[FIRRTL] Prefix for Seq Mem Group Extract

[seldridge]

Fix a bug in the composition of the PrefixModules and ExtractInstances passes. Because the latter can generate modules with new names when using the grouping feature, this module needs a prefix and does not currently get one. Change the PrefixModules pass to add a wildcat attribute "prefix" to the DUT annotation. This prefix is then used by ExtractInstances to properly generate the module name.

This is a variant of the solution used for the GrandCentral pass where the companion module annotation is given a wildcat attribute that stores the prefix which is then used by the pass.

A better solution would be to reorder PrefixModules after ExtractInstances. However, this has complications with verbatim metadata emission and the possibility of PrefixModules manipulating the hierarchy (duplicating modules to resolve non-local prefixes). There is more discussion about this on the #4593.

Fixes #4593.

Signed-off-by: Schuyler Eldridge schuyler.eldridge@sifive.com

[fabianschuiki]

LGTM! I think this is a good fix given the current pass ordering.

It makes me sad that we have can have verbatim placeholders for module/instance names, but we have to prescribed the exact number of placeholders for the different levels of hierarchy. It feels like we want something like a #hw.hierpath.sv<@foo::@bar> or #hw.hierpath.sdc<@foo::@bar> attribute that would expand to an SV-style or SDC-style (or any others we cook up) hierarchical path in the output. That way we could do hierarchy transformations and have the output of the verbatims reflect them.

[seldridge]

The XMRRefOp has some of those features. You just give it a symbol which references a #hw.hierpath op and it will resolve it to the path encoded by that. Maybe that should be extended to work for verbatims? (In the future...)

[seldridge]

Landed in 092cb81.