Joseph Myers <jos...@codesourcery.com> writes: > On Wed, 4 Jan 2017, Maciej W. Rozycki wrote: > > > AFAIR we deliberately decided not to define a 2008-NaN soft-float > > ABI, and chose to require all soft-float binaries to use the legacy > encoding. > > Soft-float and 2008-NaN are naturally completely orthogonal and the > combination works fine (of course, it doesn't need any special kernel or > hardware support). There's no need to disallow the combination. > > In any case, the soft-fp change is relevant in the hard-float case as > well, to make software TFmode behave consistently with hardware SFmode > and DFmode regarding NaN payload preservation.
I agree here. It is true to say that users are discouraged from using 2008-NaN with soft-float for pre-R6 architectures simply to avoid further fragmentation of software for no real gain. However, for R6 then soft-float is 2008-NaN otherwise we are stuck with legacy-NaN forever. If someone did want to build a system from source with soft-float as 2008-NaN then I see no reason to stop them but I doubt they would and I don't expect the --with-nan GCC configure option to be used in conjunction with --with-float=soft for the same reason. The most likely use of --with-nan is to build a distribution specifically to target an MSA capable system like P5600 or perhaps an M5150 with an FPU. The NaN interlinking work will make these use-cases less important still though I think. Matthew
