[gcc r12-4328] libstdc++: Simplify std::basic_regex::assign

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:247bac507e63b32d4dc23ef1c55f300aafea24c6

commit r12-4328-g247bac507e63b32d4dc23ef1c55f300aafea24c6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Oct 11 17:19:43 2021 +0100

    libstdc++: Simplify std::basic_regex::assign
    
    We know that if __is_contiguous_iterator is true then we have a pointer
    or a __normal_iterator that wraps a pointer, so we don't need to use
    std::__to_address.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/regex.h (basic_regex::assign(Iter, Iter)): Avoid
            std::__to_address by using poitner directly or using base()
            member of __normal_iterator.

Diff:
---
 libstdc++-v3/include/bits/regex.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index 3c44bcd7e33..a3990183580 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -682,15 +682,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	assign(_InputIterator __first, _InputIterator __last,
 	       flag_type __flags = ECMAScript)
 	{
-#if __cplusplus >= 201703L
+#if __cpp_if_constexpr >= 201606L
 	  using _ValT = typename iterator_traits<_InputIterator>::value_type;
 	  if constexpr (__detail::__is_contiguous_iter<_InputIterator>::value
 			&& is_same_v<_ValT, value_type>)
 	    {
 	      __glibcxx_requires_valid_range(__first, __last);
-	      const auto __len = __last - __first;
-	      const _Ch_type* __p = std::__to_address(__first);
-	      _M_compile(__p, __p + __len, __flags);
+	      if constexpr (is_pointer_v<_InputIterator>)
+		_M_compile(__first, __last, __flags);
+	      else // __normal_iterator<_T*, C>
+		_M_compile(__first.base(), __last.base(), __flags);
 	    }
 	  else
 #endif