Re: [PATCH v4] c++: Implement -Wself-move warning [PR81159]

[Marek Polacek <polacek@redhat.com>]

On Tue, Aug 23, 2022 at 05:27:00PM -0400, Jason Merrill wrote:
> On 8/23/22 09:39, Marek Polacek wrote:
> > +  tree arg = CALL_EXPR_ARG (fn, 0);
> > +  extract_op (arg);
> > +  if (TREE_CODE (arg) == ADDR_EXPR)
> > +    arg = TREE_OPERAND (arg, 0);
> > +  tree type = TREE_TYPE (lhs);
> > +  lhs = maybe_undo_parenthesized_ref (lhs);
> > +  STRIP_ANY_LOCATION_WRAPPER (lhs);
> > +  const bool print_var_p = (DECL_P (lhs)
> > +			    || REFERENCE_REF_P (lhs)
> > +			    || TREE_CODE (lhs) == COMPONENT_REF);
> 
> Why include REFERENCE_REF_P and COMPONENT_REF?  Reference refs should be
> stripped before this test, member refs aren't variables.

I'm checking REFERENCE_REF_P and COMPONENT_REF to say "moving a variable"
in #1 and #3.  The REFERENCE_REF_P check means that we also say "variable"
for #2.  Sure, "A variable is introduced by the declaration of a reference
other than a non-static data member", but I'm not sure if users care about
that here?

If I strip REFERENCE_REFs before the check then the result will be the
same.  Or I could keep only the DECL_P check, but then we'll say "moving
an expression" for #1 and #2, which seems strange.

struct S {
  int x;
  int &r;
  void foo () {
    x = std::move (x); // #1
    r = std::move (r); // #2
  };
};

void
foo (int &r)
{
  r = std::move (r); // #3
}

Marek