Work from RER

report/report.tex

@@ -429,7 +429,26 @@ addition of five heuristics. \qtodo{Why not use it then?}
 
 \subsection{Corner cases}
 
-\todo{}
+There were a few observed cases where the algorithm tends to be slower on
+certain configurations.
+
+\paragraph{Split/merge trees.} A common pattern that tends to slow down the
+algorithm is split/merge trees. Those patterns occur when one wants to merge
+$n$ one bit wires into a single $n$ bits wire, or the other way around.
+
+These patterns are pretty common, for instance when an opcode is run through a
+MUX tree to perform the requested operation.
+
+Though, this pattern generates a lot of collisions in signatures. Indeed, for a
+tree of depth \eg{} 8, a node just below the root will need a signature of
+order 7 to have a different signature than another one at the same depth. With
+a signature of order up to 6, only other gates from the tree will be included
+in the signature when going down in the tree; the exact same gates will be
+included above the tree's root. Thus, nothing will differentiate one gate from another while
+the boundary of the tree is not reached (assuming the gates below the tree's
+leaves are not all the same; if so, more levels will be needed).
+
+\todo{Figure describing the problem}
 
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