I upgraded my SWI-Prolog version 8.1.19 to version 8.1.26.
I witness increases in execution times for certain executions of the program, while the rest is pretty much stable.
The most notable execution-time differences are:
From 012s to 042s
From 012s to 020s
From 154s to 205s
From 069s to 086s
From 005s to 016s
From 042s to 145s
The following is a graph that shows them all (SVG: open in new tab and zoom in).
Other than the usual Prolog predicates, I use tabling. What could have possibly given rise to these differences?