[llvm] [InstCombine] Support DemandedElts in SimplifyDemandedFPClass (Re-land of #174176) (PR #212183)

[Seung-hyeon Lim via llvm-commits]

kevinlim17 wrote:

Hi @arsenm — gentle ping for a review here. This is the re-land of 
#174176, which you reviewed and merged, rebased onto the current SimplifyQuery-threaded code.

The only behavioral difference from the version you approved: at the lane-count-changing sites (extractelement / shufflevector / insertvalue) I build the demanded-elements mask from the operand type instead of forwarding the result-width mask. That width mismatch is what tripped an APInt out-of-bounds assertion and caused the revert (
#174242) — I reproduced it locally and added a regression test (simplify-demanded-fpclass-demanded-elts-width.ll). Everything else is NFC.

Since you mentioned you'd need this, would you mind taking a look when you get a chance? No rush. (@nikic is also on it as code owner.)

https://github.com/llvm/llvm-project/pull/212183