These are called through function pointers so that different implementations
can be provided for cheetah, where the block load instructions may or may
not be a win, and so they can be disabled with the machdep.use_vis tunable.
In terms of raw bandwidth the integer versions are faster, but not allocating
lines in the L2 cache for useless data gives a measurable improvement in user
time for the benchmarks I tested (mostly buildworld with -j8).
As far as I can tell the instructions used are implemented on everything
back to UltraSPARC I, so there should not be a problem with different cpu
types.
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