[Analysis] Introduce a new InstructionCost class

Hi,

For people who are interested I have posted an initial patch on phabricator to

introduce a new class for the instruction cost:

https://reviews.llvm.org/D91174

This follows on from a proposal I posted earlier to the LLVM dev mailing list.

The initial patch doesn’t change all the interfaces in one go, but it does introduce

the class and future patches can migrate more of the code over to use the new

class.

Please feel free to comment on the patch!

Kind Regards,

David Sherwood.