[llvm] [GlobalISel][LLT] Introduce FPInfo for LLT (Enable bfloat, ppc128float and others in GlobalISel) (PR #155107)

[Ryan Cowan via llvm-commits]

HolyMolyCowMan wrote:

There are lots of places that use legalizer mutations to modify types. Many of these call `changeElementTo` under the hood. This used to be fine, as there was no different types. This now causes a lot of issues in different parts of the codebase as types are changed to generic scalars, when the intent was just to change the size. This causes some optimisations/selection attempts to fail.

I've included an attempt at solving this issue in the attached patch. Please note the changes to `changeElementSize`. We need to include some kind of functionality like this for floating point values as it is otherwise very cumbersome to change the size of floating point types without first checking the type of floating point number used & building the correct type.

[modify-size.patch](https://github.com/user-attachments/files/24393593/modify-size.patch)

https://github.com/llvm/llvm-project/pull/155107