Hi,
On 05/24/2013 03:36 PM, Jason Merrill wrote:
Why would we want to pedwarn? As far as I can tell, the standard
doesn't say this is ill-formed. 9.6 says,
"The value of the integral constant expression may be larger than the
number of bits in the object representation (3.9) of the bit-field’s
type; in such cases the extra bits are used as padding bits and do not
participate in the value representation (3.9) of the bit-field."
and
"A bool value can successfully be stored in a bit-field of any nonzero
size."
I'm sure that lots of users would complain about the compiler starting
to reject bool bitfields of 2-8 bits.
Thanks Jason. Shame on me, I was totally confused, I guess I need some
time off (*).
I'm not opposed to warning about excessive size for bool and enum
here, but the warning should be based on TYPE_SIZE rather than
TYPE_PRECISION.
Makes perfect sense. Thus I'm finishing testing the below. Better?
Thanks again,
Paolo.
(*) For real, next week vacations for me.
////////////////////////
Index: cp/class.c
===================================================================
--- cp/class.c (revision 199287)
+++ cp/class.c (working copy)
@@ -3140,9 +3140,14 @@ check_bitfield_decl (tree field)
error ("zero width for bit-field %q+D", field);
w = error_mark_node;
}
- else if (compare_tree_int (w, TYPE_PRECISION (type)) > 0
- && TREE_CODE (type) != ENUMERAL_TYPE
- && TREE_CODE (type) != BOOLEAN_TYPE)
+ else if ((TREE_CODE (type) != ENUMERAL_TYPE
+ && TREE_CODE (type) != BOOLEAN_TYPE
+ && compare_tree_int (w, TYPE_PRECISION (type)) > 0)
+ || ((TREE_CODE (type) == ENUMERAL_TYPE
+ && (tree_int_cst_lt
+ (TYPE_SIZE (ENUM_UNDERLYING_TYPE (type)), w)))
+ || (TREE_CODE (type) == BOOLEAN_TYPE
+ && tree_int_cst_lt (TYPE_SIZE (type), w))))
warning (0, "width of %q+D exceeds its type", field);
else if (TREE_CODE (type) == ENUMERAL_TYPE
&& (0 > (compare_tree_int
Index: testsuite/g++.dg/expr/bitfield12.C
===================================================================
--- testsuite/g++.dg/expr/bitfield12.C (revision 0)
+++ testsuite/g++.dg/expr/bitfield12.C (working copy)
@@ -0,0 +1,19 @@
+// PR c++/19618
+
+struct bset1 {
+ bool bit : sizeof(bool) * __CHAR_BIT__ + 1; // { dg-warning "exceeds" }
+};
+
+enum E {};
+
+struct bset2 {
+ E bit : sizeof(__underlying_type(E)) * __CHAR_BIT__ + 1; // { dg-warning
"exceeds" }
+};
+
+struct bset3 {
+ bool bit : sizeof(bool) * __CHAR_BIT__;
+};
+
+struct bset4 {
+ E bit : sizeof(__underlying_type(E)) * __CHAR_BIT__;
+};
