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Chandler Carruth
217c7ba0b2
This builds on the previous work to flesh out more on-demand runtimes building. It adds building of the `libc++.a` archive runtime. A number of changes are required for this to work: - The runtimes build infrastructure needs to support building sources from multiple parts of LLVM rather than a single part. We do this by lifting the root of the runtimes source paths up a level to a common runtimes tree, and installing the runtimes sources below this directory. - Both libc++ and libc++abi runtimes sources need to be installed, and we even need to install some interesting parts of llvm-libc that are used in the build of libc++. - We need to generate the site configuration header file for libc++ from the CMake template. This includes both setting up a set of platform-independent defines and introducing some basic Bazel support for processing the CMake template itself. Doing all of this also exposed some missing features and limitations of the runtimes building infrastructure that are addressed here. One note is that all of this just adds libc++ to the explicit `build-runtimes` command for testing. It doesn't yet trigger automatically building these prior to linking, or configuring any of the other subcommands to automatically use these runtimes. All of that will come in follow-up PRs. Also, this makes the `clang_runtimes_test` ... _very_ slow in our default build configuration. Compiling libc++, even with many threads on a large Linux server requires up to 50 seconds. I'm open to any suggestions on how to handle this, including disabling the test in non-optimized builds. I have some ideas to speed this up, but fundamentally building libc++ is... not cheap. I did look at some of the existing Bazel tools to process the CMake template, but they all seemed significantly more complex than what we need and didn't have broad adoption. Given that, it seemed slightly better to just roll our own given the simple format. Two of the new LLVM patch are currently under review upstream and so hopefully temporary: - https://github.com/llvm/llvm-project/pull/169155 - https://github.com/llvm/llvm-project/pull/169292