https://gcc.gnu.org/g:e99040403f70cd4741f876bffa64259df8ab2199
commit r16-1739-ge99040403f70cd4741f876bffa64259df8ab2199
Author: Tomasz Kamiński <tkami...@redhat.com>
Date: Fri Jun 27 09:50:18 2025 +0200
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:
---
libstdc++-v3/include/bits/chrono_io.h | 37 +++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/chrono_io.h
b/libstdc++-v3/include/bits/chrono_io.h
index 0ffbf06a7ff4..bcf9830fb9e2 100644
--- 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);
