https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119665
Bug ID: 119665
Summary: False positive warning about unitialized variable
while compiling with -Og
Product: gcc
Version: 14.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: Volodymyr_Babchuk at epam dot com
Target Milestone: ---
Created attachment 61029
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61029&action=edit
Minimal reproduce, pre-processed.
This issue was spotted in the wild. GCC produces false positive warning about
an unitialized variable in a for loop, but only when compiling with -Og (or
-fcondition-coverage):
$ gcc -v -save-temps 1.c -c -Og -Wall -Werror -Wextra
Using built-in specs.
COLLECT_GCC=gcc
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=ada,c,c++,d,fortran,go,lto,m2,objc,obj-c++,rust
--enable-bootstrap --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://gitlab.archlinux.org/archlinux/packaging/packages/gcc/-/issues
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.2.1 20250207 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Og' '-Wall' '-Werror' '-Wextra'
'-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.1/cc1 -E -quiet -v 1.c -mtune=generic
-march=x86-64 -Wall -Werror -Wextra -Og -fpch-preprocess -o 1.i
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.1/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.1/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-Og' '-Wall' '-Werror' '-Wextra'
'-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-pc-linux-gnu/14.2.1/cc1 -fpreprocessed 1.i -quiet
-dumpbase 1.c -dumpbase-ext .c -mtune=generic -march=x86-64 -Og -Wall -Werror
-Wextra -version -o 1.s
GNU C17 (GCC) version 14.2.1 20250207 (x86_64-pc-linux-gnu)
compiled by GNU C version 14.2.1 20250207, GMP version 6.3.0, MPFR
version 4.2.1, MPC version 1.3.1, isl version isl-0.27-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 26a734649dd11ad41e6b2b442beb07a7
1.c: In function ‘create_irq’:
1.c:27:20: error: ‘desc’ may be used uninitialized
[-Werror=maybe-uninitialized]
27 | return desc->dummy;
| ~~~~^~~~~~~
1.c:15:26: note: ‘desc’ was declared here
15 | struct irq_desc *desc;
| ^~~~
cc1: all warnings being treated as errors
When compiling with any other optimization level, it behaves as expected.
