Unreachable code warnings while building latest main at 48c70b8 #128086

srinivasreddy · 2024-12-19T05:32:33Z

Bug report

Bug description:

I ran the ./configure and make, here are the warnings shown.

gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/ast.o Python/ast.c
gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/ast_opt.o Python/ast_opt.c
gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/ast_unparse.o Python/ast_unparse.c
gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/bltinmodule.o Python/bltinmodule.c
gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/brc.o Python/brc.c
gcc -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/ceval.o Python/ceval.c
In file included from Python/ceval.c:904:
Python/generated_cases.c.h:808:31: warning: code will never be executed [-Wunreachable-code]
  808 |                 for (int _i = oparg; --_i >= 0;) {
      |                               ^~~~~
Python/generated_cases.c.h:694:31: warning: code will never be executed [-Wunreachable-code]
  694 |                 for (int _i = oparg*2; --_i >= 0;) {
      |                               ^~~~~
2 warnings generated.

Operating System:

➜  cpython git:(main) uname -a
Darwin SREDDY- 24.1.0 Darwin Kernel Version 24.1.0: Thu Oct 10 21:02:27 PDT 2024; root:xnu-11215.41.3~2/RELEASE_X86_64 x86_64

Main branch commit : 48c70b8

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

The text was updated successfully, but these errors were encountered:

srinivasreddy · 2024-12-19T06:30:36Z

I have updated the tcl-tk to version 9.0.0_1, the warnings are gone. Please refer - build.log

erlend-aasland · 2025-01-03T11:24:27Z

I cannot reproduce this on my MacBook. The tcl-tk comment seems off-topic for this issue. Can you provide more information about your environment?

srinivasreddy · 2025-01-03T12:13:10Z

Like gcc compiler version? and ...?

erlend-aasland · 2025-01-03T12:16:57Z

Include everything that is needed to reproduce the failure you are seeing. Are you still seeing these failures? Did you compile from a clean source tree (git clean -fdx)?

srinivasreddy · 2025-01-03T12:54:11Z

➜  cpython git:(main) env
TERM_SESSION_ID=REDACTED
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.xFPWqTHwrg/Listeners
LC_TERMINAL_VERSION=3.5.10
COLORFGBG=7;0
ITERM_PROFILE=REDACTED
XPC_FLAGS=0x0
LANG=en_US.UTF-8
PWD=/Users/REDACTED/workspace/github_repos/cpython
SHELL=/bin/zsh
__CFBundleIdentifier=com.googlecode.iterm2
TERM_FEATURES=REDACTED
TERM_PROGRAM_VERSION=3.5.10
TERM_PROGRAM=iTerm.app
PATH=/Users/REDACTED/.nvm/versions/node/v20.17.0/bin:/Library/Frameworks/Python.framework/Versions/3.8/bin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Library/Apple/usr/bin:/Users/REDACTED/.cargo/bin:/Applications/iTerm.app/Contents/Resources/utilities:/Users/REDACTED/.local/bin
LC_TERMINAL=iTerm2
COLORTERM=truecolor
COMMAND_MODE=unix2003
TERM=xterm-256color
TERMINFO_DIRS=/Applications/iTerm.app/Contents/Resources/terminfo:/usr/share/terminfo
HOME=/Users/REDACTED
TMPDIR=/var/folders/6v/n8nm5d6136b0br85j6llcy3c0000gn/T/
USER=REDACTED
XPC_SERVICE_NAME=0
LOGNAME=REDACTED
ITERM_SESSION_ID=REDACTED
__CF_USER_TEXT_ENCODING=0x0:0:0
SHLVL=1
OLDPWD=/Users/REDACTED/workspace/github_repos
ZSH=/Users/REDACTED/.oh-my-zsh
PAGER=less
LESS=-R
LSCOLORS=Gxfxcxdxbxegedabagacad
NVM_DIR=/Users/REDACTED/.nvm
NVM_CD_FLAGS=-q
NVM_BIN=/Users/REDACTED/.nvm/versions/node/v20.17.0/bin
NVM_INC=/Users/REDACTED/.nvm/versions/node/v20.17.0/include/node
LC_ALL=en_US.UTF-8
_=/usr/bin/env

➜  cpython git:(main) sw_vers
ProductName:		macOS
ProductVersion:		15.1.1
BuildVersion:		24B91

➜  cpython git:(main) gcc --version
Apple clang version 16.0.0 (clang-1600.0.26.6)
Target: x86_64-apple-darwin24.1.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

➜  cpython git:(main) xcodebuild -version
Xcode 16.2
Build version 16C5032a

➜  cpython git:(main) clang --version
Apple clang version 16.0.0 (clang-1600.0.26.6)
Target: x86_64-apple-darwin24.1.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

erlend-aasland · 2025-01-03T13:00:44Z

Still unable to reproduce. I'm on the same macOS version and the same compiler.

srinivasreddy · 2025-01-03T13:00:48Z

Here is the ./configure output i have captured.

config.log

srinivasreddy · 2025-01-03T13:11:12Z

Here is the make output i have capture with the command - make &> make.log. You should be able to see the warnings in the make.log file.

make.log

In file included from Python/ceval.c:904:
Python/generated_cases.c.h:808:31: warning: code will never be executed [-Wunreachable-code]
  808 |                 for (int _i = oparg; --_i >= 0;) {
      |                               ^~~~~
Python/generated_cases.c.h:694:31: warning: code will never be executed [-Wunreachable-code]
  694 |                 for (int _i = oparg*2; --_i >= 0;) {
      |                               ^~~~~
2 warnings generated.

Main branch at b4f799b

picnixz · 2025-01-03T16:57:13Z

Try to also do a make distclean, make clean and make cleantest. Some files might be left.

erlend-aasland · 2025-01-03T20:41:09Z

Actually, to be on the safe side, please do the following, then build again:

$ git reset --hard HEAD
$ git clean -fdx

picnixz · 2025-01-03T21:28:05Z

FTR: git clean -fdx would also remove all files that you manually added to the CPython project but are not in .gitignore and not committed (I have some) so I'd advise using a different directory than the directory you're usually using for development.

ned-deily · 2025-01-14T11:48:24Z

I also see unreachable-code warnings in generated_cases.c.h but only when not using --with-pydebug.

FTR, using the current HEAD of main using Apple-supplied clang. Environment is current macOS and Xcode releases. Also same warnings with a slightly older release of Xcode and clang.

$ git show
commit 1153e66e20124b8f3484bcaddbc0e252d31161a6 (HEAD -> main, upstream/main, upstream/HEAD)
Author: Victor Stinner <vstinner@python.org>
Date:   Tue Jan 14 11:18:52 2025 +0100

    gh-109959: Skip test_glob.test_selflink() flaky test (#128812)  
[...]
$ clang --version
Apple clang version 16.0.0 (clang-1600.0.26.6)
Target: arm64-apple-darwin24.2.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$ xcodebuild -version
Xcode 16.2
Build version 16C5032a
$ sw_vers
ProductName:		macOS
ProductVersion:		15.2
BuildVersion:		24C101
$ CC=clang ./configure && make -j4
[...]
clang -c -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall    -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden -Werror=unguarded-availability  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include    -DPy_BUILD_CORE -o Python/ceval.o Python/ceval.c
In file included from Python/ceval.c:906:
Python/generated_cases.c.h:4489:34: warning: code will never be executed [-Wunreachable-code]
                    for (int i = 0; i < total_args; i++) {
                                 ^
Python/generated_cases.c.h:965:34: warning: code will never be executed [-Wunreachable-code]
                    for (int i = 0; i < total_args; i++) {
                                 ^
Python/generated_cases.c.h:824:31: warning: code will never be executed [-Wunreachable-code]
                for (int _i = oparg; --_i >= 0;) {
                              ^~~~~
Python/generated_cases.c.h:710:31: warning: code will never be executed [-Wunreachable-code]
                for (int _i = oparg*2; --_i >= 0;) {
                              ^~~~~

picnixz · 2025-01-14T11:51:45Z

cc @markshannon

chris-eibl · 2025-01-14T18:31:20Z

Those are preceded by if (CONVERSION_FAILED(...)) which expands to if (0) in a "regular GIL" build, i.e. when Py_GIL_DISABLED is not defined. Interestingly, there are more such ifs, but not in all cases the warning is emitted for the following code line.

I think like unused labels are suppressed in generated code, these should be suppressed, too.
I've added # pragma GCC diagnostic ignored "-Wunreachable-code" to

cpython/Python/ceval.c

Lines 725 to 727 in f26daa9

    
           #if defined(__GNUC__) 
        
           #  pragma GCC diagnostic push 
        
           #  pragma GCC diagnostic ignored "-Wunused-label"

and also added || defined(__clang_) to get rid of this warning in clang-cl based builds ...

picnixz · 2025-01-14T18:50:25Z

For clang, can't we add #pragma clang diagnostic? Also, I believe we should patch Tools/generator_cases.py instead of ceval.c as this is the script responsible for generating Python/generated_cases.c.h and only patch it locally and not make a global #pragma (but I don't know if it's feasible)

chris-eibl · 2025-01-14T19:07:43Z

"Regular" clangs react on __GNUC__, I only added __clang__ because I did not want to see those warnings in Windows using clang-cl, which does (must) not define __GNU__.

I agree that patching Tools/generator_cases.py would be even better if someone wants to bite that bullet :)

srinivasreddy · 2025-01-15T13:18:22Z

I’m still able to reproduce the warnings with this workflow, which effectively eliminates the possibility that any custom settings or files are causing interference.

git clone https://github.com/python/cpython.git cpython_dev --depth=1
cd cpython_dev
./configure
make

srinivasreddy added the type-bug An unexpected behavior, bug, or error label Dec 19, 2024

srinivasreddy changed the title ~~Warnings while building latest main~~ Unreachable code warnings while building latest main at 48c70b8 Dec 19, 2024

srinivasreddy mentioned this issue Dec 19, 2024

Tcl warnings while building latest main - #128087

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picnixz added build The build process and cross-build interpreter-core (Objects, Python, Grammar, and Parser dirs) labels Dec 20, 2024

erlend-aasland added the pending The issue will be closed if no feedback is provided label Jan 3, 2025

ned-deily removed the pending The issue will be closed if no feedback is provided label Jan 14, 2025

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Unreachable code warnings while building latest main at 48c70b8 #128086

Unreachable code warnings while building latest main at 48c70b8 #128086

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Unreachable code warnings while building latest main at 48c70b8 #128086

Unreachable code warnings while building latest main at 48c70b8 #128086

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srinivasreddy commented Dec 19, 2024 • edited Loading

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

srinivasreddy commented Dec 19, 2024

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