Re: [PATCH] c++: set loc on call even if result is discarded

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Apr 8, 2022 at 12:49 AM Alexandre Oliva via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Apr  6, 2022, Jason Merrill <jason@redhat.com> wrote:
>
> > On 4/6/22 15:37, Alexandre Oliva wrote:
> > Need to adjust this subject line, as well.
>
> *nod*, thanks
>
> >> * tree.cc (protected_set_expr_location): Propagate locus to
> >> call wrapped in cast-to-void.
>
> > I'm reluctant to put this C++-specific change in a simple function
> > shared by all languages;
>
> Perhaps it benefits other languages as well?  The effect is presumably
> desirable on other languages too: setting a cast-to-void's location
> seems completely ineffective, as it's eventually thrown away, and
> perhaps propagating the location to any operand (rather than just calls)
> would carry out the intent of [protected_]set_expr_location more
> effectively.  It doesn't feel right to require every caller to worry
> about that.

Hmm, but then maybe it would be better the task of the code
actually throwing away the cast?  I agree the original
proposed location to fix this looks bad.

> > how about handling it in set_cleanup_locs instead?
>
> Like this?  That seems reasonable to me.  I'll give it a spin.
>
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index a7f6449dafd2e..43627ed30afcb 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -609,7 +609,17 @@ set_cleanup_locs (tree stmts, location_t loc)
>  {
>    if (TREE_CODE (stmts) == CLEANUP_STMT)
>      {
> -      protected_set_expr_location (CLEANUP_EXPR (stmts), loc);
> +      tree t = CLEANUP_EXPR (stmts);
> +      protected_set_expr_location (t, loc);
> +      /* Avoid locus differences for C++ cdtor calls depending on whether
> +        cdtor_returns_this: a conversion to void is added to discard the return
> +        value, and this conversion ends up carrying the location, and when it
> +        gets discarded, the location is lost.  So hold it in the call as
> +        well.  */
> +      if (TREE_CODE (t) == NOP_EXPR
> +         && TREE_TYPE (t) == void_type_node
> +         && TREE_CODE (TREE_OPERAND (t, 0)) == CALL_EXPR)
> +       protected_set_expr_location (TREE_OPERAND (t, 0), loc);
>        set_cleanup_locs (CLEANUP_BODY (stmts), loc);
>      }
>    else if (TREE_CODE (stmts) == STATEMENT_LIST)
>
>
> --
> Alexandre Oliva, happy hacker                https://FSFLA.org/blogs/lxo/
>    Free Software Activist                       GNU Toolchain Engineer
> Disinformation flourishes because many people care deeply about injustice
> but very few check the facts.  Ask me about <https://stallmansupport.org>