From e85c596ae2d1e5f5b769b5af4c0a8e7d055e40d7 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 17 Nov 2023 17:17:32 -0500
Subject: c++: compare one level of template parms

There should never be a reason to compare more than one level of template
parameters; additional levels are for the enclosing context, which is either
irrelevant (for a template template parameter) or already compared (for a
member template).

Also, the comp_template_parms handling of type parameters was wrongly
checking for TEMPLATE_TYPE_PARM when a type parameter appears here as a
TYPE_DECL.

gcc/cp/ChangeLog:

	* pt.cc (comp_template_parms): Just one level.
	(template_parameter_lists_equivalent_p): Likewise.
---
 gcc/cp/pt.cc | 90 ++++++++++++++++++++++--------------------------------------
 1 file changed, 33 insertions(+), 57 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 1de9d3e..ed681af 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3274,53 +3274,40 @@ check_explicit_specialization (tree declarator,
 int
 comp_template_parms (const_tree parms1, const_tree parms2)
 {
-  const_tree p1;
-  const_tree p2;
-
   if (parms1 == parms2)
     return 1;
 
-  for (p1 = parms1, p2 = parms2;
-       p1 != NULL_TREE && p2 != NULL_TREE;
-       p1 = TREE_CHAIN (p1), p2 = TREE_CHAIN (p2))
-    {
-      tree t1 = TREE_VALUE (p1);
-      tree t2 = TREE_VALUE (p2);
-      int i;
+  tree t1 = TREE_VALUE (parms1);
+  tree t2 = TREE_VALUE (parms2);
+  int i;
 
-      gcc_assert (TREE_CODE (t1) == TREE_VEC);
-      gcc_assert (TREE_CODE (t2) == TREE_VEC);
+  gcc_assert (TREE_CODE (t1) == TREE_VEC);
+  gcc_assert (TREE_CODE (t2) == TREE_VEC);
 
-      if (TREE_VEC_LENGTH (t1) != TREE_VEC_LENGTH (t2))
-	return 0;
+  if (TREE_VEC_LENGTH (t1) != TREE_VEC_LENGTH (t2))
+    return 0;
 
-      for (i = 0; i < TREE_VEC_LENGTH (t2); ++i)
-	{
-          tree parm1 = TREE_VALUE (TREE_VEC_ELT (t1, i));
-          tree parm2 = TREE_VALUE (TREE_VEC_ELT (t2, i));
+  for (i = 0; i < TREE_VEC_LENGTH (t2); ++i)
+    {
+      tree parm1 = TREE_VALUE (TREE_VEC_ELT (t1, i));
+      tree parm2 = TREE_VALUE (TREE_VEC_ELT (t2, i));
 
-          /* If either of the template parameters are invalid, assume
-             they match for the sake of error recovery. */
-          if (error_operand_p (parm1) || error_operand_p (parm2))
-            return 1;
+      /* If either of the template parameters are invalid, assume
+	 they match for the sake of error recovery. */
+      if (error_operand_p (parm1) || error_operand_p (parm2))
+	return 1;
 
-	  if (TREE_CODE (parm1) != TREE_CODE (parm2))
-	    return 0;
+      if (TREE_CODE (parm1) != TREE_CODE (parm2))
+	return 0;
 
-	  if (TREE_CODE (parm1) == TEMPLATE_TYPE_PARM
-              && (TEMPLATE_TYPE_PARAMETER_PACK (parm1)
-                  == TEMPLATE_TYPE_PARAMETER_PACK (parm2)))
-	    continue;
-	  else if (!same_type_p (TREE_TYPE (parm1), TREE_TYPE (parm2)))
-	    return 0;
-	}
+      if (TREE_CODE (parm1) == TYPE_DECL
+	  && (TEMPLATE_TYPE_PARAMETER_PACK (TREE_TYPE (parm1))
+	      == TEMPLATE_TYPE_PARAMETER_PACK (TREE_TYPE (parm2))))
+	continue;
+      else if (!same_type_p (TREE_TYPE (parm1), TREE_TYPE (parm2)))
+	return 0;
     }
 
-  if ((p1 != NULL_TREE) != (p2 != NULL_TREE))
-    /* One set of parameters has more parameters lists than the
-       other.  */
-    return 0;
-
   return 1;
 }
 
@@ -3403,31 +3390,20 @@ template_parameter_lists_equivalent_p (const_tree parms1, const_tree parms2)
   if (parms1 == parms2)
     return true;
 
-  const_tree p1 = parms1;
-  const_tree p2 = parms2;
-  while (p1 != NULL_TREE && p2 != NULL_TREE)
-    {
-      tree list1 = TREE_VALUE (p1);
-      tree list2 = TREE_VALUE (p2);
+  tree list1 = TREE_VALUE (parms1);
+  tree list2 = TREE_VALUE (parms2);
 
-      if (TREE_VEC_LENGTH (list1) != TREE_VEC_LENGTH (list2))
-	return 0;
-
-      for (int i = 0; i < TREE_VEC_LENGTH (list2); ++i)
-	{
-	  tree parm1 = TREE_VEC_ELT (list1, i);
-	  tree parm2 = TREE_VEC_ELT (list2, i);
-	  if (!template_parameters_equivalent_p (parm1, parm2))
-	    return false;
-	}
+  if (TREE_VEC_LENGTH (list1) != TREE_VEC_LENGTH (list2))
+    return 0;
 
-      p1 = TREE_CHAIN (p1);
-      p2 = TREE_CHAIN (p2);
+  for (int i = 0; i < TREE_VEC_LENGTH (list2); ++i)
+    {
+      tree parm1 = TREE_VEC_ELT (list1, i);
+      tree parm2 = TREE_VEC_ELT (list2, i);
+      if (!template_parameters_equivalent_p (parm1, parm2))
+	return false;
     }
 
-  if ((p1 != NULL_TREE) != (p2 != NULL_TREE))
-    return false;
-
   return true;
 }
 
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