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 #include "llvm/Transforms/Scalar.h"
20 using namespace llvm;
21 
22 #define DEBUG_TYPE "loweratomic"
23 
24 bool llvm::lowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
25   IRBuilder<> Builder(CXI);
26   Value *Ptr = CXI->getPointerOperand();
27   Value *Cmp = CXI->getCompareOperand();
28   Value *Val = CXI->getNewValOperand();
29 
30   LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
31   Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
32   Value *Res = Builder.CreateSelect(Equal, Val, Orig);
33   Builder.CreateStore(Res, Ptr);
34 
35   Res = Builder.CreateInsertValue(UndefValue::get(CXI->getType()), Orig, 0);
36   Res = Builder.CreateInsertValue(Res, Equal, 1);
37 
38   CXI->replaceAllUsesWith(Res);
39   CXI->eraseFromParent();
40   return true;
41 }
42 
43 bool llvm::lowerAtomicRMWInst(AtomicRMWInst *RMWI) {
44   IRBuilder<> Builder(RMWI);
45   Value *Ptr = RMWI->getPointerOperand();
46   Value *Val = RMWI->getValOperand();
47 
48   LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
49   Value *Res = nullptr;
50 
51   switch (RMWI->getOperation()) {
52   default: llvm_unreachable("Unexpected RMW operation");
53   case AtomicRMWInst::Xchg:
54     Res = Val;
55     break;
56   case AtomicRMWInst::Add:
57     Res = Builder.CreateAdd(Orig, Val);
58     break;
59   case AtomicRMWInst::Sub:
60     Res = Builder.CreateSub(Orig, Val);
61     break;
62   case AtomicRMWInst::And:
63     Res = Builder.CreateAnd(Orig, Val);
64     break;
65   case AtomicRMWInst::Nand:
66     Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val));
67     break;
68   case AtomicRMWInst::Or:
69     Res = Builder.CreateOr(Orig, Val);
70     break;
71   case AtomicRMWInst::Xor:
72     Res = Builder.CreateXor(Orig, Val);
73     break;
74   case AtomicRMWInst::Max:
75     Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
76                                Val, Orig);
77     break;
78   case AtomicRMWInst::Min:
79     Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
80                                Orig, Val);
81     break;
82   case AtomicRMWInst::UMax:
83     Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
84                                Val, Orig);
85     break;
86   case AtomicRMWInst::UMin:
87     Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
88                                Orig, Val);
89     break;
90   case AtomicRMWInst::FAdd:
91     Res = Builder.CreateFAdd(Orig, Val);
92     break;
93   case AtomicRMWInst::FSub:
94     Res = Builder.CreateFSub(Orig, Val);
95     break;
96   }
97   Builder.CreateStore(Res, Ptr);
98   RMWI->replaceAllUsesWith(Orig);
99   RMWI->eraseFromParent();
100   return true;
101 }
102