Emit slices as constants in the bytecode compiler

[mdboom]

Feature or enhancement

Proposal:

Constant slices are currently emitted as multiple bytecodes by the Python bytecode compiler.

For example, x[:-2, 1:-1] generates:

              LOAD_CONST               4 (0)
              LOAD_CONST               5 (-2)
              BUILD_SLICE              2
              LOAD_CONST               1 (1)
              LOAD_CONST               2 (-1)
              BUILD_SLICE              2
              BUILD_TUPLE              2

Then tuples of slices are constant like this, this could instead be compiled down to a single LOAD_CONST instruction:

              LOAD_CONST                1 ((slice(0, -2, None), slice(1, -1, None))

According to @fberlakovich and Stefan Brunthaler's paper on Cross module quickening, this can have a significant impact on Numpy benchmarks.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-125063: Emit slices as constants in the bytecode compiler #125064

[nineteendo]

Shouldn't this be closed now?

[mdboom]

Shouldn't this be closed now?

Yep -- sorry, I forgot that step.