c++: DECL_BUILTIN_P for builtins

We currently detect builtin decls via DECL_ARTIFICIAL &&
!DECL_HIDDEN_FUNCTION_P, which, besides being clunky, is a problem as
hiddenness is a property of the symbol table -- not the decl being
hidden.  This adds DECL_BUILTIN_P, which just looks at the
SOURCE_LOCATION -- we have a magic one for builtins.

One of the consequential changes is to make function-scope omp udrs
have function context (needed because otherwise duplicate-decls thinks
the types don't match at the point we check).  This is also morally
better, because that's what they are -- nested functions, stop lying.

(That's actually my plan for all DECL_LOCAL_DECL_P decls, as they are
distinct decls to the namespace-scope decl they alias.)

	gcc/cp/
	* cp-tree.h (DECL_BUILTIN_P): New.
	* decl.c (duplicate_decls): Use it.  Do not treat omp-udr as a
	builtin.
	* name-lookup.c (anticipated_builtin): Use it.
	(set_decl_context_in_fn): Function-scope OMP UDRs have function context.
	(do_nonmember_using_decl): Use DECL_BUILTIN_P.
	* parser.c (cp_parser_omp_declare_reduction): Function-scope OMP
	UDRs have function context.  Assert we never find a valid duplicate.
	* pt.c (tsubst_expr): Function-scope OMP UDRs have function context.
	libcc1/
	* libcp1plugin.cc (supplement_binding): Use DECL_BULTIN_P.

5 files changed, 32 insertions, 28 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 3ae4874..bd78f00 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4040,6 +4040,10 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter)
 #define FNDECL_USED_AUTO(NODE) \
   TREE_LANG_FLAG_2 (FUNCTION_DECL_CHECK (NODE))
 
+/* True if NODE is a builtin decl.  */
+#define DECL_BUILTIN_P(NODE) \
+  (DECL_SOURCE_LOCATION(NODE) == BUILTINS_LOCATION)
+
 /* Nonzero if NODE is a DECL which we know about but which has not
    been explicitly declared, such as a built-in function or a friend
    declared inside a class.  In the latter case DECL_HIDDEN_FRIEND_P
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 6019051..1709dd9 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -1464,9 +1464,7 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
 
   /* Check for redeclaration and other discrepancies.  */
   if (TREE_CODE (olddecl) == FUNCTION_DECL
-      && DECL_ARTIFICIAL (olddecl)
-      /* A C++20 implicit friend operator== uses the normal path (94462).  */
-      && !DECL_HIDDEN_FRIEND_P (olddecl))
+      && DECL_BUILTIN_P (olddecl))
     {
       if (TREE_CODE (newdecl) != FUNCTION_DECL)
 	{
@@ -1508,15 +1506,6 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
 		      "declaration %q#D", newdecl, olddecl);
 	  return NULL_TREE;
 	}
-      else if (DECL_OMP_DECLARE_REDUCTION_P (olddecl))
-	{
-	  gcc_assert (DECL_OMP_DECLARE_REDUCTION_P (newdecl));
-	  error_at (newdecl_loc,
-		    "redeclaration of %<pragma omp declare reduction%>");
-	  inform (olddecl_loc,
-		  "previous %<pragma omp declare reduction%> declaration");
-	  return error_mark_node;
-	}
       else if (!types_match)
 	{
 	  /* Avoid warnings redeclaring built-ins which have not been
@@ -1816,6 +1805,17 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
 	}
     }
   else if (TREE_CODE (newdecl) == FUNCTION_DECL
+	   && DECL_OMP_DECLARE_REDUCTION_P (newdecl))
+    {
+      /* OMP UDRs are never duplicates. */
+      gcc_assert (DECL_OMP_DECLARE_REDUCTION_P (olddecl));
+      error_at (newdecl_loc,
+		"redeclaration of %<pragma omp declare reduction%>");
+      inform (olddecl_loc,
+	      "previous %<pragma omp declare reduction%> declaration");
+      return error_mark_node;
+    }
+  else if (TREE_CODE (newdecl) == FUNCTION_DECL
 	    && ((DECL_TEMPLATE_SPECIALIZATION (olddecl)
 		 && (!DECL_TEMPLATE_INFO (newdecl)
 		     || (DECL_TI_TEMPLATE (newdecl)
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index e7764ab..dbc6cc3 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -2119,10 +2119,10 @@ anticipated_builtin_p (tree ovl)
   tree fn = OVL_FUNCTION (ovl);
   gcc_checking_assert (DECL_ANTICIPATED (fn));
 
-  if (DECL_HIDDEN_FRIEND_P (fn))
-    return false;
+  if (DECL_BUILTIN_P (fn))
+    return true;
 
-  return true;
+  return false;
 }
 
 /* BINDING records an existing declaration for a name in the current scope.
@@ -2857,9 +2857,12 @@ set_decl_context_in_fn (tree ctx, tree decl)
 {
   if (TREE_CODE (decl) == FUNCTION_DECL
       || (VAR_P (decl) && DECL_EXTERNAL (decl)))
-    /* Make sure local externs are marked as such.  */
+    /* Make sure local externs are marked as such.  OMP UDRs really
+       are nested functions.  */
     gcc_checking_assert (DECL_LOCAL_DECL_P (decl)
-			 && DECL_NAMESPACE_SCOPE_P (decl));
+			 && (DECL_NAMESPACE_SCOPE_P (decl)
+			     || (TREE_CODE (decl) == FUNCTION_DECL
+				 && DECL_OMP_DECLARE_REDUCTION_P (decl))));
 
   if (!DECL_CONTEXT (decl)
       /* When parsing the parameter list of a function declarator,
@@ -3934,7 +3937,7 @@ do_nonmember_using_decl (name_lookup &lookup, bool fn_scope_p,
 		}
 	      else if (old.using_p ())
 		continue; /* This is a using decl. */
-	      else if (old.hidden_p () && !DECL_HIDDEN_FRIEND_P (old_fn))
+	      else if (old.hidden_p () && DECL_BUILTIN_P (old_fn))
 		continue; /* This is an anticipated builtin.  */
 	      else if (!matching_fn_p (new_fn, old_fn))
 		continue; /* Parameters do not match.  */
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index fba3fcc..ccfae78 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -42567,7 +42567,7 @@ cp_parser_omp_declare_reduction (cp_parser *parser, cp_token *pragma_tok,
       if (current_function_decl)
 	{
 	  block_scope = true;
-	  DECL_CONTEXT (fndecl) = global_namespace;
+	  DECL_CONTEXT (fndecl) = current_function_decl;
 	  DECL_LOCAL_DECL_P (fndecl) = true;
 	  if (!processing_template_decl)
 	    pushdecl (fndecl);
@@ -42592,7 +42592,9 @@ cp_parser_omp_declare_reduction (cp_parser *parser, cp_token *pragma_tok,
       else
 	{
 	  DECL_CONTEXT (fndecl) = current_namespace;
-	  pushdecl (fndecl);
+	  tree d = pushdecl (fndecl);
+	  /* We should never meet a matched duplicate decl.  */
+	  gcc_checking_assert (d == error_mark_node || d == fndecl);
 	}
       if (!block_scope)
 	start_preparsed_function (fndecl, NULL_TREE, SF_PRE_PARSED);
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 6f8dbc3..a4530db 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18109,16 +18109,11 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
 		else if (DECL_IMPLICIT_TYPEDEF_P (t))
 		  /* We already did a pushtag.  */;
 		else if (TREE_CODE (decl) == FUNCTION_DECL
-			 && DECL_OMP_DECLARE_REDUCTION_P (decl)
-			 && DECL_FUNCTION_SCOPE_P (pattern_decl))
+			 && DECL_LOCAL_DECL_P (decl)
+			 && DECL_OMP_DECLARE_REDUCTION_P (decl))
 		  {
-		    /* We pretend this is regular local extern decl of
-		       a namespace-scope fn.  Then we make it really
-		       local, it is a nested function.  */
-		    gcc_checking_assert (DECL_LOCAL_DECL_P (decl));
-		    DECL_CONTEXT (decl) = global_namespace;
-		    pushdecl (decl);
 		    DECL_CONTEXT (decl) = current_function_decl;
+		    pushdecl (decl);
 		    if (cp_check_omp_declare_reduction (decl))
 		      instantiate_body (pattern_decl, args, decl, true);
 		  }