InstCombine: Filter reported classes from SimplifyDemandedFPClass (#176885)
When reporting the known class result, apply the demanded mask to
filter out rejected cases. This can simplify known-source checks
further up the call stack. There are a few improved test diffs. This
does not yet try to clean up now redundant result checks.
Do an initial brute-force scope_exit to ensure these are cleared.
Later we can do a better job by pushing this into the individual
instruction cases.