🚀 go-pugleaf

In article <1176@bobkat.UUCP> m5@bobkat.UUCP (Mike McNally (Man from Mars)) writes:
>In article <122@spdcc.COM> dyer@spdcc.COM (Steve Dyer) writes:
> >               IBM PC/AT 8mhz          IBM PC/AT with Intel Inboard 386/AT
> >                                       16-bit mem      32-bit mem
> >Drystone 1.0   no reg  reg             no reg  reg     no reg  reg
> >               1278    1292            2293    2304    3429    3405
> >Drystone 1.1   1084    1094            1957    1963    2906    2893
>
>Why is the with-register-variables time for the 32-bit version *slower*
>than the without-register-variables time?  Isn't that sort-of strange?
>-- 
>Mike McNally, mercifully employed at Digital Lynx ---

No, its not strange when you consider that Dhrystone is not register-
intensive.   Saving the registers used for register variables on entry
to a procedure and restoring them at exit takes time (PUSH/POP).  If the
register variable is not referenced often enough that the reduced access
time to the variable makes up for the overhead of pushing and popping
the register.  The time savings for access to a register variable may be
as little as three or four clock cycles (depending on wait states), while
pushing and popping take 8 to 10 clocks (again, dep on wait states).  Thus,
if the register variable is accessed less than four times, you have a net
increase in execution time.

BTW, Turbo C with all optimizations on shows the same effect on an AT when
running Dhrystone.

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