[fpc-devel] [Suggestion] Enumeration range-check intrinsic

[J. Gareth Moreton]

In the meantime, I've extended your AS/IS patch over here 
<https://bugs.freepascal.org/view.php?id=33603> to create efficient code 
for x86 platforms, although currently it only does a range check and 
won't correctly handle enumerations with holes.  If non-contiguous 
enumerations are going to be allowed, we'll need to design an algorithm 
that can cover these holes with the smallest number of Boolean conditions.

Gareth aka. Kit

On 05/07/2019 21:13, Ondrej Pokorny wrote:
> On 05.07.2019 16:51, Pierre Muller wrote:
>> This means that using pred() or succ() intrinsics on enumerated types 
>> with
>> holes will generate a Compile Time Error.
>>
>>    To be consistent, I would propose that we also generate
>> a Compile Time Error if 'is' or 'as' keyword is used on such a type,
>> unless there is a code that really check that the value is not in
>> one of the holes ...
>
> I have to strongly disagree here. We need the IS/AS operators to 
> prevent undefined behavior. And if undefined behavior is only outside 
> the low/high bounds of the enumeration values and not within the holes 
> - then the IS/AS that checks only the bounds is very consequent 
> indeed. It's also consequent with the case-of statement for an enum 
> with holes. (See the thread I linked before.)
>
> Ondrej
>
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