//===-- CodeGen.cpp -- bridge to lower to LLVM ----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
//
//===----------------------------------------------------------------------===//

#include "flang/Optimizer/CodeGen/CodeGen.h"
#include "PassDetail.h"
#include "flang/Optimizer/Dialect/FIROps.h"
#include "flang/Optimizer/Dialect/FIRType.h"
#include "mlir/Conversion/ArithmeticToLLVM/ArithmeticToLLVM.h"
#include "mlir/Conversion/LLVMCommon/Pattern.h"
#include "mlir/Conversion/LLVMCommon/TypeConverter.h"
#include "mlir/Conversion/StandardToLLVM/ConvertStandardToLLVM.h"
#include "mlir/IR/BuiltinTypes.h"
#include "mlir/IR/Matchers.h"
#include "mlir/Pass/Pass.h"
#include "llvm/ADT/ArrayRef.h"

#define DEBUG_TYPE "flang-codegen"

// fir::LLVMTypeConverter for converting to LLVM IR dialect types.
#include "TypeConverter.h"

namespace {
/// FIR conversion pattern template
template <typename FromOp>
class FIROpConversion : public mlir::ConvertOpToLLVMPattern<FromOp> {
public:
  explicit FIROpConversion(fir::LLVMTypeConverter &lowering)
      : mlir::ConvertOpToLLVMPattern<FromOp>(lowering) {}

protected:
  mlir::Type convertType(mlir::Type ty) const {
    return lowerTy().convertType(ty);
  }

  fir::LLVMTypeConverter &lowerTy() const {
    return *static_cast<fir::LLVMTypeConverter *>(this->getTypeConverter());
  }
};

/// FIR conversion pattern template
template <typename FromOp>
class FIROpAndTypeConversion : public FIROpConversion<FromOp> {
public:
  using FIROpConversion<FromOp>::FIROpConversion;
  using OpAdaptor = typename FromOp::Adaptor;

  mlir::LogicalResult
  matchAndRewrite(FromOp op, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const final {
    mlir::Type ty = this->convertType(op.getType());
    return doRewrite(op, ty, adaptor, rewriter);
  }

  virtual mlir::LogicalResult
  doRewrite(FromOp addr, mlir::Type ty, OpAdaptor adaptor,
            mlir::ConversionPatternRewriter &rewriter) const = 0;
};

// Lower `fir.address_of` operation to `llvm.address_of` operation.
struct AddrOfOpConversion : public FIROpConversion<fir::AddrOfOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::AddrOfOp addr, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    auto ty = convertType(addr.getType());
    rewriter.replaceOpWithNewOp<mlir::LLVM::AddressOfOp>(
        addr, ty, addr.symbol().getRootReference().getValue());
    return success();
  }
};

/// Lower `fir.has_value` operation to `llvm.return` operation.
struct HasValueOpConversion : public FIROpConversion<fir::HasValueOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::HasValueOp op, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    rewriter.replaceOpWithNewOp<LLVM::ReturnOp>(op, adaptor.getOperands());
    return success();
  }
};

/// Lower `fir.global` operation to `llvm.global` operation.
/// `fir.insert_on_range` operations are replaced with constant dense attribute
/// if they are applied on the full range.
struct GlobalOpConversion : public FIROpConversion<fir::GlobalOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::GlobalOp global, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    auto tyAttr = convertType(global.getType());
    if (global.getType().isa<fir::BoxType>())
      tyAttr = tyAttr.cast<mlir::LLVM::LLVMPointerType>().getElementType();
    auto loc = global.getLoc();
    mlir::Attribute initAttr{};
    if (global.initVal())
      initAttr = global.initVal().getValue();
    auto linkage = convertLinkage(global.linkName());
    auto isConst = global.constant().hasValue();
    auto g = rewriter.create<mlir::LLVM::GlobalOp>(
        loc, tyAttr, isConst, linkage, global.sym_name(), initAttr);
    auto &gr = g.getInitializerRegion();
    rewriter.inlineRegionBefore(global.region(), gr, gr.end());
    if (!gr.empty()) {
      // Replace insert_on_range with a constant dense attribute if the
      // initialization is on the full range.
      auto insertOnRangeOps = gr.front().getOps<fir::InsertOnRangeOp>();
      for (auto insertOp : insertOnRangeOps) {
        if (isFullRange(insertOp.coor(), insertOp.getType())) {
          auto seqTyAttr = convertType(insertOp.getType());
          auto *op = insertOp.val().getDefiningOp();
          auto constant = mlir::dyn_cast<mlir::arith::ConstantOp>(op);
          if (!constant) {
            auto convertOp = mlir::dyn_cast<fir::ConvertOp>(op);
            if (!convertOp)
              continue;
            constant = cast<mlir::arith::ConstantOp>(
                convertOp.value().getDefiningOp());
          }
          mlir::Type vecType = mlir::VectorType::get(
              insertOp.getType().getShape(), constant.getType());
          auto denseAttr = mlir::DenseElementsAttr::get(
              vecType.cast<ShapedType>(), constant.value());
          rewriter.setInsertionPointAfter(insertOp);
          rewriter.replaceOpWithNewOp<mlir::arith::ConstantOp>(
              insertOp, seqTyAttr, denseAttr);
        }
      }
    }
    rewriter.eraseOp(global);
    return success();
  }

  bool isFullRange(mlir::ArrayAttr indexes, fir::SequenceType seqTy) const {
    auto extents = seqTy.getShape();
    if (indexes.size() / 2 != extents.size())
      return false;
    for (unsigned i = 0; i < indexes.size(); i += 2) {
      if (indexes[i].cast<IntegerAttr>().getInt() != 0)
        return false;
      if (indexes[i + 1].cast<IntegerAttr>().getInt() != extents[i / 2] - 1)
        return false;
    }
    return true;
  }

  // TODO: String comparaison should be avoided. Replace linkName with an
  // enumeration.
  mlir::LLVM::Linkage convertLinkage(Optional<StringRef> optLinkage) const {
    if (optLinkage.hasValue()) {
      auto name = optLinkage.getValue();
      if (name == "internal")
        return mlir::LLVM::Linkage::Internal;
      if (name == "linkonce")
        return mlir::LLVM::Linkage::Linkonce;
      if (name == "common")
        return mlir::LLVM::Linkage::Common;
      if (name == "weak")
        return mlir::LLVM::Linkage::Weak;
    }
    return mlir::LLVM::Linkage::External;
  }
};

template <typename OP>
void selectMatchAndRewrite(fir::LLVMTypeConverter &lowering, OP select,
                           typename OP::Adaptor adaptor,
                           mlir::ConversionPatternRewriter &rewriter) {
  unsigned conds = select.getNumConditions();
  auto cases = select.getCases().getValue();
  mlir::Value selector = adaptor.selector();
  auto loc = select.getLoc();
  assert(conds > 0 && "select must have cases");

  llvm::SmallVector<mlir::Block *> destinations;
  llvm::SmallVector<mlir::ValueRange> destinationsOperands;
  mlir::Block *defaultDestination;
  mlir::ValueRange defaultOperands;
  llvm::SmallVector<int32_t> caseValues;

  for (unsigned t = 0; t != conds; ++t) {
    mlir::Block *dest = select.getSuccessor(t);
    auto destOps = select.getSuccessorOperands(adaptor.getOperands(), t);
    const mlir::Attribute &attr = cases[t];
    if (auto intAttr = attr.template dyn_cast<mlir::IntegerAttr>()) {
      destinations.push_back(dest);
      destinationsOperands.push_back(destOps.hasValue() ? *destOps
                                                        : ValueRange());
      caseValues.push_back(intAttr.getInt());
      continue;
    }
    assert(attr.template dyn_cast_or_null<mlir::UnitAttr>());
    assert((t + 1 == conds) && "unit must be last");
    defaultDestination = dest;
    defaultOperands = destOps.hasValue() ? *destOps : ValueRange();
  }

  // LLVM::SwitchOp takes a i32 type for the selector.
  if (select.getSelector().getType() != rewriter.getI32Type())
    selector =
        rewriter.create<LLVM::TruncOp>(loc, rewriter.getI32Type(), selector);

  rewriter.replaceOpWithNewOp<mlir::LLVM::SwitchOp>(
      select, selector,
      /*defaultDestination=*/defaultDestination,
      /*defaultOperands=*/defaultOperands,
      /*caseValues=*/caseValues,
      /*caseDestinations=*/destinations,
      /*caseOperands=*/destinationsOperands,
      /*branchWeights=*/ArrayRef<int32_t>());
}

/// conversion of fir::SelectOp to an if-then-else ladder
struct SelectOpConversion : public FIROpConversion<fir::SelectOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::SelectOp op, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    selectMatchAndRewrite<fir::SelectOp>(lowerTy(), op, adaptor, rewriter);
    return success();
  }
};

/// conversion of fir::SelectRankOp to an if-then-else ladder
struct SelectRankOpConversion : public FIROpConversion<fir::SelectRankOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::SelectRankOp op, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    selectMatchAndRewrite<fir::SelectRankOp>(lowerTy(), op, adaptor, rewriter);
    return success();
  }
};

// convert to LLVM IR dialect `undef`
struct UndefOpConversion : public FIROpConversion<fir::UndefOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::UndefOp undef, OpAdaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    rewriter.replaceOpWithNewOp<mlir::LLVM::UndefOp>(
        undef, convertType(undef.getType()));
    return success();
  }
};

// convert to LLVM IR dialect `unreachable`
struct UnreachableOpConversion : public FIROpConversion<fir::UnreachableOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::UnreachableOp unreach, OpAdaptor adaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    rewriter.replaceOpWithNewOp<mlir::LLVM::UnreachableOp>(unreach);
    return success();
  }
};

struct ZeroOpConversion : public FIROpConversion<fir::ZeroOp> {
  using FIROpConversion::FIROpConversion;

  mlir::LogicalResult
  matchAndRewrite(fir::ZeroOp zero, OpAdaptor,
                  mlir::ConversionPatternRewriter &rewriter) const override {
    auto ty = convertType(zero.getType());
    if (ty.isa<mlir::LLVM::LLVMPointerType>()) {
      rewriter.replaceOpWithNewOp<mlir::LLVM::NullOp>(zero, ty);
    } else if (ty.isa<mlir::IntegerType>()) {
      rewriter.replaceOpWithNewOp<mlir::LLVM::ConstantOp>(
          zero, ty, mlir::IntegerAttr::get(zero.getType(), 0));
    } else if (mlir::LLVM::isCompatibleFloatingPointType(ty)) {
      rewriter.replaceOpWithNewOp<mlir::LLVM::ConstantOp>(
          zero, ty, mlir::FloatAttr::get(zero.getType(), 0.0));
    } else {
      // TODO: create ConstantAggregateZero for FIR aggregate/array types.
      return rewriter.notifyMatchFailure(
          zero,
          "conversion of fir.zero with aggregate type not implemented yet");
    }
    return success();
  }
};

// Code shared between insert_value and extract_value Ops.
struct ValueOpCommon {
  // Translate the arguments pertaining to any multidimensional array to
  // row-major order for LLVM-IR.
  static void toRowMajor(SmallVectorImpl<mlir::Attribute> &attrs,
                         mlir::Type ty) {
    assert(ty && "type is null");
    const auto end = attrs.size();
    for (std::remove_const_t<decltype(end)> i = 0; i < end; ++i) {
      if (auto seq = ty.dyn_cast<mlir::LLVM::LLVMArrayType>()) {
        const auto dim = getDimension(seq);
        if (dim > 1) {
          auto ub = std::min(i + dim, end);
          std::reverse(attrs.begin() + i, attrs.begin() + ub);
          i += dim - 1;
        }
        ty = getArrayElementType(seq);
      } else if (auto st = ty.dyn_cast<mlir::LLVM::LLVMStructType>()) {
        ty = st.getBody()[attrs[i].cast<mlir::IntegerAttr>().getInt()];
      } else {
        llvm_unreachable("index into invalid type");
      }
    }
  }

  static llvm::SmallVector<mlir::Attribute>
  collectIndices(mlir::ConversionPatternRewriter &rewriter,
                 mlir::ArrayAttr arrAttr) {
    llvm::SmallVector<mlir::Attribute> attrs;
    for (auto i = arrAttr.begin(), e = arrAttr.end(); i != e; ++i) {
      if (i->isa<mlir::IntegerAttr>()) {
        attrs.push_back(*i);
      } else {
        auto fieldName = i->cast<mlir::StringAttr>().getValue();
        ++i;
        auto ty = i->cast<mlir::TypeAttr>().getValue();
        auto index = ty.cast<fir::RecordType>().getFieldIndex(fieldName);
        attrs.push_back(mlir::IntegerAttr::get(rewriter.getI32Type(), index));
      }
    }
    return attrs;
  }

private:
  static unsigned getDimension(mlir::LLVM::LLVMArrayType ty) {
    unsigned result = 1;
    for (auto eleTy = ty.getElementType().dyn_cast<mlir::LLVM::LLVMArrayType>();
         eleTy;
         eleTy = eleTy.getElementType().dyn_cast<mlir::LLVM::LLVMArrayType>())
      ++result;
    return result;
  }

  static mlir::Type getArrayElementType(mlir::LLVM::LLVMArrayType ty) {
    auto eleTy = ty.getElementType();
    while (auto arrTy = eleTy.dyn_cast<mlir::LLVM::LLVMArrayType>())
      eleTy = arrTy.getElementType();
    return eleTy;
  }
};

/// Extract a subobject value from an ssa-value of aggregate type
struct ExtractValueOpConversion
    : public FIROpAndTypeConversion<fir::ExtractValueOp>,
      public ValueOpCommon {
  using FIROpAndTypeConversion::FIROpAndTypeConversion;

  mlir::LogicalResult
  doRewrite(fir::ExtractValueOp extractVal, mlir::Type ty, OpAdaptor adaptor,
            mlir::ConversionPatternRewriter &rewriter) const override {
    auto attrs = collectIndices(rewriter, extractVal.coor());
    toRowMajor(attrs, adaptor.getOperands()[0].getType());
    auto position = mlir::ArrayAttr::get(extractVal.getContext(), attrs);
    rewriter.replaceOpWithNewOp<mlir::LLVM::ExtractValueOp>(
        extractVal, ty, adaptor.getOperands()[0], position);
    return success();
  }
};

/// InsertValue is the generalized instruction for the composition of new
/// aggregate type values.
struct InsertValueOpConversion
    : public FIROpAndTypeConversion<fir::InsertValueOp>,
      public ValueOpCommon {
  using FIROpAndTypeConversion::FIROpAndTypeConversion;

  mlir::LogicalResult
  doRewrite(fir::InsertValueOp insertVal, mlir::Type ty, OpAdaptor adaptor,
            mlir::ConversionPatternRewriter &rewriter) const override {
    auto attrs = collectIndices(rewriter, insertVal.coor());
    toRowMajor(attrs, adaptor.getOperands()[0].getType());
    auto position = mlir::ArrayAttr::get(insertVal.getContext(), attrs);
    rewriter.replaceOpWithNewOp<mlir::LLVM::InsertValueOp>(
        insertVal, ty, adaptor.getOperands()[0], adaptor.getOperands()[1],
        position);
    return success();
  }
};

/// InsertOnRange inserts a value into a sequence over a range of offsets.
struct InsertOnRangeOpConversion
    : public FIROpAndTypeConversion<fir::InsertOnRangeOp> {
  using FIROpAndTypeConversion::FIROpAndTypeConversion;

  // Increments an array of subscripts in a row major fasion.
  void incrementSubscripts(const SmallVector<uint64_t> &dims,
                           SmallVector<uint64_t> &subscripts) const {
    for (size_t i = dims.size(); i > 0; --i) {
      if (++subscripts[i - 1] < dims[i - 1]) {
        return;
      }
      subscripts[i - 1] = 0;
    }
  }

  mlir::LogicalResult
  doRewrite(fir::InsertOnRangeOp range, mlir::Type ty, OpAdaptor adaptor,
            mlir::ConversionPatternRewriter &rewriter) const override {

    llvm::SmallVector<uint64_t> dims;
    auto type = adaptor.getOperands()[0].getType();

    // Iteratively extract the array dimensions from the type.
    while (auto t = type.dyn_cast<mlir::LLVM::LLVMArrayType>()) {
      dims.push_back(t.getNumElements());
      type = t.getElementType();
    }

    SmallVector<uint64_t> lBounds;
    SmallVector<uint64_t> uBounds;

    // Extract integer value from the attribute
    SmallVector<int64_t> coordinates = llvm::to_vector<4>(
        llvm::map_range(range.coor(), [](Attribute a) -> int64_t {
          return a.cast<IntegerAttr>().getInt();
        }));

    // Unzip the upper and lower bound and convert to a row major format.
    for (auto i = coordinates.rbegin(), e = coordinates.rend(); i != e; ++i) {
      uBounds.push_back(*i++);
      lBounds.push_back(*i);
    }

    auto &subscripts = lBounds;
    auto loc = range.getLoc();
    mlir::Value lastOp = adaptor.getOperands()[0];
    mlir::Value insertVal = adaptor.getOperands()[1];

    auto i64Ty = rewriter.getI64Type();
    while (subscripts != uBounds) {
      // Convert uint64_t's to Attribute's.
      SmallVector<mlir::Attribute> subscriptAttrs;
      for (const auto &subscript : subscripts)
        subscriptAttrs.push_back(IntegerAttr::get(i64Ty, subscript));
      lastOp = rewriter.create<mlir::LLVM::InsertValueOp>(
          loc, ty, lastOp, insertVal,
          ArrayAttr::get(range.getContext(), subscriptAttrs));

      incrementSubscripts(dims, subscripts);
    }

    // Convert uint64_t's to Attribute's.
    SmallVector<mlir::Attribute> subscriptAttrs;
    for (const auto &subscript : subscripts)
      subscriptAttrs.push_back(
          IntegerAttr::get(rewriter.getI64Type(), subscript));
    mlir::ArrayRef<mlir::Attribute> arrayRef(subscriptAttrs);

    rewriter.replaceOpWithNewOp<mlir::LLVM::InsertValueOp>(
        range, ty, lastOp, insertVal,
        ArrayAttr::get(range.getContext(), arrayRef));

    return success();
  }
};
} // namespace

namespace {
/// Convert FIR dialect to LLVM dialect
///
/// This pass lowers all FIR dialect operations to LLVM IR dialect. An
/// MLIR pass is used to lower residual Std dialect to LLVM IR dialect.
///
/// This pass is not complete yet. We are upstreaming it in small patches.
class FIRToLLVMLowering : public fir::FIRToLLVMLoweringBase<FIRToLLVMLowering> {
public:
  mlir::ModuleOp getModule() { return getOperation(); }

  void runOnOperation() override final {
    auto *context = getModule().getContext();
    fir::LLVMTypeConverter typeConverter{getModule()};
    mlir::OwningRewritePatternList pattern(context);
    pattern.insert<
        AddrOfOpConversion, ExtractValueOpConversion, HasValueOpConversion,
        GlobalOpConversion, InsertOnRangeOpConversion, InsertValueOpConversion,
        SelectOpConversion, SelectRankOpConversion, UndefOpConversion,
        UnreachableOpConversion, ZeroOpConversion>(typeConverter);
    mlir::populateStdToLLVMConversionPatterns(typeConverter, pattern);
    mlir::arith::populateArithmeticToLLVMConversionPatterns(typeConverter,
                                                            pattern);
    mlir::ConversionTarget target{*context};
    target.addLegalDialect<mlir::LLVM::LLVMDialect>();

    // required NOPs for applying a full conversion
    target.addLegalOp<mlir::ModuleOp>();

    // apply the patterns
    if (mlir::failed(mlir::applyFullConversion(getModule(), target,
                                               std::move(pattern)))) {
      signalPassFailure();
    }
  }
};
} // namespace

std::unique_ptr<mlir::Pass> fir::createFIRToLLVMPass() {
  return std::make_unique<FIRToLLVMLowering>();
}