[Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og

[egall at gwmail dot gwu.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394

Eric Gallager <egall at gwmail dot gwu.edu> changed:

           What    |Removed                     |Added
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                 CC|                            |egall at gwmail dot gwu.edu

--- Comment #2 from Eric Gallager <egall at gwmail dot gwu.edu> ---
I can confirm it only happens with the -Og optimization level; I also tested
-Ofast and -Os, and neither of those triggered it either.

gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O0 maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Og maybe_uninit_00.cpp
maybe_uninit_00.cpp: In function ‘float foo()’:
maybe_uninit_00.cpp:19:17: warning: ‘vy’ may be used uninitialized in this
function [-Wmaybe-uninitialized]
     return vx + vy;
                 ^~
maybe_uninit_00.cpp:19:17: warning: ‘vx’ may be used uninitialized in this
function [-Wmaybe-uninitialized]
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O1 maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O2 maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O3 maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Ofast maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Os maybe_uninit_00.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O0 maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -O0 -g maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Og maybe_uninit_01.cpp
maybe_uninit_01.cpp: In function ‘float foo()’:
maybe_uninit_01.cpp:19:17: warning: ‘vy’ may be used uninitialized in this
function [-Wmaybe-uninitialized]
     return vx + vy;
                 ^~
maybe_uninit_01.cpp:19:17: warning: ‘vx’ may be used uninitialized in this
function [-Wmaybe-uninitialized]
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Ofast maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Ofast -g maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Os maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -Wall -Wextra -pedantic -Wmaybe-uninitialized
-Weffc++ -Winline -Wfloat-conversion -c -Os -g maybe_uninit_01.cpp
gcc_bugs root$ /usr/local/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/i386-apple-darwin9.8.0/7.0.0/lto-wrapper
Target: i386-apple-darwin9.8.0
Configured with: ../configure --disable-werror --disable-werror-always
--enable-languages=c,c++,lto,objc,obj-c++ --enable-stage1-checking=release -C
--with-system-libunwind --enable-secureplt --enable-frame-pointer
--enable-debug --with-isl --enable-objc-gc --disable-host-shared
--enable-maintainer-mode --disable-default-pie --with-ld64 --without-pic
CC=/usr/local/bin/gcc CXX=/usr/local/bin/g++ AUTOCONF=/usr/local/bin/autoconf
AUTOHEADER=/usr/local/bin/autoheader AUTORECONF=/usr/local/bin/autoreconf
AUTOM4TE=/usr/local/bin/autom4te AUTOSCAN=/usr/local/bin/autoscan
AUTOUPDATE=/usr/local/bin/autoupdate IFNAMES=/usr/local/bin/ifnames
Thread model: posix
gcc version 7.0.0 20161027 (experimental) (GCC)