[12] RFR(M): 8210215: C2 should optimize trichotomy calculations

[Tobias Hartmann]

Hi John,

thanks for looking at this again!

On 26.09.2018 01:57, John Rose wrote:
> `res[9][9]` should be `res[illegal+1][illegal+1]` and should have rows and columns for `never`
> (code smell:  `9` is a naked constant; makes it hard to tell your table is out of date)

Right, I've updated the table.

> In the test cases `compare1` has `(a < b) ? -1 : (a == b) ? 0 : 1`.
> Shouldn’t you also test `(a < b) ? -1 : (a <= b) ? 0 : 1`?
> And similarly, for other cases where the second test overlaps
> with the first.

I did not add tests for all the 6² operator combinations but I think more overlapping tests won't
hurt. I've added

 (a < b)  ? -1 : (a <= b) ?  0 :  1;
 (a > b)  ?  1 : (a >= b) ?  0 : -1;
 (a == b) ?  0 : (a <= b) ? -1 :  1;
 (a == b) ?  0 : (a >= b) ?  1 : -1;

and verified that all inlined comparisons fold.

Here's the new webrev:
http://cr.openjdk.java.net/~thartmann/8210215/webrev.01/

Thanks,
Tobias