MI: -var-update performance

[Vladimir Prus <ghost at cs dot msu dot su>]

Hi,
I'm running into a case where -var-update takes about 2 seconds to execute.
There's quite a lot of varobjs, but 2 seconds is beyond any expectation.

Here's the profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  Ts/call  Ts/call  name
 22.44     70.23    70.23                             lookup_partial_symbol
 19.65    131.72    61.49                            
lookup_minimal_symbol_by_pc_section
 15.80    181.16    49.44                            
basic_lookup_transparent_type
 10.39    213.67    32.51                             find_pc_sect_psymtab
  5.25    230.11    16.45                             strcmp_iw_ordered
  2.50    237.93     7.82                             find_pc_sect_section
  1.96    244.06     6.13                             dwarf2_frame_find_fde
  1.88    249.94     5.89                             strcmp_iw
  1.21    253.72     3.78                             read_partial_die
  1.02    256.90     3.18                            
lookup_symbol_aux_psymtabs
  0.97    259.94     3.04                             symbol_search_name



Any ideas what's up? Should I try to rebuild gdb with --enable-profiling to
get call graph?

- Volodya