revng-revng/variablemanager.cpp

/// \file
/// \brief This file handles the creation and management of global variables,
///        i.e. mainly parts of the CPU state

// Standard includes
#include <cstdint>
#include <stack>
#include <sstream>
#include <set>
#include <string>

// LLVM includes
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Casting.h"

// Local includes
#include "ir-helpers.h"
#include "variablemanager.h"
#include "revamb.h"
#include "ptcdump.h"

using namespace llvm;

template<typename T>
static void pushIfNew(std::set<T>& Seen, std::stack<T>& Queue, T Element) {
  if (Seen.find(Element) == Seen.end()) {
    Seen.insert(Element);
    Queue.push(Element);
  }
}

bool CorrectCPUStateUsagePass::runOnModule(Module& TheModule) {
  using OffsetValuePair = std::pair<int64_t, Value *>;
  std::set<OffsetValuePair> SeenArgs;
  std::stack<OffsetValuePair> WorkList;

  Value *CPUStatePtr = TheModule.getGlobalVariable("env");

  // Do we even have "env"?
  if (CPUStatePtr == nullptr)
    return false;

  assert(CPUStatePtr->getType()->isPointerTy());

  // Initialize the worklist with all the instructions loading env
  for (Use& CPUStateUse : CPUStatePtr->uses()) {
    auto *Load = cast<LoadInst>(CPUStateUse.getUser());
    assert(Load->getPointerOperand() == CPUStatePtr);

    WorkList.push(std::make_pair(Variables->EnvOffset, Load));
  }

  const DataLayout& DL = TheModule.getDataLayout();

  while (!WorkList.empty()) {
    int64_t CurrentOffset;
    Value *CurrentValue;
    std::tie(CurrentOffset, CurrentValue) = WorkList.top();
    WorkList.pop();

    std::vector<std::tuple<User *, Value *, Value *>> Replacements;

    for (Use& TheUse : CurrentValue->uses()) {
      Instruction *TheUser = cast<Instruction>(TheUse.getUser());
      switch(TheUser->getOpcode()) {
      case Instruction::Load:
      case Instruction::Store:
        {
          if (TheUser->getOpcode() == Instruction::Store) {
            // It's a store, just change the destination pointer
            assert(cast<StoreInst>(TheUser)->getPointerOperand() == CurrentValue
                   && "Pointer cannot be used as source of a store instruction");
          } else if (TheUser->getOpcode() == Instruction::Load) {
            // It's a load, just change the source pointer
            assert(cast<LoadInst>(TheUser)->getPointerOperand() == CurrentValue
                   && "Pointer cannot be used as destination of a load"
                   " instruction");
          }

          GlobalVariable *Var = Variables->getByCPUStateOffset(CurrentOffset);
          Constant *Ptr = Var;

          // Sadly, we have to allow this, mainly due to unions
          if (CurrentValue->getType() != Var->getType())
            Ptr = ConstantExpr::getPointerCast(Ptr, CurrentValue->getType());

          Replacements.push_back(std::make_tuple(TheUser, CurrentValue, Ptr));
          break;
        }
      case Instruction::BitCast:
        {
          // A bitcast, just propagate it
          WorkList.push(std::make_pair(CurrentOffset, TheUser));
          break;
        }
      case Instruction::GetElementPtr:
        {
          // A GEP requires to update the offset
          auto *GEP = cast<GetElementPtrInst>(TheUser);
          unsigned AS = GEP->getPointerAddressSpace();
          APInt APOffset(DL.getPointerSizeInBits(AS), 0, true);
          bool Result = GEP->accumulateConstantOffset(DL, APOffset);
          assert(Result && "Only constant offsets into the CPU state"
                 " structure are supported");

          int64_t NewOffset = APOffset.getSExtValue();
          WorkList.push(std::make_pair(CurrentOffset + NewOffset, TheUser));
          break;
        }
      case Instruction::Add:
        {
          unsigned OtherOperandIndex = 1 - TheUse.getOperandNo();
          Value *OtherOperand = TheUser->getOperand(OtherOperandIndex);
          assert(isa<ConstantInt>(OtherOperand));
          int64_t Addend = cast<ConstantInt>(OtherOperand)->getSExtValue();
          WorkList.push(std::make_pair(CurrentOffset + Addend, TheUser));
          break;
        }
      case Instruction::Call:
        {
          auto *Call = cast<CallInst>(TheUser);
          Function *Callee = Call->getCalledFunction();

          // Some casting with constant expressions?
          if (Callee == nullptr) {
            auto *Cast = cast<ConstantExpr>(Call->getCalledValue());
            assert(Cast->getOpcode() == Instruction::BitCast);
            Callee = cast<Function>(Cast->getOperand(0));
          }

          assert(!Callee->empty() && "external functions are not supported");

          // Find the corresponding argument
          auto ArgsI = Callee->arg_begin();
          unsigned I = 0;

          for (I = 0;
               I < Call->getNumArgOperands() && ArgsI != Callee->arg_end();
               I++, ArgsI++) {
            Use& ArgUse = Call->getArgOperandUse(I);
            if (ArgUse.getOperandNo() == TheUse.getOperandNo())
              break;
          }
          assert(I < Call->getNumArgOperands()
                 && ArgsI != Callee->arg_end());

          Value *TargetArg = static_cast<Value *>(&*ArgsI);

          if (TargetArg->use_begin() != TargetArg->use_end()) {
            assert(!Callee->isVarArg());

            // If not already considered, enqueue the argument to the worklist
            pushIfNew(SeenArgs,
                      WorkList,
                      std::make_pair(CurrentOffset, TargetArg));
          }
          break;
        }
      case Instruction::Ret:
        {
          // This function returns a pointer to the state
          Function *CurrentFunction = TheUser->getParent()->getParent();
          for (User *FunctionUse : CurrentFunction->users()) {
            auto Call = cast<CallInst>(FunctionUse);
            assert(Call->getCalledFunction() == CurrentFunction);
            pushIfNew(SeenArgs,
                      WorkList,
                      std::make_pair(CurrentOffset,
                                     static_cast<Value *>(Call)));
          }
          break;
        }
      default:
        llvm_unreachable("Unexpected instruction using the pointer");
      }
    }

    for (auto Replacement : Replacements)
      std::get<0>(Replacement)->replaceUsesOfWith(std::get<1>(Replacement),
                                                  std::get<2>(Replacement));
  }

  return true;
}

char CorrectCPUStateUsagePass::ID = 0;

static RegisterPass<CorrectCPUStateUsagePass> X("correct-cpustate-usage",
                                                "Correct CPUState Usage Pass",
                                                false,
                                                false);

static Type *getTypeAtOffset(const DataLayout *TheLayout,
                             StructType *TheStruct,
                             intptr_t Offset) {
  const StructLayout *Layout = TheLayout->getStructLayout(TheStruct);
  unsigned FieldIndex = Layout->getElementContainingOffset(Offset);
  uint64_t FieldOffset = Layout->getElementOffset(FieldIndex);

  Type *VariableType = TheStruct->getTypeAtIndex(FieldIndex);

  if (VariableType->isIntegerTy())
    return VariableType;
  else if (VariableType->isArrayTy()) {
    Type *ElementType = VariableType->getArrayElementType();
    if (ElementType->isIntegerTy())
      return ElementType;

    uint64_t ElementSize = TheLayout->getTypeSizeInBits(ElementType) / 8;
    return getTypeAtOffset(TheLayout,
                           cast<StructType>(ElementType),
                           (Offset - FieldOffset) % ElementSize);

  } else if (VariableType->isStructTy())
    return getTypeAtOffset(TheLayout,
                           cast<StructType>(VariableType),
                           Offset - FieldOffset);
  else
    llvm_unreachable("Unexpected data type");
}

VariableManager::VariableManager(Module& TheModule,
                                 Module& HelpersModule) :
  TheModule(TheModule),
  Builder(TheModule.getContext()),
  CPUStateType(nullptr),
  HelpersModuleLayout(&HelpersModule.getDataLayout()),
  EnvOffset(0),
  Env(nullptr) {

  using ElectionMap = std::map<StructType *, unsigned>;
  using ElectionMapElement = std::pair<StructType * const, unsigned>;
  ElectionMap EnvElection;
  const std::string HelperPrefix = "helper_";
  std::set<StructType *> Structs;
  for (Function& HelperFunction : HelpersModule) {
    FunctionType *HelperType = HelperFunction.getFunctionType();
    Type *ReturnType = HelperType->getReturnType();
    if (ReturnType->isPointerTy())
      Structs.insert(dyn_cast<StructType>(ReturnType->getPointerElementType()));

    for (Type *Candidate : HelperType->params())
      if (Candidate->isPointerTy())
        Structs.insert(dyn_cast<StructType>(Candidate->getPointerElementType()));

    if (startsWith(HelperFunction.getName(), HelperPrefix)
        && HelperFunction.getFunctionType()->getNumParams() > 1) {


      for (Type *Candidate : HelperType->params()) {
        Structs.insert(dyn_cast<StructType>(Candidate));
        if (Candidate->isPointerTy()) {
          auto *PointeeType = Candidate->getPointerElementType();
          auto *EnvType = dyn_cast<StructType>(PointeeType);
          // Ensure it is a struct and not a union
          if (EnvType != nullptr && EnvType->getNumElements() > 1) {

            auto It = EnvElection.find(EnvType);
            if (It != EnvElection.end())
              EnvElection[EnvType]++;
            else
              EnvElection[EnvType] = 1;
          }
        }
      }
    }
  }

  Structs.erase(nullptr);

  assert(EnvElection.size() > 0);

  CPUStateType = std::max_element(EnvElection.begin(),
                                  EnvElection.end(),
                                  [] (ElectionMapElement& It1,
                                      ElectionMapElement& It2) {
                                    return It1.second < It2.second;
                                  })->first;

  // Look for structures containing CPUStateType as a member and promove them
  // to CPUStateType. Basically this is a flexible way to keep track of the *CPU
  // struct too (e.g. MIPSCPU).
  std::set<StructType *> Visited;
  bool Changed = true;
  Visited.insert(CPUStateType);
  while (Changed) {
    Changed = false;
    for (StructType *TheStruct : Structs) {
      if (Visited.find(TheStruct) != Visited.end())
        continue;

      auto Begin = TheStruct->element_begin();
      auto End = TheStruct->element_end();
      auto Found = std::find(Begin, End, CPUStateType);
      if (Found != End) {
        unsigned Index = Found - Begin;
        const StructLayout *Layout = nullptr;
        Layout = HelpersModuleLayout->getStructLayout(TheStruct);
        EnvOffset += Layout->getElementOffset(Index);
        CPUStateType = TheStruct;
        Visited.insert(CPUStateType);
        Changed = true;
        break;
      }
    }
  }
}

void VariableManager::newFunction(Instruction *Delimiter,
                                  PTCInstructionList *Instructions) {
  LocalTemporaries.clear();
  newBasicBlock(Delimiter, Instructions);
}

/// Informs the VariableManager that a new basic block has begun, so it can
/// discard basic block-level variables.
///
/// \param Delimiter the new point where to insert allocations for local
/// variables.
/// \param Instructions the new PTCInstructionList to use from now on.
void VariableManager::newBasicBlock(Instruction *Delimiter,
                                    PTCInstructionList *Instructions) {
  Temporaries.clear();
  if (Instructions != nullptr)
    this->Instructions = Instructions;

  if (Delimiter != nullptr)
    Builder.SetInsertPoint(Delimiter);
}

void VariableManager::newBasicBlock(BasicBlock *Delimiter,
                                    PTCInstructionList *Instructions) {
  Temporaries.clear();
  if (Instructions != nullptr)
    this->Instructions = Instructions;

  if (Delimiter != nullptr)
    Builder.SetInsertPoint(Delimiter);
}

bool VariableManager::isEnv(Value *TheValue) {
  auto *Load = dyn_cast<LoadInst>(TheValue);
  if (Load != nullptr)
    return Load->getPointerOperand() == Env;

  return TheValue == Env;
}

// TODO: document that it can return nullptr
GlobalVariable* VariableManager::getByCPUStateOffset(intptr_t Offset,
                                                     std::string Name) {

  GlobalsMap::iterator it = CPUStateGlobals.find(Offset);
  if (it == CPUStateGlobals.end() ||
      (Name.size() != 0 && !it->second->getName().equals_lower(Name))) {
    Type *VariableType = getTypeAtOffset(HelpersModuleLayout,
                                         CPUStateType,
                                         Offset);

    // Unsupported type, let the caller handle the situation
    if (VariableType == nullptr)
      return nullptr;

    if (Name.size() == 0) {
      std::stringstream NameStream;
      NameStream << "state_0x" << std::hex << Offset;
      Name = NameStream.str();
    }

    auto *NewVariable = new GlobalVariable(TheModule,
                                           VariableType,
                                           false,
                                           GlobalValue::ExternalLinkage,
                                           ConstantInt::get(VariableType, 0),
                                           Name);
    assert(NewVariable != nullptr);

    if (it != CPUStateGlobals.end()) {
      it->second->replaceAllUsesWith(NewVariable);
      it->second->eraseFromParent();
    }

    CPUStateGlobals[Offset] = NewVariable;

    return NewVariable;
  } else {
    return it->second;
  }
}

Value* VariableManager::getOrCreate(unsigned int TemporaryId) {
  assert(Instructions != nullptr);

  PTCTemp *Temporary = ptc_temp_get(Instructions, TemporaryId);
  Type *VariableType = Temporary->type == PTC_TYPE_I32 ?
    Builder.getInt32Ty() : Builder.getInt64Ty();

  if (ptc_temp_is_global(Instructions, TemporaryId)) {
    // Basically we use fixed_reg to detect "env"
    if (Temporary->fixed_reg == 0) {
      return getByCPUStateOffset(EnvOffset + Temporary->mem_offset,
                                 StringRef(Temporary->name));
    } else {
      GlobalsMap::iterator it = OtherGlobals.find(TemporaryId);
      if (it != OtherGlobals.end()) {
        return it->second;
      } else {
        auto InitialValue = ConstantInt::get(VariableType, 0);
        GlobalVariable *Result = new GlobalVariable(TheModule,
                                                    VariableType,
                                                    false,
                                                    GlobalValue::CommonLinkage,
                                                    InitialValue,
                                                    StringRef(Temporary->name));

        if (Result->getName() == "env")
          Env = Result;

        OtherGlobals[TemporaryId] = Result;
        return Result;
      }
    }
  } else if (Temporary->temp_local) {
    TemporariesMap::iterator it = LocalTemporaries.find(TemporaryId);
    if (it != LocalTemporaries.end()) {
      return it->second;
    } else {
      AllocaInst *NewTemporary = Builder.CreateAlloca(VariableType);
      LocalTemporaries[TemporaryId] = NewTemporary;
      return NewTemporary;
    }
  } else {
    TemporariesMap::iterator it = Temporaries.find(TemporaryId);
    if (it != Temporaries.end()) {
      return it->second;
    } else {
      AllocaInst *NewTemporary = Builder.CreateAlloca(VariableType);
      Temporaries[TemporaryId] = NewTemporary;
      return NewTemporary;
    }
  }
}