Attaching a second version of the patch.  (BTW, Serhiy, I tried your idea of using a switch statement to optimize branches (https://github.com/1st1/cpython/blob/fastint2/Python/ceval.c#L5390) -- no detectable speed improvement).


I decided to add fast path for floats & single-digit longs and their combinations.  +, -, *, /, //, and their inplace versions are optimized now.  


I'll have a full result of macro-benchmarks run tomorrow morning, but here's a result for spectral_norm (rigorous run, best of 3):

### spectral_norm ###
Min: 0.300269 -> 0.233037: 1.29x faster
Avg: 0.301700 -> 0.234282: 1.29x faster
Significant (t=399.89)
Stddev: 0.00147 -> 0.00083: 1.7619x smaller


Some nano-benchmarks (best of 3):

-m timeit -s "loops=tuple(range(100))" "sum([x + x + 1 for x in loops])"
2.7  7.23    3.5  8.17      3.6  7.57

-m timeit -s "loops=tuple(range(100))" "sum([x + x + 1.0 for x in loops])"
2.7  9.08    3.5  11.7      3.6  7.22

-m timeit -s "loops=tuple(range(100))" "sum([x/2.2 + 2 + x*2.5 + 1.0 for x in loops])"
2.7  17.9    3.5  24.3      3.6  11.8