JDevlieghere added a comment.
In https://reviews.llvm.org/D48241#1134240, @dblaikie wrote:
> Not sure I should get too involved in this discussion, knowing so little
> about Objective C - but if it seems sensible, could you provide some examples
> (just in comments/description in this code review) of what the DWARF used to
> look like and what it looks like after this change?
After this change we emit a forward declaration as a child of the
DW_TAG_structure_type. The definition (below) remains unchanged.
0x00000027: DW_TAG_structure_type
DW_AT_APPLE_objc_complete_type (true)
DW_AT_name ()
DW_AT_byte_size (0x04)
DW_AT_decl_file ("cat.m")
DW_AT_decl_line (1)
DW_AT_APPLE_runtime_class (0x10)
0x0000002d: DW_TAG_member
DW_AT_name ()
DW_AT_type (0x0000007b "base ")
DW_AT_decl_file ("cat.m")
DW_AT_decl_line (2)
DW_AT_data_member_location (0x00)
DW_AT_accessibility (DW_ACCESS_protected)
0x00000037: DW_TAG_subprogram
DW_AT_name ()
DW_AT_decl_file ("cat.m")
DW_AT_decl_line (10)
DW_AT_prototyped (true)
DW_AT_type (0x0000007b "base ")
DW_AT_declaration (true)
0x0000003f: DW_TAG_formal_parameter
DW_AT_type (0x0000007f "structure *")
DW_AT_artificial (true)
0x00000044: DW_TAG_formal_parameter
DW_AT_type (0x00000084 "structure *")
DW_AT_artificial (true)
0x00000049: NULL
...
0x0000007a: NULL
...
0x000000b5: DW_TAG_subprogram
DW_AT_low_pc (0x0000000000000000)
DW_AT_high_pc (0x000000000000001c)
DW_AT_frame_base (DW_OP_reg6 RBP)
DW_AT_object_pointer (0x000000cf)
DW_AT_name ()
DW_AT_decl_file ("cat.m")
DW_AT_decl_line (10)
DW_AT_prototyped (true)
DW_AT_type (0x0000007b "base ")
0x000000cf: DW_TAG_formal_parameter
DW_AT_location (DW_OP_fbreg -8)
DW_AT_name ()
DW_AT_type (0x000000b0 "structure *")
DW_AT_artificial (true)
0x000000d8: DW_TAG_formal_parameter
DW_AT_location (DW_OP_fbreg -16)
DW_AT_name ()
DW_AT_type (0x00000195 "structure *")
DW_AT_artificial (true)
0x000000e1: NULL
> Does this address the discoverability that's being discussed in the llvm-dev
> thread? There were concerns there about having to search through all the
> instances of a type to find all of its functions - I imagine, since Objective
> C classes aren't closed (if I understand correctly) that would still be a
> concern here? If it is, what is the benefit/tradeoff of this change (if it
> doesn't address the discoverability/still requires the Objective C
> accelerator table)?
Following this approach we have the exact same problem (and I believe we could
use the same solution). The motivation for this change is that there's no clean
way to implement the .apple_objc accelerator table using the debug_names,
because it's conceptually different from the other tables. It maps an interface
name to the DIEs of its methods, as opposed to all the other tables that map a
name to their corresponding DIE. The only way this could work is as a separate
table, because otherwise you'd have to ensure, for every entry, if it's a
"regular" one, which obviously violates the standard. Putting it in a separate
column is also a bad idea, because that means the column is present for all the
entries, including the ones that don't need it.
================
Comment at: clang/lib/CodeGen/CGDebugInfo.h:111
+ // methods.
+ llvm::DICompositeType *DIInterfaceDecl;
+ std::vector<MethodData> Methods;
----------------
aprantl wrote:
> Isn't the interface already the key in the DenseMap?
That's the `ObjCInterfaceDecl` while this is the `DICompositeType`.
https://reviews.llvm.org/D48241
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