[clang] [CIR] Initial implementation of CIR-to-LLVM IR lowering pass (PR #125260)

[Erich Keane via cfe-commits]

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@@ -22,16 +34,156 @@ using namespace llvm;
 namespace cir {
 namespace direct {
 
+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"; }
+};
+
+// This pass requires the CIR to be in a "flat" state. All blocks in each
+// function must belong to the parent region.
+mlir::LogicalResult CIRToLLVMGlobalOpLowering::matchAndRewrite(
+    cir::GlobalOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+
+  // Fetch required values to create LLVM op.
+  const mlir::Type cirSymType = op.getSymType();
+
+  // This is the LLVM dialect type.
+  const mlir::Type llvmType = getTypeConverter()->convertType(cirSymType);
+  // FIXME: These default values are placeholders until the the equivalent
+  //        attributes are available on cir.global ops.  
+  const bool isConst = false;
+  const unsigned addrSpace = 0;
+  const bool isDsoLocal = true;
+  const bool isThreadLocal = false;
+  const uint64_t alignment = 0;
+  const mlir::LLVM::Linkage linkage = mlir::LLVM::Linkage::External;
+  const StringRef symbol = op.getSymName();
+  std::optional<mlir::Attribute> init = op.getInitialValue();
+
+  SmallVector<mlir::NamedAttribute> attributes;
+
+  if (init.has_value()) {
+    if (auto fltAttr = mlir::dyn_cast<cir::FPAttr>(init.value())) {
+      // Initializer is a constant floating-point number: convert to MLIR
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erichkeane wrote:

At a certain point, a type-visitor is going to be something we want for here, but ATM this is fine.

https://github.com/llvm/llvm-project/pull/125260