LowerAtomic.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
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.h"
16#include "llvm/IR/Function.h"
17#include "llvm/IR/IRBuilder.h"
18#include "llvm/IR/IntrinsicInst.h"
19#include "llvm/Pass.h"
20using namespace llvm;
21
22#define DEBUG_TYPE "loweratomic"
23
24static bool LowerAtomicCmpXchgInst(AtomicCmpXchgInst *CXI) {
25  IRBuilder<> Builder(CXI->getParent(), CXI);
26  Value *Ptr = CXI->getPointerOperand();
27  Value *Cmp = CXI->getCompareOperand();
28  Value *Val = CXI->getNewValOperand();
29
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);
34
35  CXI->replaceAllUsesWith(Orig);
36  CXI->eraseFromParent();
37  return true;
38}
39
40static bool LowerAtomicRMWInst(AtomicRMWInst *RMWI) {
41  IRBuilder<> Builder(RMWI->getParent(), RMWI);
42  Value *Ptr = RMWI->getPointerOperand();
43  Value *Val = RMWI->getValOperand();
44
45  LoadInst *Orig = Builder.CreateLoad(Ptr);
46  Value *Res = nullptr;
47
48  switch (RMWI->getOperation()) {
49  default: llvm_unreachable("Unexpected RMW operation");
50  case AtomicRMWInst::Xchg:
51    Res = Val;
52    break;
53  case AtomicRMWInst::Add:
54    Res = Builder.CreateAdd(Orig, Val);
55    break;
56  case AtomicRMWInst::Sub:
57    Res = Builder.CreateSub(Orig, Val);
58    break;
59  case AtomicRMWInst::And:
60    Res = Builder.CreateAnd(Orig, Val);
61    break;
62  case AtomicRMWInst::Nand:
63    Res = Builder.CreateNot(Builder.CreateAnd(Orig, Val));
64    break;
65  case AtomicRMWInst::Or:
66    Res = Builder.CreateOr(Orig, Val);
67    break;
68  case AtomicRMWInst::Xor:
69    Res = Builder.CreateXor(Orig, Val);
70    break;
71  case AtomicRMWInst::Max:
72    Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
73                               Val, Orig);
74    break;
75  case AtomicRMWInst::Min:
76    Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Val),
77                               Orig, Val);
78    break;
79  case AtomicRMWInst::UMax:
80    Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
81                               Val, Orig);
82    break;
83  case AtomicRMWInst::UMin:
84    Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Val),
85                               Orig, Val);
86    break;
87  }
88  Builder.CreateStore(Res, Ptr);
89  RMWI->replaceAllUsesWith(Orig);
90  RMWI->eraseFromParent();
91  return true;
92}
93
94static bool LowerFenceInst(FenceInst *FI) {
95  FI->eraseFromParent();
96  return true;
97}
98
99static bool LowerLoadInst(LoadInst *LI) {
100  LI->setAtomic(NotAtomic);
101  return true;
102}
103
104static bool LowerStoreInst(StoreInst *SI) {
105  SI->setAtomic(NotAtomic);
106  return true;
107}
108
109namespace {
110  struct LowerAtomic : public BasicBlockPass {
111    static char ID;
112    LowerAtomic() : BasicBlockPass(ID) {
113      initializeLowerAtomicPass(*PassRegistry::getPassRegistry());
114    }
115    bool runOnBasicBlock(BasicBlock &BB) override {
116      if (skipOptnoneFunction(BB))
117        return false;
118      bool Changed = false;
119      for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE; ) {
120        Instruction *Inst = DI++;
121        if (FenceInst *FI = dyn_cast<FenceInst>(Inst))
122          Changed |= LowerFenceInst(FI);
123        else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(Inst))
124          Changed |= LowerAtomicCmpXchgInst(CXI);
125        else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(Inst))
126          Changed |= LowerAtomicRMWInst(RMWI);
127        else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
128          if (LI->isAtomic())
129            LowerLoadInst(LI);
130        } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
131          if (SI->isAtomic())
132            LowerStoreInst(SI);
133        }
134      }
135      return Changed;
136    }
137  };
138}
139
140char LowerAtomic::ID = 0;
141INITIALIZE_PASS(LowerAtomic, "loweratomic",
142                "Lower atomic intrinsics to non-atomic form",
143                false, false)
144
145Pass *llvm::createLowerAtomicPass() { return new LowerAtomic(); }
146