1 //===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass lowers atomic intrinsics to non-atomic form for use in a known
11 // non-preemptible environment.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Scalar/LowerAtomic.h"
16 #include "llvm/IR/Function.h"
17 #include "llvm/IR/IRBuilder.h"
18 #include "llvm/Pass.h"
19 #include "llvm/Transforms/Scalar.h"
22 #define DEBUG_TYPE "loweratomic"
24 static bool LowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
25 IRBuilder<> Builder(CXI);
26 Value *Ptr = CXI->getPointerOperand();
27 Value *Cmp = CXI->getCompareOperand();
28 Value *Val = CXI->getNewValOperand();
30 LoadInst *Orig = Builder.CreateLoad(Ptr);
31 Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
32 Value *Res = Builder.CreateSelect(Equal, Val, Orig);
33 Builder.CreateStore(Res, Ptr);
35 Res = Builder.CreateInsertValue(UndefValue::get(CXI->getType()), Orig, 0);
36 Res = Builder.CreateInsertValue(Res, Equal, 1);
38 CXI->replaceAllUsesWith(Res);
39 CXI->eraseFromParent();
43 static bool LowerAtomicRMWInst(AtomicRMWInst *RMWI) {
44 IRBuilder<> Builder(RMWI);
45 Value *Ptr = RMWI->getPointerOperand();
46 Value *Val = RMWI->getValOperand();
48 LoadInst *Orig = Builder.CreateLoad(Ptr);
51 switch (RMWI->getOperation()) {
52 default: llvm_unreachable("Unexpected RMW operation");
53 case AtomicRMWInst::Xchg:
56 case AtomicRMWInst::Add:
57 Res = Builder.CreateAdd(Orig, Val);
59 case AtomicRMWInst::Sub:
60 Res = Builder.CreateSub(Orig, Val);
62 case AtomicRMWInst::And:
63 Res = Builder.CreateAnd(Orig, Val);
65 case AtomicRMWInst::Nand:
66 Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val));
68 case AtomicRMWInst::Or:
69 Res = Builder.CreateOr(Orig, Val);
71 case AtomicRMWInst::Xor:
72 Res = Builder.CreateXor(Orig, Val);
74 case AtomicRMWInst::Max:
75 Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
78 case AtomicRMWInst::Min:
79 Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
82 case AtomicRMWInst::UMax:
83 Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
86 case AtomicRMWInst::UMin:
87 Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
91 Builder.CreateStore(Res, Ptr);
92 RMWI->replaceAllUsesWith(Orig);
93 RMWI->eraseFromParent();
97 static bool LowerFenceInst(FenceInst *FI) {
98 FI->eraseFromParent();
102 static bool LowerLoadInst(LoadInst *LI) {
103 LI->setAtomic(AtomicOrdering::NotAtomic);
107 static bool LowerStoreInst(StoreInst *SI) {
108 SI->setAtomic(AtomicOrdering::NotAtomic);
112 static bool runOnBasicBlock(BasicBlock &BB) {
113 bool Changed = false;
114 for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE;) {
115 Instruction *Inst = &*DI++;
116 if (FenceInst *FI = dyn_cast<FenceInst>(Inst))
117 Changed |= LowerFenceInst(FI);
118 else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(Inst))
119 Changed |= LowerAtomicCmpXchgInst(CXI);
120 else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(Inst))
121 Changed |= LowerAtomicRMWInst(RMWI);
122 else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
125 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
133 static bool lowerAtomics(Function &F) {
134 bool Changed = false;
135 for (BasicBlock &BB : F) {
136 Changed |= runOnBasicBlock(BB);
141 PreservedAnalyses LowerAtomicPass::run(Function &F, FunctionAnalysisManager &) {
143 return PreservedAnalyses::none();
144 return PreservedAnalyses::all();
148 class LowerAtomicLegacyPass : public FunctionPass {
152 LowerAtomicLegacyPass() : FunctionPass(ID) {
153 initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry());
156 bool runOnFunction(Function &F) override {
157 // Don't skip optnone functions; atomics still need to be lowered.
158 FunctionAnalysisManager DummyFAM;
159 auto PA = Impl.run(F, DummyFAM);
160 return !PA.areAllPreserved();
164 LowerAtomicPass Impl;
168 char LowerAtomicLegacyPass::ID = 0;
169 INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic",
170 "Lower atomic intrinsics to non-atomic form", false, false)
172 Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); }