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//===-- IndMemRemoval.cpp - Remove indirect allocations and frees ----------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass finds places where memory allocation functions may escape into
// indirect land. Some transforms are much easier (aka possible) only if free
// or malloc are not called indirectly.
// Thus find places where the address of memory functions are taken and construct
// bounce functions with direct calls of those functions.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "indmemrem"
#include "llvm/Transforms/IPO.h"
#include "llvm/Pass.h"
#include "llvm/Module.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/DerivedTypes.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;
STATISTIC(NumBounceSites, "Number of sites modified");
STATISTIC(NumBounce , "Number of bounce functions created");
namespace {
class VISIBILITY_HIDDEN IndMemRemPass : public ModulePass {
public:
virtual bool runOnModule(Module &M);
};
RegisterPass<IndMemRemPass> X("indmemrem","Indirect Malloc and Free Removal");
} // end anonymous namespace
bool IndMemRemPass::runOnModule(Module &M) {
//in Theory, all direct calls of malloc and free should be promoted
//to intrinsics. Therefor, this goes through and finds where the
//address of free or malloc are taken and replaces those with bounce
//functions, ensuring that all malloc and free that might happen
//happen through intrinsics.
bool changed = false;
if (Function* F = M.getFunction("free")) {
assert(F->isDeclaration() && "free not external?");
if (!F->use_empty()) {
Function* FN = new Function(F->getFunctionType(),
GlobalValue::LinkOnceLinkage,
"free_llvm_bounce", &M);
BasicBlock* bb = new BasicBlock("entry",FN);
Instruction* R = new ReturnInst(bb);
new FreeInst(FN->arg_begin(), R);
++NumBounce;
NumBounceSites += F->getNumUses();
F->replaceAllUsesWith(FN);
changed = true;
}
}
if (Function* F = M.getFunction("malloc")) {
assert(F->isDeclaration() && "malloc not external?");
if (!F->use_empty()) {
Function* FN = new Function(F->getFunctionType(),
GlobalValue::LinkOnceLinkage,
"malloc_llvm_bounce", &M);
BasicBlock* bb = new BasicBlock("entry",FN);
Instruction* c = CastInst::createIntegerCast(
FN->arg_begin(), Type::Int32Ty, false, "c", bb);
Instruction* a = new MallocInst(Type::Int8Ty, c, "m", bb);
new ReturnInst(a, bb);
++NumBounce;
NumBounceSites += F->getNumUses();
F->replaceAllUsesWith(FN);
changed = true;
}
}
return changed;
}
ModulePass *llvm::createIndMemRemPass() {
return new IndMemRemPass();
}
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