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

[Pedro Alves <palves@redhat.com>]

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.

Thanks,
Pedro Alves