[perl #131297] [PERF][REGEX] `|@a` is apparently-equivalent to just `@a` but is 70x slower

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https://irclog.perlgeek.de/perl6-dev/2017-05-12#i_14572067

14:49           m: my @a = 1..12; for ('a' x 100 ~ " -- Jan-12-2017") xx 100 {  
when /'-- ' |@a '-' \d**2 '-' \d**4 / { } }; say now - INIT now
14:49   camelia         rakudo-moar 94c4e7: OUTPUT: «4.269762␤»
14:49   Zoffix  m: my @a = 1..12; for ('a' x 100 ~ " -- Jan-12-2017") xx 100 {  
when /'-- ' ||@a '-' \d**2 '-' \d**4 / { } }; say now - INIT now
14:49   camelia         rakudo-moar 94c4e7: OUTPUT: «0.3336069␤»
14:49   Zoffix  m: my @a = 1..12; for ('a' x 100 ~ " -- Jan-12-2017") xx 100 {  
when /'-- ' @a '-' \d**2 '-' \d**4 / { } }; say now - INIT now
14:49   camelia         rakudo-moar 94c4e7: OUTPUT: «0.0607072␤»
14:49   Zoffix  m: say 4.269762/0.0607072
14:49   camelia         rakudo-moar 94c4e7: OUTPUT: «70.3337001␤»
14:49   Zoffix  apparently-equivalent but 70x slower
14:50   timotimo        well well, we still have a lot of opportunities to 
improve these things