Comment by flanked-evergl
1 year ago
If adding more instructions negatively impacts efficiency, performance, cost and complexity, nobody would do it.
1 year ago
If adding more instructions negatively impacts efficiency, performance, cost and complexity, nobody would do it.
Probably true now, but in ye olde days, some instructions existed primarily to make assembly programming more convenient.
Assembly programming is a real pain in the RISCiest of RISC architectures, like SPARC. Here's an example from https://www.cs.clemson.edu/course/cpsc827/material/Code%20Ge...:
• All branches (including the one caused by CALL, below) take place after execution of the following instruction.
• The position immediately after a branch is the “delay slot” and the instruction found there is the “delay instruction”.
• If possible, place a useful instruction in the delay slot (one which can safely be done whether or not a conditional branch is taken).
• If not, place a NOP in the delay slot.
• Never place any other branch instruction in a delay slot.
• Do not use SET in a delay slot (only half of it is really there).
Delay slots were such a hack. ARM never needed them.
Only if decoder complexity/ efficiency is you bottleneck