[Bug c++/81408] Lots of new -Wunsafe-loop-optimizations warnings with 7 compared to 6

["jak at jak-linux dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81408

--- Comment #2 from Julian Andres Klode <jak@jak-linux.org> ---
Build log with -v:

Using built-in specs.
COLLECT_GCC=/usr/bin/g++-7
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 7.1.0-9'
--with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--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 --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.1.0 (Debian 7.1.0-9) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-Wunsafe-loop-optimizations'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/7/cc1plus -E -quiet -v -imultiarch
x86_64-linux-gnu -D_GNU_SOURCE a.cc -mtune=generic -march=x86-64
-Wunsafe-loop-optimizations -O2 -fpch-preprocess -o a.ii
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/7"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/7
 /usr/include/x86_64-linux-gnu/c++/7
 /usr/include/c++/7/backward
 /usr/lib/gcc/x86_64-linux-gnu/7/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-Wunsafe-loop-optimizations'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/7/cc1plus -fpreprocessed a.ii -quiet -dumpbase
a.cc -mtune=generic -march=x86-64 -auxbase a -O2 -Wunsafe-loop-optimizations
-version -o a.s
GNU C++14 (Debian 7.1.0-9) version 7.1.0 (x86_64-linux-gnu)
        compiled by GNU C version 7.1.0, GMP version 6.1.2, MPFR version 3.1.5,
MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (Debian 7.1.0-9) version 7.1.0 (x86_64-linux-gnu)
        compiled by GNU C version 7.1.0, GMP version 6.1.2, MPFR version 3.1.5,
MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 3681302eda59faba4e53a905eca4bf72
a.cc: In function ‘void ShowHelpListCommands(const
std::vector<aptDispatchWithHelp>&)’:
a.cc:11:24: warning: missed loop optimization, the loop counter may overflow
[-Wunsafe-loop-optimizations]
    for (auto const &c: Cmds)
                        ^~~~
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-Wunsafe-loop-optimizations'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
 as -v --64 -o a.o a.s
GNU assembler version 2.28 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Debian) 2.28
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/7/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-Wunsafe-loop-optimizations'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'