lifting-bits-mcsema/mcsema/BC/Optimize.cpp

/*
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#include <glog/logging.h>

#include <llvm/IR/Constants.h>
#include <llvm/IR/DataLayout.h>
#include <llvm/IR/DebugInfo.h>
#include <llvm/IR/InstIterator.h>
#include <llvm/IR/IRBuilder.h>
#include <llvm/IR/LegacyPassManager.h>
#include <llvm/IR/LLVMContext.h>
#include <llvm/IR/Metadata.h>
#include <llvm/IR/MDBuilder.h>
#include <llvm/IR/Module.h>
#include <llvm/IR/PassManager.h>
#include <llvm/IR/Type.h>

#include <llvm/Transforms/IPO.h>
#include <llvm/Transforms/IPO/PassManagerBuilder.h>
#include <llvm/Transforms/Scalar.h>
#include <llvm/Transforms/Utils/Local.h>
#include <llvm/Transforms/Utils/Cloning.h>
#include <llvm/Transforms/Utils/ValueMapper.h>

#include "mcsema/BC/Optimize.h"
#include "mcsema/BC/Util.h"

namespace mcsema {
namespace {
static void RunO3(void) {
  llvm::legacy::FunctionPassManager func_manager(gModule);
  llvm::legacy::PassManager module_manager;

  auto TLI = new llvm::TargetLibraryInfoImpl(
      llvm::Triple(gModule->getTargetTriple()));
  TLI->disableAllFunctions();

  llvm::PassManagerBuilder builder;
  builder.OptLevel = 0;  // -O0.
  builder.SizeLevel = 0;  // -Oz
  builder.Inliner = llvm::createFunctionInliningPass(999);
  builder.LibraryInfo = TLI;  // Deleted by `llvm::~PassManagerBuilder`.
  builder.DisableTailCalls = false;  // Enable tail calls.
  builder.DisableUnrollLoops = false;  // Unroll loops!
  builder.DisableUnitAtATime = false;
  builder.SLPVectorize = false;  // Don't produce vector operations.
  builder.LoopVectorize = false;  // Don't produce vector operations.
  builder.LoadCombine = false;  // Don't coalesce loads.
  builder.MergeFunctions = false;  // Try to deduplicate functions.
  builder.VerifyInput = false;
  builder.VerifyOutput = false;

  builder.populateFunctionPassManager(func_manager);
  builder.populateModulePassManager(module_manager);

  func_manager.add(llvm::createCFGSimplificationPass());
  func_manager.add(llvm::createPromoteMemoryToRegisterPass());
  func_manager.add(llvm::createReassociatePass());
  func_manager.add(llvm::createInstructionCombiningPass());
  func_manager.add(llvm::createDeadStoreEliminationPass());
  func_manager.add(llvm::createDeadCodeEliminationPass());

  func_manager.doInitialization();
  for (auto &func : *gModule) {
    if (func.getName().startswith("sub_")) {
      func_manager.run(func);
    }
  }
  func_manager.doFinalization();
  module_manager.run(*gModule);
}

static std::vector<llvm::GlobalVariable *> FindISELs(void) {
  std::vector<llvm::GlobalVariable *> isels;
  auto basic_block = gModule->getFunction("__remill_basic_block");
  if (!basic_block) {
    LOG(ERROR)
        << "Not removing any ISELs or SEMs; can't find __remill_basic_block.";
    return isels;
  }

  auto lifted_func_type = basic_block->getFunctionType();
  auto mem_type = lifted_func_type->getParamType(0);
  auto state_type = lifted_func_type->getParamType(1);

  isels.reserve(gModule->size());
  for (auto &isel : gModule->globals()) {
    if (!isel.hasInitializer()) {
      continue;
    }

    auto sem = llvm::dyn_cast<llvm::Function>(
        isel.getInitializer()->stripPointerCasts());
    if (!sem) {
      continue;
    }

    auto sem_type = sem->getFunctionType();

    if (mem_type == sem_type->getParamType(0) &&
        state_type == sem_type->getParamType(1)) {
      DLOG(INFO)
          << "Found ISEL " << isel.getName().str();
      isels.push_back(&isel);
    }
  }

  return isels;
}

// Remove the ISEL variables used for finding the instruction semantics.
static void RemoveISELs(std::vector<llvm::GlobalVariable *> &isels) {
  std::vector<llvm::GlobalVariable *> next_isels;
  while (isels.size()) {
    next_isels.clear();
    for (auto isel : isels) {
      isel->setLinkage(llvm::GlobalValue::InternalLinkage);
      if (1 >= isel->getNumUses()) {
        DLOG(INFO)
            << "Removing ISEL " << isel->getName().str();
        isel->eraseFromParent();
      } else {
        next_isels.push_back(isel);
      }
    }
    isels.swap(next_isels);
  }
}

// Remove some of the remill intrinsics.
static void RemoveIntrinsics(void) {
  if (auto used = gModule->getGlobalVariable("llvm.used")) {
    used->eraseFromParent();
  }

  if (auto intrinsic_keeper = gModule->getFunction("__remill_intrinsics")) {
    intrinsic_keeper->eraseFromParent();
  }

  if (auto basic_block = gModule->getFunction("__remill_basic_block")) {
    basic_block->eraseFromParent();
  }

  if (auto mark_used = gModule->getFunction("__remill_mark_as_used")) {
    mark_used->eraseFromParent();
  }
}

}  // namespace

void OptimizeBitcode(void) {
  auto isels = FindISELs();
  RemoveIntrinsics();
  LOG(INFO)
      << "Optimizing module.";
  RemoveISELs(isels);
  RunO3();
}

}  // namespace mcsema