[interchange] Remove requirement to have wire_lut.

Signed-off-by: Keith Rothman <537074+litghost@users.noreply.github.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fpga_interchange/arch.h b/fpga_interchange/arch.h
index a6ea70d8..e9c2802a 100644
--- a/fpga_interchange/arch.h
+++ b/fpga_interchange/arch.h
@@ -1065,6 +1065,9 @@ struct Arch : ArchAPI<ArchRanges>
     std::unordered_map<IdString, const LutCellPOD *> lut_cells;
 
     // Of the LUT cells, which is used for wires?
+    // Note: May be null in arch's without wire LUT types.  Assumption is
+    // that these arch's don't need wire LUT's because the LUT share is simple
+    // enough to avoid it.
     const LutCellPOD * wire_lut;
 
     std::regex raw_bin_constant;