[PATCH] D104291: [Debug-Info] strict dwarf for DW_LANG_C_plus_plus_14

Wed Jun 16 22:30:33 PDT 2021

dblaikie added a comment.

In D104291#2823594 <https://reviews.llvm.org/D104291#2823594>, @shchenz wrote:

> In D104291#2821581 <https://reviews.llvm.org/D104291#2821581>, @stuart wrote:
>
>>> There is no `CPlusPlus03` in `LangOptions`, so it is better not to merge `DW_LANG_C_plus_plus_03` support with D99250 <https://reviews.llvm.org/D99250>.
>>
>> Oh - I see, `c++03` is defined in LangStandards.def an alias for `c++98`, as the former essentially consists of bugfixes for the latter. This loosely suggests to me that C++03 implementations are (likely to be / mostly?) conformant to C++98, but that C++98 implementations may not be fully conformant to C++03. Given this alias, it doesn't seem at all clear to me which of DW_LANG_C_plus_plus_98 and DW_LANG_C_plus_plus_03 would be the better choice, if both C++98 and C++03 must share a language tag... but I presume this has been discussed before. (It also doesn't seem clear whether it would be better to model "c++98" as an alias for "c++03".)
>>
>>> Yes, we don't have `DW_LANG_C_plus_plus_17` and `DW_LANG_C_plus_plus_20` in clang for now. I guess this is because clang does not support DWARF 6. DWARF 6 is not officially released? Once DWARF 6 is released and clang starts to support DWARF 6, I think we should add the support for `DW_LANG_C_plus_plus_17` and `DW_LANG_C_plus_plus_20` in the place that this patch changes.
>>
>> New DWARF language codes <http://dwarfstd.org/Languages.php> are published ahead of the release of the next version of DWARF, so that they may be used by implementations without having to wait for new DWARF version.
>>
>> It would therefore make sense to go ahead and add `DW_LANG_C_plus_plus_17` and `DW_LANG_C_plus_plus_20` now, without waiting, but only in the non-strict DWARF mode. (There would be the question of whether it would still make sense in the code to say "DwarfVersion >= 6" given that DWARF 6 would be otherwise unsupported... but I don't have a strong view on that question.)
>
> I think it would be strange to check `DwarfVersion >= 6` if we can not set dwarf version to 6 by anyways. Maybe we can first add the DWARF 6 support to the front end first(Need a wider discussion). This is the patch where `-gdwarf-5` was introduced https://reviews.llvm.org/rG3cb592d6b60c. Seems it was also before DWARF 5 was official released.

Yeah, sounds alright to me. Certainly if we add the version check, there should be test coverage for it - and that can only be done with the flag support for it. (& it's understandable/expected that the flag is not complete from day 1 - same thing is true of language versions (though they get speculative version numbering because the number isn't known until it's released (because it's based on the year) - but even then, once known/added, it still may not be complete because features may not have been implemented yet))

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https://reviews.llvm.org/D104291