[Bug c/59871] No unused value warning for comma expression

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59871

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |mpolacek at gcc dot gnu.org
   Target Milestone|---                         |4.9.0

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Confirmed, for say:
extern int bar ();

void
foo (int *p)
{
  p[0] = (bar (), 1, bar ());
  p[1] = (1, bar ());
  bar (), 1, bar ();
  bar (), 1;
  1, bar ();
}

both g++ and clang warn about all 5 cases, while gcc only about 2 of them.
g++ gives:
pr59871.c:6:27: warning: right operand of comma operator has no effect
[-Wunused-value]
pr59871.c:7:19: warning: left operand of comma operator has no effect
[-Wunused-value]
pr59871.c:8:19: warning: right operand of comma operator has no effect
[-Wunused-value]
pr59871.c:9:12: warning: right operand of comma operator has no effect
[-Wunused-value]
pr59871.c:10:11: warning: left operand of comma operator has no effect
[-Wunused-value]
and gcc only:
pr59871.c:7:12: warning: left-hand operand of comma expression has no effect
[-Wunused-value]
pr59871.c:10:4: warning: left-hand operand of comma expression has no effect
[-Wunused-value]

I'd say we want to follow what C++ FE does.