revng-revng/lib/IRCanonicalization/MakeModelCastPass.cpp

//
// Copyright rev.ng Srls. See LICENSE.md for details.
//

#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Use.h"
#include "llvm/Pass.h"

#include "revng/ABI/FunctionType.h"
#include "revng/EarlyFunctionAnalysis/IRHelpers.h"
#include "revng/Model/Binary.h"
#include "revng/Model/IRHelpers.h"
#include "revng/Model/LoadModelPass.h"
#include "revng/Model/QualifiedType.h"
#include "revng/Support/Assert.h"
#include "revng/Support/FunctionTags.h"
#include "revng/Support/YAMLTraits.h"

#include "revng-c/InitModelTypes/InitModelTypes.h"
#include "revng-c/Support/FunctionTags.h"
#include "revng-c/Support/IRHelpers.h"
#include "revng-c/Support/ModelHelpers.h"
#include "revng-c/TypeNames/LLVMTypeNames.h"

using namespace llvm;
using ModelTypesMap = std::map<const llvm::Value *, const model::QualifiedType>;

struct SerializedType {
  Constant *StringType;
  uint64_t OperandId;

  SerializedType(Constant *StringType, uint64_t OperandId = 0) :
    StringType(StringType), OperandId(OperandId) {}
};

struct MakeModelCastPass : public llvm::FunctionPass {
private:
  ModelTypesMap TypeMap;
  const model::Function *ModelFunction = nullptr;

public:
  static char ID;

  MakeModelCastPass() : FunctionPass(ID) {}

  bool runOnFunction(llvm::Function &F) override;

  void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
    AU.setPreservesCFG();
    AU.addRequired<LoadModelWrapperPass>();
  }

private:
  std::vector<SerializedType>
  serializeTypesForModelCast(Instruction *, const model::Binary &);
  void createAndInjectModelCast(Instruction *,
                                const SerializedType &,
                                OpaqueFunctionsPool<Type *> &);
};

using MMCP = MakeModelCastPass;

std::vector<SerializedType>
MMCP::serializeTypesForModelCast(Instruction *I, const model::Binary &Model) {
  using namespace model;
  using namespace abi::FunctionType;

  std::vector<SerializedType> Result;
  Module *M = I->getModule();

  auto SerializeTypeFor = [this, &Model, &Result, &M](const llvm::Use &Op) {
    // Check if we have strong model information about this operand
    auto ModelTypes = getExpectedModelType(&Op, Model);

    // Aggregates that do not correspond to model structs (e.g. return types of
    // RawFunctionTypes that return more than one value) cannot be handled with
    // casts, since we don't have a model::Type to cast them to.
    if (ModelTypes.size() == 1) {
      QualifiedType ExpectedType = ModelTypes.back();
      revng_assert(ExpectedType.UnqualifiedType.isValid());

      if (ExpectedType != TypeMap.at(Op.get())) {
        // Create a cast only if the expected type is different from the actual
        // type propagated until here
        auto Type = SerializedType(serializeToLLVMString(ExpectedType, *M),
                                   Op.getOperandNo());
        Result.emplace_back(std::move(Type));
      }
    }
  };

  if (auto *Call = dyn_cast<CallInst>(I)) {
    // Lifted functions have their prototype on the model
    auto *Callee = Call->getCalledFunction();

    if (FunctionTags::CallToLifted.isTagOf(Call)) {
      // For indirect calls, cast the callee to the right function type
      if (not Callee)
        SerializeTypeFor(Call->getCalledOperandUse());

      // For all calls, check the formal arguments types
      for (llvm::Use &Op : Call->arg_operands())
        SerializeTypeFor(Op);

    } else if (FunctionTags::ModelGEP.isTagOf(Callee)
               or FunctionTags::ModelGEPRef.isTagOf(Callee)
               or FunctionTags::AddressOf.isTagOf(Callee)) {
      // Check the type of the base operand
      SerializeTypeFor(Call->getArgOperandUse(1));

    } else if (FunctionTags::StructInitializer.isTagOf(Callee)) {
      // StructInitializers are used to pack together a returned struct, so we
      // know the types of each element by looking at the Prototype
      for (llvm::Use &Op : Call->arg_operands())
        SerializeTypeFor(Op);
    }
  } else if (auto *Ret = dyn_cast<ReturnInst>(I)) {
    // Check the formal return type
    if (Ret->getNumOperands() > 0)
      SerializeTypeFor(Ret->getOperandUse(0));

  } else if (auto *SI = dyn_cast<StoreInst>(I)) {
    auto &PtrOperandPtrType = TypeMap.at(SI->getPointerOperand());
    auto &ValOperandType = TypeMap.at(SI->getValueOperand());

    QualifiedType ValOperandPtrType = ValOperandType;
    addPointerQualifier(ValOperandPtrType, Model);

    if (PtrOperandPtrType != ValOperandPtrType) {
      bool IsPtrOperandOfAggregateType = false;
      QualifiedType PtrOperandType;

      if (PtrOperandPtrType.isPointer()) {
        PtrOperandType = dropPointer(PtrOperandPtrType);
        const auto *Unqualified = PtrOperandType.UnqualifiedType.getConst();
        IsPtrOperandOfAggregateType = isa<model::StructType>(Unqualified)
                                      || isa<model::UnionType>(Unqualified);
      }

      if (isa<ConstantPointerNull>(SI->getPointerOperand())
          || IsPtrOperandOfAggregateType) {
        // Pointer operand needs to be casted to the model::QualifiedType of
        // the value operand, added pointer qualified.
        auto Type = SerializedType(serializeToLLVMString(ValOperandPtrType, *M),
                                   SI->getPointerOperandIndex());
        Result.emplace_back(std::move(Type));
      } else {
        // Value operand needs to be casted to the drop'd ptr of the
        // model::QualifiedType of the pointer type.
        revng_assert(PtrOperandPtrType.isPointer());
        auto Type = SerializedType(serializeToLLVMString(PtrOperandType, *M));
        Result.emplace_back(std::move(Type));
      }
    }
  }

  return Result;
}

void MMCP::createAndInjectModelCast(Instruction *Ins,
                                    const SerializedType &ST,
                                    OpaqueFunctionsPool<Type *> &Pool) {
  IRBuilder<> Builder(Ins);

  uint64_t OperandId = ST.OperandId;
  Constant *StringType = ST.StringType;
  Type *BaseAddressTy = Ins->getOperand(OperandId)->getType();

  auto *ModelCastType = FunctionType::get(BaseAddressTy,
                                          { getStringPtrType(Ins->getContext()),
                                            BaseAddressTy },
                                          false);
  auto *ModelCastFunction = Pool.get(BaseAddressTy, ModelCastType, "modelCast");

  Value *Call = Builder.CreateCall(ModelCastFunction,
                                   { StringType, Ins->getOperand(OperandId) });
  Ins->setOperand(OperandId, Call);
}

bool MMCP::runOnFunction(Function &F) {
  bool Changed = false;

  OpaqueFunctionsPool<Type *> ModelCastPool(F.getParent(), false);
  initModelCastPool(ModelCastPool);

  auto &ModelWrapper = getAnalysis<LoadModelWrapperPass>().get();
  const TupleTree<model::Binary> &Model = ModelWrapper.getReadOnlyModel();

  ModelFunction = llvmToModelFunction(*Model, F);
  revng_assert(ModelFunction != nullptr);

  TypeMap = initModelTypes(F, ModelFunction, *Model, false);

  for (BasicBlock &BB : F) {
    for (Instruction &I : BB) {
      auto SerializedTypes = serializeTypesForModelCast(&I, *Model);

      if (!SerializedTypes.empty()) {
        Changed = true;

        for (unsigned Idx = 0; Idx < SerializedTypes.size(); ++Idx)
          createAndInjectModelCast(&I, SerializedTypes[Idx], ModelCastPool);
      }
    }
  }

  return Changed;
}

char MakeModelCastPass::ID = 0;

using Pass = MakeModelCastPass;
static RegisterPass<MakeModelCastPass> X("make-model-cast",
                                         "A pass that pulls out casts from "
                                         "some instructions that embed casts "
                                         "into their own dedicated calls.",
                                         false,
                                         false);