perl5.8.8 -wle '$s = "x" x 40_000;
    $s =~ /^(.)(\1*)/ and print length $2'

# (segfaults)

perl5.10.0 -wle '$s = "x" x 40_000;
    $s =~ /^(.)(\1*)/ and print length $2'
Complex regular subexpression recursion limit (32766) exceeded at -e line 1.
32767