[cfe-dev] Oldest supported libstdc++

[David Blaikie via cfe-dev]

On Fri, Apr 16, 2021 at 2:10 PM Richard Smith <richard at metafoo.co.uk> wrote:
>
> On Fri, 16 Apr 2021 at 13:27, David Blaikie <dblaikie at gmail.com> wrote:
>>
>> Was there any oldest supported libstdc++ version previously documented?
>
>
> I think this might be the only place we talk about it: https://clang.llvm.org/docs/Toolchain.html#libstdc-gnu
>
> "Clang supports a wide range of versions of libstdc++, from around version 4.2 onwards, and will implicitly work around some bugs in older versions of libstdc++."
>
>> How's this compare (is there any insight to be gained by such
>> comparison?) with the oldest supported gcc?
>
>
> Do you mean the oldest GCC that we support as a host compiler? That's GCC 5.1 (https://llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library), so bumping our minimum libstdc++ to 4.9 brings these closer together.

yeah, though fair point that it's a pretty significant distinction
between what you need to compile LLVM versus what you need to run/link
to LLVM, so it's not a huge indicator of much. But good to know.

Agreed re: Google. Not sure about the issue Erich mentions re: Redhat.
it's a long time to keep these workarounds around... though not sure
how much they cost us to keep either. Doesn't seem likely to be hugely
costly?

>
>> On Fri, Apr 16, 2021 at 1:01 PM Nathan Sidwell via cfe-dev
>> <cfe-dev at lists.llvm.org> wrote:
>> >
>> > I came across a couple of clang workarounds for old libstdc++ issues.
>> > One of them seems good for removal, by documenting the oldest supported
>> > libstdc++ as 4.9, which is what https://reviews.llvm.org/D100465 does.
>> >
>> > The other is more recent, and proposing to keep that (see
>> > https://reviews.llvm.org/D100469)
>
>
> Here are a few more that we may be able to remove:
>
> https://github.com/llvm/llvm-project/blob/main/clang/lib/Parse/ParseDecl.cpp#L6568
> https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp#L859
> https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp#L1524
>
>>
>> > any objections on the oldest libstdc++ version?
>> >
>> > nathan
>> >
>> > --
>> > Nathan Sidwell
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