[cfe-dev] RFC: Place libs in Clang-dedicated directories (affects openmp, libcxx, libunwind, compiler-rt)

[Brian Cain via cfe-dev]

On Mon, Feb 25, 2019 at 4:17 AM Petr Hosek via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On Wed, Feb 20, 2019 at 6:14 PM Joel E. Denny <jdenny.ornl at gmail.com>
> wrote:
>
>> My alternative to LLVM_ENABLE_PER_TARGET_RUNTIME_DIR is the preceding
>> bullets.  In other words, you wouldn't need to specify
>> LLVM_ENABLE_PER_TARGET_RUNTIME_DIR because it would effectively be
>> always on (except the directories might be different than now if the
>> version locking issue is important, as noted above).  Is that what
>> you're asking?
>>
>
> That would be my preference. I always hoped that
> LLVM_ENABLE_PER_TARGET_RUNTIME_DIR would eventually become the default. It
> would be nice to finish the Darwin support so we can completely deprecate
> the old layout, but I don't know how far along beanz is in his effort. We
> should also update openmp to stop using the custom Android-specific runtime
> layout.
>
> There's also the unresolved question of where should libc++ headers and
> libraries go. Currently, in LLVM_ENABLE_PER_TARGET_RUNTIME_DIR we use the
> resource dir, but some people expressed the opinion that we shouldn't be
> using these for libc++ et al. since they're not version-locked to Clang.
> This is different from what GCC does (e.g. GCC would use
> $prefix/lib/gcc/x86_64-linux-gnu/8/libstdc++.a) and it's one of the reasons
> why I used the resource dir for libc++ et al. when implementing
> LLVM_ENABLE_PER_TARGET_RUNTIME_DIR.
>
> So concretely, today LLVM_ENABLE_PER_TARGET_RUNTIME_DIR uses the following
> layout:
>
> headers: $prefix/lib/clang/$version/include(/$triple)(/c++/v1)
> libraries: $prefix/lib/clang/$version/$triple/lib/$name.$ext
>
> The alternative that doesn't use resource dir for libc++ would be the
> following:
>
> compiler-rt:
>   headers: $prefix/lib/clang/$version/include
>   libraries: $prefix/lib/clang/$version/$triple/lib/$name.$ext
>
> libc++, libc++abi, libunwind:
>   headers: $prefix/include/c++/v1
>   libraries: $prefix/lib/$triple/$name.$ext
>

Petr,

One thing I was considering tinkering with was producing additional,
msan-enabled libs for libc++/libc++abi in test-release.sh and changing
Clang's driver to look for those first when "-fsanitize=memory" and
"GetCXXStdlibType(Args) == ToolChain::CST_Libcxx".  This should give folks
who want to use MSan a much easier path to do so.  Does this make that
design change easier?  Say, if libc++/abi were found by looking in
"$prefix/lib/$triple/$name-msan.$ext" ?

>

-Brian
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