[Bug c/84900] New: Compiler report a error unexpectedly.

[141242068 at smail dot nju.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84900

            Bug ID: 84900
           Summary: Compiler report a error unexpectedly.
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 141242068 at smail dot nju.edu.cn
  Target Milestone: ---

Here is my code:


$cat main.c

struct S2 { int m1; };

int test = 0;

int main() {
        struct S2 *p = &(struct S2) (struct S2) {
                (test = 0), // gcc report error here
        };
        return 0;
}


When I compile it with gcc-7.2.0, it give me an error:

$ gcc main.c
main.c: In function ‘main’:
main.c:6:17: error: lvalue required as unary ‘&’ operand
  struct S2 *p = &(struct S2) (struct S2) {


It seems the initializer was viewed as rvalue, but when I replace the
expression `(test = 0)` by 0, like below:


$ cat main.c 
struct S2 { int m1; };

int test = 0;

int main() {
        struct S2 *p = &(struct S2) (struct S2) {
                0,
        };
        return 0;
}


It compiles successfully and give me no errors, the expression kind in the
initializer affects the error reported ?


My gcc details:

$ 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
7.2.0-1ubuntu1~16.04' --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 --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 --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 7.2.0 (Ubuntu 7.2.0-1ubuntu1~16.04)