[PATCH 1/4] c++: Avoid building garbage trees from tsubst_requires_expr

[Jason Merrill]

On 2/8/21 2:03 PM, Patrick Palka wrote:
> Since we no longer partially instantiate REQUIRES_EXPRs, we don't need
> to rebuild its requirements during tsubst_requires_expr.

OK.

> gcc/cp/ChangeLog:
> 
> 	* constraint.cc (tsubst_simple_requirement): Just return
> 	boolean_true_node on success.
> 	(tsubst_type_requirement): Likewise.
> 	(tsubst_compound_requirement): Likewise.
> 	(tsubst_nested_requirement): Likewise.
> 	(tsubst_requirement_body): Remove.
> 	(check_constaint_variables): Rename to ...
> 	(check_constraint_variables): ... this.
> 	(tsubst_constraint_variables): Adjust.
> 	(tsubst_requires_expr): Fold tsubst_requirement_body into here.
> ---
>   gcc/cp/constraint.cc | 46 ++++++++++++++------------------------------
>   1 file changed, 14 insertions(+), 32 deletions(-)
> 
> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> index 31e0fb5079a..3e599fe8c47 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -1962,7 +1962,7 @@ tsubst_simple_requirement (tree t, tree args, subst_info info)
>     tree expr = tsubst_valid_expression_requirement (t0, args, info);
>     if (expr == error_mark_node)
>       return error_mark_node;
> -  return finish_simple_requirement (EXPR_LOCATION (t), expr);
> +  return boolean_true_node;
>   }
>   
>   /* Substitute through the type requirement.  */
> @@ -1974,7 +1974,7 @@ tsubst_type_requirement (tree t, tree args, subst_info info)
>     tree type = tsubst (t0, args, info.complain, info.in_decl);
>     if (type == error_mark_node)
>       return error_mark_node;
> -  return finish_type_requirement (EXPR_LOCATION (t), type);
> +  return boolean_true_node;
>   }
>   
>   /* True if TYPE can be deduced from EXPR.  */
> @@ -2080,8 +2080,7 @@ tsubst_compound_requirement (tree t, tree args, subst_info info)
>   	return error_mark_node;
>       }
>   
> -  return finish_compound_requirement (EXPR_LOCATION (t),
> -				      expr, type, noexcept_p);
> +  return boolean_true_node;
>   }
>   
>   static tree
> @@ -2100,7 +2099,7 @@ tsubst_nested_requirement (tree t, tree args, subst_info info)
>       }
>     if (result != boolean_true_node)
>       return error_mark_node;
> -  return result;
> +  return boolean_true_node;
>   }
>   
>   /* Substitute ARGS into the requirement T.  */
> @@ -2125,24 +2124,6 @@ tsubst_requirement (tree t, tree args, subst_info info)
>     gcc_unreachable ();
>   }
>   
> -/* Substitute ARGS into the list of requirements T. Note that
> -   substitution failures here result in ill-formed programs. */
> -
> -static tree
> -tsubst_requirement_body (tree t, tree args, subst_info info)
> -{
> -  tree result = NULL_TREE;
> -  while (t)
> -    {
> -      tree req = tsubst_requirement (TREE_VALUE (t), args, info);
> -      if (req == error_mark_node)
> -	return error_mark_node;
> -      result = tree_cons (NULL_TREE, req, result);
> -      t = TREE_CHAIN (t);
> -    }
> -  return nreverse (result);
> -}
> -
>   static tree
>   declare_constraint_vars (tree parms, tree vars)
>   {
> @@ -2168,7 +2149,7 @@ declare_constraint_vars (tree parms, tree vars)
>      if an error occurred.  */
>   
>   static tree
> -check_constaint_variables (tree t, tree args, subst_info info)
> +check_constraint_variables (tree t, tree args, subst_info info)
>   {
>     tree types = NULL_TREE;
>     tree p = t;
> @@ -2193,7 +2174,7 @@ static tree
>   tsubst_constraint_variables (tree t, tree args, subst_info info)
>   {
>     /* Perform a trial substitution to check for type errors.  */
> -  tree parms = check_constaint_variables (t, args, info);
> +  tree parms = check_constraint_variables (t, args, info);
>     if (parms == error_mark_node)
>       return error_mark_node;
>   
> @@ -2253,19 +2234,20 @@ tsubst_requires_expr (tree t, tree args,
>         return t;
>       }
>   
> -  tree parms = REQUIRES_EXPR_PARMS (t);
> -  if (parms)
> +  if (tree parms = REQUIRES_EXPR_PARMS (t))
>       {
>         parms = tsubst_constraint_variables (parms, args, info);
>         if (parms == error_mark_node)
>   	return boolean_false_node;
>       }
>   
> -  tree reqs = REQUIRES_EXPR_REQS (t);
> -  reqs = tsubst_requirement_body (reqs, args, info);
> -  if (reqs == error_mark_node)
> -    return boolean_false_node;
> -
> +  for (tree reqs = REQUIRES_EXPR_REQS (t); reqs; reqs = TREE_CHAIN (reqs))
> +    {
> +      tree req = TREE_VALUE (reqs);
> +      tree result = tsubst_requirement (req, args, info);
> +      if (result == error_mark_node)
> +	return boolean_false_node;
> +    }
>     return boolean_true_node;
>   }
>   
>