https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101062
--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:3587c2c241eda0f3ab54ea60d46e9caf12d69b5a commit r11-8615-g3587c2c241eda0f3ab54ea60d46e9caf12d69b5a Author: Jakub Jelinek <ja...@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 <ja...@redhat.com> PR middle-end/101062 * stor-layout.c (finish_bitfield_layout): Don't add bitfield representatives in QUAL_UNION_TYPE.
