https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79517
Bug ID: 79517
Summary: using a deque supresses compiler warning for undefined
behavior
Product: gcc
Version: 6.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gnu at oss dot m-berberich.de
Target Milestone: ---
Created attachment 40740
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40740&action=edit
source-code
This attached code terminates if compiled without optimization, but does not
terminate if compiled with ‘-O2’ or ‘-O3’. This is due to undefined behavior
caused by an signed integer overflow.
g++ does not give any warning on compiling. If the the line ‘std::deque<float>
d;’ is removed g++ does give a warning as expected.
> g++ -O3 bug.cc
bug.cc: In function ‘int main()’:
bug.cc:7:16: warning: iteration 447392 invokes undefined behavior
[-Waggressive-loop-optimizations]
data[i] = n++;
~^~
bug.cc:16:17: note: within this loop
for(int i=0; i<800000; ++i) {
~^~~~~~~
So creating an unused deque suppresses the compilerwarning. I don’t think this
should happen.
> g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 6.3.0-6'
--with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-6 --program-prefix=x86_64-linux-gnu- --enable-shared
--enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-amd64/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--with-target-system-zlib --enable-objc-gc=auto --enable-multiarch
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --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 6.3.0 20170205 (Debian 6.3.0-6)
