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Optimize string comparison used to implement CTTI comparison.

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When the strings are known to be runtime objects, use compiler builtin
for strcmp for comparing strings. The compiler will generate a runtime
call for the (presumably, well-optimized) strcmp instead of rolling
a local per-character comparison loop. When the builtin is not available
or we cannot detect compile-time strings, use the local loop as before.

Also, when C++14 constexpr is not available, use strcmp right away,
since there is no use for the local loop in this case.
This commit is contained in:
Andrey Semashev
2018-10-28 02:56:30 +03:00
parent f3da852bca
commit cd1c905f87
1 changed files with 38 additions and 2 deletions
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40
include/boost/type_index/detail/compile_time_type_info.hpp
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@ -13,6 +13,7 @@
/// \brief Contains helper macros and implementation details of boost::typeindex::ctti_type_index.
/// Not intended for inclusion from user's code.
#include <cstring>
#include <boost/config.hpp>
#include <boost/static_assert.hpp>
#include <boost/type_traits/integral_constant.hpp>
@ -22,6 +23,18 @@
#endif
/// @cond
#if defined(__has_builtin)
#if __has_builtin(__builtin_constant_p)
#define BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT(x) __builtin_constant_p(x)
#endif
#if __has_builtin(__builtin_strcmp)
#define BOOST_TYPE_INDEX_DETAIL_BUILTIN_STRCMP(str1, str2) __builtin_strcmp(str1, str2)
#endif
#elif defined(__GNUC__)
#define BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT(x) __builtin_constant_p(x)
#define BOOST_TYPE_INDEX_DETAIL_BUILTIN_STRCMP(str1, str2) __builtin_strcmp(str1, str2)
#endif
#define BOOST_TYPE_INDEX_REGISTER_CTTI_PARSING_PARAMS(begin_skip, end_skip, runtime_skip, runtime_skip_until) \
namespace boost { namespace typeindex { namespace detail { \
BOOST_STATIC_CONSTEXPR std::size_t ctti_skip_size_at_begin = begin_skip; \
@ -105,6 +118,17 @@ namespace boost { namespace typeindex { namespace detail {
);
}
#if defined(BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT)
BOOST_CXX14_CONSTEXPR BOOST_FORCEINLINE bool is_constant_string(const char* str) BOOST_NOEXCEPT {
while (BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT(*str)) {
if (*str == '\0')
return true;
++str;
}
return false;
}
#endif // defined(BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT)
template <unsigned int ArrayLength>
BOOST_CXX14_CONSTEXPR inline const char* skip_begining_runtime(const char* begin, boost::false_type) BOOST_NOEXCEPT {
return begin;
@ -138,15 +162,27 @@ namespace boost { namespace typeindex { namespace detail {
return last1;
}
BOOST_CXX14_CONSTEXPR inline int constexpr_strcmp(const char *v1, const char *v2) BOOST_NOEXCEPT {
BOOST_CXX14_CONSTEXPR inline int constexpr_strcmp_loop(const char *v1, const char *v2) BOOST_NOEXCEPT {
while (*v1 != '\0' && *v1 == *v2) {
++v1;
++v2;
};
}
return static_cast<int>(*v1) - *v2;
}
BOOST_CXX14_CONSTEXPR inline int constexpr_strcmp(const char *v1, const char *v2) BOOST_NOEXCEPT {
#if !defined(BOOST_NO_CXX14_CONSTEXPR) && defined(BOOST_TYPE_INDEX_DETAIL_IS_CONSTANT) && defined(BOOST_TYPE_INDEX_DETAIL_BUILTIN_STRCMP)
if (boost::typeindex::detail::is_constant_string(v1) && boost::typeindex::detail::is_constant_string(v2))
return boost::typeindex::detail::constexpr_strcmp_loop(v1, v2);
return BOOST_TYPE_INDEX_DETAIL_BUILTIN_STRCMP(v1, v2);
#elif !defined(BOOST_NO_CXX14_CONSTEXPR)
return boost::typeindex::detail::constexpr_strcmp_loop(v1, v2);
#else
return std::strcmp(v1, v2);
#endif
}
template <unsigned int ArrayLength>
BOOST_CXX14_CONSTEXPR inline const char* skip_begining_runtime(const char* begin, boost::true_type) BOOST_NOEXCEPT {
const char* const it = constexpr_search(