Re: Add more supported primitives in libgccjit IR (was: Shrinking the C core)

[Gregory Heytings <gregory@heytings.org>]

>> Take this equally trivial example:
>>
>> (setq a most-positive-fixnum)
>> (setq a (1+ a))
>>
>> The 'a' object was an integer, and became a bignum.
>
> I understand. I doubt that Emacs native compiler checks this far. 
> However, such checks are definitely doable - integer bounds are not 
> unknown and can certainly be handled.
>

They cannot, certainly not in general.  In the trivial example above the 
compiler could know that 'a' is most-positive-fixnum.  But if you have a 
'1+' somewhere in an actual piece of code, you cannot, except in rare 
cases, know at compile time its argument (whose value may, for example, 
depend on the value of a function argument) is an integer and that adding 
1 to that integer will not overflow.