bpo-42246: Remove DO_NOT_EMIT_BYTECODE macros, so that while loops and if statements conform to PEP 626.

[markshannon]

PEP 626 requires all expressions and statements to be traced, even if the code is redundant.
This PR does that for while and if statements.
The performance impact on while 1: loops is minimized by copying the test to the end of the loop.

while test:
     body

used to compile to:

start:
    if not test: goto end
    body
    goto start
end:

It now compiles to:

    if not test: goto end
loop:
    body
    if test goto loop
end:

which will be a tiny bit slower for while 1 loops and a bit faster for other while loops.

I'm skipping news, as this PR is part of PEP 626 and is covered by that.

https://bugs.python.org/issue42246

[markshannon]

I've removed this test, as doesn't test what it claims to test. There is no dead code in

def f(cond1, cond2):
    while 1:
        if cond1: return 4

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @markshannon for commit c15f5ab 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[markshannon]

The three failures are, in order:

• An asyncio test timeout. Comments about the reliability of asyncio are for another issue.
• A pre-existing failure.
• Missing symbols in LTO, possibly caused by a (wrong) warning about buffer overflow when resizing a bytes object.

No leaks, or real failures, so I'm merging.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 RHEL7 3.x has failed when building commit 8473cf8.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/539/builds/421) and take a look at the build logs.
4. Check if the failure is related to this commit (8473cf8) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/539/builds/421

Summary of the results of the build (if available):

== Tests result: ENV CHANGED ==

412 tests OK.

10 slowest tests:

• test_concurrent_futures: 4 min 22 sec
• test_unparse: 4 min 9 sec
• test_tokenize: 3 min 34 sec
• test_capi: 3 min 10 sec
• test_peg_generator: 3 min
• test_asyncio: 3 min
• test_multiprocessing_spawn: 2 min 50 sec
• test_lib2to3: 2 min 15 sec
• test_multiprocessing_forkserver: 1 min 24 sec
• test_nntplib: 1 min 22 sec

1 test altered the execution environment:
test_asyncio

13 tests skipped:
test_devpoll test_ioctl test_kqueue test_msilib test_ossaudiodev
test_startfile test_tix test_tk test_ttk_guionly test_winconsoleio
test_winreg test_winsound test_zipfile64

Total duration: 7 min 13 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/sslproto.py", line 321, in __del__
    self.close()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/sslproto.py", line 316, in close
    self._ssl_protocol._start_shutdown()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/sslproto.py", line 590, in _start_shutdown
    self._abort()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/sslproto.py", line 731, in _abort
    self._transport.abort()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/selector_events.py", line 680, in abort
    self._force_close(None)
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/selector_events.py", line 731, in _force_close
    self._loop.call_soon(self._call_connection_lost, exc)
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/base_events.py", line 745, in call_soon
    self._check_closed()
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL7-aarch64/build/Lib/asyncio/base_events.py", line 510, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed