Fwiw the https://en.wikipedia.org/wiki/AMD_Am29000 RISC CPU and the https://en.wikipedia.org/wiki/AMD_K5 are a good example of this. As in AMD took their existing RISC CPU to make the K5 x86 CPU.

Almost the same in die shots except the K5 had more transistors for the x86 decoding. The AM29000's instruction set is actually very close to RISC-V too!

Very hard to find benchmarks comparing the two directly though.

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throwawaymaths 3 days ago | parent [-]

TIL the k5 was RISC. thank you

	▲	TheAmazingRace 3 days ago \| parent [-]
		It was a valiant effort by AMD when they made their first attempt at an in-house x86 chip design. Prior to this, AMD effectively cloned Intel designs under license. Sadly, the K5 was pretty underwhelming upon release, and it wasn’t until AMD acquired NexGen and integrated their special sauce into their next version core, the K6, that things started getting interesting. I was quite fond of my old AMD K6 II+ based PC back in the day. It had good value for the money. Then you see the K7/Athlon core, complete with inspiration from the DEC Alpha thanks to none other than Jim Keller, and AMD was on a serious tear for a good while after that, beating Intel to 1 GHz.