[google] Patch to add compiler flag to dump callgraph edge profiles in special .note sections (issue4591045)

Xinliang David Li davidxl@google.com
Wed Jun 8 16:37:00 GMT 2011


ok for google/main.

David

On Wed, Jun 8, 2011 at 9:13 AM, Sriraman Tallam <tmsriram@google.com> wrote:
> +davidxl
>
> On Tue, Jun 7, 2011 at 7:05 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> Patch Description:
>> =================
>>
>> I am working on a project to do global function layout in the linker where the linker reads the callgraph edge profile information, generated by FDO, and uses that to find a ordering of functions that will place functions calling each other frequently closer, like the Pettis-Hansen code ordering algorithm described in the paper "Profile-guided Code Poisitioning" in PLDI 1990.
>>
>> This patch adds a flag that allows the callgraph edge profile information to be stored .note sections called ".note.callgraph.text". The new compiler flag -fcallgraph-profiles-sections generates these sections and must be used along with -fprofile-use. I have added a PARAM to only output callgraph edges greater than a specified threshold. Once this is available, the linker can read these sections and generate a global callgraph which can be used to determine a global function ordering.
>>
>> I am adding plugin support in the gold linker to allow linker plugins to be able to read the contents of sections and also adding plugin hooks to specify a desired ordering of functions to the linker. The linker patch is available here : http://sourceware.org/ml/binutils/2011-03/msg00043.html. Once this is available, linker plugins can be used to determine the function layout, like the Pettis-Hansen algorithm, of the final binary.
>>
>> Example: The new .note.callgraph.text sections looks like this for a function foo that calls bar 100 times and zap 50 times:
>> ****************************
>> .section        .note.callgraph.text._Z3foov,"",@progbits
>>        .string "Function _Z3foov"
>>        .string "_Z3barv"
>>        .string "100"
>>        .string "_Z3zapv"
>>        .string "50"
>> ***************************
>>
>> For now, this is for google/main. I will re-submit for review to trunk along with data layout.
>>
>> Google ref 41940
>>
>> 2011-06-07  Sriraman Tallam  <tmsriram@google.com>
>>
>>        * doc/invoke.texi: document option -fcallgraph-profiles-sections.
>>        * final.c  (dump_cgraph_profiles): New function.
>>        (rest_of_handle_final): Create new section '.note.callgraph.text'
>>        with compiler flag -fcallgraph-profiles-sections
>>        * common.opt: New option -fcallgraph-profiles-sections.
>>        * params.def (DEFPARAM): New param
>>        PARAM_NOTE_CGRAPH_SECTION_EDGE_THRESHOLD.
>>
>> Index: doc/invoke.texi
>> ===================================================================
>> --- doc/invoke.texi     (revision 174789)
>> +++ doc/invoke.texi     (working copy)
>> @@ -351,7 +351,7 @@ Objective-C and Objective-C++ Dialects}.
>>  -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
>>  -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
>>  -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
>> --fcheck-data-deps -fclone-hot-version-paths @gol
>> +-fcallgraph-profiles-sections -fcheck-data-deps -fclone-hot-version-paths @gol
>>  -fcombine-stack-adjustments -fconserve-stack @gol
>>  -fcompare-elim -fcprop-registers -fcrossjumping @gol
>>  -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
>> @@ -8114,6 +8114,15 @@ Do not promote static functions with always inline
>>  @opindex fripa-verbose
>>  Enable printing of verbose information about dynamic inter-procedural optimizations.
>>  This is used in conjunction with the @option{-fripa}.
>> +
>> +@item -fcallgraph-profiles-sections
>> +@opindex fcallgraph-profiles-sections
>> +Emit call graph edge profile counts in .note.callgraph.text sections. This is
>> +used in conjunction with @option{-fprofile-use}. A new .note.callgraph.text
>> +section is created for each function. This section lists every callee and the
>> +number of times it is called. The params variable
>> +"note-cgraph-section-edge-threshold" can be used to only list edges above a
>> +certain threshold.
>>  @end table
>>
>>  The following options control compiler behavior regarding floating
>> Index: final.c
>> ===================================================================
>> --- final.c     (revision 174789)
>> +++ final.c     (working copy)
>> @@ -4321,13 +4321,37 @@ debug_free_queue (void)
>>       symbol_queue_size = 0;
>>     }
>>  }
>> -
>> +
>> +/* List the call graph profiled edges whise value is greater than
>> +   PARAM_NOTE_CGRAPH_SECTION_EDGE_THRESHOLD in the
>> +   ".note.callgraph.text" section. */
>> +static void
>> +dump_cgraph_profiles (void)
>> +{
>> +  struct cgraph_node *node = cgraph_node (current_function_decl);
>> +  struct cgraph_edge *e;
>> +  struct cgraph_node *callee;
>> +
>> +  for (e = node->callees; e != NULL; e = e->next_callee)
>> +    {
>> +      if (e->count <= PARAM_VALUE (PARAM_NOTE_CGRAPH_SECTION_EDGE_THRESHOLD))
>> +        continue;
>> +      callee = e->callee;
>> +      fprintf (asm_out_file, "\t.string \"%s\"\n",
>> +               IDENTIFIER_POINTER (decl_assembler_name (callee->decl)));
>> +      fprintf (asm_out_file, "\t.string \"" HOST_WIDEST_INT_PRINT_DEC "\"\n",
>> +               e->count);
>> +    }
>> +}
>> +
>>  /* Turn the RTL into assembly.  */
>>  static unsigned int
>>  rest_of_handle_final (void)
>>  {
>>   rtx x;
>>   const char *fnname;
>> +  char *profile_fnname;
>> +  unsigned int flags;
>>
>>   /* Get the function's name, as described by its RTL.  This may be
>>      different from the DECL_NAME name used in the source file.  */
>> @@ -4387,6 +4411,21 @@ rest_of_handle_final (void)
>>     targetm.asm_out.destructor (XEXP (DECL_RTL (current_function_decl), 0),
>>                                decl_fini_priority_lookup
>>                                  (current_function_decl));
>> +
>> +  /* With -fcgraph-section, add ".note.callgraph.text" section for storing
>> +     profiling information. */
>> +  if (flag_callgraph_profiles_sections
>> +      && flag_profile_use
>> +      && cgraph_node (current_function_decl) != NULL)
>> +    {
>> +      flags = SECTION_DEBUG;
>> +      asprintf (&profile_fnname, ".note.callgraph.text.%s", fnname);
>> +      switch_to_section (get_section (profile_fnname, flags, NULL));
>> +      fprintf (asm_out_file, "\t.string \"Function %s\"\n", fnname);
>> +      dump_cgraph_profiles ();
>> +      free (profile_fnname);
>> +    }
>> +
>>   return 0;
>>  }
>>
>> Index: common.opt
>> ===================================================================
>> --- common.opt  (revision 174789)
>> +++ common.opt  (working copy)
>> @@ -907,6 +907,10 @@ fcaller-saves
>>  Common Report Var(flag_caller_saves) Optimization
>>  Save registers around function calls
>>
>> +fcallgraph-profiles-sections
>> +Common Report Var(flag_callgraph_profiles_sections) Init(0)
>> +Generate .note.callgraph.text sections listing callees and edge counts.
>> +
>>  fcheck-data-deps
>>  Common Report Var(flag_check_data_deps)
>>  Compare the results of several data dependence analyzers.
>> Index: params.def
>> ===================================================================
>> --- params.def  (revision 174789)
>> +++ params.def  (working copy)
>> @@ -1002,6 +1002,15 @@ DEFPARAM (PARAM_MVERSN_CLONE_CGRAPH_DEPTH,
>>          "maximum length of the call graph path to be cloned "
>>           "while doing multiversioning",
>>          2, 0, 5)
>> +
>> +/* Only output those call graph edges in .note.callgraph.text sections
>> +   whose count is greater than this value. */
>> +DEFPARAM (PARAM_NOTE_CGRAPH_SECTION_EDGE_THRESHOLD,
>> +         "note-cgraph-section-edge-threshold",
>> +         "minimum call graph edge count for inclusion in "
>> +          ".note.callgraph.text section",
>> +         0, 0, 0)
>> +
>>  /*
>>  Local variables:
>>  mode:c
>>
>> --
>> This patch is available for review at http://codereview.appspot.com/4591045
>>
>



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