People recognized ~20 years ago that, semantically, SSA is just reinventing lexical scope:
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.34.3...
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.34.3...
The original pass was called RNN - right number of names.