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[CIR] Initial implementation of CIR-to-LLVM IR lowering pass (#125260)
This change introduces lowering from CIR to LLVM IR of global integer and floating-point variables, using defaults for attributes that aren't yet implemented.
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‎clang/include/clang/CIR/LowerToLLVM.h‎

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#ifndef CLANG_CIR_LOWERTOLLVM_H
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#define CLANG_CIR_LOWERTOLLVM_H
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#include "mlir/Pass/Pass.h"
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#include <memory>
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namespace llvm {

‎clang/include/clang/CIR/MissingFeatures.h‎

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//===---- MissingFeatures.h - Checks for unimplemented features -*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file introduces some helper classes to guard against features that
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// CIR dialect supports that we do not have and also do not have great ways to
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// assert against.
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//
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//===----------------------------------------------------------------------===//
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#ifndef CLANG_CIR_MISSINGFEATURES_H
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#define CLANG_CIR_MISSINGFEATURES_H
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namespace cir {
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// As a way to track features that haven't yet been implemented this class
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// explicitly contains a list of static fns that will return false that you
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// can guard against. If and when a feature becomes implemented simply changing
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// this return to true will cause compilation to fail at all the points in which
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// we noted that we needed to address. This is a much more explicit way to
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// handle "TODO"s.
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struct MissingFeatures {
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// Address space related
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static bool addressSpace() { return false; }
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// Unhandled global/linkage information.
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static bool opGlobalDSOLocal() { return false; }
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static bool opGlobalThreadLocal() { return false; }
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static bool opGlobalConstant() { return false; }
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static bool opGlobalAlignment() { return false; }
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static bool opGlobalLinkage() { return false; }
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};
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} // namespace cir
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#endif // CLANG_CIR_MISSINGFEATURES_H

‎clang/lib/CIR/Lowering/DirectToLLVM/CMakeLists.txt‎

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@@ -3,9 +3,15 @@ set(LLVM_LINK_COMPONENTS
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Support
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)
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get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
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add_clang_library(clangCIRLoweringDirectToLLVM
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LowerToLLVM.cpp
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LINK_LIBS
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MLIRIR
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${dialect_libs}
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MLIRCIR
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MLIRBuiltinToLLVMIRTranslation
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MLIRLLVMToLLVMIRTranslation
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)

‎clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp‎

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//
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//===----------------------------------------------------------------------===//
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#include "clang/CIR/LowerToLLVM.h"
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#include "LowerToLLVM.h"
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#include "mlir/Conversion/LLVMCommon/TypeConverter.h"
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#include "mlir/Dialect/DLTI/DLTI.h"
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#include "mlir/Dialect/Func/IR/FuncOps.h"
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#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
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#include "mlir/IR/BuiltinDialect.h"
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#include "mlir/IR/BuiltinOps.h"
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#include "mlir/Pass/Pass.h"
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#include "mlir/Pass/PassManager.h"
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#include "mlir/Target/LLVMIR/Dialect/Builtin/BuiltinToLLVMIRTranslation.h"
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#include "mlir/Target/LLVMIR/Dialect/LLVMIR/LLVMToLLVMIRTranslation.h"
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#include "mlir/Target/LLVMIR/Export.h"
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#include "mlir/Transforms/DialectConversion.h"
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#include "clang/CIR/Dialect/IR/CIRDialect.h"
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#include "clang/CIR/MissingFeatures.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/TimeProfiler.h"
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@@ -22,16 +35,165 @@ using namespace llvm;
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namespace cir {
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namespace direct {
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// This pass requires the CIR to be in a "flat" state. All blocks in each
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// function must belong to the parent region. Once scopes and control flow
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// are implemented in CIR, a pass will be run before this one to flatten
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// the CIR and get it into the state that this pass requires.
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struct ConvertCIRToLLVMPass
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: public mlir::PassWrapper<ConvertCIRToLLVMPass,
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mlir::OperationPass<mlir::ModuleOp>> {
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void getDependentDialects(mlir::DialectRegistry &registry) const override {
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registry.insert<mlir::BuiltinDialect, mlir::DLTIDialect,
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mlir::LLVM::LLVMDialect, mlir::func::FuncDialect>();
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}
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void runOnOperation() final;
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StringRef getDescription() const override {
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return "Convert the prepared CIR dialect module to LLVM dialect";
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}
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StringRef getArgument() const override { return "cir-flat-to-llvm"; }
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};
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mlir::LogicalResult CIRToLLVMGlobalOpLowering::matchAndRewrite(
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cir::GlobalOp op, OpAdaptor adaptor,
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mlir::ConversionPatternRewriter &rewriter) const {
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// Fetch required values to create LLVM op.
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const mlir::Type cirSymType = op.getSymType();
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// This is the LLVM dialect type.
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const mlir::Type llvmType = getTypeConverter()->convertType(cirSymType);
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// FIXME: These default values are placeholders until the the equivalent
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// attributes are available on cir.global ops.
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assert(!cir::MissingFeatures::opGlobalConstant());
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const bool isConst = false;
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assert(!cir::MissingFeatures::addressSpace());
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const unsigned addrSpace = 0;
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assert(!cir::MissingFeatures::opGlobalDSOLocal());
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const bool isDsoLocal = true;
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assert(!cir::MissingFeatures::opGlobalThreadLocal());
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const bool isThreadLocal = false;
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assert(!cir::MissingFeatures::opGlobalAlignment());
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const uint64_t alignment = 0;
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assert(!cir::MissingFeatures::opGlobalLinkage());
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const mlir::LLVM::Linkage linkage = mlir::LLVM::Linkage::External;
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const StringRef symbol = op.getSymName();
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std::optional<mlir::Attribute> init = op.getInitialValue();
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SmallVector<mlir::NamedAttribute> attributes;
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if (init.has_value()) {
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if (const auto fltAttr = mlir::dyn_cast<cir::FPAttr>(init.value())) {
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// Initializer is a constant floating-point number: convert to MLIR
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// builtin constant.
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init = rewriter.getFloatAttr(llvmType, fltAttr.getValue());
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} else if (const auto intAttr =
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mlir::dyn_cast<cir::IntAttr>(init.value())) {
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// Initializer is a constant array: convert it to a compatible llvm init.
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init = rewriter.getIntegerAttr(llvmType, intAttr.getValue());
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} else {
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op.emitError() << "unsupported initializer '" << init.value() << "'";
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return mlir::failure();
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}
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}
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// Rewrite op.
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rewriter.replaceOpWithNewOp<mlir::LLVM::GlobalOp>(
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op, llvmType, isConst, linkage, symbol, init.value_or(mlir::Attribute()),
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alignment, addrSpace, isDsoLocal, isThreadLocal,
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/*comdat=*/mlir::SymbolRefAttr(), attributes);
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return mlir::success();
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}
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static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
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mlir::DataLayout &dataLayout) {
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converter.addConversion([&](cir::IntType type) -> mlir::Type {
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// LLVM doesn't work with signed types, so we drop the CIR signs here.
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return mlir::IntegerType::get(type.getContext(), type.getWidth());
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});
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converter.addConversion([&](cir::SingleType type) -> mlir::Type {
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return mlir::Float32Type::get(type.getContext());
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});
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converter.addConversion([&](cir::DoubleType type) -> mlir::Type {
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return mlir::Float64Type::get(type.getContext());
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});
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converter.addConversion([&](cir::FP80Type type) -> mlir::Type {
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return mlir::Float80Type::get(type.getContext());
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});
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converter.addConversion([&](cir::FP128Type type) -> mlir::Type {
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return mlir::Float128Type::get(type.getContext());
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});
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converter.addConversion([&](cir::LongDoubleType type) -> mlir::Type {
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return converter.convertType(type.getUnderlying());
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});
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converter.addConversion([&](cir::FP16Type type) -> mlir::Type {
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return mlir::Float16Type::get(type.getContext());
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});
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converter.addConversion([&](cir::BF16Type type) -> mlir::Type {
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return mlir::BFloat16Type::get(type.getContext());
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});
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}
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void ConvertCIRToLLVMPass::runOnOperation() {
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llvm::TimeTraceScope scope("Convert CIR to LLVM Pass");
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mlir::ModuleOp module = getOperation();
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mlir::DataLayout dl(module);
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mlir::LLVMTypeConverter converter(&getContext());
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prepareTypeConverter(converter, dl);
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mlir::RewritePatternSet patterns(&getContext());
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patterns.add<CIRToLLVMGlobalOpLowering>(converter, patterns.getContext(), dl);
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mlir::ConversionTarget target(getContext());
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target.addLegalOp<mlir::ModuleOp>();
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target.addLegalDialect<mlir::LLVM::LLVMDialect>();
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target.addIllegalDialect<mlir::BuiltinDialect, cir::CIRDialect,
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mlir::func::FuncDialect>();
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if (failed(applyPartialConversion(module, target, std::move(patterns))))
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signalPassFailure();
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}
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static std::unique_ptr<mlir::Pass> createConvertCIRToLLVMPass() {
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return std::make_unique<ConvertCIRToLLVMPass>();
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}
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static void populateCIRToLLVMPasses(mlir::OpPassManager &pm) {
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pm.addPass(createConvertCIRToLLVMPass());
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}
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std::unique_ptr<llvm::Module>
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lowerDirectlyFromCIRToLLVMIR(mlir::ModuleOp mlirModule, LLVMContext &llvmCtx) {
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llvm::TimeTraceScope scope("lower from CIR to LLVM directly");
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std::optional<StringRef> moduleName = mlirModule.getName();
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auto llvmModule = std::make_unique<llvm::Module>(
31-
moduleName ? *moduleName : "CIRToLLVMModule", llvmCtx);
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mlir::MLIRContext *mlirCtx = mlirModule.getContext();
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mlir::PassManager pm(mlirCtx);
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populateCIRToLLVMPasses(pm);
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if (mlir::failed(pm.run(mlirModule))) {
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// FIXME: Handle any errors where they occurs and return a nullptr here.
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report_fatal_error(
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"The pass manager failed to lower CIR to LLVMIR dialect!");
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}
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mlir::registerBuiltinDialectTranslation(*mlirCtx);
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mlir::registerLLVMDialectTranslation(*mlirCtx);
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llvm::TimeTraceScope translateScope("translateModuleToLLVMIR");
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StringRef moduleName = mlirModule.getName().value_or("CIRToLLVMModule");
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std::unique_ptr<llvm::Module> llvmModule =
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mlir::translateModuleToLLVMIR(mlirModule, llvmCtx, moduleName);
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if (!llvmModule)
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if (!llvmModule) {
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// FIXME: Handle any errors where they occurs and return a nullptr here.
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report_fatal_error("Lowering from LLVMIR dialect to llvm IR failed!");
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}
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return llvmModule;
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}

‎clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h‎

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//====- LowerToLLVM.h- Lowering from CIR to LLVM --------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file declares an interface for converting CIR modules to LLVM IR.
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//
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//===----------------------------------------------------------------------===//
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#ifndef CLANG_CIR_LOWERTOLLVM_H
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#define CLANG_CIR_LOWERTOLLVM_H
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#include "mlir/Transforms/DialectConversion.h"
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#include "clang/CIR/Dialect/IR/CIRDialect.h"
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namespace cir {
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namespace direct {
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class CIRToLLVMGlobalOpLowering
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: public mlir::OpConversionPattern<cir::GlobalOp> {
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const mlir::DataLayout &dataLayout;
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public:
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CIRToLLVMGlobalOpLowering(const mlir::TypeConverter &typeConverter,
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mlir::MLIRContext *context,
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const mlir::DataLayout &dataLayout)
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: OpConversionPattern(typeConverter, context), dataLayout(dataLayout) {
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setHasBoundedRewriteRecursion();
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}
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mlir::LogicalResult
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matchAndRewrite(cir::GlobalOp op, OpAdaptor adaptor,
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mlir::ConversionPatternRewriter &rewriter) const override;
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};
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} // namespace direct
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} // namespace cir
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#endif // CLANG_CIR_LOWERTOLLVM_H

‎clang/test/CIR/Lowering/global-var-simple.cpp‎

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// Global variables of intergal types
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// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s
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// Note: Currently unsupported features include default zero-initialization
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// and alignment. The fact that "external" is only printed for globals
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// without an initializer is a quirk of the LLVM AsmWriter.
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char c;
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// CHECK: @c = external dso_local global i8
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signed char sc;
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// CHECK: @sc = external dso_local global i8
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unsigned char uc;
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// CHECK: @uc = external dso_local global i8
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short ss;
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// CHECK: @ss = external dso_local global i16
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unsigned short us = 100;
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// CHECK: @us = dso_local global i16 100
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int si = 42;
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// CHECK: @si = dso_local global i32 42
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unsigned ui;
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// CHECK: @ui = external dso_local global i32
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long sl;
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// CHECK: @sl = external dso_local global i64
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unsigned long ul;
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// CHECK: @ul = external dso_local global i64
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long long sll;
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// CHECK: @sll = external dso_local global i64
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unsigned long long ull = 123456;
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// CHECK: @ull = dso_local global i64 123456
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__int128 s128;
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// CHECK: @s128 = external dso_local global i128
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unsigned __int128 u128;
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// CHECK: @u128 = external dso_local global i128
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wchar_t wc;
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// CHECK: @wc = external dso_local global i32
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char8_t c8;
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// CHECK: @c8 = external dso_local global i8
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char16_t c16;
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// CHECK: @c16 = external dso_local global i16
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char32_t c32;
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// CHECK: @c32 = external dso_local global i32
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_BitInt(20) sb20;
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// CHECK: @sb20 = external dso_local global i20
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unsigned _BitInt(48) ub48;
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// CHECK: @ub48 = external dso_local global i48
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_Float16 f16;
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// CHECK: @f16 = external dso_local global half
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__bf16 bf16;
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// CHECK: @bf16 = external dso_local global bfloat
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float f;
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// CHECK: @f = external dso_local global float
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double d = 1.25;
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// CHECK: @d = dso_local global double 1.250000e+00
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long double ld;
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// CHECK: @ld = external dso_local global x86_fp80
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__float128 f128;
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// CHECK: @f128 = external dso_local global fp128

‎clang/test/CIR/Lowering/hello.c‎

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// Smoke test for ClangIR-to-LLVM IR code generation
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// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s
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// TODO: Add checks when proper lowering is implemented.
5-
// For now, we're just creating an empty module.
6-
// CHECK: ModuleID
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int a;
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8-
void foo() {}
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// CHECK: @a = external dso_local global i32
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int b = 2;
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// CHECK: @b = dso_local global i32 2

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