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

[Jason Merrill via Gcc-patches]

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;
  }