Class#subclasses slows down with larger sets #8457
Description
When Class#subclasses returns a longer list, we appear to slow down more relative to CRuby.
With the four classes from Numeric:
$ ruby -rbenchmark -e '5.times { puts Benchmark.measure { 10_000_000.times { Numeric.subclasses } } }'
0.840000 0.040000 0.880000 ( 0.719652)
0.610000 0.000000 0.610000 ( 0.597529)
0.610000 0.010000 0.620000 ( 0.598173)
0.600000 0.000000 0.600000 ( 0.600692)
0.650000 0.010000 0.660000 ( 0.600609)
$ chruby-exec 3.3 -- ruby -rbenchmark -e '5.times { puts Benchmark.measure { 10_000_000.times { Numeric.subclasses } } }'
0.892543 0.003522 0.896065 ( 0.896127)
0.880852 0.002772 0.883624 ( 0.883620)
0.902136 0.003467 0.905603 ( 0.905592)
0.902449 0.003406 0.905855 ( 0.905844)
0.888070 0.003159 0.891229 ( 0.891218)
And the 83 subclasses (82 in CRuby) of Object (note reduced iterations in benchmark):
$ ruby -rbenchmark -e '5.times { puts Benchmark.measure { 1_000_000.times { Object.subclasses } } }'
2.090000 0.020000 2.110000 ( 1.885031)
1.780000 0.020000 1.800000 ( 1.813361)
1.800000 0.010000 1.810000 ( 1.821201)
1.760000 0.010000 1.770000 ( 1.754643)
1.810000 0.010000 1.820000 ( 1.777603)
$ chruby-exec 3.3 -- ruby -rbenchmark -e '5.times { puts Benchmark.measure { 1_000_000.times { Object.subclasses } } }'
1.006108 0.018142 1.024250 ( 1.024307)
0.989379 0.014869 1.004248 ( 1.004562)
1.006066 0.018692 1.024758 ( 1.024845)
1.022598 0.022539 1.045137 ( 1.091699)
0.985969 0.019927 1.005896 ( 1.006522)
Ignoring the overhead of the benchmark, it appears CRuby slows down about 11x and we slow down 30x for an increased class count of 20x.