[Bug c/17855] New: modification of function return not diagnosed

[rth at gcc dot gnu dot org]

struct foo {char x, y, z[2];};
struct foo f();
void bar(int baz)
{
        f().z[baz] = 1;
}

Generates

  z.c:5: internal compiler error: gimplification failed

But I don't see that this is legal according to [6.5.2.2]/5

  # If an attempt is made to modify the result of a function
  # call ... behaviour is undefined.

If we must accept this construct because it might not be
executed, a possible solution is to notice fallback==fb_lvalue
for a CALL_EXPR in c_gimplify_expr and create a temporary for
the call result, and which will also satisfy the lvalue.

This test has crashed in all versions since at least 2.96.

-- 
           Summary: modification of function return not diagnosed
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rth at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17855