[PATCH] D145619: extend llvm variables for build flexibility

[Onur via Phabricator via llvm-commits]

ozkanonur added a comment.

> We've generally tried to move away from the direction of having CMake variables to include/exclude parts of the build, and instead encourage users to only build the specific targets they need instead of the all target. LLVM's CMake has support for distributions to make that more ergonomic. LLVM also exports its targets, so Rust could import them and add a dependency on them directly. Do either of those work for you?

We are already specify only required targets to reduce compilation and it's helping a lot. But still, a lot of compilation happens for things that we absolutely don't need in Rust. And, I don't think any of those really helps.

Here is the part where we configure llvm build https://github.com/rust-lang/rust/blob/66a2d6221069e0d08ceacf2a3201600e2092d2e0/src/bootstrap/native.rs#L248-L520

On top of our existing llvm build flow, with the PR I am proposing here, we will be able to do the following:

  diff
  @@ -326,10 +319,18 @@ fn run(self, builder: &Builder<'_>) -> LlvmResult {
               .define("LLVM_ENABLE_LIBEDIT", "OFF")
               .define("LLVM_ENABLE_BINDINGS", "OFF")
               .define("LLVM_ENABLE_Z3_SOLVER", "OFF")
  +            .define("LLVM_ENABLE_TOOLS", "llvm-bcanalyzer;llvm-cov;llvm-dis;llvm-dwarfdump;llvm-dwp;llvm-nm;llvm-objdump")
  +            .define("LLVM_ENABLE_UTILS", "FileCheck")
  +            .define("LLVM_ENABLE_LIBS", "only needed libraries will be here")
  +            .define("LLVM_ENABLE_WARNINGS", enable_warnings)
               .define("LLVM_PARALLEL_COMPILE_JOBS", builder.jobs().to_string())
               .define("LLVM_TARGET_ARCH", target_native.split('-').next().unwrap())
               .define("LLVM_DEFAULT_TARGET_TRIPLE", target_native);

Which will help us(not only us for sure, ref stackoverflow topic: https://stackoverflow.com/questions/71614937/llvm-build-only-selected-tools-or-targets) a lot by reducing compilation times.

I understand the design concerns here. But wouldn't be possible if we inform the developer in docs? Like "this might break builds/tests when incorrectly used". If I am not mistaken llvm already warns such things for some of the flags/variables.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D145619/new/

https://reviews.llvm.org/D145619