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

[lanza]

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.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Nathan Lanza (lanza)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/86078.diff

7 Files Affected:

• (modified) clang/CMakeLists.txt (+7)
• (added) clang/include/clang/CIR/CMakeLists.txt ()
• (modified) clang/include/clang/CMakeLists.txt (+3)
• (modified) clang/include/clang/Config/config.h.cmake (+3)
• (added) clang/lib/CIR/CMakeLists.txt ()
• (modified) clang/lib/CMakeLists.txt (+4)
• (modified) clang/test/CMakeLists.txt (+1)

diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index 47fc2e4886cfc2..0e2e9dbf7b2528 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -164,6 +164,13 @@ 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)
 
diff --git a/clang/include/clang/CIR/CMakeLists.txt b/clang/include/clang/CIR/CMakeLists.txt
new file mode 100644
index 00000000000000..e69de29bb2d1d6
diff --git a/clang/include/clang/CMakeLists.txt b/clang/include/clang/CMakeLists.txt
index 0dc9ea5ed8ac8a..47ac70cd21690f 100644
--- a/clang/include/clang/CMakeLists.txt
+++ b/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)
diff --git a/clang/include/clang/Config/config.h.cmake b/clang/include/clang/Config/config.h.cmake
index 4015ac8040861c..27ed69e21562bf 100644
--- a/clang/include/clang/Config/config.h.cmake
+++ b/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
diff --git a/clang/lib/CIR/CMakeLists.txt b/clang/lib/CIR/CMakeLists.txt
new file mode 100644
index 00000000000000..e69de29bb2d1d6
diff --git a/clang/lib/CMakeLists.txt b/clang/lib/CMakeLists.txt
index 0cac86451f39e4..14ba55360fe050 100644
--- a/clang/lib/CMakeLists.txt
+++ b/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()
diff --git a/clang/test/CMakeLists.txt b/clang/test/CMakeLists.txt
index fcfca354f4a75f..df34a5707da33e 100644
--- a/clang/test/CMakeLists.txt
+++ b/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

[AaronBallman]

The changes seem reasonable to me, but I've added the CMake code owners for final approval.