bool <=> int. WTF. (DIP0015)

[lithium iodate]

On Friday, 5 July 2019 at 09:04:26 UTC, Patrick Schluter wrote:
> On Friday, 5 July 2019 at 03:10:06 UTC, Exil wrote:
>> On Thursday, 4 July 2019 at 16:31:11 UTC, Patrick Schluter 
>> wrote:
>>> that's the issue. D's bool type follows exactly C (C has bool 
>>> since C99) and C++ way.
>>> bool b; will behave exactly like your bool b = void;
>>
>> It doesn't have the same behavior. Currently DMD's codegen is 
>> bad, sometimes it checks the entire byte value and other times 
>> it only checks the first bit. All C/C++ compilers I've used 
>> check the entire value, consistently.
>
> if the codegen does something like (x & 1) then it is indeed a 
> BUG and should be corrected.

Bug because it is inefficient or incorrect?
To the best of my knowledge C does only mandate that _Bool must 
be able to store 0 and 1, and  imposes no requirements on how 
other representations have to be treated. GCC treats _Bool as 
having 2 valid representations and 254 trap representations, so x 
== 1, x & 1 and x > 0 are all necessarily equivalent given this 
assumption. Not sure about Clang, in my quick test it always only 
checked the least significant bit.

Does D really not have more specific requirements for bool? (Does 
D even allow anything to have trap representations? There doesn't 
really seem to be any info on that)