Data movement requires that data be moved from a source to a destination. What are the practical issues that a designer must be aware of when implementing a data move instruction?

Question

What will be an ideal response?

Answer 1

One consideration is addressing modes. The question was not specifically aimed at that point. However, if a load is being performed from memory, addressing is a consideration. Generally, an address is register indirect and is given by r1 + r2 + C where r1 and r2 are registers and c is a constant. In general, most processors allow either (r1 + C) or ( r1 + r2), but not both a second register and a constant. Moreover, addressing modes can be pre? or post?indexed in the sense that the offset register or constant is added to the pointer register either before or after use.

The question was more about what happens to load and stores that are shorter than the target data. When loading into a register, if the value loaded is shorter than the register (e.g., 16 bits loaded into a 32 bit register)
then the bits in the register not loaded into can be set to zero, left unchanged, or sign?extended. This problem
does not arise when storing data in memory because the location is always the same size as the data being
stored.

Finally, there is the consideration of byte ordering. Some move instructions can change the byte order as the
data is stored.