lib/Transforms/Scalar/LowerAtomic.cpp

   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 #define DEBUG_TYPE "loweratomic"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/BasicBlock.h"
  18 #include "llvm/Function.h"
  19 #include "llvm/Instruction.h"
  20 #include "llvm/Instructions.h"
  21 #include "llvm/Intrinsics.h"
  22 #include "llvm/Pass.h"
  23 #include "llvm/Support/IRBuilder.h"
  24
  25 using namespace llvm;
  26
  27 namespace {
  28
  29 bool LowerAtomicIntrinsic(CallInst *CI) {
  30   IRBuilder<> Builder(CI->getParent(), CI);
  31
  32   Function *Callee = CI->getCalledFunction();
  33   if (!Callee)
  34     return false;
  35
  36   unsigned IID = Callee->getIntrinsicID();
  37   switch (IID) {
  38   case Intrinsic::memory_barrier:
  39     break;
  40
  41   case Intrinsic::atomic_load_add:
  42   case Intrinsic::atomic_load_sub:
  43   case Intrinsic::atomic_load_and:
  44   case Intrinsic::atomic_load_nand:
  45   case Intrinsic::atomic_load_or:
  46   case Intrinsic::atomic_load_xor:
  47   case Intrinsic::atomic_load_max:
  48   case Intrinsic::atomic_load_min:
  49   case Intrinsic::atomic_load_umax:
  50   case Intrinsic::atomic_load_umin: {
  51     Value *Ptr = CI->getArgOperand(0);
  52     Value *Delta = CI->getArgOperand(1);
  53
  54     LoadInst *Orig = Builder.CreateLoad(Ptr);
  55     Value *Res = NULL;
  56     switch (IID) {
  57       default: assert(0 && "Unrecognized atomic modify operation");
  58       case Intrinsic::atomic_load_add:
  59         Res = Builder.CreateAdd(Orig, Delta);
  60         break;
  61       case Intrinsic::atomic_load_sub:
  62         Res = Builder.CreateSub(Orig, Delta);
  63         break;
  64       case Intrinsic::atomic_load_and:
  65         Res = Builder.CreateAnd(Orig, Delta);
  66         break;
  67       case Intrinsic::atomic_load_nand:
  68         Res = Builder.CreateNot(Builder.CreateAnd(Orig, Delta));
  69         break;
  70       case Intrinsic::atomic_load_or:
  71         Res = Builder.CreateOr(Orig, Delta);
  72         break;
  73       case Intrinsic::atomic_load_xor:
  74         Res = Builder.CreateXor(Orig, Delta);
  75         break;
  76       case Intrinsic::atomic_load_max:
  77         Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Delta),
  78                                    Delta,
  79                                    Orig);
  80         break;
  81       case Intrinsic::atomic_load_min:
  82         Res = Builder.CreateSelect(Builder.CreateICmpSLT(Orig, Delta),
  83                                    Orig,
  84                                    Delta);
  85         break;
  86       case Intrinsic::atomic_load_umax:
  87         Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Delta),
  88                                    Delta,
  89                                    Orig);
  90         break;
  91       case Intrinsic::atomic_load_umin:
  92         Res = Builder.CreateSelect(Builder.CreateICmpULT(Orig, Delta),
  93                                    Orig,
  94                                    Delta);
  95         break;
  96     }
  97     Builder.CreateStore(Res, Ptr);
  98
  99     CI->replaceAllUsesWith(Orig);
 100     break;
 101   }
 102
 103   case Intrinsic::atomic_swap: {
 104     Value *Ptr = CI->getArgOperand(0);
 105     Value *Val = CI->getArgOperand(1);
 106
 107     LoadInst *Orig = Builder.CreateLoad(Ptr);
 108     Builder.CreateStore(Val, Ptr);
 109
 110     CI->replaceAllUsesWith(Orig);
 111     break;
 112   }
 113
 114   case Intrinsic::atomic_cmp_swap: {
 115     Value *Ptr = CI->getArgOperand(0);
 116     Value *Cmp = CI->getArgOperand(1);
 117     Value *Val = CI->getArgOperand(2);
 118
 119     LoadInst *Orig = Builder.CreateLoad(Ptr);
 120     Value *Equal = Builder.CreateICmpEQ(Orig, Cmp);
 121     Value *Res = Builder.CreateSelect(Equal, Val, Orig);
 122     Builder.CreateStore(Res, Ptr);
 123
 124     CI->replaceAllUsesWith(Orig);
 125     break;
 126   }
 127
 128   default:
 129     return false;
 130   }
 131
 132   assert(CI->use_empty() &&
 133          "Lowering should have eliminated any uses of the intrinsic call!");
 134   CI->eraseFromParent();
 135
 136   return true;
 137 }
 138
 139 struct LowerAtomic : public BasicBlockPass {
 140   static char ID;
 141   LowerAtomic() : BasicBlockPass(ID) {}
 142   bool runOnBasicBlock(BasicBlock &BB) {
 143     bool Changed = false;
 144     for (BasicBlock::iterator DI = BB.begin(), DE = BB.end(); DI != DE; ) {
 145       Instruction *Inst = DI++;
 146       if (CallInst *CI = dyn_cast<CallInst>(Inst))
 147         Changed |= LowerAtomicIntrinsic(CI);
 148     }
 149     return Changed;
 150   }
 151
 152 };
 153
 154 }
 155
 156 char LowerAtomic::ID = 0;
 157 static RegisterPass<LowerAtomic>
 158 X("loweratomic", "Lower atomic intrinsics to non-atomic form");
 159
 160 Pass *llvm::createLowerAtomicPass() { return new LowerAtomic(); }