diff options
Diffstat (limited to 'runtime/base/macros.h')
| -rw-r--r-- | runtime/base/macros.h | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/runtime/base/macros.h b/runtime/base/macros.h index b66d528d1b..f5a38bbf35 100644 --- a/runtime/base/macros.h +++ b/runtime/base/macros.h @@ -181,6 +181,48 @@ char (&ArraySizeHelper(T (&array)[N]))[N]; template<typename T> void UNUSED(const T&) {} #define UNREACHABLE __builtin_unreachable +// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through +// between switch labels: +// switch (x) { +// case 40: +// case 41: +// if (truth_is_out_there) { +// ++x; +// FALLTHROUGH_INTENDED; // Use instead of/along with annotations in +// // comments. +// } else { +// return x; +// } +// case 42: +// ... +// +// As shown in the example above, the FALLTHROUGH_INTENDED macro should be +// followed by a semicolon. It is designed to mimic control-flow statements +// like 'break;', so it can be placed in most places where 'break;' can, but +// only if there are no statements on the execution path between it and the +// next switch label. +// +// When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is +// expanded to [[clang::fallthrough]] attribute, which is analysed when +// performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough'). +// See clang documentation on language extensions for details: +// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough +// +// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no +// effect on diagnostics. +// +// In either case this macro has no effect on runtime behavior and performance +// of code. +#if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning) +#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") +#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT +#endif +#endif + +#ifndef FALLTHROUGH_INTENDED +#define FALLTHROUGH_INTENDED do { } while (0) +#endif + // Annotalysis thread-safety analysis support. #if defined(__SUPPORT_TS_ANNOTATION__) || defined(__clang__) #define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x)) |