Treat slices with constant parts as constants and remove BINARY_SLICE opcodes

[markshannon]

This is in support of #118093, where we want to merge BINARY_SUBSCR into BINARY_OP.

Prior to merging BINARY_SUBSCR into BINARY_OP, we want to get rid of the BINARY_SLICE opcodes as they complicate specialization. Without BINARY_SLICE we want to treat constant slices as constants, to reduce the overhead of computing slices.

With this change the bytecode for seq[:-1] goes from:

  LOAD_FAST                0 (seq)
  LOAD_CONST               0 (None)
  LOAD_CONST               1 (-1)
  BINARY_SLICE

to:

  LOAD_FAST                0 (seq)
  LOAD_CONST               1 (slice(None, -1, None))
  BINARY_SUBSCR

Linked PRs

• GH-119500: Remove slice opcodes and handle constant slices in the compiler. #119502

[markshannon]

Benchmarking suggests that it is worth keeping BINARY_SLICE. If we implement tagged ints, the performance benefit of BINARY_SLICE is likely to increase.