[CMake] Match LLVM EH and RTTI defaults

Disable C++ exceptions and RTTI by default while retaining explicit, validated opt-in switches. Replace the arena's exception syntax with an RAII construction guard so both configurations share one implementation.

3 files changed, 25 insertions, 10 deletions

diff --git a/backend/CMakeLists.txt b/backend/CMakeLists.txt
index 2d5cc82..0f983d0 100644
--- a/backend/CMakeLists.txt
+++ b/backend/CMakeLists.txt
@@ -44,6 +44,12 @@ include(RCCBackendDeveloperTools)
 option(RCC_BACKEND_BUILD_TESTS "Build RCC Backend tests" "${BUILD_TESTING}")
 option(RCC_BACKEND_WARNINGS_AS_ERRORS "Treat compiler warnings as errors" OFF)
 option(RCC_BACKEND_ENABLE_CLANG_TIDY "Run clang-tidy during each compilation" OFF)
+option(RCC_BACKEND_ENABLE_EH "Enable C++ exception handling" OFF)
+option(RCC_BACKEND_ENABLE_RTTI "Enable C++ run-time type information" OFF)
+
+if(RCC_BACKEND_ENABLE_EH AND NOT RCC_BACKEND_ENABLE_RTTI)
+  message(FATAL_ERROR "RCC Backend exception handling requires RTTI")
+endif()
 
 rcc_backend_initialize_toolchain()
 
diff --git a/backend/cmake/modules/RCCBackendBuild.cmake b/backend/cmake/modules/RCCBackendBuild.cmake
index 79e7bb1..52e3a71 100644
--- a/backend/cmake/modules/RCCBackendBuild.cmake
+++ b/backend/cmake/modules/RCCBackendBuild.cmake
@@ -70,6 +70,18 @@ function(rcc_backend_configure_target Target)
       -Wformat=2
   )
 
+  if(RCC_BACKEND_ENABLE_EH)
+    target_compile_options("${Target}" PRIVATE -fexceptions)
+  else()
+    target_compile_options("${Target}" PRIVATE -fno-exceptions)
+  endif()
+
+  if(RCC_BACKEND_ENABLE_RTTI)
+    target_compile_options("${Target}" PRIVATE -frtti)
+  else()
+    target_compile_options("${Target}" PRIVATE -fno-rtti)
+  endif()
+
   if(RCC_BACKEND_WARNINGS_AS_ERRORS)
     target_compile_options("${Target}" PRIVATE -Werror)
   endif()
diff --git a/backend/lib/CodeGen/MachineFunction.cpp b/backend/lib/CodeGen/MachineFunction.cpp
index e19c115..fc1508c 100644
--- a/backend/lib/CodeGen/MachineFunction.cpp
+++ b/backend/lib/CodeGen/MachineFunction.cpp
@@ -35,16 +35,13 @@ public:
   [[nodiscard]] ObjectT *create(ArgumentTs &&...Arguments) {
     void *Storage = Resource.allocate(sizeof(ObjectT), alignof(ObjectT));
     ObjectT *Object = ::new (Storage) ObjectT(std::forward<ArgumentTs>(Arguments)...);
-    try {
-      Destructors.push_back(DestructorRecord{
-          Object,
-          [](void *RawObject) noexcept { std::destroy_at(static_cast<ObjectT *>(RawObject)); },
-      });
-    } catch (...) {
-      std::destroy_at(Object);
-      throw;
-    }
-    return Object;
+    auto DestroyObject = [](ObjectT *TypedObject) noexcept { std::destroy_at(TypedObject); };
+    std::unique_ptr<ObjectT, decltype(DestroyObject)> ConstructionGuard(Object, DestroyObject);
+    Destructors.push_back(DestructorRecord{
+        Object,
+        [](void *RawObject) noexcept { std::destroy_at(static_cast<ObjectT *>(RawObject)); },
+    });
+    return ConstructionGuard.release();
   }
 
 private: