pure functions cannot be removed, actually: pure vs. total

[Steven Schveighoffer]

On 6/11/18 10:43 AM, Timon Gehr wrote:
> On 11.06.2018 16:39, Timon Gehr wrote:
>>
>> FeepingCreature's example does not really qualify as a do-nothing 
>> loop, because the loop produces a value that you (presumably) later 
>> access.
> 
> Hm, ok. The problem is actually there, but it is not that the 'find' 
> call will get removed, it is that the loop within find's implementation 
> will be seen as doing nothing and producing nothing after inlining, 
> breaking find's postcondition.

Actually, one thing that can be determined statically is that it will 
never return. Essentially, this particular find function (with predicate 
inlining) will fold to:

while(true) {}

Since the final return outside the loop is obviously never reached, and 
the return inside the loop cannot be reached.

So I would assume this would properly be translated to an infinite loop.

I was not expecting that the compiler might eliminate infinite loops 
that it can prove are infinite loops, more like it should eliminate 
calls that trivially can be proven to do nothing based on the signature 
of the function.

-Steve