Re: [PATCH] Dump probability for edges a frequency for BBs

[Martin Liška]

On 11/30/2016 11:46 PM, Martin Sebor wrote:
On 11/24/2016 05:59 AM, Martin Liška wrote:
On 11/24/2016 09:29 AM, Richard Biener wrote:
Please guard with ! TDF_GIMPLE, otherwise the output will not be parseable
with the GIMPLE FE.
RIchard.

Done and verified that and it provides equal dumps for -fdump*-gimple.
Installed as r242837.

Hi Martin,

I'm trying to understand how to interpret the probabilities (to
make sure one of my tests, builtin-sprintf-2.c, is testing what
it's supposed to be testing).

With this example:

  char d2[2];

  void f (void)
  {
    if (2 != __builtin_sprintf (d2, "%i", 12))
      __builtin_abort ();
  }

the probability of the branch to abort is 0%:

  f1 ()
  {
    int _1;

    <bb 2> [100.0%]:
    _1 = __builtin_sprintf (&d, "%i", 12);
    if (_1 != 2)
      goto <bb 3>; [0.0%]
    else
      goto <bb 4>; [100.0%]

    <bb 3> [0.0%]:
    __builtin_abort ();

    <bb 4> [100.0%]:
    return;
  }

Hello Martin.

Looks I did a small error. I use only only one digit after decimal point, which 
is unable to
display noreturn predictor (defined as PROB_VERY_UNLIKELY):

#define PROB_VERY_UNLIKELY      (REG_BR_PROB_BASE / 2000 - 1) // this is 4

I would suggest to use following patch to display at least 2 digits, that would 
distinguish
between real zero and PROB_VERY_UNLIKELY:

x.c.046t.profile_estimate:

f ()
{
  int _1;

  <bb 2> [100.00%]:
  _1 = __builtin_sprintf (&d2, "%i", 12);
  if (_1 != 2)
    goto <bb 3>; [0.04%]
  else
    goto <bb 4>; [99.96%]

  <bb 3> [0.04%]:
  __builtin_abort ();

  <bb 4> [99.96%]:
  return;

}


Yet the call to abort is in the assembly so I would expect its
probability to be more than zero.  So my question is: it it safe
to be testing for calls to abort in the optimized dump as a way
of verifying that the call has not been eliminated from the program
regardless of their probabilities?

I think so, otherwise the call would be removed.

I'm going to test the patch (and eventually update scanned patterns).

Martin

Patch candidate:

diff --git a/gcc/gimple-pretty-print.c b/gcc/gimple-pretty-print.c
index b5e866d..de57e89 100644
--- a/gcc/gimple-pretty-print.c
+++ b/gcc/gimple-pretty-print.c
@@ -72,12 +72,17 @@ debug_gimple_stmt (gimple *gs)
   print_gimple_stmt (stderr, gs, 0, TDF_VOPS|TDF_MEMSYMS);
 }
 
+/* Print format used for displaying probability of an edge or frequency
+   of a basic block.  */
+
+#define PROBABILITY_FORMAT "[%.2f%%]"
+
 /* Dump E probability to BUFFER.  */
 
 static void
 dump_edge_probability (pretty_printer *buffer, edge e)
 {
-  pp_scalar (buffer, " [%.1f%%]",
+  pp_scalar (buffer, " " PROBABILITY_FORMAT,
             e->probability * 100.0 / REG_BR_PROB_BASE);
 }
 
@@ -1023,7 +1028,7 @@ dump_gimple_label (pretty_printer *buffer, glabel *gs, int spc, int flags)
       dump_generic_node (buffer, label, spc, flags, false);
       basic_block bb = gimple_bb (gs);
       if (bb && !(flags & TDF_GIMPLE))
-       pp_scalar (buffer, " [%.1f%%]",
+       pp_scalar (buffer, " " PROBABILITY_FORMAT,
                   bb->frequency * 100.0 / REG_BR_PROB_BASE);
       pp_colon (buffer);
     }
@@ -2590,7 +2595,8 @@ dump_gimple_bb_header (FILE *outf, basic_block bb, int 
indent, int flags)
          if (flags & TDF_GIMPLE)
            fprintf (outf, "%*sbb_%d:\n", indent, "", bb->index);
          else
-           fprintf (outf, "%*s<bb %d> [%.1f%%]:\n", indent, "", bb->index,
+           fprintf (outf, "%*s<bb %d> " PROBABILITY_FORMAT ":\n",
+                    indent, "", bb->index,
                     bb->frequency * 100.0 / REG_BR_PROB_BASE);
        }
     }


For reference, the directive the test uses since this change was
committed looks like this:

{ dg-final { scan-tree-dump-times "> \\\[\[0-9.\]+%\\\]:\n *__builtin_abort" 114 
"optimized" }

If I'm reading the heavily escaped regex right it matches any
percentage, even 0.0% (and the test passes).

Thanks
Martin