On 11/18/22 16:59, Patrick Palka wrote:
IIUC the only practical difference between coerce_innermost_template_parms
and the main function coerce_template_parms is that the former takes
a multi-level template parameter list and returns a template argument
vector of the same depth, whereas the latter takes a single-level
template parameter vector and returns a single-level template argument
vector.

This patch gets rid of the wrapper function and just overloads the
behavior of the main function according to whether 'parms' is a
multi-level template parameter list or a single-level template argument
vector.  It turns out we can assume parms and args have the same depth
in the multi-level case, which simplifies the overloading logic.

Besides the (subjective) simplificatio benefit, another benefit of this
unification is that it avoids a redundant copy of a multi-level 'args'.
Now, we can return new_args directly from c_t_p.  (And because of this,
we need to turn new_inner_args into a reference so that updating it also
updates new_args.)

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

OK. But this doesn't really seem like stage 3 material; let's hold off on further cleanups like this until next stage 1.

gcc/cp/ChangeLog:

        * pt.cc (coerce_template_parms): Salvage part of the function
        comment from c_innermost_t_p.  Handle parms being a full
        template parameter list.
        (coerce_innermost_template_parms): Remove.
        (lookup_template_class): Use c_t_p instead of c_innermost_t_p.
        (finish_template_variable): Likewise.
        (tsubst_decl): Likewise.
        (instantiate_alias_template): Likewise.
---
  gcc/cp/pt.cc | 92 +++++++++++++++-------------------------------------
  1 file changed, 27 insertions(+), 65 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 0310e38c9b9..2666e455edf 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -148,8 +148,6 @@ static void add_pending_template (tree);
  static tree reopen_tinst_level (struct tinst_level *);
  static tree tsubst_initializer_list (tree, tree);
  static tree get_partial_spec_bindings (tree, tree, tree);
-static tree coerce_innermost_template_parms (tree, tree, tree, tsubst_flags_t,
-                                            bool = true);
  static void tsubst_enum       (tree, tree, tree);
  static bool check_instantiated_args (tree, tree, tsubst_flags_t);
  static int check_non_deducible_conversion (tree, tree, unification_kind_t, 
int,
@@ -8827,6 +8825,14 @@ pack_expansion_args_count (tree args)
     arguments.  If any error occurs, return error_mark_node. Error and
     warning messages are issued under control of COMPLAIN.
+ If PARMS represents all template parameters levels, this function
+   returns a vector of vectors representing all the resulting argument
+   levels.  Note that in this case, only the innermost arguments are
+   coerced because the outermost ones are supposed to have been coerced
+   already.  Otherwise, if PARMS represents only (the innermost) vector
+   of parameters, this function returns a vector containing just the
+   innermost resulting arguments.
+
     If REQUIRE_ALL_ARGS is false, argument deduction will be performed
     for arguments not specified in ARGS.  If REQUIRE_ALL_ARGS is true,
     arguments not specified in ARGS must have default arguments which
@@ -8842,8 +8848,6 @@ coerce_template_parms (tree parms,
    int nparms, nargs, parm_idx, arg_idx, lost = 0;
    tree orig_inner_args;
    tree inner_args;
-  tree new_args;
-  tree new_inner_args;
/* When used as a boolean value, indicates whether this is a
       variadic template parameter list. Since it's an int, we can also
@@ -8864,6 +8868,17 @@ coerce_template_parms (tree parms,
    if (args == error_mark_node)
      return error_mark_node;
+ bool return_full_args = false;
+  if (TREE_CODE (parms) == TREE_LIST)
+    {
+      if (TMPL_PARMS_DEPTH (parms) > 1)
+       {
+         gcc_assert (TMPL_PARMS_DEPTH (parms) == TMPL_ARGS_DEPTH (args));
+         return_full_args = true;
+       }
+      parms = INNERMOST_TEMPLATE_PARMS (parms);
+    }
+
    nparms = TREE_VEC_LENGTH (parms);
/* Determine if there are any parameter packs or default arguments. */
@@ -8961,8 +8976,8 @@ coerce_template_parms (tree parms,
       template-id may be nested within a "sizeof".  */
    cp_evaluated ev;
- new_inner_args = make_tree_vec (nparms);
-  new_args = add_outermost_template_args (args, new_inner_args);
+  tree new_args = add_outermost_template_args (args, make_tree_vec (nparms));
+  tree& new_inner_args = TMPL_ARGS_LEVEL (new_args, TMPL_ARGS_DEPTH 
(new_args));
    int pack_adjust = 0;
    for (parm_idx = 0, arg_idx = 0; parm_idx < nparms; parm_idx++, arg_idx++)
      {
@@ -9164,59 +9179,7 @@ coerce_template_parms (tree parms,
      SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (new_inner_args,
                                         TREE_VEC_LENGTH (new_inner_args));
- return new_inner_args;
-}
-
-/* Like coerce_template_parms.  If PARMS represents all template
-   parameters levels, this function returns a vector of vectors
-   representing all the resulting argument levels.  Note that in this
-   case, only the innermost arguments are coerced because the
-   outermost ones are supposed to have been coerced already.
-
-   Otherwise, if PARMS represents only (the innermost) vector of
-   parameters, this function returns a vector containing just the
-   innermost resulting arguments.  */
-
-static tree
-coerce_innermost_template_parms (tree parms,
-                                tree args,
-                                tree in_decl,
-                                tsubst_flags_t complain,
-                                bool require_all_args /* = true */)
-{
-  int parms_depth = TMPL_PARMS_DEPTH (parms);
-  int args_depth = TMPL_ARGS_DEPTH (args);
-  tree coerced_args;
-
-  if (parms_depth > 1)
-    {
-      coerced_args = make_tree_vec (parms_depth);
-      tree level;
-      int cur_depth;
-
-      for (level = parms, cur_depth = parms_depth;
-          parms_depth > 0 && level != NULL_TREE;
-          level = TREE_CHAIN (level), --cur_depth)
-       {
-         tree l;
-         if (cur_depth == args_depth)
-           l = coerce_template_parms (TREE_VALUE (level),
-                                      args, in_decl, complain,
-                                      require_all_args);
-         else
-           l = TMPL_ARGS_LEVEL (args, cur_depth);
-
-         if (l == error_mark_node)
-           return error_mark_node;
-
-         SET_TMPL_ARGS_LEVEL (coerced_args, cur_depth, l);
-       }
-    }
-  else
-    coerced_args = coerce_template_parms (INNERMOST_TEMPLATE_PARMS (parms),
-                                         args, in_decl, complain,
-                                         require_all_args);
-  return coerced_args;
+  return return_full_args ? new_args : new_inner_args;
  }
/* Returns true if T is a wrapper to make a C++20 template parameter
@@ -9909,8 +9872,7 @@ lookup_template_class (tree d1, tree arglist, tree 
in_decl, tree context,
        /* Calculate the BOUND_ARGS.  These will be the args that are
         actually tsubst'd into the definition to create the
         instantiation.  */
-      arglist = coerce_innermost_template_parms (parmlist, arglist, gen_tmpl,
-                                                complain);
+      arglist = coerce_template_parms (parmlist, arglist, gen_tmpl, complain);
if (arglist == error_mark_node)
        /* We were unable to bind the arguments.  */
@@ -10326,7 +10288,7 @@ finish_template_variable (tree var, tsubst_flags_t 
complain)
    tree arglist = TREE_OPERAND (var, 1);
tree parms = DECL_TEMPLATE_PARMS (templ);
-  arglist = coerce_innermost_template_parms (parms, arglist, templ, complain);
+  arglist = coerce_template_parms (parms, arglist, templ, complain);
    if (arglist == error_mark_node)
      return error_mark_node;
@@ -14962,7 +14924,7 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
                  /* We're fully specializing a template declaration, so
                     we need to coerce the innermost arguments corresponding to
                     the template.  */
-                 argvec = (coerce_innermost_template_parms
+                 argvec = (coerce_template_parms
                            (DECL_TEMPLATE_PARMS (gen_tmpl),
                             argvec, t, complain));
                if (argvec == error_mark_node)
@@ -21800,8 +21762,8 @@ instantiate_alias_template (tree tmpl, tree args, 
tsubst_flags_t complain)
    if (tmpl == error_mark_node || args == error_mark_node)
      return error_mark_node;
- args = coerce_innermost_template_parms (DECL_TEMPLATE_PARMS (tmpl),
-                                         args, tmpl, complain);
+  args = coerce_template_parms (DECL_TEMPLATE_PARMS (tmpl),
+                               args, tmpl, complain);
/* FIXME check for satisfaction in check_instantiated_args. */
    if (flag_concepts

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