llvm-project/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

//====- LowerToLLVM.cpp - Lowering from CIR to LLVMIR ---------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements lowering of CIR operations to LLVMIR.
//
//===----------------------------------------------------------------------===//

#include "LowerToLLVM.h"

#include "mlir/Conversion/LLVMCommon/TypeConverter.h"
#include "mlir/Dialect/DLTI/DLTI.h"
#include "mlir/Dialect/Func/IR/FuncOps.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/IR/BuiltinDialect.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Pass/PassManager.h"
#include "mlir/Target/LLVMIR/Dialect/Builtin/BuiltinToLLVMIRTranslation.h"
#include "mlir/Target/LLVMIR/Dialect/LLVMIR/LLVMToLLVMIRTranslation.h"
#include "mlir/Target/LLVMIR/Export.h"
#include "mlir/Transforms/DialectConversion.h"
#include "clang/CIR/Dialect/IR/CIRAttrVisitor.h"
#include "clang/CIR/Dialect/IR/CIRDialect.h"
#include "clang/CIR/MissingFeatures.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/TimeProfiler.h"

using namespace cir;
using namespace llvm;

namespace cir {
namespace direct {

class CIRAttrToValue : public CirAttrVisitor<CIRAttrToValue, mlir::Value> {
public:
  CIRAttrToValue(mlir::Operation *parentOp,
                 mlir::ConversionPatternRewriter &rewriter,
                 const mlir::TypeConverter *converter)
      : parentOp(parentOp), rewriter(rewriter), converter(converter) {}

  mlir::Value lowerCirAttrAsValue(mlir::Attribute attr) { return visit(attr); }

  mlir::Value visitCirIntAttr(cir::IntAttr intAttr) {
    mlir::Location loc = parentOp->getLoc();
    return rewriter.create<mlir::LLVM::ConstantOp>(
        loc, converter->convertType(intAttr.getType()), intAttr.getValue());
  }

  mlir::Value visitCirFPAttr(cir::FPAttr fltAttr) {
    mlir::Location loc = parentOp->getLoc();
    return rewriter.create<mlir::LLVM::ConstantOp>(
        loc, converter->convertType(fltAttr.getType()), fltAttr.getValue());
  }

  mlir::Value visitCirConstPtrAttr(cir::ConstPtrAttr ptrAttr) {
    mlir::Location loc = parentOp->getLoc();
    if (ptrAttr.isNullValue()) {
      return rewriter.create<mlir::LLVM::ZeroOp>(
          loc, converter->convertType(ptrAttr.getType()));
    }
    mlir::DataLayout layout(parentOp->getParentOfType<mlir::ModuleOp>());
    mlir::Value ptrVal = rewriter.create<mlir::LLVM::ConstantOp>(
        loc,
        rewriter.getIntegerType(layout.getTypeSizeInBits(ptrAttr.getType())),
        ptrAttr.getValue().getInt());
    return rewriter.create<mlir::LLVM::IntToPtrOp>(
        loc, converter->convertType(ptrAttr.getType()), ptrVal);
  }

private:
  mlir::Operation *parentOp;
  mlir::ConversionPatternRewriter &rewriter;
  const mlir::TypeConverter *converter;
};

// This class handles rewriting initializer attributes for types that do not
// require region initialization.
class GlobalInitAttrRewriter
    : public CirAttrVisitor<GlobalInitAttrRewriter, mlir::Attribute> {
public:
  GlobalInitAttrRewriter(mlir::Type type,
                         mlir::ConversionPatternRewriter &rewriter)
      : llvmType(type), rewriter(rewriter) {}

  mlir::Attribute rewriteInitAttr(mlir::Attribute attr) { return visit(attr); }

  mlir::Attribute visitCirIntAttr(cir::IntAttr attr) {
    return rewriter.getIntegerAttr(llvmType, attr.getValue());
  }
  mlir::Attribute visitCirFPAttr(cir::FPAttr attr) {
    return rewriter.getFloatAttr(llvmType, attr.getValue());
  }

private:
  mlir::Type llvmType;
  mlir::ConversionPatternRewriter &rewriter;
};

// This pass requires the CIR to be in a "flat" state. All blocks in each
// function must belong to the parent region. Once scopes and control flow
// are implemented in CIR, a pass will be run before this one to flatten
// the CIR and get it into the state that this pass requires.
struct ConvertCIRToLLVMPass
    : public mlir::PassWrapper<ConvertCIRToLLVMPass,
                               mlir::OperationPass<mlir::ModuleOp>> {
  void getDependentDialects(mlir::DialectRegistry &registry) const override {
    registry.insert<mlir::BuiltinDialect, mlir::DLTIDialect,
                    mlir::LLVM::LLVMDialect, mlir::func::FuncDialect>();
  }
  void runOnOperation() final;

  StringRef getDescription() const override {
    return "Convert the prepared CIR dialect module to LLVM dialect";
  }

  StringRef getArgument() const override { return "cir-flat-to-llvm"; }
};

bool CIRToLLVMGlobalOpLowering::attrRequiresRegionInitialization(
    mlir::Attribute attr) const {
  // There will be more cases added later.
  return isa<cir::ConstPtrAttr>(attr);
}

/// Replace CIR global with a region initialized LLVM global and update
/// insertion point to the end of the initializer block.
void CIRToLLVMGlobalOpLowering::setupRegionInitializedLLVMGlobalOp(
    cir::GlobalOp op, mlir::ConversionPatternRewriter &rewriter) const {
  assert(!cir::MissingFeatures::convertTypeForMemory());
  const mlir::Type llvmType = getTypeConverter()->convertType(op.getSymType());

  // FIXME: These default values are placeholders until the the equivalent
  //        attributes are available on cir.global ops. This duplicates code
  //        in CIRToLLVMGlobalOpLowering::matchAndRewrite() but that will go
  //        away when the placeholders are no longer needed.
  assert(!cir::MissingFeatures::opGlobalConstant());
  const bool isConst = false;
  assert(!cir::MissingFeatures::addressSpace());
  const unsigned addrSpace = 0;
  assert(!cir::MissingFeatures::opGlobalDSOLocal());
  const bool isDsoLocal = true;
  assert(!cir::MissingFeatures::opGlobalThreadLocal());
  const bool isThreadLocal = false;
  assert(!cir::MissingFeatures::opGlobalAlignment());
  const uint64_t alignment = 0;
  assert(!cir::MissingFeatures::opGlobalLinkage());
  const mlir::LLVM::Linkage linkage = mlir::LLVM::Linkage::External;
  const StringRef symbol = op.getSymName();

  SmallVector<mlir::NamedAttribute> attributes;
  auto newGlobalOp = rewriter.replaceOpWithNewOp<mlir::LLVM::GlobalOp>(
      op, llvmType, isConst, linkage, symbol, nullptr, alignment, addrSpace,
      isDsoLocal, isThreadLocal,
      /*comdat=*/mlir::SymbolRefAttr(), attributes);
  newGlobalOp.getRegion().push_back(new mlir::Block());
  rewriter.setInsertionPointToEnd(newGlobalOp.getInitializerBlock());
};

mlir::LogicalResult
CIRToLLVMGlobalOpLowering::matchAndRewriteRegionInitializedGlobal(
    cir::GlobalOp op, mlir::Attribute init,
    mlir::ConversionPatternRewriter &rewriter) const {
  // TODO: Generalize this handling when more types are needed here.
  assert(isa<cir::ConstPtrAttr>(init));

  // TODO(cir): once LLVM's dialect has proper equivalent attributes this
  // should be updated. For now, we use a custom op to initialize globals
  // to the appropriate value.
  const mlir::Location loc = op.getLoc();
  setupRegionInitializedLLVMGlobalOp(op, rewriter);
  CIRAttrToValue attrVisitor(op, rewriter, typeConverter);
  mlir::Value value = attrVisitor.lowerCirAttrAsValue(init);
  rewriter.create<mlir::LLVM::ReturnOp>(loc, value);
  return mlir::success();
}

mlir::LogicalResult CIRToLLVMGlobalOpLowering::matchAndRewrite(
    cir::GlobalOp op, OpAdaptor adaptor,
    mlir::ConversionPatternRewriter &rewriter) const {

  std::optional<mlir::Attribute> init = op.getInitialValue();

  // If we have an initializer and it requires region initialization, handle
  // that separately
  if (init.has_value() && attrRequiresRegionInitialization(init.value())) {
    return matchAndRewriteRegionInitializedGlobal(op, init.value(), rewriter);
  }

  // Fetch required values to create LLVM op.
  const mlir::Type cirSymType = op.getSymType();

  // This is the LLVM dialect type.
  assert(!cir::MissingFeatures::convertTypeForMemory());
  const mlir::Type llvmType = getTypeConverter()->convertType(cirSymType);
  // FIXME: These default values are placeholders until the the equivalent
  //        attributes are available on cir.global ops.
  assert(!cir::MissingFeatures::opGlobalConstant());
  const bool isConst = false;
  assert(!cir::MissingFeatures::addressSpace());
  const unsigned addrSpace = 0;
  assert(!cir::MissingFeatures::opGlobalDSOLocal());
  const bool isDsoLocal = true;
  assert(!cir::MissingFeatures::opGlobalThreadLocal());
  const bool isThreadLocal = false;
  assert(!cir::MissingFeatures::opGlobalAlignment());
  const uint64_t alignment = 0;
  assert(!cir::MissingFeatures::opGlobalLinkage());
  const mlir::LLVM::Linkage linkage = mlir::LLVM::Linkage::External;
  const StringRef symbol = op.getSymName();
  SmallVector<mlir::NamedAttribute> attributes;

  if (init.has_value()) {
    GlobalInitAttrRewriter initRewriter(llvmType, rewriter);
    init = initRewriter.rewriteInitAttr(init.value());
    // If initRewriter returned a null attribute, init will have a value but
    // the value will be null. If that happens, initRewriter didn't handle the
    // attribute type. It probably needs to be added to GlobalInitAttrRewriter.
    if (!init.value()) {
      op.emitError() << "unsupported initializer '" << init.value() << "'";
      return mlir::failure();
    }
  }

  // Rewrite op.
  rewriter.replaceOpWithNewOp<mlir::LLVM::GlobalOp>(
      op, llvmType, isConst, linkage, symbol, init.value_or(mlir::Attribute()),
      alignment, addrSpace, isDsoLocal, isThreadLocal,
      /*comdat=*/mlir::SymbolRefAttr(), attributes);

  return mlir::success();
}

static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
                                 mlir::DataLayout &dataLayout) {
  converter.addConversion([&](cir::PointerType type) -> mlir::Type {
    // Drop pointee type since LLVM dialect only allows opaque pointers.
    assert(!cir::MissingFeatures::addressSpace());
    unsigned targetAS = 0;

    return mlir::LLVM::LLVMPointerType::get(type.getContext(), targetAS);
  });
  converter.addConversion([&](cir::IntType type) -> mlir::Type {
    // LLVM doesn't work with signed types, so we drop the CIR signs here.
    return mlir::IntegerType::get(type.getContext(), type.getWidth());
  });
  converter.addConversion([&](cir::SingleType type) -> mlir::Type {
    return mlir::Float32Type::get(type.getContext());
  });
  converter.addConversion([&](cir::DoubleType type) -> mlir::Type {
    return mlir::Float64Type::get(type.getContext());
  });
  converter.addConversion([&](cir::FP80Type type) -> mlir::Type {
    return mlir::Float80Type::get(type.getContext());
  });
  converter.addConversion([&](cir::FP128Type type) -> mlir::Type {
    return mlir::Float128Type::get(type.getContext());
  });
  converter.addConversion([&](cir::LongDoubleType type) -> mlir::Type {
    return converter.convertType(type.getUnderlying());
  });
  converter.addConversion([&](cir::FP16Type type) -> mlir::Type {
    return mlir::Float16Type::get(type.getContext());
  });
  converter.addConversion([&](cir::BF16Type type) -> mlir::Type {
    return mlir::BFloat16Type::get(type.getContext());
  });
}

void ConvertCIRToLLVMPass::runOnOperation() {
  llvm::TimeTraceScope scope("Convert CIR to LLVM Pass");

  mlir::ModuleOp module = getOperation();
  mlir::DataLayout dl(module);
  mlir::LLVMTypeConverter converter(&getContext());
  prepareTypeConverter(converter, dl);

  mlir::RewritePatternSet patterns(&getContext());

  patterns.add<CIRToLLVMGlobalOpLowering>(converter, patterns.getContext(), dl);

  mlir::ConversionTarget target(getContext());
  target.addLegalOp<mlir::ModuleOp>();
  target.addLegalDialect<mlir::LLVM::LLVMDialect>();
  target.addIllegalDialect<mlir::BuiltinDialect, cir::CIRDialect,
                           mlir::func::FuncDialect>();

  if (failed(applyPartialConversion(module, target, std::move(patterns))))
    signalPassFailure();
}

static std::unique_ptr<mlir::Pass> createConvertCIRToLLVMPass() {
  return std::make_unique<ConvertCIRToLLVMPass>();
}

static void populateCIRToLLVMPasses(mlir::OpPassManager &pm) {
  pm.addPass(createConvertCIRToLLVMPass());
}

std::unique_ptr<llvm::Module>
lowerDirectlyFromCIRToLLVMIR(mlir::ModuleOp mlirModule, LLVMContext &llvmCtx) {
  llvm::TimeTraceScope scope("lower from CIR to LLVM directly");

  mlir::MLIRContext *mlirCtx = mlirModule.getContext();

  mlir::PassManager pm(mlirCtx);
  populateCIRToLLVMPasses(pm);

  if (mlir::failed(pm.run(mlirModule))) {
    // FIXME: Handle any errors where they occurs and return a nullptr here.
    report_fatal_error(
        "The pass manager failed to lower CIR to LLVMIR dialect!");
  }

  mlir::registerBuiltinDialectTranslation(*mlirCtx);
  mlir::registerLLVMDialectTranslation(*mlirCtx);

  llvm::TimeTraceScope translateScope("translateModuleToLLVMIR");

  StringRef moduleName = mlirModule.getName().value_or("CIRToLLVMModule");
  std::unique_ptr<llvm::Module> llvmModule =
      mlir::translateModuleToLLVMIR(mlirModule, llvmCtx, moduleName);

  if (!llvmModule) {
    // FIXME: Handle any errors where they occurs and return a nullptr here.
    report_fatal_error("Lowering from LLVMIR dialect to llvm IR failed!");
  }

  return llvmModule;
}
} // namespace direct
} // namespace cir