Re: [RFA] massively speed up "info var foo" on large programs

[Doug Evans <dje at google dot com>]

On Thu, May 24, 2012 at 2:28 PM, Doug Evans <dje@google.com> wrote:
> On Thu, May 24, 2012 at 10:58 AM, Doug Evans <dje@google.com> wrote:
>> Hi.
>>
>> I'm not entirely sure this patch is correct, but it feels correct (*1),
>> and is a massive win.
>> "info var Task" in one large program goes from 350 seconds to 28 seconds.
>>
>> [...]
>>
>> 2012-05-23 ?Doug Evans ?<dje@google.com>
>>
>> ? ? ? ?* symtab.c (lookup_msymbol_in_objfile): New function.
>> ? ? ? ?(search_symbols): Call it.
>
> Hmmm.
> One thing that occurs to me is separate debug objfiles.
> lookup_msymbol_in_objfile should probably search them.

This is a revised patch.
It scans separate debug files.
I think I understand the code better so I've removed the FIXME: The
comments in the code were misleading, find_pc_symtab is, I think, an
optimization to avoid unnecessarily calling lookup_symbol.
This patch also adds a (nfiles == 0) check to the second minsym loop:
there's no point in scanning minsyms for specific files.

The output is different from the previous code, I didn't take into
account the symbols that gdb creates for @plt entries.  I think if we
want to continue to provide the current output, we should add an
option to "info var|fun|type" to produce it: the normal case shouldn't
be that slow.

This patch removes the gdb-created minsyms from the output.
Another way to go is to print them.  I don't have a strong opinion on
either choice.
[The different with the current behaviour is that if the minsym is
found in any objfile then the current code won't print it in the
"Non-debugging symbols" section of the output.]

Ok to check in?

2012-05-25  Doug Evans  <dje@google.com>

        * symtab.c (minimal_symbol): New member created_by_gdb.
        * elfread.c (elf_symtab_read): Set created_by_gdb for @plt minsym
        created by gdb.
        * symtab.c (lookup_msymbol_in_objfile): New function.
        (search_symbols): Call it.  Only scan minsyms if nfiles == 0.

Attachment: gdb-120525-search-symbols-speedup-2.patch.txt
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