`LOAD_FAST_BORROW; POP_TOP` pairs should be removed

Feature or enhancement

Proposal:

I noticed that

def f(x):
    x

produces these instructions:

  3           RESUME                   0

  4           LOAD_FAST_BORROW         0 (x)
              POP_TOP
              LOAD_COMMON_CONSTANT     7 (None)
              RETURN_VALUE

from dis import dis

def f(x):
    x

dis(f)

The compiler should get rid of any LOAD_FAST_BORROW; POP_TOP pairs.

I will work on this.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-152643

Start by tracing the CPython compiler path that emits the LOAD_FAST_BORROW and POP_TOP instructions for the provided function reproducer. Use dis(f) to verify that the pair is gone while the function still returns None; the issue also links PR gh-152643, so check that work before starting.