SPICE "ideal" diodes follow the Shockley function without series resistance or reverse recovery. That's as reasonably "ideal" as one should hope to expect from any diode you'd want to simulate.
An ""ideal"" diode (meaning, zero forward drop, zero reverse current) would never simulate because it's an absolute discontinuity: unrealistic both in regards to real diodes, and to numerical solutions that depend upon having continuous derivatives to produce a solution.
(You can make arbitrarily "ideal" diodes by using a switch (both in simulation and real life), but the difference is, it takes time to decide whether voltage is positive, or current is negative; which leads to finite forward and reverse recovery times. So there's still mathematical continuity on a fine enough timescale -- which SPICE needs to dip down to, to make sure it's getting it right -- which makes this okay. Basically, what happens at DC is meaningless; what happens at AC is where things get interesting.)
Tim