[llvm-dev] (Thin)LTO llvm build

[Teresa Johnson via llvm-dev]

On Thu, Dec 22, 2016 at 2:45 AM, Carsten Mattner <carstenmattner at gmail.com>
wrote:

> On Wed, Dec 21, 2016 at 6:10 PM, Teresa Johnson <tejohnson at google.com>
> wrote:
>
> > Or maybe it is picking up a different libstdc++ from somewhere else on
> your
> > system?
> > Here's the check from the cmake file:
> >
> >     # There doesn't seem to be an easy way to check the library version.
> Instead,
> >     # we rely on the fact that std::set did not have the allocator
> constructor available
> >     # until version 4.9
> >     check_cxx_source_compiles("
> >             #include <set>
> >             std::set<int> s = std::set<int>(std::allocator<int>());
> >             int main() { return 0; }"
>
> I cannot make g++ 6.2.1 fail to build the test snippet with
> or without the archlinux-default/custom CXXFLAGS and LDFLAGS.
>
> Time to find the real error and what's happening.
>
> > LLDB_USING_LIBSTDCXX_4_9)
> >
> > So the version check isn't precise, but unless libstdc++ 6.2.1 doesn't
> have this
> > interface available, which seems unlikely, something else is going wrong.
>
> That seems risky to ignore then. I guess I'll postpone the rebuild until
> this
> can be resolved/explained.
>
> Also because ideally I want to do it that way, and it's a goal for a
> future default
> build config of llvm as discussed recently here, I'd prefer to build
> and then use
> the in-tree libc++. But it doesn't seem like -DLLVM_ENABLE_LIBCXX has that
> effect. Shouldn't it or if not why can't it? I would certainly welcome
> and find natural
> that the in-tree libc++ is used when LLVM_ENABLE_LIBCXX=ON. The need for
> a pre-built and installed libc++ is less practical.
>

I'm really not sure, and I don't build or use libc++ myself. I was hoping
someone else would answer this part, so maybe fork it into a different
thread about that specifically so that the question gets more visibility.

Teresa



-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
<(408)%20460-2413>
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