[Lldb-commits] [PATCH] D74637: Separate DIERef vs. user_id_t: m_function_scope_qualified_name_map

[Jan Kratochvil via Phabricator via lldb-commits]

jankratochvil added a comment.

In D74637#1878655 <https://reviews.llvm.org/D74637#1878655>, @labath wrote:

> In fact, this field used to hold a DIERef until I changed that in D63322 <https://reviews.llvm.org/D63322>.


I did not expect that. OK, this D74637 <https://reviews.llvm.org/D74637> + my D74690 <https://reviews.llvm.org/D74690> try to just revert D63322 <https://reviews.llvm.org/D63322>.

> I did it because it was
>  b) more memory-efficient.

Why? Both `DIERef` and `user_id_t` sizeof is 8.

> Maybe you could give a rough outline of where are you going with this.

I am trying to reduce `user_id_t` usage as much as possible.  And then to add MainCU to `user_id_t` (but no longer to `DIERef`). As construction of `user_id_t` with MainCU needs additional information no longer contained in `DIERef` it will need some additional parameter in the caller chain like I did in D73206 <https://reviews.llvm.org/D73206>. As the new parameter is used only for DWZ its addition is not much popular so it should be limited to as few cases as possible.

> For example, how will the user_id_t decoding process look like in the end?

In my dwz branch <https://github.com/jankratochvil/llvm-project/tree/dwz> the MainCU encoding is now combined for both `DIERef` and `user_id_t` but the plan is to encode it only into `user_id_t`. It still fits into 64-bits reusing the DWO field (which is never used together with DWZ). Current implementation:

- `DIERef`->`user_id_t` <https://github.com/jankratochvil/llvm-project/blob/fa83503513696b53c9cc2d20964ee27c375c2ef7/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp#L1226>
- `user_id_`->`DecodedUID` <https://github.com/jankratochvil/llvm-project/blob/fa83503513696b53c9cc2d20964ee27c375c2ef7/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp#L1262>
- `DWARFDIE`->`DIERef` <https://github.com/jankratochvil/llvm-project/blob/fa83503513696b53c9cc2d20964ee27c375c2ef7/lldb/source/Plugins/SymbolFile/DWARF/DWARFBaseDIE.cpp#L26>
- `DIERef`->`DWARFUnit *` <https://github.com/jankratochvil/llvm-project/blob/fa83503513696b53c9cc2d20964ee27c375c2ef7/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp#L157> wrt DWZ common file
- `DIERef`->`DWARFUnit *` <https://github.com/jankratochvil/llvm-project/blob/fa83503513696b53c9cc2d20964ee27c375c2ef7/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp#L168> for MainCU


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