e902136b31
The removal of remove_zero_width_bitfields function and its call from C++ FE layout_class_type (which I've done in the P0466R5 layout-compatible helper intrinsics patch, so that the FE can actually determine what is and isn't layout-compatible according to the spec) unfortunately changed the ABI on various platforms. The C FE has been keeping zero-width bitfields in the types, while the C++ FE has been removing them after structure layout, so in various cases when passing such structures in registers we had different ABI between C and C++. While both the C and C++ FE had some code to remove zero width bitfields after structure layout, in both FEs it was buggy and didn't really remove any. In the C FE that code has been removed later on, while in the C++ FE for GCC 4.5 in PR42217 it has been actually fixed, so the C++ FE started to remove those bitfields. The following patch doesn't change anything ABI-wise, but allows the targets to decide what to do, emit -Wpsabi warnings etc. Non-C zero width bitfields will be seen by the backends as normal zero width bitfields, C++ zero width bitfields that used to be previously removed will have DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD flag set. I've reused the DECL_FIELD_ABI_IGNORED flag which is only used on non-bitfield FIELD_DECLs right now, but the macros now check DECL_BIT_FIELD flag. Each backend can then decide what it wants, whether it wants to keep different ABI between C and C++ as in GCC 11 and older (i.e. incompatible with G++ <= 4.4, compatible with G++ 4.5 .. 11), for that it would ignore for the aggregate passing/returning decisions all DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD FIELD_DECLs), whether it wants to never ignore zero width bitfields (no changes needed for that case, except perhaps -Wpsabi warning should be added and for that DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD can be tested), or whether it wants to always ignore zero width bitfields (I think e.g. riscv in GCC 10+ does that). All this patch does is set the flag which the backends can then use. 2021-09-03 Jakub Jelinek <jakub@redhat.com> PR target/102024 gcc/ * tree.h (DECL_FIELD_ABI_IGNORED): Changed into rvalue only macro that is false if DECL_BIT_FIELD. (SET_DECL_FIELD_ABI_IGNORED, DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD, SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD): Define. * tree-streamer-out.c (pack_ts_decl_common_value_fields): For DECL_BIT_FIELD stream DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD instead of DECL_FIELD_ABI_IGNORED. * tree-streamer-in.c (unpack_ts_decl_common_value_fields): Use SET_DECL_FIELD_ABI_IGNORED instead of writing to DECL_FIELD_ABI_IGNORED and for DECL_BIT_FIELD use SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD instead. * lto-streamer-out.c (hash_tree): For DECL_BIT_FIELD hash DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD instead of DECL_FIELD_ABI_IGNORED. gcc/cp/ * class.c (build_base_field): Use SET_DECL_FIELD_ABI_IGNORED instead of writing to DECL_FIELD_ABI_IGNORED. (layout_class_type): Likewise. In the place where zero-width bitfields used to be removed, use SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD on those fields instead. gcc/lto/ * lto-common.c (compare_tree_sccs_1): Also compare DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD values. |
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