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/Scalar/LowerAtomicPass.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 #include "llvm/Transforms/Utils/LowerAtomic.h"
21 using namespace llvm;
22 
23 #define DEBUG_TYPE "loweratomic"
24 
25 static bool LowerFenceInst(FenceInst *FI) {
26   FI->eraseFromParent();
27   return true;
28 }
29 
30 static bool LowerLoadInst(LoadInst *LI) {
31   LI->setAtomic(AtomicOrdering::NotAtomic);
32   return true;
33 }
34 
35 static bool LowerStoreInst(StoreInst *SI) {
36   SI->setAtomic(AtomicOrdering::NotAtomic);
37   return true;
38 }
39 
40 static bool runOnBasicBlock(BasicBlock &BB) {
41   bool Changed = false;
42   for (Instruction &Inst : make_early_inc_range(BB)) {
43     if (FenceInst *FI = dyn_cast<FenceInst>(&Inst))
44       Changed |= LowerFenceInst(FI);
45     else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(&Inst))
46       Changed |= lowerAtomicCmpXchgInst(CXI);
47     else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(&Inst))
48       Changed |= lowerAtomicRMWInst(RMWI);
49     else if (LoadInst *LI = dyn_cast<LoadInst>(&Inst)) {
50       if (LI->isAtomic())
51         LowerLoadInst(LI);
52     } else if (StoreInst *SI = dyn_cast<StoreInst>(&Inst)) {
53       if (SI->isAtomic())
54         LowerStoreInst(SI);
55     }
56   }
57   return Changed;
58 }
59 
60 static bool lowerAtomics(Function &F) {
61   bool Changed = false;
62   for (BasicBlock &BB : F) {
63     Changed |= runOnBasicBlock(BB);
64   }
65   return Changed;
66 }
67 
68 PreservedAnalyses LowerAtomicPass::run(Function &F, FunctionAnalysisManager &) {
69   if (lowerAtomics(F))
70     return PreservedAnalyses::none();
71   return PreservedAnalyses::all();
72 }
73 
74 namespace {
75 class LowerAtomicLegacyPass : public FunctionPass {
76 public:
77   static char ID;
78 
79   LowerAtomicLegacyPass() : FunctionPass(ID) {
80     initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry());
81   }
82 
83   bool runOnFunction(Function &F) override {
84     // Don't skip optnone functions; atomics still need to be lowered.
85     FunctionAnalysisManager DummyFAM;
86     auto PA = Impl.run(F, DummyFAM);
87     return !PA.areAllPreserved();
88   }
89 
90 private:
91   LowerAtomicPass Impl;
92   };
93 }
94 
95 char LowerAtomicLegacyPass::ID = 0;
96 INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic",
97                 "Lower atomic intrinsics to non-atomic form", false, false)
98 
99 Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); }
100