[libcxx-commits] [libcxx] 148ef80 - [libc++] Add GCC workaround in std::char_traits<char>::length()

[Nikolas Klauser via libcxx-commits]

Author: Nikolas Klauser
Date: 2021-12-16T14:27:51+01:00
New Revision: 148ef80f895297975b95800f6fa989674767c5a2

URL: https://github.com/llvm/llvm-project/commit/148ef80f895297975b95800f6fa989674767c5a2
DIFF: https://github.com/llvm/llvm-project/commit/148ef80f895297975b95800f6fa989674767c5a2.diff

LOG: [libc++] Add GCC workaround in std::char_traits<char>::length()

GCC currently does not allow `__builtin_strlen()` during constant evaluation. This PR adds a workaround in `std::char_traits<char>::length()`

Reviewed By: Quuxplusone, ldionne, #libc, Mordante

Spies: Mordante, libcxx-commits

Differential Revision: https://reviews.llvm.org/D115795

Added: 
    

Modified: 
    libcxx/include/__string
    libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__string b/libcxx/include/__string
index e3fd0c270b2bc..2840819529ce0 100644
--- a/libcxx/include/__string
+++ b/libcxx/include/__string
@@ -337,8 +337,21 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char>
 
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     int compare(const char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT;
-    static inline size_t _LIBCPP_CONSTEXPR_AFTER_CXX14
-    length(const char_type* __s)  _NOEXCEPT {return __builtin_strlen(__s);}
+
+    static inline size_t _LIBCPP_CONSTEXPR_AFTER_CXX14 length(const char_type* __s)  _NOEXCEPT {
+      // GCC currently does not support __builtin_strlen during constant evaluation.
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
+#ifdef _LIBCPP_COMPILER_GCC
+      if (__libcpp_is_constant_evaluated()) {
+        size_t __i = 0;
+        for (; __s[__i] != char_type('\0'); ++__i)
+            ;
+        return __i;
+      }
+#endif
+      return __builtin_strlen(__s);
+    }
+
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
     static inline _LIBCPP_CONSTEXPR_AFTER_CXX17

diff  --git a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
index d07e0b0d5255a..8e612db365275 100644
--- a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// GCC's __builtin_strlen isn't constexpr yet
-// XFAIL: gcc-11 && !(c++11 || c++14 || c++17)
-
 // <string_view>
 
 // size_type copy(charT* s, size_type n, size_type pos = 0) const;