[PATCH] D131052: [CMake] Allow setting the location of host tools with LLVM_NATIVE_TOOL_DIR

Fri Aug 19 06:15:24 PDT 2022

mstorsjo added a comment.

In D131052#3731894 <https://reviews.llvm.org/D131052#3731894>, @sammccall wrote:

> FWIW I have no idea: in principle this makes sense, but I don't use such a configuration and don't have a clear idea of what people who do use it want.

Thanks for having a look and discussing the matter! FWIW, my current cross compilation script does something like this: https://github.com/mstorsjo/llvm-mingw/blob/master/build-llvm.sh#L176-L195 All of those lines could be changed into setting this one option.

When there's more native tools added, I want to keep this in sync to avoid needless recompilation of those tools - which is kinda burdensome in the current setup - while with this option, we'd only need to set one option and be done with it. (As long as everything else works, if there's a new tool that I haven't got hooked up, it "only" makes things slower to build.)

> It also adds significant CMake complexity: e.g. clang-pseudo-gen now has 30 lines just to support the non-default "native tools" configuration, and this is duplicated for each tool. Maybe this could be made cheaper by sharing more of this logic in a separate place, but we should probably only add it at all if this really is helping someone significantly.
>
> (Lines of CMake logic are extremely expensive to maintain IME: tooling and diagnostics are poor, there are no tests, there are too many configurations to reason about, interacting components are not documented, the language is inherently confusing and many of us that maintain it have only a rudimentary understanding)

This is a very good point indeed.

Most of the boilerplate for setting up clang-pseudo-gen and clang-tidy-confusable-chars-gen is identical, so those could probably be merged into a macro (hiding all the cross/native complexity entirely from the business logic, just like for tablegen) - but the complexity is still there. (It would end up in at least three cases; tablegen, llvm-config and in a generic-buildtime-tool-macro.)

On the topic of "really is helping someone significantly" - if we wouldn't have the burden of existing users using the existing options (for setting the path to each tool individually), picking this new option is a nobrainer - doing the same thing but in a much less annoying way. But since we have existing users with the existing options (which would need to be kept for some time transitionally), it's much less clear cut whether it's a "significant" improvement.

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https://reviews.llvm.org/D131052