[clang] [CIR][X86] Add CIR codegen support for fpclass x86 builtins (PR #172813)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> > @jacquesguan I've just posted #174670 to handle the constant folding. Can you try that with your patch to verify that it handles the 'all ones' case without the need for extra handling?
> 
> I notice that you have a new pr #174861 to implement the constant folding of castop. I rebase it in my local env, it doesn't fix 'all ones' case. The reason is that we do op fold during cir-canonicalize pass, which is a cir pass after codegen. So we still can't get the all ones constant in codegen.
> 
> One solution might be that we just generate the `andop` with true mask and also fold it in cir-canonicalize. What's your point?

@jacquesguan I reimplemented the folding based on feedback in the review for #174670 and in the process split it up into multiple PRs, the last of which has not landed yet. The final PR (https://github.com/llvm/llvm-project/pull/175675) should fix the all ones case. I observed a change in behavior with an earlier builtin handler that was checking for all ones.

https://github.com/llvm/llvm-project/pull/172813