value range propagation for _bitwise_ OR

["Jérôme M. Berger"]

Steven Schveighoffer wrote:
> Jérôme M. Berger Wrote:
> 
>> Steven Schveighoffer wrote:
>>> When we're talking about the difference between O(1) and O(lgn), I'll
>>> take accuracy over speed in my compiler any day.
>> 	And when we're talking about the difference between 10s and 55s for
>> a minimal loss of accuracy, which will you take? Especially if the
>> accuracy loss is less than is lost elsewhere (due to holes in the
>> ranges).
> 
> Really?  You rebuilt the compiler with your range propagation algorithm and verified that it adds 10 seconds versus an accurate one that adds 55s?  How much time did the compiler spend to compile?  I'd hazard to guess that a code base that adds 10s worth of your algorithm takes at least a few hours to compile.  Is 55s that bad at that point?
> 
> Again, if it takes the compiler an extra insignificant amount of time to be more accurate, I'm all for accuracy over speed when you get down to that level of insignificance.  I'd say the point of pain has to be at least 10% of the compile time before it makes any sizable difference.
> 
	My point is that if you always choose an algorithm that is 5 to 6
times slower just because it brings extra precision which you may
not really need, then you will wind up with a compiler that is 5 to
6 times slower than it needs to be. Sure the difference on *one*
function is not great in absolute terms, but if you make the same
choice for *all* functions, then where do you go?

		Jerome
-- 
mailto:jeberger at free.fr
http://jeberger.free.fr
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