http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58455
Bug ID: 58455 Summary: spurious "may be used uninitialized" 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 (My gcc 4.8 is new enough that it has the fix for PR middle-end/58377) I have a case of C++ code that spuriously warns about a "may be used uninitialized" variable. I haven't been able to turn this into similar C code that still warns. Also the "|| false" in the if statement seems to do something -- without it I don't get the warning! $ cat y.cpp struct B { int offset; bool is_loaded(unsigned char *p1) { if (offset) { *p1 = offset; return true; } return false; } }; unsigned char match(struct B ref) { unsigned char ref_offset; if (!ref.is_loaded(&ref_offset) || false) return ref_offset; else return 0; } $ gcc -v -Wall -Og -Werror -c ~/y.cpp Using built-in specs. COLLECT_GCC=/usr/bin/gcc Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.8.1-10ubuntu3' --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 4.8.1-10ubuntu3) COLLECT_GCC_OPTIONS='-v' '-Wall' '-Og' '-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 /home/roland/y.cpp -mtune=generic -march=x86-64 -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' '-Wall' '-Og' '-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 4.8.1-10ubuntu3' --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 4.8.1-10ubuntu3) COLLECT_GCC_OPTIONS='-v' '-Wall' '-Og' '-Werror' '-c' '-o' '/home/roland/.ccache/a/4/3eaed08e6d4177435e048912941826-3578.o.tmp.roland-t410s.22760' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/4.8/cc1plus -fpreprocessed /home/roland/.ccache/tmp/y.tmp.roland-t410s.22760.ii -quiet -dumpbase y.tmp.roland-t410s.22760.ii -mtune=generic -march=x86-64 -auxbase-strip /home/roland/.ccache/a/4/3eaed08e6d4177435e048912941826-3578.o.tmp.roland-t410s.22760 -Og -Wall -Werror -version -fstack-protector -Wformat -Wformat-security -o /tmp/cc6olJBS.s GNU C++ (Ubuntu/Linaro 4.8.1-10ubuntu3) 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 4.8.1-10ubuntu3) 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: 9d410e3e527a5e0f1d5bb684c93d46d6 /home/roland/y.cpp: In function ‘unsigned char match(B)’: /home/roland/y.cpp:16:23: error: ‘ref_offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized] unsigned char ref_offset; ^ cc1plus: all warnings being treated as errors $ for o in Og O0 O1 O2 O3; do echo == $o ==; gcc -Wall -$o -Werror -c ~/y.cpp; done == Og == /home/roland/y.cpp: In function ‘unsigned char match(B)’: /home/roland/y.cpp:16:23: error: ‘ref_offset’ may be used uninitialized in this function [-Werror=maybe-uninitialized] unsigned char ref_offset; ^ cc1plus: all warnings being treated as errors == O0 == == O1 == == O2 == == O3 ==