[llvm-branch-commits] [RFC][Clang] Allow plugins to hook into back-end (PR #165257)

[Stefan Gränitz via llvm-branch-commits]

weliveindetail wrote:

> The front-end should be in full control of which back-end it uses

Yes, as a pure backend selection feature in the frontend, this is fair. It doesn't fit my use-case where a pass plugin requires a different/modified codegen backend, but that might just be a different story. I think we should wait for feedback from clang maintainers then.

> While I think that our current addPassesToEmitX + PM.run API is not good, it's there and used.. a new API would need to be picked up by front-ends and it's not very likely that we'd deprecate the existing API?

The switch to the new pass manager might actually be a good opportunity to revisit the interface. It follows the same approach to split populate and run, but it wouldn't need to be exposed that way. [llc implements it here](https://github.com/llvm/llvm-project/blob/4254f2777cd3dccf160c79e36ce091d58b4e99c1/llvm/tools/llc/NewPMDriver.cpp#L88) and calls into TargetMachine's new `buildCodeGenPipeline()` callback.

https://github.com/llvm/llvm-project/pull/165257