This patch overloads GCC option -freorder-functions with -freoder-functions=* 
which will invoke the linker plugin libfunction_reordering_plugin.so. For now, 
the only accepted option is -freoder-functions=cgedge, where the functions 
which are connected by hot callgraph edges are placed closer.  When 
-freorder-functions is specified without the '=', the original behaviour is 
maintained.  This patch also removes the -fcallgraph-profiles-sections option.

For context, the function_reordering_plugin is only available in gcc-4_6 
branch. I am working on porting this to trunk and will send out a patch soon.


        * cgraphbuild.c (remove_cgraph_callee_edges): Replace
        flag_callgraph_profiles_sections with flag_reorder_functions.
        * final.c (rest_of_handle_final): Ditto.
        * configure: Regenerate.
        * config.in: undef FRPLUGINSONAME.
        * congifure.ac: Define FRPLUGINSONAME.
        * config.host: Set host_function_reordering_plugin_soname.
        * gcc.c: Invoke function_reordering linker plugin with
        -freorder-functions=* option.
        (set_func_reorder_linker_plugin_spec): New function.
        (main): Call set_func_reorder_linker_plugin_spec when
        -freorder-functions=* option is seen.
        * common.opt (fcallgraph-profiles-sections):  Remove.
        (freorder-functions=): New option.

        * function_reordering_plugin.c (register_claim_file_hook): New function
        pointer.
        (register_all_symbols_read_hook): Ditto.
        (no_op): New global.
        (out_file): Make static.
        (is_api_exist): Make static.
        (process_option): New function.
        (onload): Return if no_op is set. Do not register handlers until
        necessary.


Index: function_reordering_plugin/function_reordering_plugin.c
===================================================================
--- function_reordering_plugin/function_reordering_plugin.c     (revision 
185372)
+++ function_reordering_plugin/function_reordering_plugin.c     (working copy)
@@ -64,6 +64,9 @@ enum ld_plugin_status claim_file_hook (const struc
                                        int *claimed);
 enum ld_plugin_status all_symbols_read_hook ();
 
+static ld_plugin_register_claim_file register_claim_file_hook = NULL;
+static ld_plugin_register_all_symbols_read
+  register_all_symbols_read_hook = NULL;
 static ld_plugin_get_input_section_count get_input_section_count = NULL;
 static ld_plugin_get_input_section_type get_input_section_type = NULL;
 static ld_plugin_get_input_section_name get_input_section_name = NULL;
@@ -73,12 +76,16 @@ static ld_plugin_allow_section_ordering allow_sect
 
 /* The file where the final function order will be stored.
    It is "./final_layout.txt".  It can be changed by passing
-   new name to --plugin-opt  */
+   new name to --plugin-opt  as --plugin-opt "file=<name>".
+   To dump to stderr, say --plugin-opt "file=stderr".  */
 
-char *out_file = "./final_layout.txt";
+static char *out_file = "./final_layout.txt";
 
-int is_api_exist = 0;
+static int is_api_exist = 0;
 
+/* The plugin does nothing when no-op is 1.  */
+static int no_op = 0;
+
 /* Copies new output file name out_file  */
 void get_filename (const char *name)
 {
@@ -91,6 +98,39 @@ void get_filename (const char *name)
   strcpy (out_file, name);
 }
 
+/* Process options to plugin.  Options with prefix "group=" are special.
+   They specify the type of grouping. The option "group=none" makes the
+   plugin do nothing.   Options with prefix "file=" set the output file
+   where the final function order must be stored.  */
+void
+process_option (const char *name)
+{
+  const char *option_group = "group=";
+  const char *option_file = "file=";
+
+  /* Check if option is "group="  */
+  if (strncmp (name, option_group, strlen (option_group)) == 0)
+    {
+      if (strcmp (name + strlen (option_group), "none") == 0)
+       no_op = 1;
+      else
+       no_op = 0;
+      return;
+    }
+
+  /* Check if option is "file=" */
+  if (strncmp (name, option_file, strlen (option_file)) == 0)
+    {
+      get_filename (name + strlen (option_file));
+      return;
+    }
+
+  /* Unknown option, set no_op to 1.  */
+  no_op = 1;
+  fprintf (stderr, "Unknown option to function reordering plugin :%s\n",
+          name);
+}
+
 /* Plugin entry point.  */
 enum ld_plugin_status
 onload (struct ld_plugin_tv *tv)
@@ -105,14 +145,16 @@ onload (struct ld_plugin_tv *tv)
         case LDPT_GOLD_VERSION:
           break;
         case LDPT_OPTION:
-         get_filename (entry->tv_u.tv_string);
+         process_option (entry->tv_u.tv_string);
+         /* If no_op is set, do not do anything else.  */
+         if (no_op) return LDPS_OK;
          break;
         case LDPT_REGISTER_CLAIM_FILE_HOOK:
-          assert ((*entry->tv_u.tv_register_claim_file) (claim_file_hook) == 
LDPS_OK);
+         register_claim_file_hook = *entry->tv_u.tv_register_claim_file;
           break;
        case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK:
-          assert ((*entry->tv_u.tv_register_all_symbols_read) 
(all_symbols_read_hook)
-                  == LDPS_OK);
+         register_all_symbols_read_hook
+           = *entry->tv_u.tv_register_all_symbols_read;
           break;
         case LDPT_GET_INPUT_SECTION_COUNT:
           get_input_section_count = *entry->tv_u.tv_get_input_section_count;
@@ -137,14 +179,25 @@ onload (struct ld_plugin_tv *tv)
         }
     }
 
-  if (get_input_section_count != NULL
+  assert (!no_op);
+
+  if (register_all_symbols_read_hook != NULL
+      && register_claim_file_hook != NULL
+      && get_input_section_count != NULL
       && get_input_section_type != NULL
       && get_input_section_name != NULL
       && get_input_section_contents != NULL
       && update_section_order != NULL
       && allow_section_ordering != NULL)
     is_api_exist = 1;
+  else
+    return LDPS_OK;
 
+  /* Register handlers.  */
+  assert ((*register_all_symbols_read_hook) (all_symbols_read_hook)
+          == LDPS_OK);
+  assert ((*register_claim_file_hook) (claim_file_hook)
+         == LDPS_OK);
   return LDPS_OK;
 }
 
@@ -161,9 +214,8 @@ claim_file_hook (const struct ld_plugin_input_file
 
   (void) claimed;
 
-  /* Silently return if the plugin APIs are not supported.  */
-  if (!is_api_exist)
-    return LDPS_OK;
+  /* Plugin APIs are supported if this is called.  */
+  assert (is_api_exist);
 
   if (is_ordering_specified == 0)
     {
@@ -221,9 +273,8 @@ all_symbols_read_hook (void)
   unsigned int *shndx;
   FILE *fp;
 
-  /* Silently return if the plugin APIs are not supported.  */
-  if (!is_api_exist)
-    return LDPS_OK;
+  /* Plugin APIs are supported if this is called.  */
+  assert (is_api_exist);
 
   if (is_callgraph_empty ())
     return LDPS_OK;
Index: function_reordering_plugin/ChangeLog.google-4_6
===================================================================
--- function_reordering_plugin/ChangeLog.google-4_6     (revision 185372)
+++ function_reordering_plugin/ChangeLog.google-4_6     (working copy)
@@ -1,3 +1,15 @@
+2012-03-14  Sriraman Tallam  <tmsri...@google.com>
+
+       * function_reordering_plugin.c (register_claim_file_hook): New function
+       pointer.
+       (register_all_symbols_read_hook): Ditto.
+       (no_op): New global.
+       (out_file): Make static.
+       (is_api_exist): Make static.
+       (process_option): New function.
+       (onload): Return if no_op is set. Do not register handlers until
+       necessary.      
+
 2012-02-25  Sriraman Tallam  <tmsri...@google.com>
 
        * function_reordering_plugin.c: Check for presence of elf.h.
Index: gcc/cgraphbuild.c
===================================================================
--- gcc/cgraphbuild.c   (revision 185372)
+++ gcc/cgraphbuild.c   (working copy)
@@ -703,10 +703,10 @@ extern bool cgraph_callee_edges_final_cleanup;
 static unsigned int
 remove_cgraph_callee_edges (void)
 {
-  /* The -fcallgraph-profiles-sections flag needs the call-graph preserved
+  /* The -freorder-functions=* flag needs the call-graph preserved
      till pass_final.  */
   if (cgraph_callee_edges_final_cleanup
-      && flag_callgraph_profiles_sections)
+      && flag_reorder_functions > 1)
       return 0;
 
   cgraph_node_remove_callees (cgraph_node (current_function_decl));
Index: gcc/configure
===================================================================
--- gcc/configure       (revision 185372)
+++ gcc/configure       (working copy)
@@ -4861,7 +4861,7 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $acx_cv_cc_gcc_supports_ada" 
>&5
 $as_echo "$acx_cv_cc_gcc_supports_ada" >&6; }
 
-if test x$GNATBIND != xno && test x$GNATMAKE != xno && test 
x$acx_cv_cc_gcc_supports_ada != xno; then
+if test "x$GNATBIND" != xno && test "x$GNATMAKE" != xno && test 
x$acx_cv_cc_gcc_supports_ada != xno; then
   have_gnat=yes
 else
   have_gnat=no
@@ -11480,6 +11480,12 @@ esac
 
 
 cat >>confdefs.h <<_ACEOF
+#define FRPLUGINSONAME "${host_function_reordering_plugin_soname}"
+_ACEOF
+
+
+
+cat >>confdefs.h <<_ACEOF
 #define LTOPLUGINSONAME "${host_lto_plugin_soname}"
 _ACEOF
 
@@ -17572,7 +17578,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17575 "configure"
+#line 17581 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -17678,7 +17684,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 17681 "configure"
+#line 17687 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
Index: gcc/final.c
===================================================================
--- gcc/final.c (revision 185372)
+++ gcc/final.c (working copy)
@@ -4421,9 +4421,9 @@ rest_of_handle_final (void)
                                decl_fini_priority_lookup
                                  (current_function_decl));
 
-  /* With -fcallgraph-profiles-sections, add ".gnu.callgraph.text" section
+  /* With -freorder-functions=, add ".gnu.callgraph.text" section
      for storing profiling information. */
-  if (flag_callgraph_profiles_sections
+  if (flag_reorder_functions > 1
       && flag_profile_use
       && cgraph_node (current_function_decl) != NULL
       && (cgraph_node (current_function_decl))->callees != NULL)
Index: gcc/gcc.c
===================================================================
--- gcc/gcc.c   (revision 185372)
+++ gcc/gcc.c   (working copy)
@@ -663,6 +663,9 @@ proper position among the other output files.  */
     -plugin-opt=-fresolution=%u.res \
     %{!nostdlib:%{!nodefaultlibs:%:pass-through-libs(%(link_gcc_c_sequence))}} 
\
     }"PLUGIN_COND_CLOSE" \
+    %{freorder-functions=*: \
+    -plugin %(func_reorder_linker_plugin_file) \
+    -plugin-opt=%(func_reorder_linker_plugin_opt)} \
     %{flto|flto=*:%<fcompare-debug*} \
     %{flto} %{flto=*} %l " LINK_PIE_SPEC \
    "%{fuse-ld=gold:%{fuse-ld=bfd:%e-fuse-ld=gold and -fuse-ld=bfd may not be 
used together}} \
@@ -717,6 +720,8 @@ static const char *endfile_spec = ENDFILE_SPEC;
 static const char *startfile_spec = STARTFILE_SPEC;
 static const char *linker_name_spec = LINKER_NAME;
 static const char *linker_plugin_file_spec = "";
+static const char *func_reorder_linker_plugin_file_spec = "";
+static const char *func_reorder_linker_plugin_opt = "";
 static const char *lto_wrapper_spec = "";
 static const char *lto_gcc_spec = "";
 static const char *link_command_spec = LINK_COMMAND_SPEC;
@@ -1206,6 +1211,10 @@ static struct spec_list static_specs[] =
   INIT_STATIC_SPEC ("multilib_options",                &multilib_options),
   INIT_STATIC_SPEC ("linker",                  &linker_name_spec),
   INIT_STATIC_SPEC ("linker_plugin_file",      &linker_plugin_file_spec),
+  INIT_STATIC_SPEC ("func_reorder_linker_plugin_file",
+                   &func_reorder_linker_plugin_file_spec),
+  INIT_STATIC_SPEC ("func_reorder_linker_plugin_opt",
+                   &func_reorder_linker_plugin_opt),
   INIT_STATIC_SPEC ("lto_wrapper",             &lto_wrapper_spec),
   INIT_STATIC_SPEC ("lto_gcc",                 &lto_gcc_spec),
   INIT_STATIC_SPEC ("link_libgcc",             &link_libgcc_spec),
@@ -6108,6 +6117,51 @@ compare_files (char *cmpfile[])
   return ret;
 }
 
+/* Set func_reorder_linker_plugin_file_spec and func_reorder_linker_plugin_opt
+   here.  This is the linker plugin to do global function reordering and is
+   enabled with -freorder-functions=*. */
+
+static void
+set_func_reorder_linker_plugin_spec (void)
+{
+  int i;
+  const char *plugin_opt_none = "group=none";
+  const char *plugin_opt_cgedge = "group=cgedge";
+  
+  /* Find the linker plugin that does function ordering.  */
+  func_reorder_linker_plugin_file_spec = find_a_file (&exec_prefixes,
+                                           FRPLUGINSONAME, R_OK, false);
+
+  if (!func_reorder_linker_plugin_file_spec)
+      fatal_error ("-freorder-functions=*, but "
+                  FRPLUGINSONAME " file not found");
+
+  func_reorder_linker_plugin_opt = plugin_opt_none;
+
+  /* Set linker plugin options here.  Option ordering is also checked here.
+     -fno-reorder-functions or -freorder-functions should disable any
+     previous -freorder-functions=*. */
+  for (i = 0; (int) i < n_switches; i++)
+    {
+      /* Check for match with "-freorder-functions=cgedge".  */
+      if (func_reorder_linker_plugin_opt != plugin_opt_cgedge
+         && !strcmp (switches[i].part1, "freorder-functions=cgedge"))
+       {
+         func_reorder_linker_plugin_opt = plugin_opt_cgedge;
+         continue;
+       }
+      /* Set option to none if it matches -fno-reorder-functions
+        or -freorder-functions  */
+      if (func_reorder_linker_plugin_opt != plugin_opt_none
+         && (!strcmp (switches[i].part1, "fno-reorder-functions")
+             || !strcmp (switches[i].part1, "freorder-functions")))
+       {
+         func_reorder_linker_plugin_opt = plugin_opt_none;
+         continue;
+       }
+    }
+}
+
 extern int main (int, char **);
 
 int
@@ -6843,6 +6897,8 @@ warranty; not even for MERCHANTABILITY or FITNESS
       const char *fuse_linker_plugin = "fuse-linker-plugin";
 #endif
 
+      const char *freorder_functions_ = "freorder-functions=";
+
       /* We'll use ld if we can't find collect2.  */
       if (! strcmp (linker_name_spec, "collect2"))
        {
@@ -6866,6 +6922,12 @@ warranty; not even for MERCHANTABILITY or FITNESS
            fatal_error ("-fuse-linker-plugin, but " LTOPLUGINSONAME " not 
found");
        }
       lto_gcc_spec = argv[0];
+  
+      /* The function reordering linker plugin will be loaded if the option
+        -freorder-functions= is present in the command-line.  */ 
+      if (switch_matches (freorder_functions_,
+                         freorder_functions_ + strlen (freorder_functions_), 
1))
+       set_func_reorder_linker_plugin_spec ();
 
       /* Rebuild the COMPILER_PATH and LIBRARY_PATH environment variables
         for collect.  */
Index: gcc/config.in
===================================================================
--- gcc/config.in       (revision 185372)
+++ gcc/config.in       (working copy)
@@ -1583,13 +1583,18 @@
 #endif
 
 
+/* Define to the name of the function reordering plugin DSO that must be
+   passed to the linker's -plugin=LIB option. */
+#ifndef USED_FOR_TARGET
+#undef FRPLUGINSONAME
+#endif
+
 /* Define to the name of the LTO plugin DSO that must be passed to the
    linker's -plugin=LIB option. */
 #ifndef USED_FOR_TARGET
 #undef LTOPLUGINSONAME
 #endif
 
-
 /* Define to the sub-directory in which libtool stores uninstalled libraries.
    */
 #ifndef USED_FOR_TARGET
Index: gcc/configure.ac
===================================================================
--- gcc/configure.ac    (revision 185372)
+++ gcc/configure.ac    (working copy)
@@ -1858,6 +1858,10 @@ case $use_collect2 in
     ;;
 esac
 
+AC_DEFINE_UNQUOTED(FRPLUGINSONAME,"${host_function_reordering_plugin_soname}",
+[Define to the name of the function reordering plugin DSO that must be
+  passed to the linker's -plugin=LIB option.])
+
 AC_DEFINE_UNQUOTED(LTOPLUGINSONAME,"${host_lto_plugin_soname}",
 [Define to the name of the LTO plugin DSO that must be
   passed to the linker's -plugin=LIB option.])
Index: gcc/ChangeLog.google-4_6
===================================================================
--- gcc/ChangeLog.google-4_6    (revision 185372)
+++ gcc/ChangeLog.google-4_6    (working copy)
@@ -1,3 +1,21 @@
+2012-03-14  Sriraman Tallam  <tmsri...@google.com>
+
+       * cgraphbuild.c (remove_cgraph_callee_edges): Replace
+       flag_callgraph_profiles_sections with flag_reorder_functions.
+       * final.c (rest_of_handle_final): Ditto.
+       * configure: Regenerate.
+       * config.in: undef FRPLUGINSONAME.
+       * congifure.ac: Define FRPLUGINSONAME.
+       * config.host: Set host_function_reordering_plugin_soname.
+       * gcc.c: Invoke function_reordering linker plugin with
+       -freorder-functions=* option.
+       (set_func_reorder_linker_plugin_spec): New function.
+       (main): Call set_func_reorder_linker_plugin_spec when
+       -freorder-functions=* option is seen.
+       * common.opt: Add new option -freorder-functions=.  Remove
+       -fcallgraph-profiles-sections.
+       
+
 2012-03-12  Sterling Augustine  <saugust...@google.com>
            Cary Coutant  <ccout...@google.com>
 
Index: gcc/common.opt
===================================================================
--- gcc/common.opt      (revision 185372)
+++ gcc/common.opt      (working copy)
@@ -920,10 +920,6 @@ 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.
@@ -1758,9 +1754,19 @@ Common Report Var(flag_reorder_blocks_and_partitio
 Reorder basic blocks and partition into hot and cold sections
 
 freorder-functions
-Common Report Var(flag_reorder_functions) Optimization
+Common Report Var(flag_reorder_functions,1) Init(0) Optimization
 Reorder functions to improve code placement
 
+freorder-functions=
+Common Joined RejectNegative Enum(function_reorder) 
Var(flag_reorder_functions) Init(0) Optimization
+-freorder-functions=[cgedge]   Select the scheme for function reordering. This 
invokes a linker plugin.  Generate .note.callgraph.text sections listing 
callees and edge counts.
+
+Enum
+Name(function_reorder) Type(int) UnknownError(unrecognized function reorder 
value %qs)
+ 
+EnumValue
+Enum(function_reorder) String(cgedge) Value(2)
+
 frerun-cse-after-loop
 Common Report Var(flag_rerun_cse_after_loop) Optimization
 Add a common subexpression elimination pass after loop optimizations
Index: gcc/config.host
===================================================================
--- gcc/config.host     (revision 185372)
+++ gcc/config.host     (working copy)
@@ -76,6 +76,7 @@ out_host_hook_obj=host-default.o
 host_can_use_collect2=yes
 use_long_long_for_widest_fast_int=no
 host_lto_plugin_soname=liblto_plugin.so
+host_function_reordering_plugin_soname=libfunction_reordering_plugin.so
 
 # Unsupported hosts list.  Generally, only include hosts known to fail here,
 # since we allow hosts not listed to be supported generically.

--
This patch is available for review at http://codereview.appspot.com/5825054

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