[CIR][NFC] Add scaffolding for the CIR dialect and CIROps.td

This adds no real content, it just incrementally adds some scaffolding
necessary to enable a future patch to just add our first few ops.

Test Plan:
```
$ cmake -Sllvm -Bbuild -DCLANG_ENABLE_CIR=1 \
  -DLLVM_ENABLE_PROJECTS='clang;mlir' \
  -DCMAKE_BUILD_TYPE=Release -GNinja
$ ninja -C build check-clang
$ ninja -C build MLIRCIROpsIncGen
$ ninja -C build MLIRCIR
```

Reviewers: AaronBallman, erichkeane, bcardosolopes

Reviewed By: erichkeane, AaronBallman, bcardosolopes

Pull Request: https://github.com/llvm/llvm-project/pull/86080

clang/CMakeLists.txt

@@ -166,6 +166,10 @@ if(CLANG_ENABLE_LIBXML2)
 endif()
 
 if(CLANG_ENABLE_CIR)
+  if (CLANG_BUILT_STANDALONE)
+    message(FATAL_ERROR
+      "ClangIR is not yet supported in the standalone build.")
+  endif()
   if (NOT "${LLVM_ENABLE_PROJECTS}" MATCHES "MLIR|mlir")
     message(FATAL_ERROR
       "Cannot build ClangIR without MLIR in LLVM_ENABLE_PROJECTS")

clang/include/clang/CIR/CMakeLists.txt

@@ -0,0 +1,6 @@
+set(MLIR_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/../mlir/include ) # --includedir
+set(MLIR_TABLEGEN_OUTPUT_DIR ${CMAKE_BINARY_DIR}/tools/mlir/include)
+include_directories(${MLIR_INCLUDE_DIR})
+include_directories(${MLIR_TABLEGEN_OUTPUT_DIR})
+
+add_subdirectory(Dialect)

clang/include/clang/CIR/Dialect/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory(IR)

clang/include/clang/CIR/Dialect/IR/CIRDialect.h

@@ -0,0 +1,16 @@
+//===- CIRDialect.h - CIR dialect -------------------------------*- C++ -*-===//
+//
+// 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 declares the CIR dialect.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT_H
+#define LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT_H
+
+#endif // LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT_H

clang/include/clang/CIR/Dialect/IR/CIRDialect.td

@@ -0,0 +1,44 @@
+//===- CIRDialect.td - CIR dialect -------------------------*- tablegen -*-===//
+//
+// 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 declares the CIR dialect.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT
+#define LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT
+
+include "mlir/IR/OpBase.td"
+
+def CIR_Dialect : Dialect {
+  let name = "cir";
+
+  // A short one-line summary of our dialect.
+  let summary = "A high-level dialect for analyzing and optimizing Clang "
+                "supported languages";
+
+  let cppNamespace = "::mlir::cir";
+
+  let useDefaultAttributePrinterParser = 0;
+  let useDefaultTypePrinterParser = 0;
+
+  let extraClassDeclaration = [{
+    void registerAttributes();
+    void registerTypes();
+
+    Type parseType(DialectAsmParser &parser) const override;
+    void printType(Type type, DialectAsmPrinter &printer) const override;
+
+    Attribute parseAttribute(DialectAsmParser &parser,
+                             Type type) const override;
+
+    void printAttribute(Attribute attr, DialectAsmPrinter &os) const override;
+  }];
+}
+
+#endif // LLVM_CLANG_CIR_DIALECT_IR_CIRDIALECT

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -0,0 +1,19 @@
+//===-- CIROps.td - CIR dialect definition -----------------*- tablegen -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Definition of the CIR dialect
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_CIR_DIALECT_IR_CIROPS
+#define LLVM_CLANG_CIR_DIALECT_IR_CIROPS
+
+include "clang/CIR/Dialect/IR/CIRDialect.td"
+
+#endif // LLVM_CLANG_CIR_DIALECT_IR_CIROPS

clang/include/clang/CIR/Dialect/IR/CMakeLists.txt

@@ -0,0 +1,16 @@
+# This replicates part of the add_mlir_dialect cmake function from MLIR that
+# cannot be used here. This happens because it expects to be run inside MLIR
+# directory which is not the case for CIR (and also FIR, both have similar
+# workarounds).
+
+# Equivalent to add_mlir_dialect(CIROps cir)
+set(LLVM_TARGET_DEFINITIONS CIROps.td)
+mlir_tablegen(CIROps.h.inc -gen-op-decls)
+mlir_tablegen(CIROps.cpp.inc -gen-op-defs)
+mlir_tablegen(CIROpsTypes.h.inc -gen-typedef-decls)
+mlir_tablegen(CIROpsTypes.cpp.inc -gen-typedef-defs)
+mlir_tablegen(CIROpsDialect.h.inc -gen-dialect-decls)
+mlir_tablegen(CIROpsDialect.cpp.inc -gen-dialect-defs)
+add_public_tablegen_target(MLIRCIROpsIncGen)
+add_dependencies(mlir-headers MLIRCIROpsIncGen)
+

clang/lib/CIR/CMakeLists.txt

@@ -0,0 +1,4 @@
+include_directories(${LLVM_MAIN_SRC_DIR}/../mlir/include)
+include_directories(${CMAKE_BINARY_DIR}/tools/mlir/include)
+
+add_subdirectory(Dialect)

clang/lib/CIR/Dialect/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory(IR)

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

@@ -0,0 +1,13 @@
+//===- CIRDialect.cpp - MLIR CIR ops implementation -----------------------===//
+//
+// 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 the CIR dialect and its operations.
+//
+//===----------------------------------------------------------------------===//
+
+#include <clang/CIR/Dialect/IR/CIRDialect.h>

clang/lib/CIR/Dialect/IR/CMakeLists.txt

@@ -0,0 +1,3 @@
+add_clang_library(MLIRCIR
+  CIRDialect.cpp
+  )