[LLVMdev] i1 Values

[Rob Cameron]

If the type is interpreted as signed, then -1 is a proper value.

For signed integer type of n bits, the values that are 
representable are in the range -2^(n-1)...2^(n-1)-1), e.g.,
-128...127 for i8.    For i1, the values are in the range  -1...0.   
So -1 and 0 are the two values that can be represented.


----- Original Message -----
> I've been debugging some strange happenings over here and I put an
> assert in APInt to catch what I think is the source of the problem:
> 
>   int64_t getSExtValue() const {
>     // An i1 -1 is unrepresentable.
>     assert(BitWidth != 1 && "Signed i1 value is not representable!");
> 
> To me an i1 -1 makes no sense whatsoever.  It is not representable in
> twos-complement form.  It cannot be distinguished from unsigned i1 1.
> 
> It turns out this assert triggers all over the place.  Before I dive
> into this rat hole I'd like to confirm with others my sense that we
> shouldn't be creating i1 -1 values.  Is there some legitimate reason to
> do so?
> 
>                              -David
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