[llvm-dev] TargetMachine vs LLVMTargetMachine

[Eric Christopher via llvm-dev]

On Tue, Oct 3, 2017 at 8:54 AM Hal Finkel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> On 10/02/2017 10:57 PM, Matthias Braun via llvm-dev wrote:
>
> The distinction between the LLVMTargetMachine and TargetMachine classes
> has become somewhat muddy recently. So I created:
>
> https://reviews.llvm.org/D38482
>
> to clean things up. During review it was noted that we may rather merge
> the two instead which looks like this:
>
> https://reviews.llvm.org/D38489
>
> We really should choose one of the two over the status quo. Some points
> for the discussion:
>
> - I am not aware of any target that is actually implementing TargetMachine
> only but not LLVMTargetMachine (I assume the C backend used to do it before
> it was removed)
> - Even when merging the two, I believe it is still possible to implement a
> target without linking to lib/CodeGen by returning nullptr for the various
> methods related to CodeGen.
>
>
> If this is true, then it seems like we don't lose anything from doing this
> (and the code gets cleaner). We don't currently have anything in tree that
>

This was my suggestion of yesterday.


> motivates the current split. It does seem useful to retain the ability to
> have a direct-from-the-IR backend (mostly for translation into another IR).
>
>
I'm dubious of this need, but as long as it doesn't add any overhead to the
resultant code I'm good.

-eric


>  -Hal
>
>
> - The split would give some notion of an internal CodeGen interface and an
> external interface visible to frontend/middleend etc.
> - The code gets simpler when merging the two and we have to
> document/explain less.
>
> - Matthias
>
>
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>
>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
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