C++11 with GNU VLA extention results in ICE

[Andy Zheng]

I have just encountered an "internal compiler error" while using gcc-7.

```cpp source code
#include <cstdio>

int main()
{
    int N = 100;
    int K = 100;
    int dp[N][2][K] = {0};
    printf("%d\n", dp[0][0][0]);
    return 0;
}
```

After executing
  g++ test.cc
Output is
  test.cc: In function ‘int main()’:
  test.cc:7:25: internal compiler error: in make_decl_rtl, at varasm.c:1310
       int dp[N][2][K] = {0};
                         ^
  Please submit a full bug report,
  with preprocessed source if appropriate.
  See <file:///usr/share/doc/gcc-7/README.Bugs> for instructions.

which is exectly same with these three options: "-std=c++11", "-std=c++14", "-std=c++17".

With executing
  g++ test.cc -std=c++98
the binary is produced normally.

With executing
  g++ test.cc -std=c++98 -ansi -pedantic -Wextra -Werror
Output is
  test.cc: In function ‘int main()’:
  test.cc:7:19: error: ISO C++ forbids variable length array ‘dp’ [-Werror=vla]
       int dp[N][2][K] = {0};
                   ^
  test.cc:7:19: error: ISO C++ forbids variable length array ‘dp’ [-Werror=vla]
  cc1plus: all warnings being treated as errors
which is expected.

According to my observation, this seems to be the issue related to the order of 'N','2','K',
if I write
  int dp[N][K][2] = {0};
then everything is fine.

Here is my gcc version (gcc -v):

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.5.0-3ubuntu1~18.04' --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 --enable-bootstrap --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 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)

BTW, the preprocessed file 'test.ii' can be found in the 'Attachment' in case you need it.