Resolving-multiple-drivers
How we replace multiply driven wires with explicit resolution
modules.
We want every wire in our E modules to have at most one driver, but
the list of occurrences we get from vl-modinstlist-to-eoccs could easily
have multiple occurrences all driving the same wire. We now introduce a
transform to simplify a list of E occurrences, eliminating multiply driven
wires by inserting explicit resolution modules.
Note: In this transform we assume that the module's primary inputs
are not driven by any occurrence. This is something we explicitly check for in
vl-module-make-esim; see the warning about :vl-backflow there.
Given this assumption, we basically need to do three things:
- Identify when a wire W has multiple occurrences driving it.
Fortunately, this is completely trivial:
(duplicated-members (collect-signal-list :o occs))
- Rewrite each occurrence driving W so that it instead drives some new,
unique, freshly generated wire (say W_1, W_2, ...). We also need to
remember the names we used for each wire, for step 3. We do this with the
function vl-res-rewrite-occs.
- Insert new occurrences that drive W with the (RES W_1 W_2 ...).
This is done with vl-make-res-occs.
The top-level function is vl-add-res-modules, and it just stitches
these steps together.
Subtopics
- Vl-res-sigma-p
- An alist that records the fresh wires we introduce for multiply
driven wires.
- Vl-res-rewrite-occs
- Rewrite occurrences to drive new, fresh wires instead of multiply
driven wires.
- Vl-add-res-modules
- Top-level function for resolving multiple drivers in a list of E
occurrences.
- Vl-make-res-occs
- Convert the vl-res-sigma-p database into a list of E
occurrences to drive each multiply driven wire.
