptr;
switch (RMWI->getOperation()) {
default: llvm_unreachable("Unexpected RMW operation");
case AtomicRMWInst::Xchg:
Res = Val;
break;
case AtomicRMWInst::Add:
Res = Builder.CreateAdd(Orig, Val);
break;
case AtomicRMWInst::Sub:
Res = Builder.CreateSub(Orig, Val);
break;
case AtomicRMWInst::And:
Res = Builder.CreateAnd(Orig, Val);
break;
case AtomicRMWInst::Nand:
Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val));
break;
case AtomicRMWInst::Or:
Res = Builder.CreateOr(Orig, Val);
break;
case AtomicRMWInst::Xor:
Res = Builder.CreateXor(Orig, Val);
break;
case AtomicRMWInst::Max:
Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
Val, Orig);
break;
case AtomicRMWInst::Min:
Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
Orig, Val);
break;
case AtomicRMWInst::UMax:
Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
Val, Orig);
break;
case AtomicRMWInst::UMin:
Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
Orig, Val);
break;
case AtomicRMWInst::FAdd:
Res = Builder.CreateFAdd(Orig, Val);
break;
case AtomicRMWInst::FSub:
Res = Builder.CreateFSub(Orig, Val);
break;
}
Builder.CreateStore(Res, Ptr);
RMWI->replaceAllUsesWith(Orig);
RMWI->eraseFromParent();
return true;
}
static bool LowerFenceInst(FenceInst *FI) {
FI->eraseFromParent();
return true;
}
static bool LowerLoadInst(LoadInst *LI) {
LI->setAtomic(AtomicOrdering::NotAtomic);
return true;
}
static bool LowerStoreInst(StoreInst *SI) {
SI->setAtomic(AtomicOrdering::NotAtomic);
return true;
}
static bool runOnBasicBlock(BasicBlock &BB) {
bool Changed = false;
for (Instruction &Inst : make_early_inc_range(BB)) {
if (FenceInst *FI = dyn_cast<FenceInst>(&Inst))
Changed |= LowerFenceInst(FI);
else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(&Inst))
Changed |= LowerAtomicCmpXchgInst(CXI);
else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(&Inst))
Changed |= lowerAtomicRMWInst(RMWI);
else if (LoadInst *LI = dyn_cast<LoadInst>(&Inst)) {
if (LI->isAtomic())
LowerLoadInst(LI);
} else if (StoreInst *SI = dyn_cast<StoreInst>(&Inst)) {
if (SI->isAtomic())
LowerStoreInst(SI);
}
}
return Changed;
}
static bool lowerAtomics(Function &F) {
bool Changed = false;
for (BasicBlock &BB : F) {
Changed |= runOnBasicBlock(BB);
}
return Changed;
}
PreservedAnalyses LowerAtomicPass::run(Function &F, FunctionAnalysisManager &) {
if (lowerAtomics(F))
return PreservedAnalyses::none();
return PreservedAnalyses::all();
}
namespace {
class LowerAtomicLegacyPass : public FunctionPass {
public:
static char ID;
LowerAtomicLegacyPass() : FunctionPass(ID) {
initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
// Don't skip optnone functions; atomics still need to be lowered.
FunctionAnalysisManager DummyFAM;
auto PA = Impl.run(F, DummyFAM);
return !PA.areAllPreserved();
}
private:
LowerAtomicPass Impl;
};
}
char LowerAtomicLegacyPass::ID = 0;
INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic",
"Lower atomic intrinsics to non-atomic form", false, false)
Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); }
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