Re: The shortest way with programs (was Compile HLL to microcode)

dlmoore@ix.netcom.com (David L Moore) writes:
|> One of the other features of RISC was, of course, that the silicon
|> freed up by simplifying the instruction set could be used for more
|> registers. Modern CISC chips use REGISTER RENAMING to achieve the same
|> thing. That is, even though you think you only have 6 useful
|> registers, you really have more because when you assign to a register,
|> it is given a new name in the register file.


One more time: Adding rename registers is not equivalent to adding
more logical registers, or vice versa. They have different effects.
Consider:


        If there are not enough logical registers available to perfectly
        allocate a routine, the compiler must generate spill code.
        Regardless of the number of rename registers the machine must
        execute the extra loads and stores.


        Even if there are a surplus of logical registers, a poorly
        scheduled routine may contain WAR or WAW dependencies that
        register renaming could remove.


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