Re: PATCH 3/8] coroutines: Support for debugging implementation state.

[Jason Merrill <jason@redhat.com>]

On 9/1/21 6:53 AM, Iain Sandoe wrote:
> 
> Some of the state that is associated with the implementation
> is of interest to a user debugging a coroutine.  In particular
> items such as the suspend point, promise object, and current
> suspend point.
> 
> These variables live in the coroutine frame, but we can inject
> proxies for them into the outermost bind expression of the
> coroutine.  Such variables are automatically moved into the
> coroutine frame (if they need to persist across a suspend
> expression).  PLacing the proxies thus allows the user to
> inspect them by name in the debugger.
> 
> To implement this, we ensure that (at the outermost scope) the
> frame entries are not mangled (coroutine frame variables are
> usually mangled with scope nesting information so that they do
> not clash).  We can safely avoid doing this for the outermost
> scope so that we can map frame entries directly to the variables.
> 
> This is partial contribution to debug support (PR 99215).

OK.

> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> gcc/cp/ChangeLog:
> 
> 	* coroutines.cc (register_local_var_uses): Do not mangle
> 	frame entries for the outermost scope.  Record the outer
> 	scope as nesting depth 0.
> ---
>   gcc/cp/coroutines.cc | 16 +++++++++++-----
>   1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
> index b8501032969..a12714ea67e 100644
> --- a/gcc/cp/coroutines.cc
> +++ b/gcc/cp/coroutines.cc
> @@ -3885,8 +3885,6 @@ register_local_var_uses (tree *stmt, int *do_subtree, void *d)
>   
>     if (TREE_CODE (*stmt) == BIND_EXPR)
>       {
> -      lvd->bind_indx++;
> -      lvd->nest_depth++;
>         tree lvar;
>         for (lvar = BIND_EXPR_VARS (*stmt); lvar != NULL;
>   	   lvar = DECL_CHAIN (lvar))
> @@ -3925,11 +3923,17 @@ register_local_var_uses (tree *stmt, int *do_subtree, void *d)
>   	    continue;
>   
>   	  /* Make names depth+index unique, so that we can support nested
> -	     scopes with identically named locals.  */
> +	     scopes with identically named locals and still be able to
> +	     identify them in the coroutine frame.  */
>   	  tree lvname = DECL_NAME (lvar);
>   	  char *buf;
> -	  if (lvname != NULL_TREE)
> -	    buf = xasprintf ("__%s.%u.%u", IDENTIFIER_POINTER (lvname),
> +	  /* The outermost bind scope contains the artificial variables that
> +	     we inject to implement the coro state machine.  We want to be able
> +	     to inspect these in debugging.  */
> +	  if (lvname != NULL_TREE && lvd->nest_depth == 0)
> +	    buf = xasprintf ("%s", IDENTIFIER_POINTER (lvname));
> +	  else if (lvname != NULL_TREE)
> +	    buf = xasprintf ("%s_%u_%u", IDENTIFIER_POINTER (lvname),
>   			     lvd->nest_depth, lvd->bind_indx);
>   	  else
>   	    buf = xasprintf ("_D%u.%u.%u", DECL_UID (lvar), lvd->nest_depth,
> @@ -3942,6 +3946,8 @@ register_local_var_uses (tree *stmt, int *do_subtree, void *d)
>   	  /* We don't walk any of the local var sub-trees, they won't contain
>   	     any bind exprs.  */
>   	}
> +      lvd->bind_indx++;
> +      lvd->nest_depth++;
>         cp_walk_tree (&BIND_EXPR_BODY (*stmt), register_local_var_uses, d, NULL);
>         *do_subtree = 0; /* We've done this.  */
>         lvd->nest_depth--;
>