[LLVMdev] [RFC] Stripping unusable intrinsics

[Chris Lattner]

On Dec 23, 2014, at 10:28 AM, Chris Bieneman <beanz at apple.com> wrote:
>>> It should be straight-forward to have something like LLVMInitializeX86Target/RegisterTargetMachine install the intrinsics into a registry.
>> 
>> I tried doing that a few years ago. It’s not nearly as easy as it sounds because we’ve got hardcoded references to various target intrinsics scattered throughout the code.
> 
> I was just writing to say exactly this. There are a number of ways we could work toward something like this. I’m completely in favor of a world where Intrinsics are properties of the targets and don’t leach out, however today they do in a lot of places.

What are the specific problems here?  Anything that does an equality comparison with the IntrinsicID can be changed to do strcmp with the name.  That would handle the one-off cases like InstCombiner::SimplifyDemandedUseBits in InstCombine.

The other cases in InstCombine could be handled similarly, but may be better handled by adding a intrinsic behavior query APIs to the intrinsic registry, or would be better handled (eventually) by adding new attributes to the intrinsics themselves.

-Chris
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