Ada front-end depends on signed overflow

[Paul Schlie]

> From: Georg Bauhaus <bauhaus@futureapps.de>
>> Paul Schlie wrote:
>> - How is it necessary or desirable to define that the result is undefined
>>   vs. being target defined?
> 
> What does C say about how a target performs an instruction?
> And why shouldn't GCC take advantage of this?

- In essence I believe the difference is consistency. Where although a
  target implementation defined behavior seems no more clear, it implies
  that the semantics of an operation in question should directly result
  from it's target implementation, and any corresponding compile-time
  constant propagation optimizations should be consistent with their
  otherwise run-time computed counterparts, as otherwise they will be
  needlessly and arguably erroneously inconsistent; which an undefined
  behavior would seem to allow, without providing any tangible benefit.