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/InitializePasses.h"
17#include "llvm/Pass.h"
18#include "llvm/Transforms/Scalar.h"
19#include "llvm/Transforms/Utils/LowerAtomic.h"
20using namespace llvm;
21
22#define DEBUG_TYPE "lower-atomic"
23
24static bool LowerFenceInst(FenceInst *FI) {
25 FI->eraseFromParent();
26 return true;
27}
28
29static bool LowerLoadInst(LoadInst *LI) {
30 LI->setAtomic(Ordering: AtomicOrdering::NotAtomic);
31 return true;
32}
33
34static bool LowerStoreInst(StoreInst *SI) {
35 SI->setAtomic(Ordering: AtomicOrdering::NotAtomic);
36 return true;
37}
38
39static bool runOnBasicBlock(BasicBlock &BB) {
40 bool Changed = false;
41 for (Instruction &Inst : make_early_inc_range(Range&: BB)) {
42 if (FenceInst *FI = dyn_cast<FenceInst>(Val: &Inst))
43 Changed |= LowerFenceInst(FI);
44 else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(Val: &Inst))
45 Changed |= lowerAtomicCmpXchgInst(CXI);
46 else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(Val: &Inst))
47 Changed |= lowerAtomicRMWInst(RMWI);
48 else if (LoadInst *LI = dyn_cast<LoadInst>(Val: &Inst)) {
49 if (LI->isAtomic())
50 LowerLoadInst(LI);
51 } else if (StoreInst *SI = dyn_cast<StoreInst>(Val: &Inst)) {
52 if (SI->isAtomic())
53 LowerStoreInst(SI);
54 }
55 }
56 return Changed;
57}
58
59static bool lowerAtomics(Function &F) {
60 bool Changed = false;
61 for (BasicBlock &BB : F) {
62 Changed |= runOnBasicBlock(BB);
63 }
64 return Changed;
65}
66
67PreservedAnalyses LowerAtomicPass::run(Function &F, FunctionAnalysisManager &) {
68 if (lowerAtomics(F))
69 return PreservedAnalyses::none();
70 return PreservedAnalyses::all();
71}
72
73namespace {
74class LowerAtomicLegacyPass : public FunctionPass {
75public:
76 static char ID;
77
78 LowerAtomicLegacyPass() : FunctionPass(ID) {
79 initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry());
80 }
81
82 bool runOnFunction(Function &F) override {
83 // Don't skip optnone functions; atomics still need to be lowered.
84 FunctionAnalysisManager DummyFAM;
85 auto PA = Impl.run(F, DummyFAM);
86 return !PA.areAllPreserved();
87 }
88
89private:
90 LowerAtomicPass Impl;
91 };
92}
93
94char LowerAtomicLegacyPass::ID = 0;
95INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic",
96 "Lower atomic intrinsics to non-atomic form", false, false)
97
98Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); }
99