gh-148535: Don't use gcc -fprofile-update=atomic flag on i686

[vstinner]

The -fprofile-update=atomic flag was added to fix a random GCC internal error on PGO build (gh-145801) caused by corruption of profile data (.gcda files). The problem is that it makes the PGO build way slower (up to 47x slower) on i686. Since the GCC internal error was not seen on i686 so far, don't use -fprofile-update=atomic on i686.

• Issue: The -fprofile-update=atomic flag makes the PGO build way slower on i686 #148535

[Fidget-Spinner]

Do we need to do PGO_PROF_GEN_FLAG="PGO_PROF_GEN_FLAG -fprofile-generate" (i forgot the proper substitution) or is this something that won't be set by user?

[vstinner]

Currently, you cannot override PGO_PROF_GEN_FLAG variable when running configure. My PR doesn't change that, it just moves code around.

But if you really want to override these flags, you can override the variable when running make. Example: make PGO_PROF_GEN_FLAG="--my-flags". Again, my PR doesn't change that (it remains possible).

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @vstinner, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 2faceeec5c0fb06498a9654d429180ac4610c65a 3.13

[bedevere-app]

GH-148655 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-148656 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Refleaks 3.14 (tier-3) has failed when building commit 2fdccb3.

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/#/builders/1800/builds/1165) and take a look at the build logs.
4. Check if the failure is related to this commit (2fdccb3) 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/#/builders/1800/builds/1165

Failed tests:

• test_httpservers
• test.test_concurrent_futures.test_interpreter_pool
• test_datetime

Failed subtests:

• test_large_content_length_truncated - test.test_httpservers.CGIHTTPServerTestCase.test_large_content_length_truncated

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/test/libregrtest/single.py", line 236, in _runtest_env_changed_exc
    return
ResourceWarning: unclosed <socket.socket fd=5, family=2, type=1, proto=6, laddr=('127.0.0.1', 16947)>


Traceback (most recent call last):
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/test/test_httpservers.py", line 1139, in test_large_content_length_truncated
    res = self.request('/cgi-bin/file1.py', 'POST', b'x', headers)
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/test/test_httpservers.py", line 131, in request
    self.connection.request(method, uri, body, headers)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/http/client.py", line 1358, in request
    self._send_request(method, url, body, headers, encode_chunked)
    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/http/client.py", line 1404, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/http/client.py", line 1353, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/http/client.py", line 1152, in _send_output
    self.send(chunk)
    ~~~~~~~~~^^^^^^^
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/http/client.py", line 1077, in send
    self.sock.sendall(data)
    ~~~~~~~~~~~~~~~~~^^^^^^
BrokenPipeError: [Errno 32] Broken pipe


Traceback (most recent call last):
  File "/buildbot/buildarea/3.14.ware-freebsd.refleak/build/Lib/test/libregrtest/single.py", line 236, in _runtest_env_changed_exc
    return
ResourceWarning: unclosed <socket.socket fd=4, family=2, type=1, proto=6, laddr=('127.0.0.1', 11373)>