[comp.arch] Bifurcated Pipelines

jms@close.columbia.edu (Jonathan M. Smith) (07/05/88)

comp.arch readers:

	I need a reference on bifurcated pipelines (I don't know
whether this is trivial knowledge or not, I'm a software person and I
heard about these in an architecture class in 1982. The basic idea is
to avoid draining the pipe on a branch instruction by fetching stuff
for *both* directions of the branch into *two* pipelines, and
selecting the right stream upon evaluation of the conditional.
Supposedly, one or more models in the IBM 370 Architecture did this).
In particular, the reference should describe the assumptions made by
the designers, e.g. pipeline drain time vs. increased memory traffic,
interleaved storage, cacheing, side-effects, branch frequency, etc.
That is, I'd like to know the engineering tradeoffs which affect use
of such a design. If you are not aware of a reference, but have design
experience which includes such schemes, I'd appreciate hearing about
it.


						Thanks for any help,
						-Jonathan