Re: [RFA][PR tree-optimization/79095] [PATCH 1/4] Improve ranges for MINUS_EXPR and EXACT_DIV_EXPR V2

[Jeff Law <law at redhat dot com>]

On 02/09/2017 08:06 PM, Jeff Law wrote:
> > > +                  && *vr0min == *vr0max
> > > +                  && integer_zerop (*vr0min)
> > > +                  && TREE_CODE (vr1max) == INTEGER_CST
> > > +                  && TREE_CODE (vr1min) == INTEGER_CST
> > > +                  && difference_larger_than (vr1max, vr1min, 65536))
> > > +           ;
> >
> > in the case that interests us for the PR what is vr1?
> [-2305843009213693952, 2305843009213693951]
And just for completeness, I instrumented the compiler to dump the range 
every time this code triggered to see what kind of ranges we'd be 
changing into ~[0,0].

It triggers 1260 times during a bootstrap.  20 most common:

     20 [-1073741824,1073741823]
     20 [-65535,65535]
     22 [-2147483647,2147483646]
     23 [-1152921504606846976,1152921504606846975]
     24 [-2147483648,39]
     24 [-72057594037927936,72057594037927935]
     24 [-8388608,8388607]
     27 [-536870912,536870911]
     28 [-2305843009213693952,2305843009213693951]
     28 [-536870910,536870910]
     32 [-2147483648,113]
     41 [-2147483648,32767]
     48 [-1,2147483646]
     48 [-2147483647,2147483647]
     48 [-2147483648,63]
     48 [-9223372036854775807,9223372036854775807]
     53 [-214748364,214748364]
     70 [-2147483648,1]
    160 [-2147483648,2147483647]
    162 [-2147483648,2147483646]

Obviously it's harder to know how many of those ultimately lead to 
optimizing something better.

With your heuristic we get 378 triggers with the most common being:


     17 [-2147483648,113]
     17 [-9223372036854775808,9223372036854775806]
     18 [-1,2147483646]
     18 [-2147483648,32767]
     23 [-1152921504606846976,1152921504606846975]
     24 [-72057594037927936,72057594037927935]
     27 [-536870912,536870911]
     28 [-2305843009213693952,2305843009213693951]
     45 [-2147483648,2147483646]
     48 [-9223372036854775807,9223372036854775807]

Anyway, I'll do the usual testing with your version.

jeff