test_peg_generator fails on a PGO+LTO build with clang

[vstinner]

Bug report

Example on aarch64 Debian Clang LTO + PGO 3.x: https://buildbot.python.org/all/#/builders/1084/builds/4019

0:02:04 load avg: 5.35 [290/473/1] test_peg_generator failed (22 errors) -- running (2): test_io (32.6 sec), test_socket (32.8 sec)
(...)
Successfully installed setuptools-67.6.1 wheel-0.43.0
(...)
test_ternary_operator (test.test_peg_generator.test_c_parser.TestCParser.test_ternary_operator) ... warning: profile data may be out of date: of 9 functions, 1 has mismatched data that will be ignored [-Wprofile-instr-out-of-date]
1 warning generated.
./parse.o: file not recognized: file format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ERROR

======================================================================
ERROR: test_ternary_operator (test.test_peg_generator.test_c_parser.TestCParser.test_ternary_operator)
----------------------------------------------------------------------
(...)
distutils.errors.LinkError: command '/usr/local/bin/clang' failed with exit code 1

Linked PRs

• gh-117889: Fix PGO test in test_peg_generator #117893
• [3.12] gh-117889: Fix PGO test in test_peg_generator (GH-117893) #117895

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I can reproduce the issue on Fedora 39 with:

./configure --prefix $PWD/target CC=clang LD=clang --with-lto --enable-optimizations
time make
./python -m test test_peg_generator -v -m test_ternary_operator -u all

[vstinner]

It seems like it's a regression introduced by the change: commit 1ddbeae.

commit 1ddbeae040beb35614f3933f340e0dedcc1e98e4
Author: Erlend E. Aasland <erlend@python.org>
Date:   Fri Apr 12 11:36:40 2024 +0200

    gh-117752: Autoconf: fix PGO builds for 'make -C build' incantations (#117803)

 configure    |  8 ++++----
 configure.ac | 16 ++++++++++++----
 2 files changed, 16 insertions(+), 8 deletions(-)

cc @erlend-aasland

[erlend-aasland]

Yes, I suspected this. Perhaps we should revert that change and just don't support the make -C build scenario.

[erlend-aasland]

I still think we should keep 396b831, though.

[vstinner]

For git bisect, I used:

git clean -fdx
./configure --prefix $PWD/target CC=clang LD=clang --enable-optimizations PROFILE_TASK="-c pass" CFLAGS="-O0" --with-lto
time make
./python -m test test_peg_generator -v -m test_ternary_operator -u all

For old commits, it seems like test_ternary_operator() didn't exist, so instead I ran:

./python -m test test_peg_generator -u all -v 

[vstinner]

The test_peg_generator check for PGO build no longer works since the variable contains a shell command:

$ ./python
Python 3.13.0a6+ (heads/main:a9107fe5c0, Apr 15 2024, 15:17:09) [Clang 17.0.6 (Fedora 17.0.6-2.fc39)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sysconfig
>>> sysconfig.get_config_var('PGO_PROF_USE_FLAG')
'-fprofile-instr-use="$(shell pwd)/code.profclangd"'

I wrote PR gh-117893 to fix the test.