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 ==
