diff options
author | Tom de Vries <tdevries@suse.de> | 2020-03-17 08:56:36 +0100 |
---|---|---|
committer | Tom de Vries <tdevries@suse.de> | 2020-03-17 08:56:36 +0100 |
commit | 589902954da0d1dd140b33e578954746c9bfc374 (patch) | |
tree | 02afbab5af498c6a4ca6d481a31a2d60e1fcb310 | |
parent | 7325b16ba4dc33a54356fd2b8fde79311c51b121 (diff) | |
download | binutils-589902954da0d1dd140b33e578954746c9bfc374.zip binutils-589902954da0d1dd140b33e578954746c9bfc374.tar.gz binutils-589902954da0d1dd140b33e578954746c9bfc374.tar.bz2 |
[gdb] Skip imports of c++ CUs
The DWARF standard appendix E.1 describes techniques that can be used for
compression and deduplication: DIEs can be factored out into a new compilation
unit, and referenced using DW_FORM_ref_addr.
Such a new compilation unit can either use a DW_TAG_compile_unit or
DW_TAG_partial_unit. If a DW_TAG_compile_unit is used, its contents is
evaluated by consumers as though it were an ordinary compilation unit. If a
DW_TAG_partial_unit is used, it's only considered by consumers in the context
of a DW_TAG_imported_unit.
An example of when DW_TAG_partial_unit is required is when the factored out
DIEs are not top-level, f.i. because they were children of a namespace. In
such a case the corresponding DW_TAG_imported_unit will occur as child of the
namespace.
In the case of factoring out DIEs from c++ compilation units, we can factor
out into a new DW_TAG_compile_unit, and no DW_TAG_imported_unit is required.
This begs the question how to interpret a top-level DW_TAG_imported_unit of a
c++ DW_TAG_compile_unit compilation unit. The semantics of
DW_TAG_imported_unit describe that the imported unit logically appears at the
point of the DW_TAG_imported_unit entry. But it's not clear what the effect
should be in this case, since all the imported DIEs are already globally
visible anyway, due to the use of DW_TAG_compile_unit.
So, skip top-level imports of c++ DW_TAG_compile_unit compilation units in
process_imported_unit_die.
Using the cc1 binary from PR23710 comment 1 and setting a breakpoint on do_rpo_vn:
...
$ gdb \
-batch \
-iex "maint set dwarf max-cache-age 316" \
-iex "set language c++" \
-ex "b do_rpo_vn" \
cc1
...
we get a 8.1% reduction in execution time, due to reducing the number of
partial symtabs expanded into full symtabs from 212 to 175.
Build and reg-tested on x86_64-linux.
gdb/ChangeLog:
2020-03-17 Tom de Vries <tdevries@suse.de>
PR gdb/23710
* dwarf2/read.h (struct dwarf2_per_cu_data): Add unit_type and lang
fields.
* dwarf2/read.c (process_psymtab_comp_unit): Initialize unit_type and lang
fields.
(process_imported_unit_die): Skip import of c++ CUs.
-rw-r--r-- | gdb/ChangeLog | 9 | ||||
-rw-r--r-- | gdb/dwarf2/read.c | 22 | ||||
-rw-r--r-- | gdb/dwarf2/read.h | 6 |
3 files changed, 37 insertions, 0 deletions
diff --git a/gdb/ChangeLog b/gdb/ChangeLog index cfd8c5b..3c92150 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,12 @@ +2020-03-17 Tom de Vries <tdevries@suse.de> + + PR gdb/23710 + * dwarf2/read.h (struct dwarf2_per_cu_data): Add unit_type and lang + fields. + * dwarf2/read.c (process_psymtab_comp_unit): Initialize unit_type and lang + fields. + (process_imported_unit_die): Skip import of c++ CUs. + 2020-03-16 Tom Tromey <tom@tromey.com> * p-valprint.c (pascal_object_print_value): Initialize diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 88a60c1..0e879e0 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -7425,6 +7425,18 @@ process_psymtab_comp_unit (struct dwarf2_per_cu_data *this_cu, cutu_reader reader (this_cu, NULL, 0, false); + switch (reader.comp_unit_die->tag) + { + case DW_TAG_compile_unit: + this_cu->unit_type = DW_UT_compile; + break; + case DW_TAG_partial_unit: + this_cu->unit_type = DW_UT_partial; + break; + default: + abort (); + } + if (reader.dummy_p) { /* Nothing. */ @@ -7438,6 +7450,8 @@ process_psymtab_comp_unit (struct dwarf2_per_cu_data *this_cu, reader.comp_unit_die, pretend_language); + this_cu->lang = this_cu->cu->language; + /* Age out any secondary CUs. */ age_cached_comp_units (this_cu->dwarf2_per_objfile); } @@ -9759,6 +9773,14 @@ process_imported_unit_die (struct die_info *die, struct dwarf2_cu *cu) = dwarf2_find_containing_comp_unit (sect_off, is_dwz, cu->per_cu->dwarf2_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. */ + if (die->parent && die->parent->parent == NULL + && per_cu->unit_type == DW_UT_compile + && per_cu->lang == language_cplus) + return; + /* If necessary, add it to the queue and load its DIEs. */ if (maybe_queue_comp_unit (cu, per_cu, cu->language)) load_full_comp_unit (per_cu, false, cu->language); diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h index 00652c2..f0e3d6b 100644 --- a/gdb/dwarf2/read.h +++ b/gdb/dwarf2/read.h @@ -323,6 +323,12 @@ struct dwarf2_per_cu_data dummy CUs (a CU header, but nothing else). */ struct dwarf2_cu *cu; + /* The unit type of this CU. */ + enum dwarf_unit_type unit_type; + + /* The language of this CU. */ + enum language lang; + /* The corresponding dwarf2_per_objfile. */ struct dwarf2_per_objfile *dwarf2_per_objfile; |