revng-revng/lib/Canonicalize/SimplifySwitchPass.cpp

//
// This file is distributed under the MIT License. See LICENSE.md for details.
//

// Without this Pass the devirtualization process effectively handles indirect
// jumps, particularly those arising from C's switch statement. However, the
// output is too low-level, especially when switch statements involve jump
// tables. This results in emitted memory accesses instead of clear switch
// statements based on variable values. For instance, rather than a readable
// switch statement reflecting _argument_rdi values, the code directly accesses
// the jump table's entries. To address this readability issue, we propose
// introducing the SimplifySwtichPass. This pass should refine the output of
// switch statements by re-running the devirtualization process and adjusting
// them to a more human-readable format. This enhancement is crucial for
// improving code comprehension.

#include "llvm/IR/Dominators.h"
#include "llvm/Passes/PassBuilder.h"

#include "revng/Lift/LoadBinaryPass.h"
#include "revng/Model/Architecture.h"
#include "revng/Pipeline/ExecutionContext.h"
#include "revng/Pipeline/RegisterPipe.h"
#include "revng/Pipes/FileContainer.h"
#include "revng/Pipes/FunctionPass.h"
#include "revng/Pipes/Kinds.h"
#include "revng/Support/IRHelpers.h"
#include "revng/ValueMaterializer/DataFlowRangeAnalysis.h"
#include "revng/ValueMaterializer/ValueMaterializer.h"

using namespace llvm;
using namespace ::revng::kinds;

static Logger Log("switch-opt");

class RawBinaryMemoryOracle final : public MemoryOracle {
private:
  RawBinaryView &BinaryView;
  model::Architecture::Values Architecture = model::Architecture::Invalid;

public:
  RawBinaryMemoryOracle(RawBinaryView &BinaryView,
                        model::Architecture::Values Architecture) :
    BinaryView(BinaryView), Architecture(Architecture) {}

  MaterializedValue load(uint64_t LoadAddress, unsigned LoadSize) final {
    auto Address = MetaAddress::fromGeneric(Architecture, LoadAddress);
    return BinaryView.load(Address,
                           LoadSize,
                           model::Architecture::isLittleEndian(Architecture));
  }
};

static BasicBlock *getBlockFor(SwitchInst *Switch, Constant *C) {
  for (const auto &I : Switch->cases()) {
    const ConstantInt *CaseValue = I.getCaseValue();
    if (CaseValue == C)
      return I.getCaseSuccessor();
  }

  return nullptr;
}

static BidirectionalNode<DataFlowNode> *
findStartNode(const DataFlowGraph &DFG) {
  bool BailOut = false;
  BidirectionalNode<DataFlowNode> *Result = nullptr;
  for (const BidirectionalNode<DataFlowNode> *BidirectNode : DFG.nodes()) {
    const DataFlowNode &Node = *BidirectNode;
    // Ignore nodes that are constants in the DFG.
    if (isa<ConstantInt>(Node.Value))
      continue;

    if (Node.UseOracle) {
      if (Result != nullptr) {
        BailOut = true;
        break;
      } else {
        // TODO: Fix this const_cast.
        BidirectionalNode<DataFlowNode>
          *N = const_cast<BidirectionalNode<DataFlowNode> *>(BidirectNode);
        Result = N;
      }
    }
  }

  // We found more than one start node.
  if (Result == nullptr or BailOut)
    return nullptr;

  return Result;
}

static bool handleSwitch(SwitchInst *Switch,
                         LazyValueInfo &LVI,
                         DataFlowRangeAnalysis &DFRA,
                         DominatorTree &DT,
                         RawBinaryMemoryOracle &MO) {
  // Skip empty switches.
  if (Switch->getNumCases() == 0)
    return false;

  Value *Condition = Switch->getCondition();
  DataFlowGraph::Limits Limits(1000 /*MaxPhiLike*/, 1 /*MaxLoad*/);

  auto AVIOracle = Oracle::AdvancedValueInfo;
  ::ValueMaterializer Results = ::ValueMaterializer::getValuesFor(Switch,
                                                                  Condition,
                                                                  MO,
                                                                  LVI,
                                                                  DFRA,
                                                                  DT,
                                                                  Limits,
                                                                  AVIOracle);
  // We can not do too much without any values materialized.
  if (not Results.values())
    return false;

  // The number of values materialized should match the number of cases in
  // the switch.
  if (Results.values()->size() != Switch->getNumCases()) {
    revng_log(Log, "Unexpected number of values found!");
    return false;
  }

  const DataFlowGraph &DFG = Results.dataFlowGraph();
  // Identify the only node in the data flow graph that's associated to an
  // Oracle and use it as a switch condition.
  BidirectionalNode<DataFlowNode> *StartNode = findStartNode(DFG);
  if (!StartNode) {
    revng_log(Log, "Have not found a proper start node!");
    return false;
  }

  std::map<ConstantInt *, BasicBlock *> NewLabels;
  for (const llvm::APInt &Value : *StartNode->OracleRange) {
    std::optional<MaterializedValue> OldValue = DFG.materializeOne(StartNode,
                                                                   MO,
                                                                   Value);
    if (not OldValue) {
      revng_log(Log,
                "Have not found materialized value for "
                  << Value.getZExtValue());
      return false;
    }
    Constant *ConstantForOld = toLLVMConstant(Switch->getContext(),
                                              (*OldValue).value());
    Constant *ConstantForTheValue = toLLVMConstant(Switch->getContext(), Value);

    BasicBlock *BlockForValue = getBlockFor(Switch, ConstantForOld);

    if (not BlockForValue) {
      revng_log(Log,
                "Have not found case/BB for "
                  << ConstantForOld->getUniqueInteger().getZExtValue());
      return false;
    }
    NewLabels[cast<ConstantInt>(ConstantForTheValue)] = BlockForValue;
  }

  // We have not found all the cases for the new switch.
  if (Switch->getNumCases() != NewLabels.size())
    return false;

  // Recreate the new switch.
  auto *NewSwitch = SwitchInst::Create(StartNode->Value,
                                       Switch->getDefaultDest(),
                                       NewLabels.size(),
                                       Switch);

  for (auto &NewLabel : NewLabels)
    NewSwitch->addCase(NewLabel.first, NewLabel.second);

  Switch->replaceAllUsesWith(NewSwitch);

  return true;
}

static bool simplifySwitch(Function &F,
                           LazyValueInfo &LVI,
                           DataFlowRangeAnalysis &DFRA,
                           DominatorTree &DT,
                           RawBinaryMemoryOracle &MO) {
  bool Result = false;
  for (BasicBlock &BB : F) {
    for (Instruction &I : make_early_inc_range(BB)) {
      SwitchInst *Switch = dyn_cast<SwitchInst>(&I);
      if (not Switch)
        continue;

      if (handleSwitch(Switch, LVI, DFRA, DT, MO)) {
        Switch->eraseFromParent();
        Result |= true;
      }
    }
  }

  return Result;
}

struct SimplifySwitchPassImpl : public pipeline::FunctionPassImpl {
private:
  const model::Binary &Binary;
  DataFlowRangeAnalysis DFRA;

public:
  SimplifySwitchPassImpl(llvm::ModulePass &Pass,
                         const model::Binary &Binary,
                         llvm::Module &M) :
    pipeline::FunctionPassImpl(Pass), Binary(Binary), DFRA(M) {}

  bool runOnFunction(const model::Function &ModelFunction,
                     llvm::Function &Function) override;

public:
  static void getAnalysisUsage(llvm::AnalysisUsage &AU);
};

bool SimplifySwitchPassImpl::runOnFunction(const model::Function &ModelFunction,
                                           llvm::Function &Function) {
  auto &LVI = getAnalysis<LazyValueInfoWrapperPass>(Function).getLVI();
  auto &DT = getAnalysis<DominatorTreeWrapperPass>(Function).getDomTree();
  RawBinaryView &BinaryView = getAnalysis<LoadBinaryWrapperPass>().get();
  RawBinaryMemoryOracle MO(BinaryView, Binary.Architecture());
  return simplifySwitch(Function, LVI, DFRA, DT, MO);
}

void SimplifySwitchPassImpl::getAnalysisUsage(AnalysisUsage &AU) {
  AU.addRequired<DominatorTreeWrapperPass>();
  AU.addRequired<LazyValueInfoWrapperPass>();
  AU.addRequired<LoadBinaryWrapperPass>();
  AU.addRequired<LoadModelWrapperPass>();
}

template<>
char pipeline::FunctionPass<SimplifySwitchPassImpl>::ID = 0;

namespace revng::pipes {

class SimplifySwitch {
public:
  static constexpr auto Name = "simplify-switch";

  std::array<pipeline::ContractGroup, 1> getContract() const {
    pipeline::Contract BinaryPart(kinds::Binary, 0, kinds::Binary, 0);
    pipeline::Contract FunctionsPart(kinds::StackPointerPromoted,
                                     1,
                                     kinds::StackPointerPromoted,
                                     1);
    return { pipeline::ContractGroup({ BinaryPart, FunctionsPart }) };
  }

  void run(pipeline::ExecutionContext &EC,
           const BinaryFileContainer &SourceBinary,
           pipeline::LLVMContainer &Output);
};

void SimplifySwitch::run(pipeline::ExecutionContext &EC,
                         const BinaryFileContainer &SourceBinary,
                         pipeline::LLVMContainer &TargetsList) {
  if (not SourceBinary.exists())
    return;

  const TupleTree<model::Binary> &Model = getModelFromContext(EC);
  auto BufferOrError = MemoryBuffer::getFileOrSTDIN(*SourceBinary.path());
  auto Buffer = cantFail(errorOrToExpected(std::move(BufferOrError)));
  RawBinaryView RawBinary(*Model, Buffer->getBuffer());

  legacy::PassManager PM;
  PM.add(new LoadModelWrapperPass(Model));
  PM.add(new pipeline::LoadExecutionContextPass(&EC, TargetsList.name()));
  PM.add(new LoadBinaryWrapperPass(Buffer->getBuffer()));
  PM.add(new DominatorTreeWrapperPass);
  PM.add(new pipeline::FunctionPass<SimplifySwitchPassImpl>);
  PM.run(TargetsList.getModule());
}

} // namespace revng::pipes

static pipeline::RegisterPipe<revng::pipes::SimplifySwitch>
  RegSimplifySwitchPipe;