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* [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice
@ 2023-04-03 3:12 de34 at live dot cn
2023-04-03 10:05 ` [Bug libstdc++/109383] " redi at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: de34 at live dot cn @ 2023-04-03 3:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109383
Bug ID: 109383
Summary: [QoI] std::type_index::operator<=> should not call
__builtin_strcmp twice
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: de34 at live dot cn
Target Milestone: ---
The current the current implementation of type_index::operator<=> in libstdc++
is the following:
```
strong_ordering
operator<=>(const type_index& __rhs) const noexcept
{
if (*_M_target == *__rhs._M_target)
return strong_ordering::equal;
if (_M_target->before(*__rhs._M_target))
return strong_ordering::less;
return strong_ordering::greater;
}
```
When the two referenced type_info are not equal, the current implementation may
needed to call __builtin_strcmp twice (each in type_info::operator== and
type_info::before).
IIUC whenever it's necessary to call __builtin_strcmp from operator<=>, we
should just call it once and return __builtin_strcmp(...) <=> 0. Perhaps it
would be better to add a member function to type_info for convenience.
It's a bit strange to me that while all implementations I investigated (libc++,
libstdc++, and msvc stl) need to use strcmp/__builtin_strcmp for type_info
comparison in some cases, currently none of them avoids calling it twice from
type_index::operator<=>, although strcmp/__builtin_strcmp is already performing
three-way comparison.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/109383] [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice
2023-04-03 3:12 [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice de34 at live dot cn
@ 2023-04-03 10:05 ` redi at gcc dot gnu.org
2023-04-03 10:35 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2023-04-03 10:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109383
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2023-04-03
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I guess we've all just implemented exactly what the standard says, without
thinking about optimizing it. It's a good idea though, thanks!
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/109383] [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice
2023-04-03 3:12 [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice de34 at live dot cn
2023-04-03 10:05 ` [Bug libstdc++/109383] " redi at gcc dot gnu.org
@ 2023-04-03 10:35 ` redi at gcc dot gnu.org
2023-04-03 10:37 ` redi at gcc dot gnu.org
2023-04-04 0:50 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2023-04-03 10:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109383
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
--- a/libstdc++-v3/include/std/typeindex
+++ b/libstdc++-v3/include/std/typeindex
@@ -87,13 +87,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
strong_ordering
operator<=>(const type_index& __rhs) const noexcept
{
+#if __GXX_TYPEINFO_EQUALITY_INLINE
+# if __GXX_MERGED_TYPEINFO_NAMES
+ return _M_target->name() <=> __rhs._M_target->name();
+# else
+ return __builtin_strcmp(_M_target->name(), __rhs._M_target->name()) <=>
0;
+# endif
+#else // __GXX_TYPEINFO_EQUALITY_INLINE
if (*_M_target == *__rhs._M_target)
return strong_ordering::equal;
if (_M_target->before(*__rhs._M_target))
return strong_ordering::less;
return strong_ordering::greater;
+#endif // __GXX_TYPEINFO_EQUALITY_INLINE
}
-#endif
+#endif // __cpp_lib_three_way_comparison
size_t
hash_code() const noexcept
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/109383] [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice
2023-04-03 3:12 [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice de34 at live dot cn
2023-04-03 10:05 ` [Bug libstdc++/109383] " redi at gcc dot gnu.org
2023-04-03 10:35 ` redi at gcc dot gnu.org
@ 2023-04-03 10:37 ` redi at gcc dot gnu.org
2023-04-04 0:50 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2023-04-03 10:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109383
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For !__GXX_TYPEINFO_EQUALITY_INLINE we need to export a new symbol from the
library, so the patch above doesn't optimize that case.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/109383] [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice
2023-04-03 3:12 [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice de34 at live dot cn
` (2 preceding siblings ...)
2023-04-03 10:37 ` redi at gcc dot gnu.org
@ 2023-04-04 0:50 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-04-04 0:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109383
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-04-04 0:50 UTC | newest]
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2023-04-03 3:12 [Bug libstdc++/109383] New: [QoI] std::type_index::operator<=> should not call __builtin_strcmp twice de34 at live dot cn
2023-04-03 10:05 ` [Bug libstdc++/109383] " redi at gcc dot gnu.org
2023-04-03 10:35 ` redi at gcc dot gnu.org
2023-04-03 10:37 ` redi at gcc dot gnu.org
2023-04-04 0:50 ` pinskia at gcc dot gnu.org
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