[PATCH] D153667: [HIP]: Add gpu-link-output to control link job creation

Wed Jun 28 07:41:15 PDT 2023

jrbyrnes added a comment.

In D153667#4450724 <https://reviews.llvm.org/D153667#4450724>, @jhuber6 wrote:

> In D153667#4450705 <https://reviews.llvm.org/D153667#4450705>, @jrbyrnes wrote:
>
>> In D153667#4450517 <https://reviews.llvm.org/D153667#4450517>, @jhuber6 wrote:
>>
>>> What's the difference here between this and the existing `--hip-link`?
>>
>> Hi @jhuber6
>>
>> The commit is poorly named, the main purpose is to introduce `-no-gpu-link-output.`
>>
>> We want a way to produce relocatable from source. In terms of the Driver, this means building actions and jobs for phases up to `phases::Assemble`. `-no- gpu-link-output` does this by overriding BuildActions to stop after `phases::Assemble` (similar to `-no-gpu-bundle-output`). `-gpu-link-output` is NFCI. COMGR would be the client of this, and it would be up to COMGR to handle linking of the relocatable.
>>
>> AFAICT, `-hip-link` allows for linking of offload-bundles, so it is conceptually different. We can get (somewhat) close to what we with `-emit-llvm -hip-link`, but that is probably more due to `-emit-llvm`. `-hip-link` by itself produces linker actions / jobs which what we are trying to avoid here.
>
> So, you run the backend and obtain a relocatable ELF, but do not link it via `lld`? If I'm understanding this correctly, that would be the difference between `-flto` and `-fno-lto`, or `-foffload-lto` and `-fno-offload-lto`, AMDGPU always having `-flto` on currently. Also I recall AMDGPU / HIP completely disabling the backend step at some point, so it only emits LLVM-IR.

The whole point of this work is to give hiprtc a way to compile-to-bitcode and optimize sources in a single step, to make (user-passed) flag handling less weird. Since the intent of LTO is to defer this optimization step, I would assume any way we try to use it here would not be correct.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D153667/new/

https://reviews.llvm.org/D153667