[PATCH v4 5/8] Remove C++ special case from process_imported_unit_die

Tom Tromey
2026-02-24T01:19:53Z

process_imported_unit_die has a special case for C++, added as a
performance improvement.

While I somewhat agree with the general idea of this snippet --
importing a compilation unit seems like a strange thing to do, given
that partial units exist -- I think there are two issues with it.

First, it is specific to C++. I don't see any real reason that this
should be the case.

Second, it does not have a corresponding bit of code in the indexer.
This means that the cooked index's view of the DWARF differs from the
full reader's view here. This causes regressions in this series,
because the indexer assumes that reading a CU will cause all the
imported CUs to be read as a side effect -- but that does not happen
here.

I think fixing this in the indexer is not trivial. The reason for
this is that the indexer works in parallel, and once a reader has
acquired the "scan" bit for a CU, it is obligated to read it.
However, in this case this would require making a new cooked indexer.

Instead, because (1) this is weird and rare DWARF anyway, and (2) this
is just a performance optimization, I propose removing this.
---
gdb/dwarf2/read.c | 9 ---------
1 file changed, 9 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 5917e697aad..e48745d7969 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -4890,15 +4890,6 @@ process_imported_unit_die (struct die_info *die, struct dwarf2_cu *cu)
dwarf2_per_cu *per_cu
= dwarf2_find_containing_unit ({ &section, sect_off }, per_objfile);

- /* We're importing a C++ compilation unit with tag DW_TAG_compile_unit
- into another compilation unit, at root level. Regard this as a hint,
- and ignore it. This is a best effort, it only works if unit_type and
- lang are already set. */
- if (die->parent && die->parent->parent == NULL
- && per_cu->unit_type (false) == DW_UT_compile
- && per_cu->lang (false) == language_cplus)
- return;
-
/* If necessary, add it to the queue and load its DIEs. */
if (maybe_queue_comp_unit (cu, per_cu, per_objfile))
load_full_comp_unit (per_cu, per_objfile, false, cu->lang ());

--
2.49.0