lib/Transforms/IPO/IndMemRemoval.cpp

   1 //===-- IndMemRemoval.cpp - Remove indirect allocations and frees ----------===//
   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 finds places where memory allocation functions may escape into
  11 // indirect land.  Some transforms are much easier (aka possible) only if free
  12 // or malloc are not called indirectly.
  13 // Thus find places where the address of memory functions are taken and construct
  14 // bounce functions with direct calls of those functions.
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #define DEBUG_TYPE "indmemrem"
  19 #include "llvm/Transforms/IPO.h"
  20 #include "llvm/Pass.h"
  21 #include "llvm/Module.h"
  22 #include "llvm/Instructions.h"
  23 #include "llvm/Type.h"
  24 #include "llvm/DerivedTypes.h"
  25 #include "llvm/ADT/Statistic.h"
  26 #include "llvm/Support/Compiler.h"
  27 using namespace llvm;
  28
  29 STATISTIC(NumBounceSites, "Number of sites modified");
  30 STATISTIC(NumBounce     , "Number of bounce functions created");
  31
  32 namespace {
  33   class VISIBILITY_HIDDEN IndMemRemPass : public ModulePass {
  34   public:
  35     static char ID; // Pass identification, replacement for typeid
  36     IndMemRemPass() : ModulePass(&ID) {}
  37
  38     virtual bool runOnModule(Module &M);
  39   };
  40 } // end anonymous namespace
  41
  42 char IndMemRemPass::ID = 0;
  43 static RegisterPass<IndMemRemPass>
  44 X("indmemrem","Indirect Malloc and Free Removal");
  45
  46 bool IndMemRemPass::runOnModule(Module &M) {
  47   // In theory, all direct calls of malloc and free should be promoted
  48   // to intrinsics.  Therefore, this goes through and finds where the
  49   // address of free or malloc are taken and replaces those with bounce
  50   // functions, ensuring that all malloc and free that might happen
  51   // happen through intrinsics.
  52   bool changed = false;
  53   if (Function* F = M.getFunction("free")) {
  54     if (F->isDeclaration() && F->arg_size() == 1 && !F->use_empty()) {
  55       Function* FN = Function::Create(F->getFunctionType(),
  56                                       GlobalValue::LinkOnceAnyLinkage,
  57                                       "free_llvm_bounce", &M);
  58       BasicBlock* bb = BasicBlock::Create("entry",FN);
  59       Instruction* R = ReturnInst::Create(bb);
  60       new FreeInst(FN->arg_begin(), R);
  61       ++NumBounce;
  62       NumBounceSites += F->getNumUses();
  63       F->replaceAllUsesWith(FN);
  64       changed = true;
  65     }
  66   }
  67   if (Function* F = M.getFunction("malloc")) {
  68     if (F->isDeclaration() && F->arg_size() == 1 && !F->use_empty()) {
  69       Function* FN = Function::Create(F->getFunctionType(),
  70                                       GlobalValue::LinkOnceAnyLinkage,
  71                                       "malloc_llvm_bounce", &M);
  72       FN->setDoesNotAlias(0);
  73       BasicBlock* bb = BasicBlock::Create("entry",FN);
  74       Instruction* c = CastInst::CreateIntegerCast(
  75           FN->arg_begin(), Type::Int32Ty, false, "c", bb);
  76       Instruction* a = new MallocInst(Type::Int8Ty, c, "m", bb);
  77       ReturnInst::Create(a, bb);
  78       ++NumBounce;
  79       NumBounceSites += F->getNumUses();
  80       F->replaceAllUsesWith(FN);
  81       changed = true;
  82     }
  83   }
  84   return changed;
  85 }
  86
  87 ModulePass *llvm::createIndMemRemPass() {
  88   return new IndMemRemPass();
  89 }