[Libre-soc-dev] fantastically-weird regfile

Luke Kenneth Casson Leighton lkcl at lkcl.net
Mon Dec 14 01:17:54 GMT 2020

On 12/14/20, Cole Poirier <colepoirier at gmail.com> wrote:

> I like it a lot. Would this help with port contention?

it may increase it.  i didn't know it had been proposed so the time
budget for evaluating the idea in full hasn't been evaluated yet,
particularly for the DMs and crossbar routing.

> I also like it as it
> very much reminds me of the dependency matrices.

it reminds me of hitting potatoes really hard with a tennis racket
that's been strung with cheese wire and expecting it to produce chips.

the DMs assume a linear relationship between Regfiles and FUs.
alternative numberings create 3D relationships.  2D for Regfile, 1D
for FUs.

it is going to be a mindbender to try to compress 3D data into a 2D
matrix and an even bigger mindmelt to squeeze them through the Reg
Rename Matrix.

one solution is to ban (prohibit) horizontal and vertical regfile
hazards from being in the regfile at the same time.

this of course would result in performance degradation.

this applies to the CRs just as much to a renumbering of INT/FP regs.


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