Remove fold() closures from FieldSet._hashCode.

[LorenVS]

The fold() calls come with significant runtime cost, and make it more
difficult to hoist accesses to commonly used variables. Just rewriting
this pattern shows a significant performance improvement for both JS and
VM benchmarks.

Baseline

JS
HashCode(RunTime): 9833.333333333334 us.
HashCode(RunTime): 9891.625615763547 us.
HashCode(RunTime): 9607.655502392345 us.
HashCode(RunTime): 9661.835748792271 us.
HashCode(RunTime): 9765.853658536585 us.
VM
HashCode(RunTime): 4527.384615384615 us.
HashCode(RunTime): 4534.151583710407 us.
HashCode(RunTime): 4546.556818181818 us.
HashCode(RunTime): 4490.65470852017

Results

JS
HashCode(RunTime): 8004 us.
HashCode(RunTime): 7980.0796812749 us.
HashCode(RunTime): 7976.095617529881 us.
HashCode(RunTime): 7824.21875 us.
HashCode(RunTime): 7847.058823529412 us.
VM
HashCode(RunTime): 2474.5451174289246 us.
HashCode(RunTime): 2533.7037974683544 us.
HashCode(RunTime): 2532.4556962025317 us.
HashCode(RunTime): 2420.072551390568 us.
HashCode(RunTime): 2521.3198992443326

[rakudrama]

Looks good.
Do you think the existing tests are adequate to pick up a bug if you had introduced one?
(I don't think you did, but that is always a concern.)

[rakudrama]

_hashObjects, called at line 671, also uses fold

[LorenVS]

There is a big difference between these two patterns. The function passed to fold() in _hashObjects doesn't capture any local variables. I tested modifying that one as well and it was a regression in both JS and VM cases.

[sigurdm]

I wonder, now that we're looking into the hashing, if _HashUtils could be replaced by Object.hash() and Object.hashAll, and if it would give any performance benefit...

[rakudrama]

I wonder, now that we're looking into the hashing, if _HashUtils could be replaced by Object.hash() and Object.hashAll, and if it would give any performance benefit...

I suspect performance would be worse. There is no way way Object.hash and Object.hashAll to code a loop other than passing some Iterable to Object.hashAll. I think Loren's code would have the performance benefit since it combines the hash the tag and the values for each field. These would end up being in a temporary list if one had to use Object.hashAll.

I recommend this change goes ahead as-is. It is a nice performance boost for real apps.

Sigurd, are you an 'owner' that can approve this change?

[sigurdm]

I think protobuf is a bit "between owners". My main worry is the syncing to our internal repo. But besides that I approve - feel free to merge.

[osa1]

LGTM. I also run the benchmarks locally again and got similar improvements.

One of the CI checks was cancelled but for some reason I can't restart it now. Merging.

[osa1]

Ported to internal in cl/449694660.