[CIR][cmake] Add support for cmake variable CLANG_ENABLE_CIR

Introduce a cmake variable that guards the inclusion of ClangIR into the
build of clang. Guard that we aren't trying to build without MLIR. Add
two subdirectories that, as of now, don't do anything.

Reviewers: bcardosolopes, erichkeane, petrhosek, Ericson2314

Reviewed By: bcardosolopes

Pull Request: https://github.com/llvm/llvm-project/pull/86078

clang/CMakeLists.txt

@@ -165,6 +165,13 @@ if(CLANG_ENABLE_LIBXML2)
   endif()
 endif()
 
+if(CLANG_ENABLE_CIR)
+  if (NOT "${LLVM_ENABLE_PROJECTS}" MATCHES "MLIR|mlir")
+    message(FATAL_ERROR
+      "Cannot build ClangIR without MLIR in LLVM_ENABLE_PROJECTS")
+  endif()
+endif()
+
 include(CheckIncludeFile)
 check_include_file(sys/resource.h CLANG_HAVE_RLIMITS)
 

clang/include/clang/CMakeLists.txt

@@ -1,5 +1,8 @@
 add_subdirectory(AST)
 add_subdirectory(Basic)
+if(CLANG_ENABLE_CIR)
+  add_subdirectory(CIR)
+endif()
 add_subdirectory(Driver)
 add_subdirectory(Parse)
 add_subdirectory(Sema)

clang/include/clang/Config/config.h.cmake

@@ -83,4 +83,7 @@
 /* Spawn a new process clang.exe for the CC1 tool invocation, when necessary */
 #cmakedefine01 CLANG_SPAWN_CC1
 
+/* Whether CIR is built into Clang */
+#cmakedefine01 CLANG_ENABLE_CIR
+
 #endif

clang/lib/CMakeLists.txt

@@ -31,3 +31,7 @@ if(CLANG_INCLUDE_TESTS)
 endif()
 add_subdirectory(Interpreter)
 add_subdirectory(Support)
+
+if(CLANG_ENABLE_CIR)
+  add_subdirectory(CIR)
+endif()

clang/test/CMakeLists.txt

@@ -9,6 +9,7 @@ llvm_canonicalize_cmake_booleans(
   CLANG_ENABLE_STATIC_ANALYZER
   CLANG_PLUGIN_SUPPORT
   CLANG_SPAWN_CC1
+  CLANG_ENABLE_CIR
   ENABLE_BACKTRACES
   LLVM_ENABLE_ZLIB
   LLVM_ENABLE_ZSTD

clang/test/lit.site.cfg.py.in

@@ -27,6 +27,7 @@ config.clang_default_pie_on_linux = @CLANG_DEFAULT_PIE_ON_LINUX@
 config.clang_default_cxx_stdlib = "@CLANG_DEFAULT_CXX_STDLIB@"
 config.clang_staticanalyzer = @CLANG_ENABLE_STATIC_ANALYZER@
 config.clang_staticanalyzer_z3 = @LLVM_WITH_Z3@
+config.clang_enable_cir = @CLANG_ENABLE_CIR@
 config.clang_examples = @CLANG_BUILD_EXAMPLES@
 config.enable_shared = @ENABLE_SHARED@
 config.enable_backtrace = @ENABLE_BACKTRACES@