diff options
| -rw-r--r-- | absl/strings/str_cat.h | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/absl/strings/str_cat.h b/absl/strings/str_cat.h index 57a5823f..554c89de 100644 --- a/absl/strings/str_cat.h +++ b/absl/strings/str_cat.h @@ -498,11 +498,28 @@ inline std::string SingleArgStrCat(unsigned long long x) { inline std::string SingleArgStrCat(float x) { return FloatToString(x); } inline std::string SingleArgStrCat(double x) { return FloatToString(x); } - -template <typename T, typename = std::enable_if_t<std::is_arithmetic<T>{} && - !std::is_same<T, char>{}>> +// As of September 2023, the SingleArgStrCat() optimization is only enabled for +// libc++. The reasons for this are: +// 1) The SSO size for libc++ is 23, while libstdc++ and MSSTL have an SSO size +// of 15. Since IntegerToString unconditionally resizes the string to 22 bytes, +// this causes both libstdc++ and MSSTL to allocate. +// 2) strings_internal::STLStringResizeUninitialized() only has an +// implementation that avoids initialization when using libc++. This isn't as +// relevant as (1), and the cost should be benchmarked if (1) ever changes on +// libstc++ or MSSTL. +#ifdef _LIBCPP_VERSION +#define ABSL_INTERNAL_STRCAT_ENABLE_FAST_CASE true +#else +#define ABSL_INTERNAL_STRCAT_ENABLE_FAST_CASE false +#endif + +template <typename T, typename = std::enable_if_t< + ABSL_INTERNAL_STRCAT_ENABLE_FAST_CASE && + std::is_arithmetic<T>{} && !std::is_same<T, char>{}>> using EnableIfFastCase = T; +#undef ABSL_INTERNAL_STRCAT_ENABLE_FAST_CASE + } // namespace strings_internal ABSL_MUST_USE_RESULT inline std::string StrCat() { return std::string(); } |