[llvm] SelectionDAG: Use qNaN constant if FCANONICALIZE not LegalOrCustom (PR #104564)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > @pawan-nirpal-031 Can we just mul * 1.0 as the default expansion for ISD::FCANONICALIZE, adding a TargetLowering::expandFCANONICALIZE method?
> 
> You cannot do that. A regular fmul does not have the same restrictions as fcanonicalize. A later canonicalize dropping combine could lose the required semantics

So we'd need ISD::STRICT_FMUL or is that still not enough?

https://github.com/llvm/llvm-project/pull/104564