lib/Transforms/Utils/LowerAllocations.cpp

   1 //===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
   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 // The LowerAllocations transformation is a target-dependent tranformation
  11 // because it depends on the size of data types and alignment constraints.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "lowerallocs"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
  18 #include "llvm/Module.h"
  19 #include "llvm/DerivedTypes.h"
  20 #include "llvm/Instructions.h"
  21 #include "llvm/Constants.h"
  22 #include "llvm/LLVMContext.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/ADT/Statistic.h"
  25 #include "llvm/Target/TargetData.h"
  26 #include "llvm/Support/Compiler.h"
  27 using namespace llvm;
  28
  29 STATISTIC(NumLowered, "Number of allocations lowered");
  30
  31 namespace {
  32   /// LowerAllocations - Turn malloc and free instructions into @malloc and
  33   /// @free calls.
  34   ///
  35   class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass {
  36     Constant *FreeFunc;   // Functions in the module we are processing
  37                           // Initialized by doInitialization
  38     bool LowerMallocArgToInteger;
  39   public:
  40     static char ID; // Pass ID, replacement for typeid
  41     explicit LowerAllocations(bool LowerToInt = false)
  42       : BasicBlockPass(&ID), FreeFunc(0),
  43         LowerMallocArgToInteger(LowerToInt) {}
  44
  45     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  46       AU.addRequired<TargetData>();
  47       AU.setPreservesCFG();
  48
  49       // This is a cluster of orthogonal Transforms:
  50       AU.addPreserved<UnifyFunctionExitNodes>();
  51       AU.addPreservedID(PromoteMemoryToRegisterID);
  52       AU.addPreservedID(LowerSwitchID);
  53       AU.addPreservedID(LowerInvokePassID);
  54     }
  55
  56     /// doPassInitialization - For the lower allocations pass, this ensures that
  57     /// a module contains a declaration for a malloc and a free function.
  58     ///
  59     bool doInitialization(Module &M);
  60
  61     virtual bool doInitialization(Function &F) {
  62       return doInitialization(*F.getParent());
  63     }
  64
  65     /// runOnBasicBlock - This method does the actual work of converting
  66     /// instructions over, assuming that the pass has already been initialized.
  67     ///
  68     bool runOnBasicBlock(BasicBlock &BB);
  69   };
  70 }
  71
  72 char LowerAllocations::ID = 0;
  73 static RegisterPass<LowerAllocations>
  74 X("lowerallocs", "Lower allocations from instructions to calls");
  75
  76 // Publically exposed interface to pass...
  77 const PassInfo *const llvm::LowerAllocationsID = &X;
  78 // createLowerAllocationsPass - Interface to this file...
  79 Pass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) {
  80   return new LowerAllocations(LowerMallocArgToInteger);
  81 }
  82
  83
  84 // doInitialization - For the lower allocations pass, this ensures that a
  85 // module contains a declaration for a malloc and a free function.
  86 //
  87 // This function is always successful.
  88 //
  89 bool LowerAllocations::doInitialization(Module &M) {
  90   const Type *BPTy = PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
  91   FreeFunc = M.getOrInsertFunction("free"  , Type::getVoidTy(M.getContext()),
  92                                    BPTy, (Type *)0);
  93   return true;
  94 }
  95
  96 // runOnBasicBlock - This method does the actual work of converting
  97 // instructions over, assuming that the pass has already been initialized.
  98 //
  99 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
 100   bool Changed = false;
 101   assert(FreeFunc && "Pass not initialized!");
 102
 103   BasicBlock::InstListType &BBIL = BB.getInstList();
 104
 105   const TargetData &TD = getAnalysis<TargetData>();
 106   const Type *IntPtrTy = TD.getIntPtrType(BB.getContext());
 107
 108   // Loop over all of the instructions, looking for malloc or free instructions
 109   for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
 110     if (MallocInst *MI = dyn_cast<MallocInst>(I)) {
 111       Value *MCast = CallInst::CreateMalloc(I, MI->getType(), IntPtrTy,
 112                                             MI->getOperand(0));
 113
 114       // Replace all uses of the old malloc inst with the cast inst
 115       MI->replaceAllUsesWith(MCast);
 116       I = --BBIL.erase(I);         // remove and delete the malloc instr...
 117       Changed = true;
 118       ++NumLowered;
 119     } else if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
 120       Value *PtrCast =
 121         new BitCastInst(FI->getOperand(0),
 122                PointerType::getUnqual(Type::getInt8Ty(BB.getContext())), "", I);
 123
 124       // Insert a call to the free function...
 125       CallInst::Create(FreeFunc, PtrCast, "", I)->setTailCall();
 126
 127       // Delete the old free instruction
 128       I = --BBIL.erase(I);
 129       Changed = true;
 130       ++NumLowered;
 131     }
 132   }
 133
 134   return Changed;
 135 }
 136