1 //===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass lowers atomic intrinsics to non-atomic form for use in a known
10 // non-preemptible environment.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Utils/LowerAtomic.h"
15 #include "llvm/IR/Function.h"
16 #include "llvm/IR/IRBuilder.h"
17 #include "llvm/InitializePasses.h"
18 #include "llvm/Pass.h"
19 using namespace llvm;
20 
21 #define DEBUG_TYPE "loweratomic"
22 
23 bool llvm::lowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
24   IRBuilder<> Builder(CXI);
25   Value *Ptr = CXI->getPointerOperand();
26   Value *Cmp = CXI->getCompareOperand();
27   Value *Val = CXI->getNewValOperand();
28 
29   LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
30   Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
31   Value *Res = Builder.CreateSelect(Equal, Val, Orig);
32   Builder.CreateStore(Res, Ptr);
33 
34   Res = Builder.CreateInsertValue(PoisonValue::get(CXI->getType()), Orig, 0);
35   Res = Builder.CreateInsertValue(Res, Equal, 1);
36 
37   CXI->replaceAllUsesWith(Res);
38   CXI->eraseFromParent();
39   return true;
40 }
41 
42 Value *llvm::buildAtomicRMWValue(AtomicRMWInst::BinOp Op,
43                                  IRBuilderBase &Builder, Value *Loaded,
44                                  Value *Inc) {
45   Value *NewVal;
46   switch (Op) {
47   case AtomicRMWInst::Xchg:
48     return Inc;
49   case AtomicRMWInst::Add:
50     return Builder.CreateAdd(Loaded, Inc, "new");
51   case AtomicRMWInst::Sub:
52     return Builder.CreateSub(Loaded, Inc, "new");
53   case AtomicRMWInst::And:
54     return Builder.CreateAnd(Loaded, Inc, "new");
55   case AtomicRMWInst::Nand:
56     return Builder.CreateNot(Builder.CreateAnd(Loaded, Inc), "new");
57   case AtomicRMWInst::Or:
58     return Builder.CreateOr(Loaded, Inc, "new");
59   case AtomicRMWInst::Xor:
60     return Builder.CreateXor(Loaded, Inc, "new");
61   case AtomicRMWInst::Max:
62     NewVal = Builder.CreateICmpSGT(Loaded, Inc);
63     return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
64   case AtomicRMWInst::Min:
65     NewVal = Builder.CreateICmpSLE(Loaded, Inc);
66     return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
67   case AtomicRMWInst::UMax:
68     NewVal = Builder.CreateICmpUGT(Loaded, Inc);
69     return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
70   case AtomicRMWInst::UMin:
71     NewVal = Builder.CreateICmpULE(Loaded, Inc);
72     return Builder.CreateSelect(NewVal, Loaded, Inc, "new");
73   case AtomicRMWInst::FAdd:
74     return Builder.CreateFAdd(Loaded, Inc, "new");
75   case AtomicRMWInst::FSub:
76     return Builder.CreateFSub(Loaded, Inc, "new");
77   case AtomicRMWInst::FMax:
78     return Builder.CreateMaxNum(Loaded, Inc);
79   case AtomicRMWInst::FMin:
80     return Builder.CreateMinNum(Loaded, Inc);
81   default:
82     llvm_unreachable("Unknown atomic op");
83   }
84 }
85 
86 bool llvm::lowerAtomicRMWInst(AtomicRMWInst *RMWI) {
87   IRBuilder<> Builder(RMWI);
88   Value *Ptr = RMWI->getPointerOperand();
89   Value *Val = RMWI->getValOperand();
90 
91   LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
92   Value *Res = buildAtomicRMWValue(RMWI->getOperation(), Builder, Orig, Val);
93   Builder.CreateStore(Res, Ptr);
94   RMWI->replaceAllUsesWith(Orig);
95   RMWI->eraseFromParent();
96   return true;
97 }
98