[Bug tree-optimization/126016] -frounding-math does not prevent removal of casts

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126016

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
> As a side-note (but existing pattern before looks the same), I wonder if
> there's any two FP formats X and Y with  TYPE_PRECISION (X) > TYPE_PRECISION (Y)
> where "extending" from Y to X can involve rounding, thus not all values in Y
> are exactly representable in X?  What about normalization to NaNs or Infs or
> denormals?

Is what I asked (being not exactly sure, possibly eyeing IBM double double
and/or x87 80bit FP).  GCC supports more than just IEEE FP formats (not to
mention
BF16, FP16 and others).

So, can we generally assume FP widening operations are exact?