Interesting. Seems to be the first modern non trivial compiler that avoids using SSA internally. I thought SSA had cornered the market, but perhaps now there is an opposite trend (ok one example doesn't make a trend)
<quote>
No SSA (single static assignment form) for:
Faster optimizations for short optimizations pipeline and small functions (a target usage scenario)
Currently SSA could be used only for two optimizations (CCP and GCSE). SSA usage would mean 4 additional passes over IR. If we implement more optimizations, SSA transition is possible when additional time for expensive in/out SSA passes will be less than additional time for non-SSA optimization implementation
Simpler and more compact generator code because we can avoid to implement a lot of nontrivial code (for dominator and dominator frontier calculation, a good out of SSA code)
</quote>
> Seems to be the first modern non trivial compiler that avoids using SSA internally.
Of course it's debatable what "modern" and "non trivial" mean, and if they apply to this project. It's very small, but on the (one!) small benchmark the author cites it seems to do quite well, so it's certainly not completely naive.
For whatever it's worth, CompCert doesn't use SSA either, and that's certainly a non-trivial compiler, though arguably the non-triviality does not stem from any advanced optimizations it does.
<quote> No SSA (single static assignment form) for:
Faster optimizations for short optimizations pipeline and small functions (a target usage scenario) Currently SSA could be used only for two optimizations (CCP and GCSE). SSA usage would mean 4 additional passes over IR. If we implement more optimizations, SSA transition is possible when additional time for expensive in/out SSA passes will be less than additional time for non-SSA optimization implementation Simpler and more compact generator code because we can avoid to implement a lot of nontrivial code (for dominator and dominator frontier calculation, a good out of SSA code) </quote>