c++, abi: Set DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD on C++ zero width bitfields [PR102024]
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.
This commit is contained in:
Jakub Jelinek
parent
de6795bbf5
commit
e902136b31
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@ -4634,7 +4634,7 @@ build_base_field (record_layout_info rli, tree binfo, tree access,
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DECL_FIELD_OFFSET (decl) = BINFO_OFFSET (binfo);
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DECL_FIELD_BIT_OFFSET (decl) = bitsize_zero_node;
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SET_DECL_OFFSET_ALIGN (decl, BITS_PER_UNIT);
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DECL_FIELD_ABI_IGNORED (decl) = 1;
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SET_DECL_FIELD_ABI_IGNORED (decl, 1);
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}
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/* An empty virtual base causes a class to be non-empty
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@ -6658,7 +6658,7 @@ layout_class_type (tree t, tree *virtuals_p)
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}
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else if (might_overlap && is_empty_class (type))
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{
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DECL_FIELD_ABI_IGNORED (field) = 1;
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SET_DECL_FIELD_ABI_IGNORED (field, 1);
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layout_empty_base_or_field (rli, field, empty_base_offsets);
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}
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else
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@ -6746,6 +6746,23 @@ layout_class_type (tree t, tree *virtuals_p)
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normalize_rli (rli);
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}
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/* We used to remove zero width bitfields at this point since PR42217,
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while the C FE never did that. That caused ABI differences on various
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targets. Set the DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD flag on them
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instead, so that the backends can emit -Wpsabi warnings in the cases
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where the ABI changed. */
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for (field = TYPE_FIELDS (t); field; field = DECL_CHAIN (field))
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if (TREE_CODE (field) == FIELD_DECL
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&& DECL_C_BIT_FIELD (field)
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/* We should not be confused by the fact that grokbitfield
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temporarily sets the width of the bit field into
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DECL_BIT_FIELD_REPRESENTATIVE (field).
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check_bitfield_decl eventually sets DECL_SIZE (field)
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to that width. */
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&& (DECL_SIZE (field) == NULL_TREE
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|| integer_zerop (DECL_SIZE (field))))
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SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (field, 1);
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if (CLASSTYPE_NON_LAYOUT_POD_P (t) || CLASSTYPE_EMPTY_P (t))
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{
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/* T needs a different layout as a base (eliding virtual bases
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@ -1271,7 +1271,10 @@ hash_tree (struct streamer_tree_cache_d *cache, hash_map<tree, hashval_t> *map,
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hstate.add_flag (DECL_PACKED (t));
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hstate.add_flag (DECL_NONADDRESSABLE_P (t));
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hstate.add_flag (DECL_PADDING_P (t));
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hstate.add_flag (DECL_FIELD_ABI_IGNORED (t));
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if (DECL_BIT_FIELD (t))
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hstate.add_flag (DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (t));
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else
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hstate.add_flag (DECL_FIELD_ABI_IGNORED (t));
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hstate.add_int (DECL_OFFSET_ALIGN (t));
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}
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else if (code == VAR_DECL)
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@ -1187,6 +1187,7 @@ compare_tree_sccs_1 (tree t1, tree t2, tree **map)
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compare_values (DECL_NONADDRESSABLE_P);
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compare_values (DECL_PADDING_P);
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compare_values (DECL_FIELD_ABI_IGNORED);
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compare_values (DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD);
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compare_values (DECL_OFFSET_ALIGN);
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}
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else if (code == VAR_DECL)
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@ -256,7 +256,11 @@ unpack_ts_decl_common_value_fields (struct bitpack_d *bp, tree expr)
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DECL_PACKED (expr) = (unsigned) bp_unpack_value (bp, 1);
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DECL_NONADDRESSABLE_P (expr) = (unsigned) bp_unpack_value (bp, 1);
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DECL_PADDING_P (expr) = (unsigned) bp_unpack_value (bp, 1);
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DECL_FIELD_ABI_IGNORED (expr) = (unsigned) bp_unpack_value (bp, 1);
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unsigned val = (unsigned) bp_unpack_value (bp, 1);
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if (DECL_BIT_FIELD (expr))
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SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (expr, val);
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else
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SET_DECL_FIELD_ABI_IGNORED (expr, val);
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expr->decl_common.off_align = bp_unpack_value (bp, 8);
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}
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@ -219,7 +219,10 @@ pack_ts_decl_common_value_fields (struct bitpack_d *bp, tree expr)
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bp_pack_value (bp, DECL_PACKED (expr), 1);
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bp_pack_value (bp, DECL_NONADDRESSABLE_P (expr), 1);
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bp_pack_value (bp, DECL_PADDING_P (expr), 1);
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bp_pack_value (bp, DECL_FIELD_ABI_IGNORED (expr), 1);
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if (DECL_BIT_FIELD (expr))
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bp_pack_value (bp, DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD (expr), 1);
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else
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bp_pack_value (bp, DECL_FIELD_ABI_IGNORED (expr), 1);
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bp_pack_value (bp, expr->decl_common.off_align, 8);
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}
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26
gcc/tree.h
26
gcc/tree.h
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@ -2852,16 +2852,34 @@ extern void decl_value_expr_insert (tree, tree);
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/* In a FIELD_DECL, indicates this field should be bit-packed. */
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#define DECL_PACKED(NODE) (FIELD_DECL_CHECK (NODE)->base.u.bits.packed_flag)
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/* Nonzero in a FIELD_DECL means it is a bit field, and must be accessed
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specially. */
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#define DECL_BIT_FIELD(NODE) (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_1)
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/* In a FIELD_DECL, indicates this field should be ignored for ABI decisions
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like passing/returning containing struct by value.
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Set for C++17 empty base artificial FIELD_DECLs as well as
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empty [[no_unique_address]] non-static data members. */
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#define DECL_FIELD_ABI_IGNORED(NODE) \
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(FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_0)
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(!DECL_BIT_FIELD (NODE) && (NODE)->decl_common.decl_flag_0)
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#define SET_DECL_FIELD_ABI_IGNORED(NODE, VAL) \
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do { \
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gcc_checking_assert (!DECL_BIT_FIELD (NODE)); \
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FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_0 = (VAL); \
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} while (0)
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/* Nonzero in a FIELD_DECL means it is a bit field, and must be accessed
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specially. */
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#define DECL_BIT_FIELD(NODE) (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_1)
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/* In a FIELD_DECL, indicates C++ zero-width bitfield that used to be
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removed from the IL since PR42217 until PR101539 and by that changed
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the ABI on several targets. This flag is provided so that the backends
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can decide on the ABI with zero-width bitfields and emit -Wpsabi
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warnings. */
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#define DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD(NODE) \
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(DECL_BIT_FIELD (NODE) && (NODE)->decl_common.decl_flag_0)
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#define SET_DECL_FIELD_CXX_ZERO_WIDTH_BIT_FIELD(NODE, VAL) \
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do { \
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gcc_checking_assert (DECL_BIT_FIELD (NODE)); \
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FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_0 = (VAL); \
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} while (0)
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/* Used in a FIELD_DECL to indicate that we cannot form the address of
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this component. This makes it possible for Type-Based Alias Analysis
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