CMake config: Fix usage issues

[dg0yt]

Don't try to create targets if they already exist. (Not just theory: Multiple calls to find_package occur with transitive dependencies.)

Add missing link libs for CUDA and OpenCL, mirroring the setup during the build.

Don't link OpenMP when it wasn't used at build time. Fixes static linkage with AppleClang.

[dg0yt]

Tested with the standalone example in vcpkg.

[dg0yt]

Let me also adopt find_dependency. This is useful even when eventually switching to exported CMake config.

[dg0yt]

The point of find_dependency, and of the changes to find_library here, is to allow for the CONFIG search mode of find_package: If a config package returns not-found, the search is to continue in other locations. It the original find_package wasn't REQUIRED, the config package must not raise an immediate fatal configuration failure.

That's why a config package must not use find_package or find_library with REQUIRED. All checks must take place before all non-reversible effects such as add_library, or even setting cache variables.

CMake can provide quite useful diagnostics for why it didn't consider a particular config package.

[dg0yt]

I added the if, but I didn't add indent to the inner code. If desired, I can change the inner lines, too.

[ggerganov]

Yes, let's indent.

[dg0yt]

Should this go to GGML_BLAS_INTERFACE_LINK_LIBRARIES/OPTIONS instead?

[dg0yt]

Gentle ping.

[ggerganov]

These are no longer "required" - isn't this a problem? My understanding is if we can't find a required dependency, CMake should stop immediately and report the error.

[dg0yt]

These are no longer "required" - isn't this a problem?

No.

My understanding is if we can't find a required dependency, CMake should stop immediately and report the error.

No. CMake config files are used via find_package().

• Nothing is required unless the consumer said REQUIRED.
• A single failing package in CONFIG mode is the end for the current config, but not the end of the search.

And find_dependency (without REQUIRED!) is the missing link.

• It knows how to deal with the consumer's REQUIRED.
• It logs why it didn't consider a particular config (with regard to transitive dependencies).

This is standard CMake.
https://cmake.org/cmake/help/latest/module/CMakeFindDependencyMacro.html

[ggerganov]

Ok, let's give this a try - will merge after the indentation.

I don't understand most of the changes here, but you seem to be fluent in this stuff. If something breaks will ping you.

[ggerganov]

Yes, let's indent.

[dg0yt]

I don't understand most of the changes here, but you seem to be fluent in this stuff. If something breaks will ping you.

Okay. FTR the experience is from packaging in vcpkg (static and dynamic, multi-config/MSVC, multi-platform, pkgconfig and cmake...). The ultimate goal is to use proper export of CMake config.

And to have the fixes and the testing here. The changes to test static libs are waiting (https://github.com/dg0yt/ggml/pull/1/files), but it won't be green until some problems are resolved.