> For consistency yes I guess but IIRC they cannot really appear in > FIELD_DECLs.
OK, i tought that if I put SVE into structures, we may end up with these. > > + /* Different fields of the same record type cannot overlap. > > + ??? Bitfields can overlap at RTL level so punt on them. */ > > + if (DECL_BIT_FIELD (field1) && DECL_BIT_FIELD (field2)) > > + return 0; > > + > > don't you need the DECL_BIT_FIELD_REPRESENTATIVE check here as well? > I'd do > > if (DECL_BIT_FIELD_REPRESENTATIVE (field1)) > field1 = DECL_BIT_FIELD_REPRESENTATIVE (field1); > if (DECL_BIT_FIELD_REPRESENTATIVE (field2)) > field2 = DECL_BIT_FIELD_REPRESENTATIVE (field2); > > thus use the representative for the overlap check. It might > be the case that we can improve here and if we do this > can do the DECL_BIT_FIELD check after this (hoping the > representative doesn't have it set). OK. > > > + if (tree_int_cst_equal (DECL_FIELD_OFFSET (field1), > > + DECL_FIELD_OFFSET (field2)) > > + && tree_int_cst_equal (DECL_FIELD_BIT_OFFSET (field1), > > + DECL_FIELD_BIT_OFFSET (field2))) > > + return 0; > > In gimple_compare_field_offset this was fast-pathed for > DECL_OFFSET_ALIGN (f1) == DECL_OFFSET_ALIGN (f2) so I suggest to > do that here as well. Note that DECL_FIELD_OFFSET can be > a non-constant which means you cannot use tree_int_cst_equal > unconditionally here but you have to use operand_equal_p. tree_int_cst_equal will return false if offsets are not INTEGER_CST. I was not sure if I can safely use operand_equal_p. What happens for fields with variable offsets when I inline two copies of same function which takes size as parameter and make the size different? Will I get here proper SSA name so operand_equal_p will work? If so, I still see no point for fast-path for DECL_OFFSET_ALIGN. In many cases BIT_OFFSET will be just 0, so even if offset alignments are different we are likely going to hit this fast path avoiding parsing trees later. > > > + /* Note that it may be possible to use component_ref_field_offset > > + which would provide offsets as trees. However constructing and folding > > + trees is expensive and does not seem to be worth the compile time > > + cost. */ > > + > > + poly_uint64 offset1, offset2; > > + poly_uint64 bit_offset1, bit_offset2; > > + poly_uint64 size1, size2; > > I think you need poly_offset_int here since you convert to bits below. > > The gimple_compare_field_offset checking way looks cheaper btw, so > I wonder why you don't simply call it but replicate things here? > When do we expect to have partially overlapping field decls? Even > when considering canonical type merging? Because the types I am comparing may not have same canonical types. nonoverlapping_component_refs_since_match_p is called when we prove that base pointers are the same (even with -fno-strict-aliasing). In such cases the access paths may be based on completely different types. The point of nonoverlapping_component_refs_since_match_p is to match them as far as possible when they are semantically equivalent in hope to get non-overlapping refs in the last step. This is stronger than the get_base_ref_and_extend based check in presence of non-constant ARRAY_REFs. Honza
