Re: [PATCH][4.3] Deprecate -ftrapv

[Robert Dewar <dewar at adacore dot com>]

Ross Ridge wrote:
> Robert Dewar write:
> > Usually there are ways of telling what is going on at a sufficiently
> > low level, but in any case, code using the conditional jump instruction
> > (jo/jno) is hugely better than what we do now (and it is often faster
> > to usea jo than into).
>
> My point is that using INTO or some other processor's overlow mechanism
> that requires operating system support wouldn't necessarily be better for
> Ada, even it performs better (or uses less space) than the alternatives.
> Having the program crash with a vague exception would meet the
> requirements of -ftrapv, but not Ada.

But, once again, using the processor specific JO instruction will be
much better for Ada than double length arithmetic, using JO does not
involve a "program crash with a vague exception". Similarly, testing
the sticky overflow flag on Power is also quite reasonable.
> 					Ross Ridge