[LLVMdev] [PATCH][RFC] Add llvm.codegen Intrinsic To Support Embedded LLVM IR Code Generation

[dag at cray.com]

Tobias Grosser <tobias at grosser.es> writes:

>> Why is this a requirement?  I think it's completely unrealistic to
>> expect to be able to do this without driver changes.
>
> It is very convenient for users and it is perfectly possible with the
> llvm.codegen intrinsic. So why going for something less comfortable
> and more complicated to implement, if the problem can really be solved
> in a nice and simple way?

It's not a nice and simple way as Evan and others have explained.

> Also, driver changes cause a maintenance nightmare. We really should
> not accept driver changes in clang, that are only needed for some
> external optimizers. Especially in case of experimental optimizer
> projects are created, requiring for each of them driver changes adds
> _unnecessary_ overhead.

We absolutely SHOULD enhance the existing drivers to handle
heterogeneous platforms.  Thaty need is not going away.  llvm.codegen is
a very specific solution to a very specific problem, one that I believe
_is_ going to go away relatively soon.

>> If you don't want to change clang, then you'll need an external wrapper
>> driver to call all the relevant tools.
>
> Again, this adds significant overhead which, I think, could be avoided
> easily. 

What overhead?  Developer time.  Yes, work will have to be done.  But
it's necessary work.

                              -Dave