This is an experimental patch to optimize some operations on small ints.
pystone is 5-10% faster, pybench 2-3% faster, and here are some relevant benchmarks from unladen swallow:
### nbody ###
Min: 0.345136 -> 0.317502: 1.09x faster
Avg: 0.346827 -> 0.319561: 1.09x faster
Significant (t=79.50)
Stddev: 0.00140 -> 0.00198: 1.4084x larger
### nqueens ###
Min: 0.339744 -> 0.313506: 1.08x faster
Avg: 0.342630 -> 0.315380: 1.09x faster
Significant (t=73.41)
Stddev: 0.00218 -> 0.00146: 1.4931x smaller
If the principle gets accepted, we could experiment with further optimizations such as dedicated opcodes for addition-with-int-constant, subscripting-with-int-constant, etc.