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[Bug gdb/13498] save-index makes gdb slow with dwarf4


http://sourceware.org/bugzilla/show_bug.cgi?id=13498

--- Comment #2 from LuboÅ LuÅÃk <l.lunak at suse dot cz> 2011-12-15 15:54:43 UTC ---
It takes so long because dw2_map_symbol_filenames() loops over both
dwarf2_per_objfile::all_comp_units and dwarf2_per_objfile::type_comp_units,
where e.g. LibreOffice's libswlo.so has ~700 of the first and ~16000 of the
second. It appears unnecessary to iterate over type_comp_units, as
all_comp_units should already include all the files encountered during
compilation.

But it turns out gdb performs poorly with DWARF4 in general. In this case
dw2_map_symbol_filenames() could be fixed, assuming what I wrote above is
correct, but there appear to be other inefficiencies (related to .debug_types
too?). E.g. 'break shared<tab>' (trying to complete a filename) is very fast
with DWARF2, but takes very long with DWARF4, with or without the gdb index,
and it also noticeably increases memory usage.

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