Register File Communication
Architecturally Invisible
- Partitioned RFs appear as one large register file to the compiler
- Copying between RFs is done by control
- Detection of when copying is needed can be complicated; goes against VLIW philosophy of minimal control overhead
Architecturally Visible, have Remote and Local versions of instructions
- Remote instructions have one or operands in non-local RF
- Copying of remote operands to local RFs takes clock cycles
- Because copying is ‘atomic’ part of remote instruction, execution unit is idle while copying is done => performance loss.