[patch] disentangle range_fold_*ary_expr into various pieces

[Marc Glisse]

On Mon, 7 Oct 2019, Aldy Hernandez wrote:

> On 10/4/19 2:09 PM, Jeff Law wrote:
>
>> You're right.  Easier to refer to the before/after directly.  Sometimes
>> diffs just suck.
>> 
>> OK
>> jeff
>
> In testing this patch in isolation from the non-zero canonicalization patch, 
> I found one regression due to the fact that:
>
> a) As discussed, two non-zero representations currently exist for unsigned 
> ranges.
>
> b) ipa-prop.c has it's own hacked up value_range structure (ipa_vr) which 
> doesn't use any API.  Since there is no agreed upon non-zero, range-ops can 
> sometimes (correctly) create an unsigned [1,MAX], and ipa-prop.c is 
> open-coding the check for a pointer non-zero to ~[0,0]. This seems like a 
> latent bug.
>
> I really have no idea, nor do I care (*), what we do with ipa-prop's lack of 
> API.  For now, I have implemented ipa_vr::nonzero_p(), and used it.  When we 
> agree on the non-zero normalization we can adjust this method if necessary.
>
> +bool
> +ipa_vr::nonzero_p (tree expr_type) const
> +{
> +  if (type == VR_ANTI_RANGE && wi::eq_p (min, 0) && wi::eq_p (max, 0))
> +    return true;
> +
> +  unsigned prec = TYPE_PRECISION (expr_type);
> +  return (type == VR_RANGE
> +         && wi::eq_p (min, wi::one (prec))
> +         && wi::eq_p (max, wi::max_value (prec, TYPE_SIGN (expr_type))));
> +}
>
> ...
>
>           else if (POINTER_TYPE_P (TREE_TYPE (ddef))
> -                  && vr[i].type == VR_ANTI_RANGE
> -                  && wi::eq_p (vr[i].min, 0)
> -                  && wi::eq_p (vr[i].max, 0))
> +                  && vr[i].nonzero_p (TREE_TYPE (ddef)))
>
> Attached is the final adjusted patch I have committed to trunk.

I wonder why we would ever want to ask "is this interval the one that 
misses exactly the value 0" instead of "does this interval contain the 
value 0". I naively believe there shouldn't even be any API for the first 
question. Or if pointers really only have 2 possible intervals (besides 
varying and undefined), aka [0,0] and ~[0,0], using intervals seems like 
overkill for them...

-- 
Marc Glisse