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What's RISC about adding more registers?
by sapiogram 2y ago
What's RISC about adding more registers?
- ajross 2y agoThe simple answer is that a big symmetric register set has always been a hallmark of RISC ISAs, because having lots of symmetric registers increases throughput by reducing compiler-generated spill/fill overhead and permits more permissive ABIs for leaf functions that need the extra space. The complicated answer is that, no, it's not especially "reduced" and you could implement all those other RISCy ideas in a much smaller set of GPRs without otherwise effecting the "RISCiness" of the design. But that answer is a little specious, since it's true of all the other RISCy traits too. Most of them stand alone, which is why the whole debate tends to be a little silly.
- Symmetry 2y agoThe name "RISC" is something we gave to a particular design philosophy, but not everything in that philosophy is summed up in the name. Classic RISC designs have 32 registers to make up for the lack of instructions that operate directly on memory addresses and to make things easier for the compiler and achieve good performance without load-op-store instructions.