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//===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass lowers atomic intrinsics to non-atomic form for use in a known
// non-preemptible environment.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loweratomic"
#include "llvm/Transforms/Scalar.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Pass.h"
using namespace llvm;
static bool LowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
IRBuilder<> Builder(CXI->getParent(), CXI);
Value *Ptr = CXI->getPointerOperand();
Value *Cmp = CXI->getCompareOperand();
Value *Val = CXI->getNewValOperand();
LoadInst *Orig = Builder.CreateLoad(Ptr);
Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
Value *Res = Builder.CreateSelect(Equal, Val, Orig);
Builder.CreateStore(Res, Ptr);
CXI->replaceAllUsesWith(Orig);
CXI->eraseFromParent();
return true;
}
static bool LowerAtomicRMWInst(AtomicRMWInst *RMWI) {
IRBuilder<> Builder(RMWI->getParent(), RMWI);
Value *Ptr = RMWI->getPointerOperand();
Value *Val = RMWI->getValOperand();
LoadInst *Orig = Builder.CreateLoad(Ptr);
Value *Res = NULL;
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;
}
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(NotAtomic);
return true;
}
static bool LowerStoreInst(StoreInst *SI) {
SI->setAtomic(NotAtomic);
return true;
}
namespace {
struct LowerAtomic : public BasicBlockPass {
static char ID;
LowerAtomic() : BasicBlockPass(ID) {
initializeLowerAtomicPass(*PassRegistry::getPassRegistry());
}
bool runOnBasicBlock(BasicBlock &BB) {
bool Changed = false;
for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE; ) {
Instruction *Inst = DI++;
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;
}
};
}
char LowerAtomic::ID = 0;
INITIALIZE_PASS(LowerAtomic, "loweratomic",
"Lower atomic intrinsics to non-atomic form",
false, false)
Pass *llvm::createLowerAtomicPass() { return new LowerAtomic(); }
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