[PATCH] D137024: [compiler-rt] Switch from llvm-config to find_package(LLVM)

Thu Nov 3 04:14:32 PDT 2022

mstorsjo added a comment.

In D137024#3901342 <https://reviews.llvm.org/D137024#3901342>, @mgorny wrote:

> Thanks! Let's hope it works this time.

FYI, this broke builds of mine (https://github.com/mstorsjo/llvm-mingw/actions/runs/3382275510/jobs/5617040099), but I just need to change/add a workaround so I don't think we need to revert it due to that.

My setup is that I'm building LLVM with `-DLLVM_INSTALL_TOOLCHAIN_ONLY=TRUE`, so it only installs toolchain binaries, but not files like LLVMConfig.cmake or the individual LLVM libraries. I then use this new toolchain to (cross-)build compiler-rt (and all other runtimes), to bootstrap new cross-sysroots.

Previously, the compiler-rt cmake files would pick up a distro-installed `llvm-config` and due to that, add systemwide install directories into the mix when building compiler-rt (for a potential cross target!). I worked around that by passing `-DLLVM_CONFIG_PATH=""` to make sure that it doesn't pick up an unrelated `llvm-config` binary. (https://github.com/mstorsjo/llvm-mingw/commit/3b96433cdf89e8ef444c6669254b386229dbddd9) Now after this change, it can again find unrelated `LLVMConfig.cmake` from the surrounding distribution, which ends up adding unexpected include directories. This time I'm working around it with https://github.com/mstorsjo/llvm-mingw/commit/486dcf32274ae6c3e0ea7916fd1e88a58742b7ca, by adding `-DCMAKE_FIND_ROOT_PATH=$PREFIX/$arch-w64-mingw32 -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY`, so that cmake won't find unrelated cmake files.

These workarounds are fine for me, but I wonder if it would be useful with a more direct cmake option to tell it not look for these files at all. I'm building out of the git monorepo checkout, so whatever source files and cmake scripts can be found there, but other LLVM build products (individual libraries etc) aren't available, and cmake shouldn't try to venture out on its own to find them in unexpected places.

@phosek - How does this work for general cross compilation of compiler-rt btw - when building compiler-rt for a cross target, but it finds `LLVMConfig.cmake` for the current host, and ends up including headers (and possibly more) from there? (If the include directory added from `LLVMConfig.cmake` is something like `/usr/include/llvm-15` it's probably benign, but in the msys2 cases, the llvm headers are installed in the toplevel include directory, so it ended up adding the equivalent of `-I/usr/include` in something which is supposed to be a cross build.) I can manually mitigate this with the `-DCMAKE_FIND_ROOT_PATH*` options in my case, but I don't see e.g. `llvm-project/llvm/runtimes` doing this anywhere?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137024/new/

https://reviews.llvm.org/D137024