http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58377
Bug ID: 58377 Summary: spurious "may be unused" warning with -Og Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: rbd at debian dot org The following code generates a spurious " ‘out’ may be used uninitialized in this function" warning when built with -Og; no optimization, -O1, -O2, -O3 and -Ofast all do not warn. // gcc -Og -std=c++0x -Wall -Werror -c xx.cpp struct ordered_tasks { int * pop (); }; struct A { ordered_tasks * tasks[]; int * pop (); }; int pop_first_bucket; int * A::pop () { int * out; int cur_bucket = 0; do { if (tasks[0]) { out = tasks[cur_bucket]->pop(); if (out) return out; } } while (pop_first_bucket); return 0; } output / details of my system: $ gcc -v -Og -std=c++0x -Wall -Werror -c xx.cpp Using built-in specs. COLLECT_GCC=/usr/bin/gcc Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.8.1-10ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu1) COLLECT_GCC_OPTIONS='-v' '-Og' '-std=c++11' '-Wall' '-Werror' '-c' '-E' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.8/cc1plus -E -quiet -v -imultiarch x86_64-linux-gnu -D_GNU_SOURCE xx.cpp -mtune=generic -march=x86-64 -std=c++11 -Wall -Werror -Og -fstack-protector -Wformat -Wformat-security ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/4.8" ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/include/c++/4.8 /usr/include/x86_64-linux-gnu/c++/4.8 /usr/include/c++/4.8/backward /usr/lib/gcc/x86_64-linux-gnu/4.8/include /usr/local/include /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/include End of search list. COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-Og' '-std=c++11' '-Wall' '-Werror' '-c' '-E' '-mtune=generic' '-march=x86-64' Using built-in specs. COLLECT_GCC=/usr/bin/gcc Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.8.1-10ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.8.1 (Ubuntu/Linaro 4.8.1-10ubuntu1) COLLECT_GCC_OPTIONS='-v' '-Og' '-std=c++11' '-Wall' '-Werror' '-c' '-o' '/home/roland/.ccache/4/3/9782563fbf89cd86ac0377b998dd1c-3528.o.tmp.roland-t410s.18048' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.8/cc1plus -fpreprocessed /home/roland/.ccache/tmp/xx.tmp.roland-t410s.18048.ii -quiet -dumpbase xx.tmp.roland-t410s.18048.ii -mtune=generic -march=x86-64 -auxbase-strip /home/roland/.ccache/4/3/9782563fbf89cd86ac0377b998dd1c-3528.o.tmp.roland-t410s.18048 -Og -Wall -Werror -std=c++11 -version -fstack-protector -Wformat -Wformat-security -o /tmp/ccZi8CJF.s GNU C++ (Ubuntu/Linaro 4.8.1-10ubuntu1) version 4.8.1 (x86_64-linux-gnu) compiled by GNU C version 4.8.1, GMP version 5.1.2, MPFR version 3.1.1-p2, MPC version 1.0.1 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++ (Ubuntu/Linaro 4.8.1-10ubuntu1) version 4.8.1 (x86_64-linux-gnu) compiled by GNU C version 4.8.1, GMP version 5.1.2, MPFR version 3.1.1-p2, MPC version 1.0.1 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: bbda97c7f6a737ad1364ffd9676a3180 xx.cpp: In member function ‘int* A::pop()’: xx.cpp:18:11: error: ‘out’ may be used uninitialized in this function [-Werror=maybe-uninitialized] int * out; ^ cc1plus: all warnings being treated as errors