pdp-11 had a very elegant unification of "immediate operand" and "pc-relative addressing". Basically one of the addressing mode is "access word pointed to by r

pdp-11 had a very elegant unification of "immediate operand" and "pc-relative addressing". Basically one of the addressing mode is "access word pointed to by register+offset and post-increment the register by word size (2 bytes)". That can be used to pop off a word from the stack if the register is the stack pointer, but if the register is the program counter, that basically reads the word following the instruction and causes the CPU to continue execution after the immediate data. A truly orthogonal instruction set :-)