Summary:
There are a few LLVM projects that produce runtime libraries. Ideally
runtime libraries should be built differently than other projects,
specifically they should be built using the just-built toolchain.
There is support for building compiler-rt in this way from the clang
build. Moving this logic into the LLVM build is interesting because it
provides a simpler way to extend the just-built toolchain to include
LLD and the LLVM object file tools.
Once this functionality is better fleshed out and tested we’ll want to
encapsulate it in a module that can be used for clang standalone
builds, and we’ll want to make it the default way to build compiler-rt.
With this patch applied there is no immediate change in the build.
Moving compiler-rt out from llvm/projects into llvm/runtimes enables
the functionality.
This code has a few improvements over the method provided by
LLVM_BUILD_EXTERNAL_COMPILER_RT. Specifically the sub-ninja command is
always invoked, so changes to compiler-rt source files will get built
properly, so this patch can be used for iterative development with
just-built tools.
This first patch only works with compiler-rt. Support for other
runtime projects will be coming in follow-up patches.
Reviewers: chandlerc, bogner
Subscribers: kubabrecka, llvm-commits
Differential Revision: http://reviews.llvm.org/D20992
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273620 91177308-0d34-0410-b5e6-96231b3b80d8
