[Bug inline-asm/68095] New: "cc" clobber with Flag Output Operands

["gccbugzilla at limegreensocks dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68095

            Bug ID: 68095
           Summary: "cc" clobber with Flag Output Operands
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: inline-asm
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gccbugzilla at limegreensocks dot com
  Target Milestone: ---

Normally when trying to use a register and clobber it at the same time, the
compiler kicks out an error (operand has impossible constraints).  However that
doesn't happen when using Flag Output Operands and the "cc" clobber:

  asm ("cmp %2, %1" : "=@ccc"(r) : "m"(*p), "ri"(2): "cc");

Should this be a conflict?

On the other hand, the asm is changing the flags.  So is the "cc" *required*? 
But it doesn't seem to be:

  asm ("cmp %2, %1" : "=@ccc"(r) : "m"(*p), "ri"(2));

Now that asm flags are a real thing, we should pick one and enforce it.