On Tue, 7 Feb 2012, Joseph S. Myers wrote:
> On Tue, 7 Feb 2012, Richard Guenther wrote:
>
> > If the C frontend would stop using DECL_INITIAL temporarily for
> > bitfield FIELD_DECLs we could avoid adding a new member to struct
> > tree_field_decl - Joseph, is it possible to avoid using DECL_INITIAL?
>
> C++ does the same thing with DECL_INITIAL so I'd expect that to need to
> change as well - Jason? C only needs an integer width within a limited
> range; C++ may actually need a general expression here.
>
> C currently uses a TREE_LIST of field declarations when parsing a
> structure. It should be reasonably straightforward to change that to a
> VEC of structures storing both the declaration and the width, so the width
> no longer need go in DECL_INITIAL of the declaration, though it will be
> necessary to check for other code using DECL_INITIAL to check for
> bit-fields. For example, c-common.c:handle_packed_attribute uses
> DECL_INITIAL like that; it should be possible to make both C and C++ set
> DECL_C_BIT_FIELD early enough that such DECL_INITIAL checks can be
> replaced by a more meaningful DECL_C_BIT_FIELD check.
That would be nice. I suppose that doing
if (DECL_INITIAL (x))
{
unsigned HOST_WIDE_INT width = tree_low_cst (DECL_INITIAL (x),
1);
DECL_SIZE (x) = bitsize_int (width);
DECL_BIT_FIELD (x) = 1;
SET_DECL_C_BIT_FIELD (x);
}
at the time we set DECL_INITIAL to the width is not possible
for some weird reason? At least the struct-layout-1.exp tests
seem to be happy with
@@ -6808,6 +6837,12 @@ grokfield (location_t loc,
finish_decl (value, loc, NULL_TREE, NULL_TREE, NULL_TREE);
DECL_INITIAL (value) = width;
+ if (width)
+ {
+ DECL_SIZE (value) = bitsize_int (tree_low_cst (width, 1));
+ DECL_BIT_FIELD (value) = 1;
+ SET_DECL_C_BIT_FIELD (value);
+ }
if (warn_cxx_compat && DECL_NAME (value) != NULL_TREE)
{
@@ -7132,14 +7167,6 @@ finish_struct (location_t loc, tree t, t
if (C_DECL_VARIABLE_SIZE (x))
C_TYPE_VARIABLE_SIZE (t) = 1;
- if (DECL_INITIAL (x))
- {
- unsigned HOST_WIDE_INT width = tree_low_cst (DECL_INITIAL (x),
1);
- DECL_SIZE (x) = bitsize_int (width);
- DECL_BIT_FIELD (x) = 1;
- SET_DECL_C_BIT_FIELD (x);
- }
-
if (TYPE_PACKED (t)
&& (DECL_BIT_FIELD (x)
|| TYPE_ALIGN (TREE_TYPE (x)) > BITS_PER_UNIT))
@@ -7195,11 +7222,12 @@ finish_struct (location_t loc, tree t, t
{
tree *fieldlistp = &fieldlist;
while (*fieldlistp)
- if (TREE_CODE (*fieldlistp) == FIELD_DECL && DECL_INITIAL
(*fieldlistp)
+ if (TREE_CODE (*fieldlistp) == FIELD_DECL
+ && DECL_C_BIT_FIELD (*fieldlistp)
&& TREE_TYPE (*fieldlistp) != error_mark_node)
{
unsigned HOST_WIDE_INT width
- = tree_low_cst (DECL_INITIAL (*fieldlistp), 1);
+ = tree_low_cst (DECL_SIZE (*fieldlistp), 1);
tree type = TREE_TYPE (*fieldlistp);
if (width != TYPE_PRECISION (type))
{
@@ -7207,7 +7235,6 @@ finish_struct (location_t loc, tree t, t
= c_build_bitfield_integer_type (width, TYPE_UNSIGNED
(type));
DECL_MODE (*fieldlistp) = TYPE_MODE (TREE_TYPE
(*fieldlistp));
}
- DECL_INITIAL (*fieldlistp) = 0;
}
else
fieldlistp = &DECL_CHAIN (*fieldlistp);
it remains of course to replace checks for bitfieldness with
DECL_C_BIT_FIELD checks. stor-layout at least doesn't seem to
mess with DECL_SIZE unless it is NULL (unless you happen to
call relayout_decl on a FIELD_DECL which I think the C FE does
not do for bitfields)
Richard.
