Re: [PATCH][4.3] Deprecate -ftrapv

[Robert Dewar <dewar at adacore dot com>]

> Robert Dewar write: 
> > 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".
>
> *sigh*  The possibility of using GCC's -ftrapv support to implement
> overlow exceptions in Ada was mentioned in this thread.  There's no
> requirement that -ftrapv do anything other than crash when overflow
> occurs.  A -ftrapv that did everything you've said you wanted, performed
> faster and caught 100% of overflows 100% reliabily wouldn't necessarily be
> better for Ada. 

Why not?

> On the 32-bit IA-32 platform, either the JO instruction
> or a INTO instruction could legitimately be used to provide a more
> optimal implementation of -ftrapv.  Even the JO instruction could do
> nothing more than jump to abort().

Yes, and that is what we would want for Ada, so I am puzzled by your
sigh. All Ada needs to do is to issue a constraint_error exception,
it does not need to know where the exception came from or why except
in very broad detail.
> 					Ross Ridge

there is some miscommmunication here, and I can't figure out what it is!