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

[James Y Knight via llvm-dev]

I guess I was thinking this was an internal switch, not really expected to
be set by users, so it didn't matter much as long as you could get
something that worked. But given that it is exposed as a driver option,
perhaps I'm just wrong about that.

On Tue, May 12, 2020 at 6:51 PM Amara Emerson <aemerson at apple.com> wrote:

>
>
> On May 12, 2020, at 1:12 PM, James Y Knight <jyknight at google.com> wrote:
>
> If you don't care about being able to select GlobalISel vs SDag separately
> per object file, it'd be a lot simpler to just also pass a flag to the
> linker, right?
>
> I think being able to select per function would actually be a nice feature
> for debugging and bug reducing purposes. The real reason I tried to not go
> for a linker flag was because it would be an exceptional case just for
> GlobalISel. No other codegen option seems to rely on a linker flag (maybe
> I’m wrong here?). Passing it via bitcode just seemed the Right Thing To Do,
> even if it was a pain to implement.
>
> If the consensus is that a one off linker flag for GlobalISel is the right
> way to go, then that’s ok with me.
>
>
> On Tue, May 5, 2020 at 5:48 PM Amara Emerson via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> 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
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>> llvm-dev at lists.llvm.org
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>>
>
>
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