RFC: Value range propagation for if-else

[Don via Digitalmars-d]

On Wednesday, 18 June 2014 at 06:40:21 UTC, Lionello Lunesu wrote:
> Hi,

> https://github.com/lionello/dmd/compare/if-else-range
>
> There, I've also added a __traits(intrange, <expression>) which 
> returns a tuple with the min and max for the given expression.

> Destroy?

The compiler uses value range propagation in this {min, max} 
form, but I think that's an implementation detail. It's well 
suited for arithmetic operations, but less suitable for logical 
operations. For example, this code can't overflow, but {min, max} 
range propagation thinks it can.

ubyte foo ( uint a) {
   return (a & 0x8081) & 0x0FFF;
}

For these types of expressions, {known_one_bits, known_zero_bits} 
works better.
Now, you can track both types of range propagation 
simultaneously, and I think we probably should improve our 
implementation in that way. It would improve the accuracy in many 
cases.

Question: If we had implemented that already, would you still 
want the interface you're proposing here?