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(UndefValue::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 bool llvm::lowerAtomicRMWInst(AtomicRMWInst *RMWI) {
43   IRBuilder<> Builder(RMWI);
44   Value *Ptr = RMWI->getPointerOperand();
45   Value *Val = RMWI->getValOperand();
46 
47   LoadInst *Orig = Builder.CreateLoad(Val->getType(), Ptr);
48   Value *Res = nullptr;
49 
50   switch (RMWI->getOperation()) {
51   default: llvm_unreachable("Unexpected RMW operation");
52   case AtomicRMWInst::Xchg:
53     Res = Val;
54     break;
55   case AtomicRMWInst::Add:
56     Res = Builder.CreateAdd(Orig, Val);
57     break;
58   case AtomicRMWInst::Sub:
59     Res = Builder.CreateSub(Orig, Val);
60     break;
61   case AtomicRMWInst::And:
62     Res = Builder.CreateAnd(Orig, Val);
63     break;
64   case AtomicRMWInst::Nand:
65     Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val));
66     break;
67   case AtomicRMWInst::Or:
68     Res = Builder.CreateOr(Orig, Val);
69     break;
70   case AtomicRMWInst::Xor:
71     Res = Builder.CreateXor(Orig, Val);
72     break;
73   case AtomicRMWInst::Max:
74     Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
75                                Val, Orig);
76     break;
77   case AtomicRMWInst::Min:
78     Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
79                                Orig, Val);
80     break;
81   case AtomicRMWInst::UMax:
82     Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
83                                Val, Orig);
84     break;
85   case AtomicRMWInst::UMin:
86     Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
87                                Orig, Val);
88     break;
89   case AtomicRMWInst::FAdd:
90     Res = Builder.CreateFAdd(Orig, Val);
91     break;
92   case AtomicRMWInst::FSub:
93     Res = Builder.CreateFSub(Orig, Val);
94     break;
95   }
96   Builder.CreateStore(Res, Ptr);
97   RMWI->replaceAllUsesWith(Orig);
98   RMWI->eraseFromParent();
99   return true;
100 }
101