[Comb][FIRRTL][Seq] Fix fusing locations to append not add as metadata.

[dtzSiFive]

Previously we created a chain of FusedLocations that had metadata point to previous, instead append to it.

Leverage (and fix interaction with) FusedLoc::get behavior that decomposes/flattens (and unique's) locs in child FusedLoc's if metadata matches (or doesn't exist, as here).

Add basic test.

[dtzSiFive]

In Dedup we have logic based on FusedLoc::get() that we used to limit maximum number of ".fir" locations in a fused list.

For now keep locations but may want to do similar here (make it utility function or pass?) if this creates monster locations.

[uenoku]

Oh, thank you for finding this! LGTM. Maybe this also has the same bug?

circt/lib/Dialect/Comb/CombFolds.cpp

Line 2389 in a2bf8ed

rewriter.getFusedLoc(trueMux.getLoc(), falseMux.getLoc()), op.getCond(),

[dtzSiFive]

Oh, thank you for finding this! LGTM. Maybe this also has the same bug?

circt/lib/Dialect/Comb/CombFolds.cpp

Line 2389 in a2bf8ed

rewriter.getFusedLoc(trueMux.getLoc(), falseMux.getLoc()), op.getCond(),

Oh, totally! I grep'd around but missed, thanks! Will pull that in too.