[PATCH] libstdc++: Lift locale initialization in main chrono format loop [PR110739]
Tomasz Kamiński
tkaminsk@redhat.com
Fri Jun 27 14:59:01 GMT 2025
This patch lifts locale initialization from locale-specific handling methods
into _M_format_to function, and pass the locale by const reference.
To avoid uncessary computation of locale::classic(), we use _Optional_locale,
and emplace __fc.locale() into it only for localized formatting
(_M_spec._M_localized) or locale::classic() if chrono-spec contains locale
specific specifiers (_M_spec._M_locale_specific).
The later is inprecise, as locale::classic() is only needed for subset of
locale-specific specifiers (%a, %A, %b, %B, %c, %p, %r) while _M_locale_specific
is set for %x,%x and if O/E modifiers are used. However, default output are not
impacted (they use %b), or in case when month (%b) and weekday (%a) is used, the
locale::classic() is be constructed once for non-localized output.
In _M_S we no longer guard quering of numpuct facet, with check that requires
potentially equally expensive construction of locale::classic. We also mark
localized as unlikely.
The _M_locale method is no longer used in __formatter_chrono, and thus was
moved to __formatter_duration.
libstdc++-v3/ChangeLog:
* include/bits/chrono_io.h (__formatter_chrono::_M_format_to):
Compute locale and pass it to specifiers method.
(__formatter_chrono::_M_a_A, __formatter_chrono::_M_b_B)
(__formatter_chrono::_M_c, __formatter_chrono::_M_p)
(__formatter_chrono::_M_r): Accept locale instead of format context.
(__formatter_chrono::_M_subsecs): Call __ctx.locale() directly,
instead of _M_locale and do not compare with locale::classic().
Add [[unlikely]] attributes.
(__formatter_chrono::_M_locale): Move to __formatter_duration.
(__formatter_duration::_M_locale): Moved from __formatter_chrono.
---
Doing this in separate patch, as I wanted to fix overlow warning soon.
I have realized that we have dedicated _Optional_locale that I can use
to avoid calling locale::classic().
Testing on x86_64-linux. OK for trunk when all test passes?
libstdc++-v3/include/bits/chrono_io.h | 71 ++++++++++++++++-----------
1 file changed, 43 insertions(+), 28 deletions(-)
diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index bcf9830fb9e..a25cb9ada01 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -964,10 +964,16 @@ namespace __format
return std::move(__out);
};
+ _Optional_locale __loc;
+ if (_M_spec._M_localized)
+ __loc = __fc.locale();
+ else if (_M_spec._M_locale_specific)
+ __loc = locale::classic();
+
struct tm __tm{};
bool __use_locale_fmt = false;
if (_M_spec._M_localized && _M_spec._M_locale_specific)
- if (__fc.locale() != locale::classic())
+ if (__loc.value() != locale::classic())
{
__use_locale_fmt = true;
@@ -1004,7 +1010,7 @@ namespace __format
{
_CharT __c = *__first++;
if (__use_locale_fmt && _S_localized_spec(__c, __mod)) [[unlikely]]
- __out = _M_locale_fmt(std::move(__out), __fc.locale(),
+ __out = _M_locale_fmt(std::move(__out), __loc.value(),
__tm, __c, __mod);
else switch (__c)
{
@@ -1014,15 +1020,17 @@ namespace __format
break;
case 'a':
case 'A':
- __out = _M_a_A(__t._M_weekday, std::move(__out), __fc, __c == 'A');
+ __out = _M_a_A(__t._M_weekday, std::move(__out),
+ __loc.value(), __c == 'A');
break;
case 'b':
case 'h':
case 'B':
- __out = _M_b_B(__t._M_month, std::move(__out), __fc, __c == 'B');
+ __out = _M_b_B(__t._M_month, std::move(__out),
+ __loc.value(), __c == 'B');
break;
case 'c':
- __out = _M_c(__t, std::move(__out), __fc);
+ __out = _M_c(__t, std::move(__out), __loc.value());
break;
case 'C':
case 'y':
@@ -1058,7 +1066,7 @@ namespace __format
__out = _M_M(__t._M_minutes, __print_sign());
break;
case 'p':
- __out = _M_p(__t._M_hours, std::move(__out), __fc);
+ __out = _M_p(__t._M_hours, std::move(__out), __loc.value());
break;
case 'q':
__out = _M_q(__t._M_unit_suffix, std::move(__out));
@@ -1067,7 +1075,7 @@ namespace __format
__out = _M_Q(__t, __print_sign(), __fc);
break;
case 'r':
- __out = _M_r(__t, __print_sign(), __fc);
+ __out = _M_r(__t, __print_sign(), __loc.value());
break;
case 'R':
case 'X':
@@ -1146,10 +1154,10 @@ namespace __format
return std::move(__out);
}
- template<typename _OutIter, typename _FormatContext>
+ template<typename _OutIter>
_OutIter
_M_a_A(chrono::weekday __wd, _OutIter __out,
- _FormatContext& __ctx, bool __full) const
+ const locale& __loc, bool __full) const
{
// %a Locale's abbreviated weekday name.
// %A Locale's full weekday name.
@@ -1165,7 +1173,6 @@ namespace __format
__string_view(_GLIBCXX_WIDEN(" is not a valid weekday")));
}
- locale __loc = _M_locale(__ctx);
const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
const _CharT* __days[7];
if (__full)
@@ -1176,10 +1183,10 @@ namespace __format
return _M_write(std::move(__out), __loc, __str);
}
- template<typename _OutIter, typename _FormatContext>
+ template<typename _OutIter>
_OutIter
_M_b_B(chrono::month __m, _OutIter __out,
- _FormatContext& __ctx, bool __full) const
+ const locale& __loc, bool __full) const
{
// %b Locale's abbreviated month name.
// %B Locale's full month name.
@@ -1195,7 +1202,6 @@ namespace __format
__string_view(_GLIBCXX_WIDEN(" is not a valid month")));
}
- locale __loc = _M_locale(__ctx);
const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
const _CharT* __months[12];
if (__full)
@@ -1206,17 +1212,17 @@ namespace __format
return _M_write(std::move(__out), __loc, __str);
}
- template<typename _OutIter, typename _FormatContext>
+ template<typename _OutIter>
_OutIter
_M_c(const _ChronoData<_CharT>& __t, _OutIter __out,
- _FormatContext& __ctx) const
+ const locale& __loc) const
{
// %c Locale's date and time representation, for C-locale: %a %b %e %T %Y
// %Ec Locale's alternate date and time representation, for C-locale same as above
- __out = _M_a_A(__t._M_weekday, std::move(__out), __ctx, false);
+ __out = _M_a_A(__t._M_weekday, std::move(__out), __loc, false);
*__out = _S_space;
- __out = _M_b_B(__t._M_month, std::move(++__out), __ctx, false);
+ __out = _M_b_B(__t._M_month, std::move(++__out), __loc, false);
*__out = _S_space;
__out = _M_d_e(__t._M_day, std::move(++__out), 'e');
*__out = _S_space;
@@ -1458,16 +1464,15 @@ namespace __format
return __format::__write(std::move(__out), _S_two_digits(__i));
}
- template<typename _OutIter, typename _FormatContext>
+ template<typename _OutIter>
_OutIter
- _M_p(chrono::hours __h, _OutIter __out, _FormatContext& __ctx) const
+ _M_p(chrono::hours __h, _OutIter __out, const locale& __loc) const
{
// %p The locale's equivalent of the AM/PM designations.
auto __hi = __h.count();
if (__hi >= 24) [[unlikely]]
__hi %= 24;
- locale __loc = _M_locale(__ctx);
const auto& __tp = use_facet<__timepunct<_CharT>>(__loc);
const _CharT* __ampm[2];
__tp._M_am_pm(__ampm);
@@ -1491,10 +1496,10 @@ namespace __format
return std::vformat_to(std::move(__out), _S_empty_spec, __t._M_ereps);
}
- template<typename _OutIter, typename _FormatContext>
+ template<typename _OutIter>
_OutIter
_M_r(const _ChronoData<_CharT>& __t, _OutIter __out,
- _FormatContext& __ctx) const
+ const locale& __loc) const
{
// %r Locale's 12-hour clock time, for C-locale: %I:%M:%S %p
auto __hi = __t._M_hours.count() % 12;
@@ -1511,7 +1516,7 @@ namespace __format
__string_view __sv(__buf, 9);
__out = __format::__write(std::move(__out), __sv);
- return _M_p(__t._M_hours, std::move(__out), __ctx);
+ return _M_p(__t._M_hours, std::move(__out), __loc);
}
template<typename _OutIter>
@@ -1575,9 +1580,9 @@ namespace __format
return __out;
_CharT __dot = _S_dot;
- if (_M_spec._M_localized)
- if (auto __loc = __ctx.locale(); __loc != locale::classic())
+ if (_M_spec._M_localized) [[unlikely]]
{
+ auto __loc = __ctx.locale();
const auto& __np = use_facet<numpunct<_CharT>>(__loc);
__dot = __np.decimal_point();
}
@@ -1587,8 +1592,8 @@ namespace __format
if (_M_spec._M_floating_point_rep)
{
_Str_sink<_CharT> __sink;
- if (_M_spec._M_localized && _M_spec._M_custom_rep)
- std::vformat_to(__sink.out(), _M_locale(__ctx),
+ if (_M_spec._M_localized && _M_spec._M_custom_rep) [[unlikely]]
+ std::vformat_to(__sink.out(), __ctx.locale(),
_GLIBCXX_WIDEN("{1:0.{2}Lf}"), __t._M_ereps);
else
std::vformat_to(__sink.out(),
@@ -1846,7 +1851,6 @@ namespace __format
};
using __formatter_chrono<_CharT>::__formatter_chrono;
- using __formatter_chrono<_CharT>::_M_locale;
using __formatter_chrono<_CharT>::_M_spec;
template<typename _Duration, typename _ParseContext>
@@ -1876,6 +1880,17 @@ namespace __format
return __res;
}
+ // Return the formatting locale.
+ template<typename _FormatContext>
+ std::locale
+ _M_locale(_FormatContext& __fc) const
+ {
+ if (!_M_spec._M_localized)
+ return std::locale::classic();
+ else
+ return __fc.locale();
+ }
+
// Format duration for empty chrono-specs, e.g. "{}" (C++20 [time.format] p6).
template<typename _Rep, typename _Period, typename _FormatContext>
typename _FormatContext::iterator
--
2.49.0
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