is it time fully optimize long loops? (JDK-8223051)

[John Rose]

On Apr 10, 2020, at 4:26 AM, Roland Westrelin <rwestrel at redhat.com> wrote:
> 
>> Once the long loop is transformed to an int counted loop what are the
>> optimizations that need to trigger reliably? In particular do we need
>> range check elimination? Can you or someone from the panama project shar
>> code samples that I can use to verify the long loop optimizes well?
> 
> I see now that you mentioned RCE in JDK-8223051.

RCE focuses on comparisons against array lengths but it is
more general than that.  If long loops are strip mined into
short loops, and if the range checks in those short loops are
somehow transformed into 32-bit comparisons, they should
be amenable to RCE transformations.

I hope we don’t need to generalize RCE transformations to
know about 64-bit comparisons; that seems to be harder.

— John