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