compiler.h — Portable Compiler Attributes

Introduction

compiler.h wraps non-portable compiler extensions (__builtin_*, __attribute__, __declspec) behind XPP_-prefixed macros that degrade gracefully on unsupported toolchains. Self-contained — no project dependencies.

Macros

Branch Prediction

Macro	Description	Fallback
`XPP_LIKELY(x)`	Branch expected true: `__builtin_expect(!!(x), 1)`	`(x)`
`XPP_UNLIKELY(x)`	Branch expected false: `__builtin_expect(!!(x), 0)`	`(x)`

Function Attributes

Macro	Description	Fallback
`XPP_NORETURN`	`[[noreturn]]`	Compiler-specific or empty
`XPP_FORCE_INLINE`	`inline __attribute__((always_inline))`	`inline`
`XPP_NOINLINE`	`__attribute__((noinline))`	Empty

Control Flow

Macro	Description	Fallback
`XPP_UNREACHABLE()`	`__builtin_unreachable()`	`std::abort()`
`XPP_FALLTHROUGH`	`[[fallthrough]]` (C++17) or `__attribute__((fallthrough))`	`((void)0)`

Deprecation

Macro	Description
`XPP_DEPRECATED(msg)`	`[[deprecated(msg)]]` (C++14) or `__attribute__((deprecated(msg)))`

Feature Detection

Macro	Description
`XPP_DEBUG`	`1` in debug (`NDEBUG` off), `0` in release. Override with `-DXPP_DEBUG=`.
`XPP_HAS_COROUTINES`	`1` if C++20 coroutines are available. Checks `__cplusplus >= 202002L` AND `__cpp_coroutines >= 201902L`. Override with `-DXPP_HAS_COROUTINES=0/1`.
`XPP_FIBER`	`1` when fiber support is enabled (`libxpp` CMake option). Enables `xpp::fiber()` and fiber-aware `.await()`.

Usage

// Cold path: assertion failure
if (XPP_UNLIKELY(!ptr)) {
    log_error_and_abort();
}

// Intentional switch fallthrough
case STATE_A:
    init_a();
    XPP_FALLTHROUGH;
case STATE_B:
    process();

// Feature-gated coroutine support
#if XPP_HAS_COROUTINES
    // C++20 coroutine code
#endif

Implementation Notes

XPP_DEBUG defaults to !defined(NDEBUG) but is overridable at the command line. This allows enabling debug assertions in release builds (-DXPP_DEBUG=1) or disabling them in debug builds (-DXPP_DEBUG=0) for benchmarking.

XPP_HAS_COROUTINES checks both __cpp_coroutines and __cpp_impl_coroutine — Apple Clang historically defined only the latter.

The X Project