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In find_data_type(), it creates and deletes a debug info whenver it
tries to find data type for a sample.  This is inefficient and it most
likely accesses the same binary again and again.

Let's add a single entry cache the debug info structure for the last DSO.
Depending on sample data, it usually gives me 2~3x (and sometimes more)
speed ups.

Note that this will introduce a little difference in the output due to
the order of checking stack operations.  It used to check the stack ops
before checking the availability of debug info but I moved it after the
symbol check.  So it'll report stack operations in DSOs without debug
info as unknown.  But I think it's ok and better to have the checking
near the caching logic.

Committer testing:

  root@x1:~# perf mem record -a sleep 5s
  root@x1:~# perf evlist
  cpu_atom/mem-loads,ldlat=30/P
  cpu_atom/mem-stores/P
  dummy:u
  root@x1:~# diff -u before after
  --- before	2024-08-08 09:33:53.880780784 -0300
  +++ after	2024-08-08 09:35:13.917325041 -0300
  @@ -81,8 +81,8 @@
   # Overhead  Data Type
   # ........  .........
   #
  -    55.43%  (unknown)
  -    11.61%  (stack operation)
  +    55.56%  (unknown)
  +    11.48%  (stack operation)
        4.93%  struct pcpu_hot
        3.26%  unsigned int
        2.48%  struct
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240805234648.1453689-1-namhyung@kernel.org

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>