Over the past 20 years, SSA has risen to become
the compiler intermediate representation of
choice. Compiler developers cite many qualitative
reasons for choosing SSA. However in this study,
we present clear \emph{quantitative} benefits of
SSA, by applying several standard software metrics
to compiler intermediate code in both SSA and
non-SSA forms. The average complexity reduction in
using SSA ranges from 7\% to 23\% with our
software metrics, over a set of standard SPEC
benchmarks.

ref: http://www.cs.man.ac.uk/~jsinger/pdfs/ssa_metrics.pdf