libstdc++: Use runtime format for internal format calls in chrono [PR110739]

This patch adjust all internal std::format call inside of __formatter_chrono,
to use runtime format string and thus avoid compile time checking of validity
of the format string. Majority of cases are covered by calling newly introduced
_S_empty_fs() function that returns __Runtime_format_string containing
_S_empty_spec, instead of passing later directly.

In case of _M_j we use _S_str_d3 function (extracted from _S_str_d2), eliminating
call to std::format outside of unlikely scenario in which day of year is greater
than 1000 (this may happen for year_month_day with month greater than 12). In
consequence, outside of handling subseconds, we no longer delegate to std::format
or construct temporary strings, when formatting chrono types with ok() values.

	PR libstdc++/110739

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_S_empty_fs): Define.
	(__formatter_chrono::_S_str_d2): Use _S_str_d3 for 3+ digits and
	place allways_inline attribute after comment.
	(__formatter_chrono::_S_str_d3): Extracted from _S_str_d2.
	(__formatter_chrono::_M_H_I, __formatter_chrono::_M_R_X): Replace
	_S_empty_spec with _S_empty_fs().
	(__formatter_chrono::_M_j): Likewise and use _S_str_d3 in common
	case.
	(__format::operator-(_ChronoParts, _ChronoParts))
	(__format::operator-=(_ChronoParts, _ChronoParts))
	(__formatter_chrono::_S_fill_two_digits)
	(__formatter_chrono::_S_str_d1): Place always_inline attribute
	after comment.

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 0ffbf06a7ff4f23e28cbe5f429d1e846f2177aed..bcf9830fb9e23890c28e5c0b0e3358b5c17283bb 100644 (file)
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -250,14 +250,14 @@ namespace __format
   operator|=(_ChronoParts& __x, _ChronoParts __y) noexcept
   { return __x = __x | __y; }
 
-  [[__gnu__::__always_inline__]]
   // returns copy of x with all bits from y unset.
+  [[__gnu__::__always_inline__]]
   constexpr _ChronoParts
   operator-(_ChronoParts __x, _ChronoParts __y) noexcept
   { return static_cast<_ChronoParts>((unsigned short)__x & ~(unsigned short)__y); }
 
-  [[__gnu__::__always_inline__]]
   // unsets all bits of x that are set in y
+  [[__gnu__::__always_inline__]]
   constexpr _ChronoParts&
   operator-=(_ChronoParts& __x, _ChronoParts __y) noexcept
   { return __x = __x - __y; }
@@ -873,6 +873,11 @@ namespace __format
       static constexpr const _CharT* _S_minus_empty_spec = _S_chars + 17;
       static constexpr const _CharT* _S_empty_spec = _S_chars + 18;
 
+      [[__gnu__::__always_inline__]]
+      static _Runtime_format_string<_CharT>
+      _S_empty_fs()
+      { return _Runtime_format_string<_CharT>(_S_empty_spec); }
+
       // Return the formatting locale.
       template<typename _FormatContext>
        std::locale
@@ -1405,7 +1410,7 @@ namespace __format
                __i = 12;
            }
          else if (__i >= 100) [[unlikely]]
-           return std::format_to(std::move(__out), _S_empty_spec, __i);
+           return std::format_to(std::move(__out), _S_empty_fs(), __i);
 
          return __format::__write(std::move(__out), _S_two_digits(__i));
        }
@@ -1418,11 +1423,15 @@ namespace __format
          {
            // Decimal number of days, without padding.
            auto __d = chrono::floor<chrono::days>(__t._M_hours).count();
-           return std::format_to(std::move(__out), _S_empty_spec, __d);
+           return std::format_to(std::move(__out), _S_empty_fs(), __d);
          }
 
-         return std::format_to(std::move(__out), _GLIBCXX_WIDEN("{:03d}"),
-                               __t._M_day_of_year.count());
+         auto __d = __t._M_day_of_year.count();
+         if (__d >= 1000) [[unlikely]]
+           return std::format_to(std::move(__out), _S_empty_fs(), __d);
+
+         _CharT __buf[3];
+         return __format::__write(std::move(__out), _S_str_d3(__buf, __d));
        }
 
       template<typename _OutIter>
@@ -1523,7 +1532,7 @@ namespace __format
 
          if (__hi >= 100) [[unlikely]]
            {
-             __out = std::format_to(std::move(__out), _S_empty_spec, __hi);
+             __out = std::format_to(std::move(__out), _S_empty_fs(), __hi);
              __sv.remove_prefix(2);
            }
          else
@@ -1728,8 +1737,8 @@ namespace __format
        };
       }
 
-      [[__gnu__::__always_inline__]]
       // Fills __buf[0] and __buf[1] with 2 digit value of __n.
+      [[__gnu__::__always_inline__]]
       static void
       _S_fill_two_digits(_CharT* __buf, unsigned __n)
       {
@@ -1738,9 +1747,9 @@ namespace __format
        __buf[1] = __sv[1];
       }
 
-      [[__gnu__::__always_inline__]]
       // Returns decimal representation of __n.
       // Returned string_view may point to __buf.
+      [[__gnu__::__always_inline__]]
       static basic_string_view<_CharT>
       _S_str_d1(span<_CharT, 3> __buf, unsigned __n)
       {
@@ -1749,15 +1758,23 @@ namespace __format
        return _S_str_d2(__buf, __n);
       }
 
-      [[__gnu__::__always_inline__]]
       // Returns decimal representation of __n, padded to 2 digits.
       // Returned string_view may point to __buf.
+      [[__gnu__::__always_inline__]]
       static basic_string_view<_CharT>
       _S_str_d2(span<_CharT, 3> __buf, unsigned __n)
       {
        if (__n < 100) [[likely]]
          return _S_two_digits(__n);
+        return _S_str_d3(__buf, __n);
+      }
 
+      // Returns decimal representation of __n, padded to 3 digits.
+      // Returned string_view points to __buf.
+      [[__gnu__::__always_inline__]]
+      static basic_string_view<_CharT>
+      _S_str_d3(span<_CharT, 3> __buf, unsigned __n)
+      {
        _S_fill_two_digits(__buf.data(), __n / 10);
        __buf[2] = _S_chars[__n % 10];
        return __string_view(__buf.data(), 3);