SimCode execution times scale as O(N^4) with large parameter arrays

[Francesco Casella]

SimCode execution times to create linear, non-linear and system jacobian parts scale very badly with size, when large parameter arrays are defined in models. See:

(​https://libraries.openmodelica.org/branches/master/ScalableTestSuite/ScalableTestSuite.html ScalableTestSuite), ScalableTestSuite.Elementary.ParameterArrays.ScaledExperiments.Table_N_XX_M_XX:

NxM	Time (s)
2500	0.30
5000	0.89
10000	4.02
20000	15.12
40000	259.00

This makes absolutely no sense. The time spent creating the code for an array with N elements should be O(N).

[Martin Sjölund]

For 100x100: Notification: Performance of createVars: known variable list: time 3.623/5.007, allocations: 14.68 MB / 0.8516 GB, free: 249.4 MB / 0.6373 GB

It seems to be that extractVarFromVar becomes slower and slower the more variables are processed...

[Martin Sjölund]

This seems to be due to the HashSet allocating space for 0 variables since the size of the system is 0. We should probably also allocate space for the parameters (which are not counted in the size of the system).

[Martin Sjölund]

Will be fixed by ​PR1961. Using AvlSet is much more convenient since you will not have this problem when you fail to estimate the final size of a hashtable... What pains you go to in order to have expected O(n) behavior instead of guaranteed O(n*log(n))

[Martin Sjölund]

800x50 with my changes takes a total of 6.1s for front-end, back-end and code generation with another 2.5s to compile the code (all using a single thread with parallel GC disabled).

[Francesco Casella]

Also the performance of CombiTimeTable_N_XXX and TimeTable_N_XXX was greatly improved, see the ​Hudson report

A realistic use case that will benefit from this bugfix is when a relatively small model is fed by a table-based signal generator with a huge database.