Re: [PATCH] Make dwarf_expr_piece::pieces an std::vector

[Simon Marchi <simon dot marchi at polymtl dot ca>]

On 2017-09-14 11:21, Pedro Alves wrote:
> On 09/14/2017 09:15 AM, Simon Marchi wrote:
>
> >  static struct piece_closure *
> >  allocate_piece_closure (struct dwarf2_per_cu_data *per_cu,
> > -			int n_pieces, struct dwarf_expr_piece *pieces,
> > +			const std::vector<dwarf_expr_piece> &&pieces,
>
> const rval reference looks odd -- you can't really move
> the internal elements out of a const vector.  I think ...
>
> >  			struct frame_info *frame)
> >  {
> > -  struct piece_closure *c = XCNEW (struct piece_closure);
> > +  struct piece_closure *c = new piece_closure;
> >    int i;
> >
> >    c->refc = 1;
> >    c->per_cu = per_cu;
> > -  c->n_pieces = n_pieces;
> > -  c->pieces = XCNEWVEC (struct dwarf_expr_piece, n_pieces);
> > +  c->pieces = std::move (pieces);
>
> ... this isn't really moving, but actually copying, because
> you'll end up calling 'std::vector(const std::vector &)', not
> 'std::vector(std::vector &&)'.
>
> I wonder if there's ever a case for 'const T &&' parameters,
> and if GCC could warn about them.  At least in non-template
> functions.

Oops, I started with a const reference, before changing it to rvalue 
reference (and forgot to remove the const).  Does the patch look good to 
you otherwise?

Simon