[Bug middle-end/101062] [10 Regression] wrong code with "-O2 -fno-toplevel-reorder -frename-registers"
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue May 10 08:19:00 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101062
--- Comment #21 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:
https://gcc.gnu.org/g:3df2f5828752a91343d01defb215de326b5ddb4c
commit r10-10623-g3df2f5828752a91343d01defb215de326b5ddb4c
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Jun 18 11:20:40 2021 +0200
stor-layout: Don't create DECL_BIT_FIELD_REPRESENTATIVE for QUAL_UNION_TYPE
[PR101062]
> 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,
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 <jakub@redhat.com>
PR middle-end/101062
* stor-layout.c (finish_bitfield_layout): Don't add bitfield
representatives in QUAL_UNION_TYPE.
(cherry picked from commit 3587c2c241eda0f3ab54ea60d46e9caf12d69b5a)
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