From: Tom de Vries Date: Tue, 17 Mar 2020 07:56:36 +0000 (+0100) Subject: [gdb] Skip imports of c++ CUs X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=589902954da0d1dd140b33e578954746c9bfc374;p=binutils-gdb.git [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 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. --- diff --git a/gdb/ChangeLog b/gdb/ChangeLog index cfd8c5b9d24..3c9215060a9 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,12 @@ +2020-03-17 Tom de Vries + + 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 * p-valprint.c (pascal_object_print_value): Initialize diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 88a60c1c73b..0e879e08a0c 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 00652c2b45a..f0e3d6bb723 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;