[llvm-dev] Codegen pass configs dependent on function attributes?

[Amara Emerson via llvm-dev]

Hi all.

I’m trying to get GlobalISel to work better with LTO. At the moment if you enable it via -fglobal-isel, it only adds the -mllvm -global-isel and related options to the cc1 invocation. With LTO, that doesn’t work as we need to encode codegen options into the bitcode, usually via function attributes.

Does anyone have any ideas on how to achieve this? The only way I can see it working is if we have a unified codegen pipeline for both GISel and SelectionDAG. Then use a function attribute to tell the GISel passes to skip and leave it to FastISel/SelectionDAG which runs afterwards. Likewise, FastISel/SelectionDAG would need to skip the function if it was marked for GISel compilation and we didn’t trigger a fallback.

Amara