1 //===- LowerAtomic.cpp - Lower atomic intrinsics --------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass lowers atomic intrinsics to non-atomic form for use in a known 11 // non-preemptible environment. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Scalar/LowerAtomic.h" 16 #include "llvm/IR/Function.h" 17 #include "llvm/IR/IRBuilder.h" 18 #include "llvm/IR/IntrinsicInst.h" 19 #include "llvm/Pass.h" 20 #include "llvm/Transforms/Scalar.h" 21 using namespace llvm; 22 23 #define DEBUG_TYPE "loweratomic" 24 25 static bool LowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) { 26 IRBuilder<> Builder(CXI); 27 Value *Ptr = CXI->getPointerOperand(); 28 Value *Cmp = CXI->getCompareOperand(); 29 Value *Val = CXI->getNewValOperand(); 30 31 LoadInst *Orig = Builder.CreateLoad(Ptr); 32 Value *Equal = Builder.CreateICmpEQ(Orig, Cmp); 33 Value *Res = Builder.CreateSelect(Equal, Val, Orig); 34 Builder.CreateStore(Res, Ptr); 35 36 Res = Builder.CreateInsertValue(UndefValue::get(CXI->getType()), Orig, 0); 37 Res = Builder.CreateInsertValue(Res, Equal, 1); 38 39 CXI->replaceAllUsesWith(Res); 40 CXI->eraseFromParent(); 41 return true; 42 } 43 44 static bool LowerAtomicRMWInst(AtomicRMWInst *RMWI) { 45 IRBuilder<> Builder(RMWI); 46 Value *Ptr = RMWI->getPointerOperand(); 47 Value *Val = RMWI->getValOperand(); 48 49 LoadInst *Orig = Builder.CreateLoad(Ptr); 50 Value *Res = nullptr; 51 52 switch (RMWI->getOperation()) { 53 default: llvm_unreachable("Unexpected RMW operation"); 54 case AtomicRMWInst::Xchg: 55 Res = Val; 56 break; 57 case AtomicRMWInst::Add: 58 Res = Builder.CreateAdd(Orig, Val); 59 break; 60 case AtomicRMWInst::Sub: 61 Res = Builder.CreateSub(Orig, Val); 62 break; 63 case AtomicRMWInst::And: 64 Res = Builder.CreateAnd(Orig, Val); 65 break; 66 case AtomicRMWInst::Nand: 67 Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val)); 68 break; 69 case AtomicRMWInst::Or: 70 Res = Builder.CreateOr(Orig, Val); 71 break; 72 case AtomicRMWInst::Xor: 73 Res = Builder.CreateXor(Orig, Val); 74 break; 75 case AtomicRMWInst::Max: 76 Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val), 77 Val, Orig); 78 break; 79 case AtomicRMWInst::Min: 80 Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val), 81 Orig, Val); 82 break; 83 case AtomicRMWInst::UMax: 84 Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val), 85 Val, Orig); 86 break; 87 case AtomicRMWInst::UMin: 88 Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val), 89 Orig, Val); 90 break; 91 } 92 Builder.CreateStore(Res, Ptr); 93 RMWI->replaceAllUsesWith(Orig); 94 RMWI->eraseFromParent(); 95 return true; 96 } 97 98 static bool LowerFenceInst(FenceInst *FI) { 99 FI->eraseFromParent(); 100 return true; 101 } 102 103 static bool LowerLoadInst(LoadInst *LI) { 104 LI->setAtomic(AtomicOrdering::NotAtomic); 105 return true; 106 } 107 108 static bool LowerStoreInst(StoreInst *SI) { 109 SI->setAtomic(AtomicOrdering::NotAtomic); 110 return true; 111 } 112 113 static bool runOnBasicBlock(BasicBlock &BB) { 114 bool Changed = false; 115 for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE;) { 116 Instruction *Inst = &*DI++; 117 if (FenceInst *FI = dyn_cast<FenceInst>(Inst)) 118 Changed |= LowerFenceInst(FI); 119 else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(Inst)) 120 Changed |= LowerAtomicCmpXchgInst(CXI); 121 else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(Inst)) 122 Changed |= LowerAtomicRMWInst(RMWI); 123 else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { 124 if (LI->isAtomic()) 125 LowerLoadInst(LI); 126 } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 127 if (SI->isAtomic()) 128 LowerStoreInst(SI); 129 } 130 } 131 return Changed; 132 } 133 134 static bool lowerAtomics(Function &F) { 135 bool Changed = false; 136 for (BasicBlock &BB : F) { 137 Changed |= runOnBasicBlock(BB); 138 } 139 return Changed; 140 } 141 142 PreservedAnalyses LowerAtomicPass::run(Function &F, FunctionAnalysisManager &) { 143 if (lowerAtomics(F)) 144 return PreservedAnalyses::none(); 145 return PreservedAnalyses::all(); 146 } 147 148 namespace { 149 class LowerAtomicLegacyPass : public FunctionPass { 150 public: 151 static char ID; 152 153 LowerAtomicLegacyPass() : FunctionPass(ID) { 154 initializeLowerAtomicLegacyPassPass(*PassRegistry::getPassRegistry()); 155 } 156 157 bool runOnFunction(Function &F) override { 158 if (skipFunction(F)) 159 return false; 160 FunctionAnalysisManager DummyFAM; 161 auto PA = Impl.run(F, DummyFAM); 162 return !PA.areAllPreserved(); 163 } 164 165 private: 166 LowerAtomicPass Impl; 167 }; 168 } 169 170 char LowerAtomicLegacyPass::ID = 0; 171 INITIALIZE_PASS(LowerAtomicLegacyPass, "loweratomic", 172 "Lower atomic intrinsics to non-atomic form", false, false) 173 174 Pass *llvm::createLowerAtomicPass() { return new LowerAtomicLegacyPass(); } 175
