[fpc-pascal]Double-precision recursion

[Marco van de Voort]

> 
> > If BP behaves the same way, we are compatible, and then it is not a bug :-)
> 
> I hope you were joking.  To emulate bugs of obsolete systems is not a
> good way to create the new.

Only partially. BP and Delphi are the reference designs, not GPC, GCC or
C++.
 
> It seems that FPC follows BP in failing to handle the FPU stack.

Are you certain that GPC does it this way? Or does it just forget about
optimalisations, and just generates slow code?

> This failure should be fixed in FPC.


How? My main concerns are:

- Disabling it all together results in severe loss of speed in FPU apps,
sacrificed for the rare recursion-with FP case. 

- Recursion is not flagged as being recursive. Auto recursion can be
checked (calling itself), but a perfect solution is hard.

- Extending FPU stacks might not be possible from user mode under most
OSes. Did you actually check that GCC does this?