Non-flow-control logical tests

[Dan Sugalski]

Okay, let me preface this by saying it is, in large part, directly 
because of my current work project, so it feels a bit self-serving. 
(One of the reasons I haven't just put them in)

But...
Right now the only good way to find out if a value is true or not is 
to do something like:

 $I0 = 1
 if $P0, done
 $I0 = 0
 done:
and look in $I0 for the result. This is OK, but if you're dealing 
with a language with relatively primitive views of logical operations 
(i.e they return 0 or 1) you end up with a *lot* of these little code 
snippets when evaluating something like:

   if ((foo or bar) and ((x1 >= 12) or (x2 < 15) or (x5 and x6 and 
x7)) goto somewhere

(And yes, that's close to a real code snippet. Feel my pain here :) 
Not a huge deal to translate, but once you hit 30K basic blocks in a 
sub the register coloring algorithm really gets unhappy and dies an 
unpleasant death after an hour or so.

Anyway, because of it I'm pondering non-flowcontrol logical ops. That 
is, something like:

   istrue I0, P5        # I0 = 1 if P5 is true
   isgt I0, P5, P6      # I0 = i if P5 > P6
The or/and/xor/not ops don't really need alternate versions, since:
   isor I0, P5, P6
can be done with
   or P4, P5, P6
   istrue P4
so there doesn't seem to be much pressure there.
Given the semi-self-serving nature of these I think some discussion's 
in order first.
--
                                        Dan

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Dan Sugalski                          even samurai
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