[llvm] IVDescriptors: cut wasteful FAnyOf checking (NFC) (PR #118393)

[David Sherwood via llvm-commits]

david-arm wrote:

> > This effectively makes FAnyOf dead, right? In that case it should be removed and `IAnyOf` -> `AnyOf`?
> 
> There is still FAnyOf matching with FCmp, and IAnyOf matching with ICmp, so I don't think it can be removed. See getReductionOpChain's call to getOpcode for example.
> 
> See also the return statement in isAnyOfPattern:
> 
> ```
>   return InstDesc(I, isa<ICmpInst>(I->getOperand(0)) ? RecurKind::IAnyOf
>                                                      : RecurKind::FAnyOf);
> ```

I agree with @fhahn. Looking at the code after this patch lands there is no logical reason for distinguishing between IAnyOf and FAnyOf. You should be able to condense the two RecurKind types into a single AnyOf I think. When creating `InstDesc` you just always initialise it with `RecurKind::AnyOf` and in `isAnyOfRecurrenceKind` just check for `AnyOf`.  It looks like the only place we actually distinguish between the two is in `RecurrenceDescriptor::getOpcode`, but you can probably infer the opcode from the type?

https://github.com/llvm/llvm-project/pull/118393