[PATCH] D26896: [libcxx] Make constexpr char_traits<T> and char_traits<char>

[Marshall Clow via Phabricator via cfe-commits]

mclow.lists added inline comments.


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Comment at: include/__string:213
 
-    static inline int compare(const char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
-        {return __n == 0 ? 0 : memcmp(__s1, __s2, __n);}
-    static inline size_t length(const char_type* __s)  _NOEXCEPT {return strlen(__s);}
-    static inline const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT
-        {return __n == 0 ? NULL : (const char_type*) memchr(__s, to_int_type(__a), __n);}
+#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_CXX14_CONSTEXPR)
+    static inline constexpr int
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AntonBikineev wrote:
> EricWF wrote:
> > wow. This is #ifdef hell. Please find a way to do it with less (or hopefully no) conditional compilation blocks.
> yep, this is generic hell. I want to cover as many cases as possible, i.e. combinations of (is_constexpr x has_builtin_xxx) for every function. I'm open to suggestions
How about (for compare, say) you just forget about `memcmp`.  Either call `__builtin_memcmp` if it is available, or use a hand-rolled loop.

Note: gcc has had `__builtin_memcmp` since at least 4.8. (and it is constexpr)

And just mark the function with `_LIBCPP_CONSTEXPR_AFTER_CXX14`.


https://reviews.llvm.org/D26896