[PATCH] D80866: [cmake] Allow llvm_ExternalProject_Add to find CMAKE_SYSTEM_NAME among ${proj}_CMAKE_ARGS

[Kristina Bessonova via Phabricator via llvm-commits]

krisb added a comment.

@compnerd @plotfi thank you for the comments! Sorry if the description looks confusing. I'll try to be more clear.
I'm trying to build something like

  cmake -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_ENABLE_PROJECTS=clang -DLLVM_ENABLE_RUNTIMES=compiler-rt ../llvm

for host Windows under MSVC. This gives me the following error:

  The Clang compiler tool
  
    "J:/llvm-project/build/./bin/clang.exe"
  
  targets the MSVC ABI but has a GNU-like command-line interface.  This is
  not supported.  Use 'clang-cl' instead, e.g.  by setting 'CC=clang-cl' in
  the environment.

`llvm_ExternalProject_Add` sets to use clang-cl when `_cmake_system_name` is equal to Windows, but `_cmake_system_name` is defined only if `-DCMAKE_SYSTEM_NAME` is coming through `CMAKE_ARGS`.
This way perfectly works if runtimes/builtins are built for a known target, because we can pass `RUNTIMES_${target}_CMAKE_SYSTEM_NAME` and it will go to these `CMAKE_ARGS`.

Building for host (default) target there is no way to pass something to the `CMAKE_ARGS`.
I'm thinking... Maybe it would be better to do something similar for the default target and respect `RUNTIMES_${var}` or `RUNTIMES_default_${var}` inside the `runtime_default_target()` of `llvm/runtimes/CMakeLists.txt` (similarly as it is done for `runtime_register_target()`)?
This can bring more flexibility.

I also found another attempt to handle `CMAKE_SYSTEM_NAME` for default target at https://reviews.llvm.org/D73811, but as far as I can see, it has been reverted.

In D80866#2080119 <https://reviews.llvm.org/D80866#2080119>, @compnerd wrote:

> Hmm, this tries to extract `CMAKE_SYSTEM_NAME` from `..._CMAKE_ARGS` if Im reading this correctly.  Why not just say that you must pass `CMAKE_SYSTEM_NAME` via `..._CMAKE_ARGS` rather than `CMAKE_ARGS` and just drop the clause above it?


Hmm. I'm not sure this would work for runtimes/builtins if they are being built for a particular target. This would require to set `CMAKE_SYSTEM_NAME` through `${tagret}_CMAKE_ARGS` and not as `RUNTIMES_${target}_CMAKE_SYSTEM_NAME` which looks as a more preferred way to me.

In D80866#2081482 <https://reviews.llvm.org/D80866#2081482>, @plotfi wrote:

> I am a little confused. Can you show an example of what would go in the cache file that would set what would otherwise be set by `CMAKE_SYSTEM_NAME` ?


Sorry, seems I didn't get your question. Did you mean what vars/options would be set depending on `CMAKE_SYSTEM_NAME`? If so, I'm mostly talking about a compiler (i.e. clang-cl.exe instead of clang.exe).


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  rG LLVM Github Monorepo

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