Add a mechanism to permit plugins running code between optimizations and
the back-end passes. Implement this through the LLVM plug-in mechanism
to make permit plugins to be written independently of the front-end.
The primary motivation for this point is TPDE-LLVM, which substitutes
the LLVM back-end (optionally falling back to it for unsupported IR). We
have been distributing a Clang patch; but requiring a custom-build
toolchain is impracticable for many users.
Front-end adjustments will follow as separate patches.
Pull Request: https://github.com/llvm/llvm-project/pull/170846
cd806d7e76