Well the two differ semantically in the first you are taking a reference to a scalar constant and in the second you are assigning a scalar constant to a dereference scalar ref. The first will be a readonly value. In these cases Devel::Peek is your friend:

$x:

SV = RV(0x8086d20) at 0x807b2e8
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,ROK)
  RV = 0x807b30c
  SV = IV(0x807ae44) at 0x807b30c
    REFCNT = 2
    FLAGS = (IOK,READONLY,pIOK)
    IV = 12


$y:

SV = RV(0x8086d24) at 0x807b2f4
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,ROK)
  RV = 0x804c500
  SV = IV(0x807ae4c) at 0x804c500
    REFCNT = 1
    FLAGS = (IOK,pIOK)
    IV = 12
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/J\