When I read the words below dot line, I don't understand why "R14 is adjusted to allow for the prefetch"
Could you explain it to me?
....... Branch with Link (BL) writes the old PC into the link register (R14) of the current bank. The PC value written into R14 is adjusted to allow for the prefetch, and contains the address of the instruction following the branch and link instruction. Note that the CPSR is not saved with the PC and R14[1:0] are always cleared.