libstdc++: Fix constexpr functions to conform to older standards

Some constexpr functions were inadvertently relying on relaxed constexpr
rules from later standards.

libstdc++-v3/ChangeLog:

	* include/bits/chrono.h (duration_cast): Do not use braces
	around statements for C++11 constexpr rules.
	* include/bits/stl_algobase.h (__lg): Rewrite as a single
	statement for C++11 constexpr rules.
	* include/experimental/bits/fs_path.h (path::string): Use
	_GLIBCXX17_CONSTEXPR not _GLIBCXX_CONSTEXPR for 'if constexpr'.
	* include/std/charconv (__to_chars_8): Initialize variable for
	C++17 constexpr rules.

(cherry picked from commit b3a2b307b9deea719fb725a86df43b82176fe459)

diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h
index f4573d27b03e4bf4b43f88494b83bcaee245740e..0aeea0ae57eb95a37706c08171335dae56051b2a 100644 (file)
--- a/libstdc++-v3/include/bits/chrono.h
+++ b/libstdc++-v3/include/bits/chrono.h
@@ -276,8 +276,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        if constexpr (is_same_v<_ToDur, duration<_Rep, _Period>>)
          return __d;
        else
+         {
 #endif
-       {
          using __to_period = typename _ToDur::period;
          using __to_rep = typename _ToDur::rep;
          using __cf = ratio_divide<_Period, __to_period>;
@@ -285,7 +285,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          using __dc = __duration_cast_impl<_ToDur, __cf, __cr,
                                            __cf::num == 1, __cf::den == 1>;
          return __dc::__cast(__d);
-       }
+#if __cpp_inline_variables && __cpp_if_constexpr
+         }
+#endif
       }
 
     /** Trait indicating whether to treat a type as a floating-point type.

diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 4a6f8195d989582b325070f9c670a6e9c3e6f955..5a8faedf92a09a33641746ff905fc09c2ed76e7e 100644 (file)
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -1518,15 +1518,12 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
       return std::__bit_width(make_unsigned_t<_Tp>(__n)) - 1;
 #else
       // Use +__n so it promotes to at least int.
-      const int __sz = sizeof(+__n);
-      int __w = __sz * __CHAR_BIT__ - 1;
-      if (__sz == sizeof(long long))
-       __w -= __builtin_clzll(+__n);
-      else if (__sz == sizeof(long))
-       __w -= __builtin_clzl(+__n);
-      else if (__sz == sizeof(int))
-       __w -= __builtin_clz(+__n);
-      return __w;
+      return (sizeof(+__n) * __CHAR_BIT__ - 1)
+              - (sizeof(+__n) == sizeof(long long)
+                   ? __builtin_clzll(+__n)
+                   : (sizeof(+__n) == sizeof(long)
+                        ? __builtin_clzl(+__n)
+                        : __builtin_clz(+__n)));
 #endif
     }
 

diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index e0e47188bb987e44a79af5f5b193cf8e0d2640d3..bf07754fd84809b4a84070acc342bcac632e413b 100644 (file)
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -1042,7 +1042,7 @@ namespace __detail
     inline std::basic_string<_CharT, _Traits, _Allocator>
     path::string(const _Allocator& __a) const
     {
-      if _GLIBCXX_CONSTEXPR (is_same<_CharT, value_type>::value)
+      if _GLIBCXX17_CONSTEXPR (is_same<_CharT, value_type>::value)
        return { _M_pathname.begin(), _M_pathname.end(), __a };
 
       using _WString = basic_string<_CharT, _Traits, _Allocator>;

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index b34d672f5bd02a3a91ded75c18c51ae4b7852a8f..cf2b1161014580efa1b55410a241812cd7a2dd0b 100644 (file)
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -242,7 +242,7 @@ namespace __detail
       static_assert(__integer_to_chars_is_unsigned<_Tp>, "implementation bug");
 
       to_chars_result __res;
-      unsigned __len;
+      unsigned __len = 0;
 
       if _GLIBCXX17_CONSTEXPR (__gnu_cxx::__int_traits<_Tp>::__digits <= 16)
        {