[C++ PATCH] Hide __for_{range,begin,end} symbols (PR c++/85515, take 2)

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Jul 13, 2018 at 06:53:30PM +0200, Jakub Jelinek wrote:
> On Fri, Jul 13, 2018 at 12:24:02PM -0400, Nathan Sidwell wrote:
> > On 07/13/2018 09:49 AM, Jakub Jelinek wrote:
> > > Hi!
> > > 
> > > I'd like to ping the following C++ patches:
> > > 
> > > - PR c++/85515
> > >    make range for temporaries unspellable during parsing and only
> > >    turn them into spellable for debug info purposes
> > >    http://gcc.gnu.org/ml/gcc-patches/2018-07/msg00086.html
> > 
> > 
> > How hard would it be to add the 6 special identifiers to the C++ global
> > table via initialize_predefined_identifiers (decl.c) and then use them
> > directly in the for range machinery?  repeated get_identifier
> > ("string-const") just smells bad.
> 
> Probably not too hard, but we have hundreds of other
> get_identifier ("string-const") calls in the middle-end, C++ FE, other FEs.
> Are those 6 more important than say "abi_tag", "gnu", "begin", "end", "get",
> "tuple_size", "tuple_element", and many others?
> 
> Is it worth caching those?

Anyway, here is an updated patch that uses the get_identifier caching.
Ok for trunk?

Shall I submit an incremental patch for the "abi_tag", "gnu", "begin", "end", "get",
"tuple_size", "tuple_element" etc. identifiers?

2018-07-18  Jakub Jelinek  <jakub@redhat.com>

	PR c++/85515
	* cp-tree.h (enum cp_tree_index): Add
	CPTI_FOR_{RANGE,BEGIN,END}{,_}_IDENTIFIER.
	(for_range__identifier, for_begin__identifier, for_end__identifier,
	for_range_identifier, for_begin_identifier, for_end_identifier):
	Define.
	* decl.c (initialize_predefined_identifiers): Initialize
	for_{range,begin,end}{,_}_identifier.
	* parser.c (build_range_temp): Use for_range__identifier instead of
	get_identifier ("__for_range").
	(cp_convert_range_for): Use for_begin__identifier and
	for_end__identifier instead of get_identifier ("__for_begin") and
	get_identifier ("__for_end").
	* semantics.c (finish_for_stmt): Rename "__for_{range,begin,end} "
	local symbols to "__for_{range,begin,end}".

	* g++.dg/pr85515-2.C: Add expected dg-error.
	* g++.dg/cpp0x/range-for36.C: New test.

--- gcc/cp/cp-tree.h.jj	2018-06-29 09:38:17.790306399 +0200
+++ gcc/cp/cp-tree.h	2018-07-18 11:57:55.980529748 +0200
@@ -154,6 +154,12 @@ enum cp_tree_index
     CPTI_AUTO_IDENTIFIER,
     CPTI_DECLTYPE_AUTO_IDENTIFIER,
     CPTI_INIT_LIST_IDENTIFIER,
+    CPTI_FOR_RANGE__IDENTIFIER,
+    CPTI_FOR_BEGIN__IDENTIFIER,
+    CPTI_FOR_END__IDENTIFIER,
+    CPTI_FOR_RANGE_IDENTIFIER,
+    CPTI_FOR_BEGIN_IDENTIFIER,
+    CPTI_FOR_END_IDENTIFIER,
 
     CPTI_LANG_NAME_C,
     CPTI_LANG_NAME_CPLUSPLUS,
@@ -274,6 +280,12 @@ extern GTY(()) tree cp_global_trees[CPTI
 #define auto_identifier			cp_global_trees[CPTI_AUTO_IDENTIFIER]
 #define decltype_auto_identifier	cp_global_trees[CPTI_DECLTYPE_AUTO_IDENTIFIER]
 #define init_list_identifier		cp_global_trees[CPTI_INIT_LIST_IDENTIFIER]
+#define for_range__identifier		cp_global_trees[CPTI_FOR_RANGE__IDENTIFIER]
+#define for_begin__identifier		cp_global_trees[CPTI_FOR_BEGIN__IDENTIFIER]
+#define for_end__identifier		cp_global_trees[CPTI_FOR_END__IDENTIFIER]
+#define for_range_identifier		cp_global_trees[CPTI_FOR_RANGE_IDENTIFIER]
+#define for_begin_identifier		cp_global_trees[CPTI_FOR_BEGIN_IDENTIFIER]
+#define for_end_identifier		cp_global_trees[CPTI_FOR_END_IDENTIFIER]
 #define lang_name_c			cp_global_trees[CPTI_LANG_NAME_C]
 #define lang_name_cplusplus		cp_global_trees[CPTI_LANG_NAME_CPLUSPLUS]
 
--- gcc/cp/decl.c.jj	2018-07-12 21:34:44.798598796 +0200
+++ gcc/cp/decl.c	2018-07-18 11:59:06.220595473 +0200
@@ -4044,6 +4044,12 @@ initialize_predefined_identifiers (void)
     {"auto", &auto_identifier, cik_normal},
     {"decltype(auto)", &decltype_auto_identifier, cik_normal},
     {"initializer_list", &init_list_identifier, cik_normal},
+    {"__for_range ", &for_range__identifier, cik_normal},
+    {"__for_begin ", &for_begin__identifier, cik_normal},
+    {"__for_end ", &for_end__identifier, cik_normal},
+    {"__for_range", &for_range_identifier, cik_normal},
+    {"__for_begin", &for_begin_identifier, cik_normal},
+    {"__for_end", &for_end_identifier, cik_normal},
     {NULL, NULL, cik_normal}
   };
 
--- gcc/cp/parser.c.jj	2018-07-18 10:09:10.655030931 +0200
+++ gcc/cp/parser.c	2018-07-18 12:00:22.907667232 +0200
@@ -11952,8 +11952,8 @@ build_range_temp (tree range_expr)
 				  type_uses_auto (range_type));
 
   /* Create the __range variable.  */
-  range_temp = build_decl (input_location, VAR_DECL,
-			   get_identifier ("__for_range"), range_type);
+  range_temp = build_decl (input_location, VAR_DECL, for_range__identifier,
+			   range_type);
   TREE_USED (range_temp) = 1;
   DECL_ARTIFICIAL (range_temp) = 1;
 
@@ -12060,8 +12060,8 @@ cp_convert_range_for (tree statement, tr
     }
 
   /* The new for initialization statement.  */
-  begin = build_decl (input_location, VAR_DECL,
-		      get_identifier ("__for_begin"), iter_type);
+  begin = build_decl (input_location, VAR_DECL, for_begin__identifier,
+		      iter_type);
   TREE_USED (begin) = 1;
   DECL_ARTIFICIAL (begin) = 1;
   pushdecl (begin);
@@ -12071,8 +12071,7 @@ cp_convert_range_for (tree statement, tr
 
   if (cxx_dialect >= cxx17)
     iter_type = cv_unqualified (TREE_TYPE (end_expr));
-  end = build_decl (input_location, VAR_DECL,
-		    get_identifier ("__for_end"), iter_type);
+  end = build_decl (input_location, VAR_DECL, for_end__identifier, iter_type);
   TREE_USED (end) = 1;
   DECL_ARTIFICIAL (end) = 1;
   pushdecl (end);
--- gcc/cp/semantics.c.jj	2018-07-10 09:11:24.254062152 +0200
+++ gcc/cp/semantics.c	2018-07-18 12:03:24.482837137 +0200
@@ -1060,7 +1060,35 @@ finish_for_stmt (tree for_stmt)
 		     : &FOR_SCOPE (for_stmt));
   tree scope = *scope_ptr;
   *scope_ptr = NULL;
+
+  /* During parsing of the body, range for uses "__for_{range,begin,end} "
+     decl names to make those unaccessible by code in the body.
+     Change it to ones with underscore instead of space, so that it can
+     be inspected in the debugger.  */
+  tree range_for_decl[3] = { NULL_TREE, NULL_TREE, NULL_TREE };
+  gcc_assert (CPTI_FOR_BEGIN__IDENTIFIER == CPTI_FOR_RANGE__IDENTIFIER + 1
+	      && CPTI_FOR_END__IDENTIFIER == CPTI_FOR_RANGE__IDENTIFIER + 2
+	      && CPTI_FOR_RANGE_IDENTIFIER == CPTI_FOR_RANGE__IDENTIFIER + 3
+	      && CPTI_FOR_BEGIN_IDENTIFIER == CPTI_FOR_BEGIN__IDENTIFIER + 3
+	      && CPTI_FOR_END_IDENTIFIER == CPTI_FOR_END__IDENTIFIER + 3);
+  for (int i = 0; i < 3; i++)
+    {
+      tree id = cp_global_trees[CPTI_FOR_RANGE__IDENTIFIER + i];
+      if (IDENTIFIER_BINDING (id)
+	  && IDENTIFIER_BINDING (id)->scope == current_binding_level)
+	{
+	  range_for_decl[i] = IDENTIFIER_BINDING (id)->value;
+	  gcc_assert (VAR_P (range_for_decl[i])
+		      && DECL_ARTIFICIAL (range_for_decl[i]));
+	}
+    }
+
   add_stmt (do_poplevel (scope));
+
+  for (int i = 0; i < 3; i++)
+    if (range_for_decl[i])
+      DECL_NAME (range_for_decl[i])
+	= cp_global_trees[CPTI_FOR_RANGE_IDENTIFIER + i];
 }
 
 /* Begin a range-for-statement.  Returns a new RANGE_FOR_STMT.
--- gcc/testsuite/g++.dg/pr85515-2.C.jj	2018-07-05 11:41:51.439718304 +0200
+++ gcc/testsuite/g++.dg/pr85515-2.C	2018-07-18 11:27:36.452850086 +0200
@@ -15,8 +15,7 @@ int test_2 ()
   int sum = 0;
   for (const auto v: arr) {
     sum += v;
-    // TODO: should we issue an error for the following assignment?
-    __for_begin = __for_end;
+    __for_begin = __for_end;	// { dg-error "was not declared in this scope" }
   }
   return sum;
 }
--- gcc/testsuite/g++.dg/cpp0x/range-for36.C.jj	2018-07-18 11:27:36.452850086 +0200
+++ gcc/testsuite/g++.dg/cpp0x/range-for36.C	2018-07-18 11:27:36.452850086 +0200
@@ -0,0 +1,32 @@
+// PR c++/85515
+// { dg-do compile { target c++11 } }
+
+int a[10];
+
+void
+foo ()
+{
+  for (auto &i : a)
+    if (i != *__for_begin		// { dg-error "was not declared in this scope" }
+	|| &i == __for_end		// { dg-error "was not declared in this scope" }
+	|| &__for_range[0] != &a[0])	// { dg-error "was not declared in this scope" }
+      __builtin_abort ();
+}
+
+template <int N>
+void
+bar ()
+{
+  for (auto &i : a)
+    if (i != *__for_begin		// { dg-error "was not declared in this scope" }
+	|| &i == __for_end		// { dg-error "was not declared in this scope" }
+	|| &__for_range[0] != &a[0])	// { dg-error "was not declared in this scope" }
+      __builtin_abort ();
+}
+
+void
+baz ()
+{
+  foo ();
+  bar <0> ();
+}


	Jakub