generic and more efficient removal of unreachable code

[doublep]

BPO	1764986
Nosy	@rhettinger
Files	unreachable-code.diff: patch

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2008-05-31.04:59:27.344>
created_at = <Date 2007-07-31.22:44:17.000>
labels = ['interpreter-core']
title = 'generic and more efficient removal of unreachable code'
updated_at = <Date 2008-05-31.04:59:27.154>
user = 'https://bugs.python.org/doublep'

bugs.python.org fields:

activity = <Date 2008-05-31.04:59:27.154>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2008-05-31.04:59:27.344>
closer = 'rhettinger'
components = ['Interpreter Core']
creation = <Date 2007-07-31.22:44:17.000>
creator = 'doublep'
dependencies = []
files = ['8146']
hgrepos = []
issue_num = 1764986
keywords = ['patch']
message_count = 2.0
messages = ['52972', '67565']
nosy_count = 2.0
nosy_names = ['rhettinger', 'doublep']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1764986'
versions = ['Python 2.6']

[doublep]

The attached patch removed unreachable code after RAISE_VARARGS, BREAK_LOOP and RETURN_VALUE in generic way (no more tests for LOAD_CONST None RETURN_VALUE, etc.)

It is possible to generalize it more for some other bytecodes. The only problem they are already used in switch() in question as labels. Probably not important enough to warrant another switch() or break this out into a function/macro.

No speedup is expected, but I think the patch is good with no drawbacks anyway.

[rhettinger]

Not too excited about this. It adds to compilation time but doesn't
save any runtime. It's not at all common for production code to have
unreachable code at RAISE_VARARGS or BREAK_LOOP, so I see no reason to
complexify to the peepholer to handle this case.