Redundant jump instructions due to deleted unreachable bytecode blocks

[OmG-117]

BPO	42615
Nosy	@markshannon, @OmG-117
PRs	bpo-42615: Delete redundant jump instructions that only bypass empty blocks #23733
Files	jmptest.py: This file contains a short function that exhibits this behavior. Notice the JUMP_FORWARD 0 instruction, which does nothing.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-12-16.14:43:48.978>
created_at = <Date 2020-12-10.16:47:13.158>
labels = ['3.10', 'performance']
title = 'Redundant jump instructions due to deleted unreachable bytecode blocks'
updated_at = <Date 2020-12-16.14:43:48.978>
user = 'https://github.com/OmG-117'

bugs.python.org fields:

activity = <Date 2020-12-16.14:43:48.978>
actor = 'OmG'
assignee = 'none'
closed = True
closed_date = <Date 2020-12-16.14:43:48.978>
closer = 'OmG'
components = []
creation = <Date 2020-12-10.16:47:13.158>
creator = 'OmG'
dependencies = []
files = ['49664']
hgrepos = []
issue_num = 42615
keywords = ['patch']
message_count = 2.0
messages = ['382834', '383157']
nosy_count = 2.0
nosy_names = ['Mark.Shannon', 'OmG']
pr_nums = ['23733']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue42615'
versions = ['Python 3.10']

[OmG-117]

During optimization, the compiler deletes blocks that are marked as unreachable. In doing so, it can render jump instructions that used to jump over the now-deleted blocks redundant, since simply falling through to the next non-empty block is now equivalent.

An example of a place where this occurs is around "if condition: statement; else: break" style structures (see attached proof of concept code below), but this is a general case and could occur in other places.

Tested on the latest 3.10 branch including all recent compile.c changes.

[markshannon]

New changeset c71581c by Om G in branch 'master':
bpo-42615: Delete redundant jump instructions that only bypass empty blocks (GH-23733)
c71581c