llvm-tutorial/source/Ast.cpp

// LLVM includes
#include "llvm/IR/Verifier.h"

// Local includes
#include "Ast.h"
#include "Parser.h"
#include "JIT.h"

using namespace jit;

namespace ast{
// attributes added from chapter 3 of the tutorial
std::unique_ptr<Module> AstObjects::TheModule =
    std::make_unique<Module>("my cool jit", getGlobalContext());
IRBuilder<> AstObjects::Builder(getGlobalContext());
std::map<std::string, Value *> AstObjects::NamedValues;

Value *ErrorV(const char *Str) {
  parser::Error(Str);
  return nullptr;
}

Value *NumberExprAST::codegen() {
  return ConstantFP::get(getGlobalContext(), APFloat(Val));
}

Value *VariableExprAST::codegen() {
  // Look this variable up in the function.
  Value *V = AstObjects::NamedValues[Name];
  if (!V)
    ErrorV("Unknown variable name");
  return V;
}

Value *BinaryExprAST::codegen() {
  Value *L = LHS->codegen();
  Value *R = RHS->codegen();
  if (!L || !R)
  return nullptr;

  switch (Op) {
    case '+':
    return AstObjects::Builder.CreateFAdd(L, R, "addtmp");
    case '-':
    return AstObjects::Builder.CreateFSub(L, R, "subtmp");
    case '*':
    return AstObjects::Builder.CreateFMul(L, R, "multmp");
    case '<':
    L = AstObjects::Builder.CreateFCmpULT(L, R, "cmptmp");
    // Convert bool 0/1 to double 0.0 or 1.0
    return AstObjects::Builder.CreateUIToFP(L,
        Type::getDoubleTy(getGlobalContext()), "booltmp");
    default:
    return ErrorV("invalid binary operator");
  }
}

Value *CallExprAST::codegen() {
  // Look up the name in the global module table.
  Function *CalleeF = getFunction(Callee);
  if (!CalleeF)
  return ErrorV("Unknown function referenced");

  // If argument mismatch error.
  if (CalleeF->arg_size() != Args.size())
  return ErrorV("Incorrect # arguments passed");

  std::vector<Value *> ArgsV;
  for (unsigned i = 0, e = Args.size(); i != e; ++i) {
    ArgsV.push_back(Args[i]->codegen());
    if (!ArgsV.back())
    return nullptr;
  }
  return AstObjects::Builder.CreateCall(CalleeF, ArgsV, "calltmp");
}

Value *IfExprAST::codegen() {
  Value *CondV = Cond->codegen();
  if (!CondV)
    return nullptr;

  // Convert condition to a bool by comparing equal to 0.0.
  CondV = AstObjects::Builder.CreateFCmpONE(
      CondV, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "ifcond");
      Function *TheFunction = AstObjects::Builder.GetInsertBlock()->getParent();

  // Create blocks for the then and else cases.  Insert the 'then' block at the
  // end of the function.
  BasicBlock *ThenBB =
      BasicBlock::Create(getGlobalContext(), "then", TheFunction);
  BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
  BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");

  AstObjects::Builder.CreateCondBr(CondV, ThenBB, ElseBB);

  // Emit then value.
  AstObjects::Builder.SetInsertPoint(ThenBB);

  Value *ThenV = Then->codegen();
  if (!ThenV)
    return nullptr;

  AstObjects::Builder.CreateBr(MergeBB);
  // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
  ThenBB = AstObjects::Builder.GetInsertBlock();

  // Emit else block.
  TheFunction->getBasicBlockList().push_back(ElseBB);
  AstObjects::Builder.SetInsertPoint(ElseBB);

  Value *ElseV = Else->codegen();
  if (!ElseV)
    return nullptr;

  AstObjects::Builder.CreateBr(MergeBB);
  // codegen of 'Else' can change the current block, update ElseBB for the PHI.
  ElseBB = AstObjects::Builder.GetInsertBlock();

  // Emit merge block.
  TheFunction->getBasicBlockList().push_back(MergeBB);
  AstObjects::Builder.SetInsertPoint(MergeBB);
  PHINode *PN =
    AstObjects::Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, "iftmp");

  PN->addIncoming(ThenV, ThenBB);
  PN->addIncoming(ElseV, ElseBB);
  return PN;
}

Value *ForExprAST::codegen() {
  // Emit the start code first, without 'variable' in scope.
  Value *StartVal = Start->codegen();
  if (StartVal == 0) return 0;
  // Make the new basic block for the loop header, inserting after current
  // block.
  Function *TheFunction = AstObjects::Builder.GetInsertBlock()->getParent();
  BasicBlock *PreheaderBB = AstObjects::Builder.GetInsertBlock();
  BasicBlock *LoopBB =
      BasicBlock::Create(getGlobalContext(), "loop", TheFunction);

  // Insert an explicit fall through from the current block to the LoopBB.
  AstObjects::Builder.CreateBr(LoopBB);
  // Start insertion in LoopBB.
  AstObjects::Builder.SetInsertPoint(LoopBB);

  // Start the PHI node with an entry for Start.
  PHINode *Variable = AstObjects::Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
                                        2, VarName.c_str());
  Variable->addIncoming(StartVal, PreheaderBB);

  // Within the loop, the variable is defined equal to the PHI node.  If it
  // shadows an existing variable, we have to restore it, so save it now.
  Value *OldVal = AstObjects::NamedValues[VarName];
  AstObjects::NamedValues[VarName] = Variable;

  // Emit the body of the loop.  This, like any other expr, can change the
  // current BB.  Note that we ignore the value computed by the body, but don't
  // allow an error.
  if (!Body->codegen())
    return nullptr;
    // Emit the step value.
  Value *StepVal = nullptr;
  if (Step) {
    StepVal = Step->codegen();
    if (!StepVal)
      return nullptr;
  } else {
    // If not specified, use 1.0.
    StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
  }

  Value *NextVar = AstObjects::Builder.CreateFAdd(Variable, StepVal, "nextvar");

  // Compute the end condition.
  Value *EndCond = End->codegen();
  if (!EndCond)
    return nullptr;

  // Convert condition to a bool by comparing equal to 0.0.
  EndCond = AstObjects::Builder.CreateFCmpONE(
      EndCond, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "loopcond");

    // Create the "after loop" block and insert it.
  BasicBlock *LoopEndBB = AstObjects::Builder.GetInsertBlock();
  BasicBlock *AfterBB =
      BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);

  // Insert the conditional branch into the end of LoopEndBB.
  AstObjects::Builder.CreateCondBr(EndCond, LoopBB, AfterBB);

  // Any new code will be inserted in AfterBB.
  AstObjects::Builder.SetInsertPoint(AfterBB);

  // Add a new entry to the PHI node for the backedge.
  Variable->addIncoming(NextVar, LoopEndBB);

  // Restore the unshadowed variable.
  if (OldVal)
    AstObjects::NamedValues[VarName] = OldVal;
  else
    AstObjects::NamedValues.erase(VarName);

  // for expr always returns 0.0.
  return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
}


Function *PrototypeAST::codegen() {
  // Make the function type:  double(double,double) etc.
  std::vector<Type *> Doubles(Args.size(),
      Type::getDoubleTy(getGlobalContext()));
  FunctionType *FT = FunctionType::get(Type::getDoubleTy(
      getGlobalContext()), Doubles, false);

  Function *F = Function::Create(FT, Function::ExternalLinkage, Name,
      AstObjects::TheModule.get());

  // Set names for all arguments.
  unsigned Idx = 0;
  for (auto &Arg : F->args())
    Arg.setName(Args[Idx++]);

  return F;
}

Function *FunctionAST::codegen() {
  // Transfer ownership of the prototype to the FunctionProtos map, but keep a
  // reference to it for use below.
  auto &P = *Proto;
  JITObjects::FunctionProtos[Proto->getName()] = std::move(Proto);
  Function *TheFunction = getFunction(P.getName());
  if (!TheFunction)
    return nullptr;

  // Create a new basic block to start insertion into.
  BasicBlock *BB = BasicBlock::Create(getGlobalContext(),
      "entry", TheFunction);
  AstObjects::Builder.SetInsertPoint(BB);

  // Record the function arguments in the NamedValues map.
  AstObjects::NamedValues.clear();
  for (auto &Arg : TheFunction->args()) {
    AstObjects::NamedValues[Arg.getName()] = &Arg;
  }

  if (Value *RetVal = Body->codegen()) {
    // Finish off the function.
    AstObjects::Builder.CreateRet(RetVal);

    // Validate the generated code, checking for consistency.
    verifyFunction(*TheFunction);

    // Optimize the function.
    JITObjects::TheFPM->run(*TheFunction);

    return TheFunction;
  }

  // Error reading body, remove function.
  TheFunction->eraseFromParent();
  return nullptr;
}

}