[PATCH] D99621: [CMake][Compiler-rt] Make it possible to configure standalone compiler-rt without `LLVMConfig.cmake`.

[Dan Liew via Phabricator via llvm-commits]

delcypher added a comment.

In D99621#2659844 <https://reviews.llvm.org/D99621#2659844>, @phosek wrote:

> Do you know what we need `LLVMConfig.cmake` for? Could we remove that dependency altogether? It's not used by any other runtime as far as I'm aware.

I wouldn't want to remove the dependency at this stage as not enough of this new code has been tested (I only tested on macOS). However, I think this patch could used as a stepping stone towards completely removing the dependency on `LLVMConfig.cmake`. If we landed this and did the necessary work to make this new code path work on all the host platforms we care about then I think we could remove the dependency on `LLVMConfig.cmake`. I'd like to see that happen because the requirement makes testing harder and seems unnecessary.

The actions that the new `compiler_rt_mock_llvm_cmake_config` macro take do what I found to be necessary to get the CMake configure to work without having `LLVMConfig.cmake` present with on a macOS host. Basically this seems to be

- Setting `TARGET_TRIPLE`. The build system fails in weird and wonderful ways when this is an empty string. **SHAKES FIST AT CMAKE**.
- Including `AddLLVM.cmake` from the LLVM source tree. It seems we have some CMake code that depends on code in this file.
- Add LLVM's CMake module directory into the CMake module search path.  This necessary for the include of `AddLLVM.cmake` to work.

It may turn out we need to do more than this to support other platforms.


Repository:
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https://reviews.llvm.org/D99621