[simias]

>Of the times I've used Asm, there's been far more situations where an extra 32-bit register would be more useful than a 64-bit one

You need a 64 bit register any time you want to store a pointer though unless you want to use some kind of a segmented memory model. I don't think anybody wants to go back to that although I'm not one to criticize weird fetishes.

Clearly when you look at the fine details of AMD64 it looks like a weird frankenstein monster of an instruction set. REX prefix holding the MSBs of registers since 32bit opcodes only allowed three bits to encode 8 registers. Same prefix used to set the width of memory target operands, except that some instructions default to 32bits while others default to 64. R12 has weird encoding quircks because it matches RSP in the "low" register set and that register has specific semantics when used as a base register...

I wonder how much die area is used on a modern CPU just to deal with all this cruft and translate it into a saner RISC instruction set internally.