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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/Utils/LowerAtomic.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
using namespace llvm;
#define DEBUG_TYPE "loweratomic"
bool llvm::lowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
IRBuilder<> Builder(CXI);
Value *Ptr = CXI->getPointerOperand();
Value *Cmp = CXI->getCompareOperand();
Value *Val = CXI->getNewValOperand();
auto [Orig, Equal] =
buildCmpXchgValue(Builder, Ptr, Cmp, Val, CXI->getAlign());
Value *Res =
Builder.CreateInsertValue(PoisonValue::get(CXI->getType()), Orig, 0);
Res = Builder.CreateInsertValue(Res, Equal, 1);
CXI->replaceAllUsesWith(Res);
CXI->eraseFromParent();
return true;
}
std::pair<Value *, Value *> llvm::buildCmpXchgValue(IRBuilderBase &Builder,
Value *Ptr, Value *Cmp,
Value *Val,
Align Alignment) {
LoadInst *Orig = Builder.CreateAlignedLoad(Val->getType(), Ptr, Alignment);
Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
Value *Res = Builder.CreateSelect(Equal, Val, Orig);
Builder.CreateAlignedStore(Res, Ptr, Alignment);
return {Orig, Equal};
}
Value *llvm::buildAtomicRMWValue(AtomicRMWInst::BinOp Op,
IRBuilderBase &Builder, Value *Loaded,
Value *Val) {
Value *NewVal;
switch (Op) {
case AtomicRMWInst::Xchg:
return Val;
case AtomicRMWInst::Add:
return Builder.CreateAdd(Loaded, Val, "new");
case AtomicRMWInst::Sub:
return Builder.CreateSub(Loaded, Val, "new");
case AtomicRMWInst::And:
return Builder.CreateAnd(Loaded, Val, "new");
case AtomicRMWInst::Nand:
return Builder.CreateNot(Builder.CreateAnd(Loaded, Val), "new");
case AtomicRMWInst::Or:
return Builder.CreateOr(Loaded, Val, "new");
case AtomicRMWInst::Xor:
return Builder.CreateXor(Loaded, Val, "new");
case AtomicRMWInst::Max:
NewVal = Builder.CreateICmpSGT(Loaded, Val);
return Builder.CreateSelect(NewVal, Loaded, Val, "new");
case AtomicRMWInst::Min:
NewVal = Builder.CreateICmpSLE(Loaded, Val);
return Builder.CreateSelect(NewVal, Loaded, Val, "new");
case AtomicRMWInst::UMax:
NewVal = Builder.CreateICmpUGT(Loaded, Val);
return Builder.CreateSelect(NewVal, Loaded, Val, "new");
case AtomicRMWInst::UMin:
NewVal = Builder.CreateICmpULE(Loaded, Val);
return Builder.CreateSelect(NewVal, Loaded, Val, "new");
case AtomicRMWInst::FAdd:
return Builder.CreateFAdd(Loaded, Val, "new");
case AtomicRMWInst::FSub:
return Builder.CreateFSub(Loaded, Val, "new");
case AtomicRMWInst::FMax:
return Builder.CreateMaxNum(Loaded, Val);
case AtomicRMWInst::FMin:
return Builder.CreateMinNum(Loaded, Val);
case AtomicRMWInst::UIncWrap: {
Constant *One = ConstantInt::get(Loaded->getType(), 1);
Value *Inc = Builder.CreateAdd(Loaded, One);
Value *Cmp = Builder.CreateICmpUGE(Loaded, Val);
Constant *Zero = ConstantInt::get(Loaded->getType(), 0);
return Builder.CreateSelect(Cmp, Zero, Inc, "new");
}
case AtomicRMWInst::UDecWrap: {
Constant *Zero = ConstantInt::get(Loaded->getType(), 0);
Constant *One = ConstantInt::get(Loaded->getType(), 1);
Value *Dec = Builder.CreateSub(Loaded, One);
Value *CmpEq0 = Builder.CreateICmpEQ(Loaded, Zero);
Value *CmpOldGtVal = Builder.CreateICmpUGT(Loaded, Val);
Value *Or = Builder.CreateOr(CmpEq0, CmpOldGtVal);
return Builder.CreateSelect(Or, Val, Dec, "new");
}
case AtomicRMWInst::USubCond: {
Value *Cmp = Builder.CreateICmpUGE(Loaded, Val);
Value *Sub = Builder.CreateSub(Loaded, Val);
return Builder.CreateSelect(Cmp, Sub, Loaded, "new");
}
case AtomicRMWInst::USubSat:
return Builder.CreateIntrinsic(Intrinsic::usub_sat, Loaded->getType(),
{Loaded, Val}, nullptr, "new");
default:
llvm_unreachable("Unknown atomic op");
}
}
bool llvm::lowerAtomicRMWInst(AtomicRMWInst *RMWI) {
IRBuilder<> Builder(RMWI);
Builder.setIsFPConstrained(
RMWI->getFunction()->hasFnAttribute(Attribute::StrictFP));
Value *Ptr = RMWI->getPointerOperand();
Value *Val = RMWI->getValOperand();
LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
Value *Res = buildAtomicRMWValue(RMWI->getOperation(), Builder, Orig, Val);
Builder.CreateStore(Res, Ptr);
RMWI->replaceAllUsesWith(Orig);
RMWI->eraseFromParent();
return true;
}
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