[Development] qtbase 5.8.0 -O3 flag causes an internal compiler error on Ubuntu 16.04

[Massimo Callegari]

Hi, I am building Qt 5.8.0 alpha on Kubuntu 16.04 and the file qtbase/src/gui/painting/qdrawhelper.cpp causes a segmentation fault in GCC 5.4.0.

In particular, it happens at line 4977: static void blend_transformed_argb(int count, const QSpan *spans, void *userData)

After a few minutes, I found out that the -O3 flag in CXXFLAGS is causing this. Manually changing it to -O2 only for that file let the build proceed.

Now, I know this most likely seems to be a GCC issue, but 16.04 is a LTS distro and the vanilla GCC is 5.4.0 (details below), so I just wanted to report this.


Should I fire a Jira ticket or is this not pertinent ?

Regards,
Massimo


Using built-in specs. 
COLLECT_GCC=gcc 
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper 
Target: x86_64-linux-gnu 
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.4.0-6ubuntu1~16.04.2' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --ena
ble-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/us
r/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-de
bug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugi
n --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --
enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64 --with-arc
h-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-a
bi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-li
nux-gnu --target=x86_64-linux-gnu 
Thread model: posix 
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.2)