On Wed, Jun 16, 2021 at 09:45:17AM +0200, Jakub Jelinek via Gcc-patches wrote:
> The following patch does create them, but treats all such bitfields as if
> they were in a structure where the particular bitfield is the only field.
While the patch passed bootstrap/regtest on the trunk, when trying to
backport it to 11 branch the bootstrap failed with
atree.ads:3844:34: size for "Node_Record" too small
errors. Turns out the error is not about size being too small, but actually
about size being non-constant, and comes from:
/* In a FIELD_DECL of a RECORD_TYPE, this is a pointer to the storage
representative FIELD_DECL. */
#define DECL_BIT_FIELD_REPRESENTATIVE(NODE) \
(FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
/* For a FIELD_DECL in a QUAL_UNION_TYPE, records the expression, which
if nonzero, indicates that the field occupies the type. */
#define DECL_QUALIFIER(NODE) (FIELD_DECL_CHECK (NODE)->field_decl.qualifier)
so by setting up DECL_BIT_FIELD_REPRESENTATIVE in QUAL_UNION_TYPE we
actually set or modify DECL_QUALIFIER and then construct size as COND_EXPRs
with those bit field representatives (e.g. with array type) as conditions
which doesn't fold into constant.
The following patch fixes it by not creating DECL_BIT_FIELD_REPRESENTATIVEs
for QUAL_UNION_TYPE as there is nowhere to store them,
Bootstrapped/regtested on x86_64-linux and i686-linux (both trunk and
11 branch - there on top of the earlier patch backport). Ok for trunk and
the backport?
Shall we change tree.h to document that DECL_BIT_FIELD_REPRESENTATIVE
is valid also on UNION_TYPE?
I see:
tree-ssa-alias.c- if (TREE_CODE (type1) == RECORD_TYPE
tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field1))
tree-ssa-alias.c: field1 = DECL_BIT_FIELD_REPRESENTATIVE (field1);
tree-ssa-alias.c- if (TREE_CODE (type2) == RECORD_TYPE
tree-ssa-alias.c: && DECL_BIT_FIELD_REPRESENTATIVE (field2))
tree-ssa-alias.c: field2 = DECL_BIT_FIELD_REPRESENTATIVE (field2);
Shall we change that to || == UNION_TYPE or do we assume all fields
are overlapping in a UNION_TYPE already?
At other spots (asan, ubsan, expr.c) it is unclear what will happen
if they see a QUAL_UNION_TYPE with a DECL_QUALIFIER (or does the Ada FE
lower that somehow)?
2021-06-18 Jakub Jelinek <ja...@redhat.com>
PR middle-end/101062
* stor-layout.c (finish_bitfield_layout): Don't add bitfield
representatives in QUAL_UNION_TYPE.
--- gcc/stor-layout.c.jj 2021-06-16 12:17:49.254221954 +0200
+++ gcc/stor-layout.c 2021-06-17 11:36:13.011822974 +0200
@@ -2172,6 +2172,9 @@ finish_bitfield_layout (tree t)
tree field, prev;
tree repr = NULL_TREE;
+ if (TREE_CODE (t) == QUAL_UNION_TYPE)
+ return;
+
for (prev = NULL_TREE, field = TYPE_FIELDS (t);
field; field = DECL_CHAIN (field))
{
Jakub
