[Lldb-commits] [PATCH] D53597: Don't type-erase the SymbolContextItem enum

[Zachary Turner via lldb-commits]

I guess the question is, How is that hash and the bucket computed?  If it's
based on the full name, then you should be able to get fast exact lookup.
If it's based on the based name, then it will indeed be slow.

On Thu, Oct 25, 2018 at 11:33 AM Jim Ingham via Phabricator via
lldb-commits <lldb-commits at lists.llvm.org> wrote:

> jingham added a comment.
>
> Ah, right...  Too many patches (a good problem!)
>
> The standard as I read it says that the name entry points into the general
> string table, but doesn't specify which entry it points to.  However, the
> current DWARF debug_info doesn't ever emit a string for the fully qualified
> name, so you would have to construct it specially to have an exact name to
> refer to.  I also couldn't see anything that said specifically whether the
> DW_AT_name for a type has to be the full name or a base name, it just says:
>
> If a name has been given to the structure, union, or class in the source
> program, then the corresponding structure type, union type, or class type
> entry has a DW_AT_name attribute whose value is a null-terminated string
> containing the type name.
>
> But it would bloat the name tables to use the full name, and since you can
> reconstruct it from the context it's not needed...  So I've only seen base
> names in the name entry for types in the debug_info.
>
> Anyway, current clang for -gdwarf-5 produces:
>
>   Bucket 1 [
>     Name 2 {
>       Hash: 0xB887389
>       String: 0x000000c3 "Foo"
>       Entry @ 0x92 {
>         Abbrev: 0x39
>         Tag: DW_TAG_namespace
>         DW_IDX_die_offset: 0x0000004c
>       }
>     }
>   ]
>   Bucket 2 [
>     Name 3 {
>       Hash: 0xB8860BA
>       String: 0x000000c7 "Bar"
>       Entry @ 0x9b {
>         Abbrev: 0x13
>         Tag: DW_TAG_structure_type
>         DW_IDX_die_offset: 0x0000004e
>       }
>     }
>     Name 4 {
>       Hash: 0x7C9A7F6A
>       String: 0x000000b5 "main"
>       Entry @ 0xa4 {
>         Abbrev: 0x2E
>         Tag: DW_TAG_subprogram
>         DW_IDX_die_offset: 0x00000026
>       }
>     }
>
> For:
>
> namespace Foo
> {
>
>   struct Bar
>   {
>     int First;
>   };
>
> }
>
> int
> main()
> {
>
>   Foo::Bar mine = {10};
>   return mine.First;
>
> }
>
> Jim
>
>
> https://reviews.llvm.org/D53597
>
>
>
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