[cfe-dev] Oldest supported libstdc++

[Shoaib Meenai via cfe-dev]

We enforce libstdc++ >= 5.1 when building LLVM (in order for C++14 support), and I would imagine that same minimum applies to being able to run the built binaries. See https://github.com/llvm/llvm-project/blob/main/llvm/cmake/modules/CheckCompilerVersion.cmake (the libstdc++ version is specifically checked towards the end of that file).

On 4/16/21, 2:26 PM, "cfe-dev on behalf of David Blaikie via cfe-dev" <cfe-dev-bounces at lists.llvm.org on behalf of cfe-dev at lists.llvm.org> wrote:

    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
    >> > _______________________________________________
    >> > cfe-dev mailing list
    >> > cfe-dev at lists.llvm.org
    >> > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev 
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