Branch causes an unconditional branch to a label at a PC-relative offset, with a hint that this is not a subroutine call or return.
26-bit signed PC-relative branch offset
bits(64) offset = SignExtend(imm26:'00', 64);
Is the program label to be unconditionally branched to. Its offset from the address of this instruction, in the range +/-128MB, is encoded as "imm26" times 4.