Weird PGO build issue on macOS 14.3

[corona10]

• Xcode: 15.3 (22618)
• Instruments: 15.3 (64565.111)

With ./configure --enable-optimizations, the PGO build itself is a success on my machine, but the status is weird.

Following build warnings are emitted at the first build

clang: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]
...

During the profiling stage, several tests are not passed as before.

# Next, run the profile task to generate the profile information.
LLVM_PROFILE_FILE="code-%p.profclangr"  ./python.exe -m test --pgo --timeout=
Using random seed: 3569111910
Raised RLIMIT_NOFILE: 256 -> 1024
0:00:00 load avg: 4.25 Run 44 tests sequentially
0:00:00 load avg: 4.25 [ 1/44] test_array
0:00:00 load avg: 4.25 [ 2/44] test_base64
0:00:00 load avg: 4.25 [ 3/44] test_binascii -- test_base64 failed (env changed)
0:00:00 load avg: 4.25 [ 4/44] test_binop
0:00:00 load avg: 4.25 [ 5/44] test_bisect
0:00:00 load avg: 4.25 [ 6/44] test_bytes
0:00:02 load avg: 4.25 [ 7/44] test_bz2 -- test_bytes failed (env changed)
0:00:02 load avg: 4.25 [ 8/44] test_cmath
0:00:02 load avg: 4.25 [ 9/44] test_codecs
0:00:03 load avg: 4.25 [10/44] test_collections
0:00:03 load avg: 4.25 [11/44] test_complex
0:00:03 load avg: 4.25 [12/44] test_dataclasses
0:00:04 load avg: 4.25 [13/44] test_datetime
0:00:06 load avg: 4.63 [14/44] test_decimal
------------------------------------ NOTICE ------------------------------------
test_decimal may generate "malloc can't allocate region"
warnings on macOS systems. This behavior is known. Do not
report a bug unless tests are also failing.
See https://github.com/python/cpython/issues/85100
--------------------------------------------------------------------------------
0:00:08 load avg: 4.63 [15/44] test_difflib
0:00:09 load avg: 4.63 [16/44] test_embed
0:00:12 load avg: 4.50 [17/44] test_float -- test_embed failed (env changed)
0:00:12 load avg: 4.50 [18/44] test_fstring
0:00:13 load avg: 4.50 [19/44] test_functools
0:00:14 load avg: 4.50 [20/44] test_generators
0:00:14 load avg: 4.50 [21/44] test_hashlib
0:00:14 load avg: 4.62 [22/44] test_heapq
0:00:15 load avg: 4.62 [23/44] test_int
0:00:15 load avg: 4.62 [24/44] test_itertools
0:00:16 load avg: 4.62 [25/44] test_json -- test_itertools failed (env changed)
0:00:18 load avg: 4.62 [26/44] test_long -- test_json failed (env changed)
0:00:19 load avg: 4.41 [27/44] test_lzma
0:00:20 load avg: 4.41 [28/44] test_math
0:00:21 load avg: 4.41 [29/44] test_memoryview
0:00:21 load avg: 4.41 [30/44] test_operator
0:00:21 load avg: 4.41 [31/44] test_ordered_dict
0:00:21 load avg: 4.41 [32/44] test_patma
0:00:22 load avg: 4.41 [33/44] test_pickle
0:00:24 load avg: 4.41 [34/44] test_pprint
0:00:24 load avg: 4.41 [35/44] test_re
0:00:24 load avg: 4.38 [36/44] test_set -- test_re failed (env changed)
0:00:26 load avg: 4.38 [37/44] test_sqlite3
0:00:26 load avg: 4.38 [38/44] test_statistics -- test_sqlite3 failed (env changed)
0:00:29 load avg: 4.11 [39/44] test_str
0:00:30 load avg: 4.11 [40/44] test_struct -- test_str failed (env changed)
0:00:30 load avg: 4.11 [41/44] test_tabnanny -- test_struct failed (env changed)
0:00:30 load avg: 4.11 [42/44] test_time -- test_tabnanny failed (env changed)
0:00:32 load avg: 4.11 [43/44] test_xml_etree
0:00:33 load avg: 4.11 [44/44] test_xml_etree_c

Total duration: 33.8 sec
Total tests: run=9,203 skipped=182
Total test files: run=44/44 env_changed=10
Result: SUCCESS

Also, writing profile files is in a weird status.

/usr/bin/xcrun llvm-profdata merge -output=code.profclangd *.profclangr
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory
LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory

cc @ned-deily @ronaldoussoren @erlend-aasland

Linked PRs

• gh-117752: Autoconf: fix -fno-semantic-interposition check #117789
• gh-117752: Autoconf: store all LLVM profile data in the build directory #117790
• [3.12] gh-117752: Autoconf: store all LLVM profile data in the build directory (GH-117790) #117795
• [3.12] gh-117752: Autoconf: fix -fno-semantic-interposition check (GH-117789) #117800
• gh-117752: Autoconf: fix PGO builds for 'make -C build' incantations #117803
• [3.12] gh-117752: Autoconf: fix PGO builds for 'make -C build' incantations (GH-117803) #117805

Retargeted PRs:

• gh-117804: Autoconf: silence some clang warnings for PGO builds #117796

[erlend-aasland]

Related to -fno-semantic-interposition:

• bpo-38980: Only apply -fno-semantic-interposition if available #22892
• bpo-38980: Add -fno-semantic-interposition when building with optimizations #22862

[erlend-aasland]

Related issues:

• Default CC is "gcc" on Mac, but should be "clang" #110577
• detecting clang in configure.ac #110034
• configure.ac: using $CC to check compiler names may result in erroneous judgements #96398
• compiler detection on macOS seems to be incorrect #88259

UPDATE: I kept #96398 open and closed the other as duplicates or superseded. Let's not forget this issue.

[erlend-aasland]

Following build warnings are emitted at the first build [...]

clang: warning: argument unused during compilation: '-fno-semantic-interposition' [-Wunused-command-line-argument]

This clang warning is also mentioned in issue #110577. Some of our $CC checks in configure.ac are inaccurate¹. However, IIUC c6d7e82 should have take care of that.

For example, applying this patch (as hinted to in #110577) gets rid of the warning:

diff --git a/configure.ac b/configure.ac
index e195e15b39..325b5b973b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1796,10 +1796,12 @@ if test "$Py_OPT" = 'true' ; then
   DEF_MAKE_RULE="build_all"
   case $CC in
     *gcc*)
-      AX_CHECK_COMPILE_FLAG([-fno-semantic-interposition],[
-      CFLAGS_NODIST="$CFLAGS_NODIST -fno-semantic-interposition"
-      LDFLAGS_NODIST="$LDFLAGS_NODIST -fno-semantic-interposition"
-      ])
+      if test -n "${cc_is_clang}"; then
+        AX_CHECK_COMPILE_FLAG([-fno-semantic-interposition],[
+        CFLAGS_NODIST="$CFLAGS_NODIST -fno-semantic-interposition"
+        LDFLAGS_NODIST="$LDFLAGS_NODIST -fno-semantic-interposition"
+        ])
+      fi
       ;;
   esac
 elif test "$ac_sys_system" = "Emscripten" -o "$ac_sys_system" = "WASI"; then

Footnotes

1. which is also mentioned in some of the other related issues I linked to]. ↩

[erlend-aasland]

Regarding this:

LLVM Profile Error: Failed to write file "code-75991.profclangr": No such file or directory

Try this patch:

diff --git a/configure.ac b/configure.ac
index 60c4141a3d..2570fc5f32 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2013,7 +2013,7 @@ case "$CC_BASENAME" in
     PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
     PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
     LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
-    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"\$(shell pwd)/code-%p.profclangr\""
     if test $LLVM_PROF_FOUND = not-found
     then
       LLVM_PROF_ERR=yes
@@ -2029,7 +2029,7 @@ case "$CC_BASENAME" in
         PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
         PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
         LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
-        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"\$(shell pwd)/code-%p.profclangr\""
         if test "${LLVM_PROF_FOUND}" = "not-found"
         then
           LLVM_PROF_ERR=yes

This should also get rid of the "env changed" warnings, as profile data will now not interfere with the test environment.

[erlend-aasland]

Moreover, we should consider compiling with -Wno-profile-instr-unprofiled (and perhaps also -Wno-profile-instr-out-of-date) when PGO is enabled. There is no need to warn about the files that lack profile data.