$ perlbrew use 5.8.9

$ perl -Mre=debug -e'qr/a|b|c|d/'
Freeing REx: `","'
Compiling REx `a|b|c|d'
size 13 Got 108 bytes for offset annotations.

   1: BRANCH(4)
   2:   EXACT <a>(13)
   4: BRANCH(7)
   5:   EXACT <b>(13)
   7: BRANCH(10)
   8:   EXACT <c>(13)
  10: BRANCH(13)
  11:   EXACT <d>(13)
  13: END(0)
minlen 1
Offsets: [13]
        0[0] 1[1] 0[0] 2[1] 3[1] 0[0] 4[1] 5[1] 0[0] 6[1] 7[1] 0[0] 8[0]
Freeing REx: `"a|b|c|d"'

$ perlbrew use 5.10.1t

$ perl -Mre=debug -e'qr/a|b|c|d/'
Compiling REx "a|b|c|d"
Final program:
   1: TRIEC-EXACT[a-d] (13)
      <a>
      <b>
      <c>
      <d>
  13: END (0)
stclass AHOCORASICKC-EXACT[a-d] minlen 1
Freeing REx: "a|b|c|d"