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You are right but RISC-V variable instruction size is indeed a good trade-off.

Unlike x86 where instructions can range from 1 up to 15 byte, current RISC-V ISA only has 2 instruction sizes.

Today x86 decoding is limiting because we want to decode more than ~4 instructions each cycle, for RISC-V to cause same decoding difficulty it would probably be required to decode more than ~20 instructions each cycle



I don’t know that it’s a good tradeoff. ARM64 has fixed length instructions with decent density and has proven to allow highly parallel decoding.




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