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Factor out ABSL_INTERNAL_UNEVALUATED() from ABSL_ASSERT()

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This makes the logic clearer and also allows reuse in other macros in the future, such as hardened assertions.

PiperOrigin-RevId: 908751829
Change-Id: Ic6f2e77755718db1df86510145e16e2ba6c83bcb
This commit is contained in:
Abseil Team
2026-05-01 08:43:40 -07:00
committed by Copybara-Service
parent acbfcef618
commit 7dcc24cf19
1 changed files with 19 additions and 12 deletions
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31
absl/base/macros.h
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@@ -56,6 +56,24 @@ auto ArraySizeHelper(const T (&array)[N]) -> char (&)[N];
ABSL_NAMESPACE_END
} // namespace absl
// ABSL_INTERNAL_UNEVALUATED()
//
// Expands into a no-op expression that contains the given expression. Used to
// avoid unused-variable warnings in configurations that don't need to evaluate
// the given expression (e.g., NDEBUG).
#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
// We use `decltype` here to avoid generating unnecessary code that the
// optimizer then has to optimize away.
// This not only improves compilation performance by reducing codegen bloat
// and optimization work, but also guarantees fast run-time performance without
// having to rely on the optimizer.
#define ABSL_INTERNAL_UNEVALUATED(expr) (decltype((void)(expr))())
#else
// Pre-C++20, lambdas can't be inside unevaluated operands, so we're forced to
// rely on the optimizer.
#define ABSL_INTERNAL_UNEVALUATED(expr) (false ? (void)(expr) : void())
#endif
// ABSL_BAD_CALL_IF()
//
// Used on a function overload to trap bad calls: any call that matches the
@@ -93,18 +111,7 @@ ABSL_NAMESPACE_END
// This macro is inspired by
// https://akrzemi1.wordpress.com/2017/05/18/asserts-in-constexpr-functions/
#if defined(NDEBUG)
#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
// We use `decltype` here to avoid generating unnecessary code that the
// optimizer then has to optimize away.
// This not only improves compilation performance by reducing codegen bloat
// and optimization work, but also guarantees fast run-time performance without
// having to rely on the optimizer.
#define ABSL_ASSERT(expr) (decltype((expr) ? void() : void())())
#else
// Pre-C++20, lambdas can't be inside unevaluated operands, so we're forced to
// rely on the optimizer.
#define ABSL_ASSERT(expr) (false ? ((expr) ? void() : void()) : void())
#endif
#define ABSL_ASSERT(expr) ABSL_INTERNAL_UNEVALUATED((expr) ? void() : void())
#else
#define ABSL_ASSERT(expr) \
(ABSL_PREDICT_TRUE((expr)) ? static_cast<void>(0) \