[Bug c/53064] New: -Wsenquence-point behaves inconsistently

[wenbin816 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53064

             Bug #: 53064
           Summary: -Wsenquence-point behaves inconsistently
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: wenbin...@gmail.com


This is my first bug report here, so please bear with me.

Compiling the following code

int f(int a)
{
  return 0;
}
main()
{
  int a = 0;
  a + f(++a ? 0 : 0);
}

with -Wall gives
test.c:8:9: warning: operation on ‘a’ may be undefined [-Wsequence-point]

while compiling

main()
{
  int a = 0;
  a + (++a ? 0 : 0);
}

with -Wall produces no warning about sequence points.

I think (not sure though) both are UB.

gcc -v information:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/src/gcc-4.7-20120414/configure --prefix=/usr
--libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared
--enable-threads=posix --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch
--enable-libstdcxx-time --enable-gnu-unique-object --enable-linker-build-id
--with-ppl --enable-cloog-backend=isl --enable-lto --enable-gold
--enable-ld=default --enable-plugin --with-plugin-ld=ld.gold
--with-linker-hash-style=gnu --disable-multilib --disable-libssp
--disable-build-with-cxx --disable-build-poststage1-with-cxx
--enable-checking=release
Thread model: posix
gcc version 4.7.0 20120414 (prerelease) (GCC) 

Sorry if the bug is invalid, or if my English is poor.