I don't think simpler to decode necessitates fewer instructions. If all your instructions put the bits describing which registers to use in the same place, use the same way to specify constants instead of registers, to specify that they operate on floating point variables, etc, using 8 bits that select the instruction gives you 256 different discussion with limited added complexity.
Of course, it is unlikely that you can make 256 instructions use the exact same format (some operations will not have any use for 3 registers, for instance) but if you can keep things as consistent as possible, decoding becomes easier. Price paid is that you sacrifice instruction space, for example because the instruction format allows you to write the result of an operation to a register hard-wired to contain a zero.
And x86 isn't that CISC-y. There were processors that basically could do a simple number to string conversion in one instruction, and there _are_ processors with an instruction that does Unicode conversions (http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/d...)
Someone|10 years ago
Of course, it is unlikely that you can make 256 instructions use the exact same format (some operations will not have any use for 3 registers, for instance) but if you can keep things as consistent as possible, decoding becomes easier. Price paid is that you sacrifice instruction space, for example because the instruction format allows you to write the result of an operation to a register hard-wired to contain a zero.
And x86 isn't that CISC-y. There were processors that basically could do a simple number to string conversion in one instruction, and there _are_ processors with an instruction that does Unicode conversions (http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/d...)