Greenwashing

[Bruce Carneal]

On Friday, 29 May 2020 at 12:52:06 UTC, Andrei Alexandrescu wrote:
> On 5/28/20 7:35 PM, Adam D. Ruppe wrote:
>> On Thursday, 28 May 2020 at 22:56:15 UTC, Andrei Alexandrescu 
>> wrote:
>>> Large projects separate compilation inter-procedural analysis 
>>> does not scale yadda yadda yadda.
>> 
>> We need to stop making assertions without measurements. This 
>> may be true, but it needs to be based on empirical fact - the 
>> one thing we should notice is compile speed is sensitive to 
>> surprising things and not to other surprising things....
>
> Needs to be based in sound analysis, not measurements, as a 
> quadratic is not scalable regardless of the constant. When I 
> was in the field there was no escaping this fact, and all 
> interprocedural analyses that did anything interesting were 
> limited to programs a few KB in size.
>
> Perhaps things have improved since, and it would be great if 
> they did. Timon should know about this.

Of course, we need both theory and the empirical.  O(N lg N) may 
be the upper limit of what is countenanced for performance work, 
a useful filter, but the constants, as Andrei knows better than 
most, can really get you.  Big-Oh is helpful but it is too loose 
to be the final word.

Additionally, the empirical can help you catch big-Oh analysis 
errors.