c++: Add __builtin_operator_{new,delete} support

clang++ adds __builtin_operator_{new,delete} builtins which as documented
work similarly to ::operator {new,delete}, except that it is an error
if the called ::operator {new,delete} is not a replaceable global operator
and allow optimizations which C++ normally allows just when those are used
from new/delete expressions https://eel.is/c++draft/expr.new#14
When using these builtins, the same optimizations can be done even when
using those builtins.

For GCC we note that in the CALL_FROM_NEW_OR_DELETE_P flag on CALL_EXPRs.
The following patch implements it as a C++ FE keyword (because passing
references through ... changes the argument and so BUILT_IN_FRONTEND
builtin can't be used), just attempts to call the ::operator {new,delete}
and if it isn't replaceable, diagnoses it.

libstdc++ already uses the builtin in some cases.

2024-11-11  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-common.h (enum rid): Add RID_BUILTIN_OPERATOR_NEW
	and RID_BUILTIN_OPERATOR_DELETE.
	(names_builtin_p): Change return type from bool to int.
	* c-common.cc (c_common_reswords): Add __builtin_operator_new
	and __builtin_operator_delete.
gcc/c/
	* c-decl.cc (names_builtin_p): Change return type from
	bool to int, adjust return statments.
gcc/cp/
	* parser.cc (cp_parser_postfix_expression): Handle
	RID_BUILTIN_OPERATOR_NEW and RID_BUILTIN_OPERATOR_DELETE.
	* cp-objcp-common.cc (names_builtin_p): Change return type from
	bool to int, adjust return statments.  Handle
	RID_BUILTIN_OPERATOR_NEW and RID_BUILTIN_OPERATOR_DELETE.
	* pt.cc (tsubst_expr) <case CALL_EXPR>: Handle
	CALL_FROM_NEW_OR_DELETE_P.
gcc/
	* doc/extend.texi (New/Delete Builtins): Document
	__builtin_operator_new and __builtin_operator_delete.
gcc/testsuite/
	* g++.dg/ext/builtin-operator-new-1.C: New test.
	* g++.dg/ext/builtin-operator-new-2.C: New test.
	* g++.dg/ext/builtin-operator-new-3.C: New test.

3 files changed, 71 insertions, 9 deletions

diff --git a/gcc/cp/cp-objcp-common.cc b/gcc/cp/cp-objcp-common.cc
index 1e43db3..921931b 100644
--- a/gcc/cp/cp-objcp-common.cc
+++ b/gcc/cp/cp-objcp-common.cc
@@ -545,10 +545,10 @@ identifier_global_tag (tree name)
   return ret;
 }
 
-/* Returns true if NAME refers to a built-in function or function-like
-   operator.  */
+/* Returns non-zero (result of __has_builtin) if NAME refers to a built-in
+   function or function-like operator.  */
 
-bool
+int
 names_builtin_p (const char *name)
 {
   tree id = get_identifier (name);
@@ -556,23 +556,23 @@ names_builtin_p (const char *name)
     {
       if (TREE_CODE (binding) == FUNCTION_DECL
 	  && DECL_IS_UNDECLARED_BUILTIN (binding))
-	return true;
+	return 1;
 
       /* Handle the case when an overload for a  built-in name exists.  */
       if (TREE_CODE (binding) != OVERLOAD)
-	return false;
+	return 0;
 
       for (ovl_iterator it (binding); it; ++it)
 	{
 	  tree decl = *it;
 	  if (DECL_IS_UNDECLARED_BUILTIN (decl))
-	    return true;
+	    return 1;
 	}
     }
 
   /* Check for built-in traits.  */
   if (IDENTIFIER_TRAIT_P (id))
-    return true;
+    return 1;
 
   /* Also detect common reserved C++ words that aren't strictly built-in
      functions.  */
@@ -587,12 +587,15 @@ names_builtin_p (const char *name)
     case RID_BUILTIN_ASSOC_BARRIER:
     case RID_BUILTIN_BIT_CAST:
     case RID_OFFSETOF:
-      return true;
+      return 1;
+    case RID_BUILTIN_OPERATOR_NEW:
+    case RID_BUILTIN_OPERATOR_DELETE:
+      return 201802L;
     default:
       break;
     }
 
-  return false;
+  return 0;
 }
 
 /* Register c++-specific dumps.  */
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index c1375ec..07b1222 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -7733,6 +7733,8 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
     case RID_BUILTIN_SHUFFLEVECTOR:
     case RID_BUILTIN_LAUNDER:
     case RID_BUILTIN_ASSOC_BARRIER:
+    case RID_BUILTIN_OPERATOR_NEW:
+    case RID_BUILTIN_OPERATOR_DELETE:
       {
 	vec<tree, va_gc> *vec;
 
@@ -7819,6 +7821,39 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
 	      }
 	    break;
 
+	  case RID_BUILTIN_OPERATOR_NEW:
+	  case RID_BUILTIN_OPERATOR_DELETE:
+	    tree fn;
+	    fn = ovl_op_identifier (keyword == RID_BUILTIN_OPERATOR_NEW
+				    ? NEW_EXPR : DELETE_EXPR);
+	    fn = lookup_qualified_name (global_namespace, fn);
+	    postfix_expression = finish_call_expr (fn, &vec, true, false,
+						   tf_warning_or_error);
+	    if (postfix_expression != error_mark_node)
+	      {
+		tree call = extract_call_expr (postfix_expression);
+		fn = cp_get_callee_fndecl_nofold (call);
+		if (fn ? !DECL_IS_REPLACEABLE_OPERATOR (fn)
+		       : !processing_template_decl)
+		  {
+		    auto_diagnostic_group d;
+		    if (keyword == RID_BUILTIN_OPERATOR_NEW)
+		      error_at (loc, "call to %<__builtin_operator_new%> "
+				     "does not select replaceable global "
+				     "allocation function");
+		    else 
+		      error_at (loc, "call to %<__builtin_operator_delete%> "
+				     "does not select replaceable global "
+				     "deallocation function");
+		    if (fn)
+		      inform (DECL_SOURCE_LOCATION (fn),
+			      "selected function declared here");
+		  }
+		else if (call && TREE_CODE (call) == CALL_EXPR)
+		  CALL_FROM_NEW_OR_DELETE_P (call) = 1;
+	      }
+	    break;
+
 	  default:
 	    gcc_unreachable ();
 	  }
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index f4213f8..35ec7eb 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -21242,6 +21242,30 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 		  else if (TREE_CODE (call) == AGGR_INIT_EXPR)
 		    AGGR_INIT_EXPR_MUST_TAIL (call) = mtc;
 		}
+	    if (CALL_FROM_NEW_OR_DELETE_P (t))
+	      {
+		tree call = extract_call_expr (ret);
+		tree fn = cp_get_callee_fndecl_nofold (call);
+		if (fn ? !DECL_IS_REPLACEABLE_OPERATOR (fn)
+		       : !processing_template_decl)
+		  {
+		    auto_diagnostic_group d;
+		    location_t loc = cp_expr_loc_or_input_loc (t);
+		    if (!fn || IDENTIFIER_NEW_OP_P (DECL_NAME (fn)))
+		      error_at (loc, "call to %<__builtin_operator_new%> "
+				     "does not select replaceable global "
+				     "allocation function");
+		    else 
+		      error_at (loc, "call to %<__builtin_operator_delete%> "
+				     "does not select replaceable global "
+				     "deallocation function");
+		    if (fn)
+		      inform (DECL_SOURCE_LOCATION (fn),
+			      "selected function declared here");
+		  }
+		else if (call && TREE_CODE (call) == CALL_EXPR)
+		  CALL_FROM_NEW_OR_DELETE_P (call) = 1;
+	      }
 	    if (warning_suppressed_p (t, OPT_Wpessimizing_move))
 	      /* This also suppresses -Wredundant-move.  */
 	      suppress_warning (ret, OPT_Wpessimizing_move);