[RFA][PR tree-optimization/79095] [PATCH 1/4] Improve ranges for MINUS_EXPR and EXACT_DIV_EXPR

[Jeff Law]

On 02/06/2017 08:33 AM, Richard Biener wrote:

> ah, indeed vr0type is VR_ANTI_RANGE and yes we have the case
> of a range with an anti-range "inside".  This also covers [-1,1] v ~[0,0]
> where you choose the much larger anti-range now.  So at least we
> want to have some idea about the sizes of the ranges (ideally we'd
> choose the smaller though for most further propagations anti-ranges
> often degenerate to varying...)
vr0 as an anti-singleton range like ~[0,0] is the only one likely of any 
interest right now and that's always going to have a range that is all 
but one value :-)

vr1 is the tricky case.  We could do v1.max - vr1.min and if that 
overflows or is some "large" value (say > 65536 just to throw out a 
value), then we conclude creating the singleton anti-range like ~[0,0] 
is more useful.

Jeff