type_index::operator<=> should not call the comparison function twice
#3600
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
StephanTLavavej
requested changes
Mar 30, 2023
StephanTLavavej
approved these changes
Mar 31, 2023
| return strong_ordering::equal; | ||
| } | ||
|
|
||
| return _CSTD strcmp(_Tptr->raw_name() + 1, _Right._Tptr->raw_name() + 1) <=> 0; |
There was a problem hiding this comment.
No change requested, note to final reviewer: This raw_name() + 1 looks like 5 squirrels out of 5 🐿️ but it's exactly the correct technique.
__std_type_info_compare()instd_type_info.cpp(internal link) comparesstrcmp(lhs->_DecoratedName + 1, rhs->_DecoratedName + 1).type_info::raw_name()invcruntime_typeinfo.h(internal link) saysreturn _Data._DecoratedName;.- The character at index 0 appears to be a dot; I'm not sure why that's stored, or why
raw_name()exposes this, but the implementation here is correct.
strega-nil-ms
approved these changes
Apr 6, 2023
|
I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
🛸 😸 🛸 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Currently, when two referenced
type_infoare not equal,type_index::operator<=>needs to call__std_type_info_comparetwice (both intype_info::operator==andtype_info::before) to determine the relative order.I think we can optimize
type_index::operator<=>by calling the comparison function at most once. However, it is currently necessary to touch the implementation details oftype_infoand__std_type_info_comparein VCRuntime. This PR is essentially mirroring the implementation of__std_type_info_comparenow.I've filed DevCom-10326599 to request a stable interface for ordering.