Hi!
While working on OpenMP range-for support, I ran into the weird thing that
the C++ FE accepts
for (auto &i : a)
if (i != *__for_begin || &i == __for_end || &__for_range[0] != &a[0])
__builtin_abort ();
outside of templates, but doesn't inside of templates.
I think we shouldn't let people do this at any time, it will just lead to
non-portable code, and when it works only outside of templates, it isn't a
well defined extension.
Now, we could just use create_tmp_var_name ("__for_range") instead of
get_identifier ("__for_range") etc. and the symbols would be non-accessible
to users (usually; if assembler doesn't support dots nor dollars in labels,
it is still a symbol with just alphanumeric chars in it, but there is a hard
to predict number suffix at least), or just NULL DECL_NAME.
But my understanding is that the intent was that in the debugger one could
use __for_range, __for_begin and __for_end to make it easier to debug
range fors. In that case, the following patch solves it by using a name
not accessible for the user when parsing the body (with space in it) and
correcting the names when the var gets out of scope.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2018-07-02 Jakub Jelinek <ja...@redhat.com>
PR c++/85515
* parser.c (build_range_temp): Use "__for range" instead of
"__for_range".
(cp_convert_range_for): Use "__for begin" and "__for end" instead of
"__for_begin" and "__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/parser.c.jj 2018-07-02 23:04:00.869370436 +0200
+++ gcc/cp/parser.c 2018-07-02 23:08:44.572618486 +0200
@@ -11953,7 +11953,7 @@ build_range_temp (tree range_expr)
/* Create the __range variable. */
range_temp = build_decl (input_location, VAR_DECL,
- get_identifier ("__for_range"), range_type);
+ get_identifier ("__for range"), range_type);
TREE_USED (range_temp) = 1;
DECL_ARTIFICIAL (range_temp) = 1;
@@ -12061,7 +12061,7 @@ 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);
+ get_identifier ("__for begin"), iter_type);
TREE_USED (begin) = 1;
DECL_ARTIFICIAL (begin) = 1;
pushdecl (begin);
@@ -12072,7 +12072,7 @@ 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);
+ get_identifier ("__for end"), iter_type);
TREE_USED (end) = 1;
DECL_ARTIFICIAL (end) = 1;
pushdecl (end);
--- gcc/cp/semantics.c.jj 2018-06-25 14:51:23.096989196 +0200
+++ gcc/cp/semantics.c 2018-07-02 23:23:40.784400542 +0200
@@ -1060,7 +1060,31 @@ 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 };
+ for (int i = 0; i < 3; i++)
+ {
+ tree id
+ = get_identifier ("__for range\0__for begin\0__for end" + 12 * 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])
+ = get_identifier ("__for_range\0__for_begin\0__for_end" + 12 * i);
}
/* Begin a range-for-statement. Returns a new RANGE_FOR_STMT.
--- gcc/testsuite/g++.dg/pr85515-2.C.jj 2018-04-27 22:28:02.889462532 +0200
+++ gcc/testsuite/g++.dg/pr85515-2.C 2018-07-02 23:33:50.638930364 +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 2018-07-02 23:35:12.796000382
+0200
+++ gcc/testsuite/g++.dg/cpp0x/range-for36.C 2018-07-02 23:35:04.018992900
+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
