+/// In the case of irreducible loops, instead of a single loop header,
+/// there will be several. The computation of backedge masses is similar
+/// but instead of having a single backedge mass, there will be one
+/// backedge per loop header. In these cases, each backedge will carry
+/// a mass proportional to the edge weights along the corresponding
+/// path.
+///
+/// At the end of propagation, the full mass assigned to the loop will be
+/// distributed among the loop headers proportionally according to the
+/// mass flowing through their backedges.
+///