diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt --- a/llvm/CMakeLists.txt +++ b/llvm/CMakeLists.txt @@ -465,6 +465,7 @@ option(LLVM_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF) option(LLVM_ENABLE_DUMP "Enable dump functions even when assertions are disabled" OFF) +option(LLVM_UNREACHABLE_OPTIMIZE "Optimize llvm_unreachable() as undefined behavior (default), guaranteed trap when OFF" ON) if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" ) option(LLVM_ENABLE_ASSERTIONS "Enable assertions" OFF) diff --git a/llvm/docs/CMake.rst b/llvm/docs/CMake.rst --- a/llvm/docs/CMake.rst +++ b/llvm/docs/CMake.rst @@ -300,6 +300,12 @@ enabled or not. A version of LLVM built with ABI breaking checks is not ABI compatible with a version built without it. +**LLVM_UNREACHABLE_OPTIMIZE**:BOOL + This flag controls the behavior of `llvm_unreachable()` in release build + (when assertions are disabled in general). When ON (default) then + `llvm_unreachable()` is considered "undefined behavior" and optimized as + such. When OFF it is instead replaced with a guaranteed "trap". + **LLVM_APPEND_VC_REV**:BOOL Embed version control revision info (Git revision id). The version info is provided by the ``LLVM_REVISION`` macro in diff --git a/llvm/include/llvm/Config/llvm-config.h.cmake b/llvm/include/llvm/Config/llvm-config.h.cmake --- a/llvm/include/llvm/Config/llvm-config.h.cmake +++ b/llvm/include/llvm/Config/llvm-config.h.cmake @@ -112,4 +112,8 @@ /* Define if building LLVM with LLVM_FORCE_USE_OLD_TOOLCHAIN_LIBS */ #cmakedefine LLVM_FORCE_USE_OLD_TOOLCHAIN ${LLVM_FORCE_USE_OLD_TOOLCHAIN} +/* Define if llvm_unreachable should be optimized with undefined behavior + * in non assert builds */ +#cmakedefine01 LLVM_UNREACHABLE_OPTIMIZE + #endif diff --git a/llvm/include/llvm/Support/ErrorHandling.h b/llvm/include/llvm/Support/ErrorHandling.h --- a/llvm/include/llvm/Support/ErrorHandling.h +++ b/llvm/include/llvm/Support/ErrorHandling.h @@ -124,15 +124,23 @@ /// Marks that the current location is not supposed to be reachable. /// In !NDEBUG builds, prints the message and location info to stderr. -/// In NDEBUG builds, becomes an optimizer hint that the current location -/// is not supposed to be reachable. On compilers that don't support -/// such hints, prints a reduced message instead and aborts the program. +/// In NDEBUG builds, the behavior is controlled by the CMake flag +/// -DLLVM_UNREACHABLE_OPTIMIZE +/// * When "ON" (default) llvm_unreachable() becomes an optimizer hint +/// that the current location is not supposed to be reachable: the hint +/// turns such code path into undefined behavior. On compilers that don't +/// support such hints, prints a reduced message instead and aborts the +/// program. +/// * When "OFF", a builtin_trap is emitted instead of an +// optimizer hint or printing a reduced message. /// /// Use this instead of assert(0). It conveys intent more clearly and /// allows compilers to omit some unnecessary code. #ifndef NDEBUG #define llvm_unreachable(msg) \ ::llvm::llvm_unreachable_internal(msg, __FILE__, __LINE__) +#elif LLVM_UNREACHABLE_OPTIMIZE +#define llvm_unreachable(msg) LLVM_BUILTIN_TRAP #elif defined(LLVM_BUILTIN_UNREACHABLE) #define llvm_unreachable(msg) LLVM_BUILTIN_UNREACHABLE #else