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[google] Instrumented sampling FDO interface cleanup (issue6210058)


Two cleanup items for the sampling instrumentation interfaces. First,
rename variables from *rate* to *period*, since what is being specified
is a sampling period (time between recorded samples) not a rate.
Second, add flag __gcov_has_sampling to indicate when a file was
compiled with -fprofile-generate-sampling, and fuction
__gcov_sampling_enabled to return the state of this flag. The flag
is checked when a call is made to set the sampling period.

Bootstrapped and tested on x86_64-unknown-linux-gnu. Ok for google branches?

Thanks,
Teresa

2012-05-14   Teresa Johnson  <tejohnson@google.com>

	* libgcc/libgcov.c (__gcov_sampling_period): Rename variable from
        "*rate*" to "*period*".
        (gcov_sampling_period_initialized): Ditto.
        (__gcov_set_sampling_period): Rename from __gcov_set_sampling_rate.
        Check __gcov_has_sampling.
	(__gcov_has_sampling): New variable.
	(__gcov_sampling_enabled): New function.
	(__gcov_init): Rename variables from "*rate*" to "*period*".
	* gcc/doc/invoke.texi (profile-generate-sampling-period): Rename
        from profile-generate-sampling-rate.
	* gcc/tree-profile.c (gcov_sampling_period_decl): Rename from
        gcov_sampling_rate_decl.
        (gcov_has_sampling_decl): New variable.
	(insert_if_then, add_sampling_wrapper): Rename variables from
        "*rate*" to "*period*".
	(gimple_init_instrumentation_sampling): Ditto, and add handling
        for gcov_has_sampling_decl.
	* gcc/params.def (profile-generate-sampling-period): Rename
        from profile-generate-sampling-rate.

Index: libgcc/libgcov.c
===================================================================
--- libgcc/libgcov.c	(revision 187470)
+++ libgcc/libgcov.c	(working copy)
@@ -141,18 +141,26 @@ extern char * __gcov_pmu_profile_filename;
 extern char * __gcov_pmu_profile_options;
 extern gcov_unsigned_t __gcov_pmu_top_n_address;
 
-/* Sampling rate.  */
-extern gcov_unsigned_t __gcov_sampling_rate;
-static int gcov_sampling_rate_initialized = 0;
-void __gcov_set_sampling_rate (unsigned int rate);
+/* Sampling period.  */
+extern gcov_unsigned_t __gcov_sampling_period;
+extern gcov_unsigned_t __gcov_has_sampling;
+static int gcov_sampling_period_initialized = 0;
+void __gcov_set_sampling_period (unsigned int period);
+unsigned int __gcov_sampling_enabled ();
 
-/* Set sampling rate to RATE.  */
+/* Set sampling period to PERIOD.  */
 
-void __gcov_set_sampling_rate (unsigned int rate)
+void __gcov_set_sampling_period (unsigned int period)
 {
-  __gcov_sampling_rate = rate;
+  gcc_assert (__gcov_has_sampling);
+  __gcov_sampling_period = period;
 }
 
+unsigned int __gcov_sampling_enabled ()
+{
+  return __gcov_has_sampling;
+}
+
 /* Per thread sample counter.  */
 THREAD_PREFIX gcov_unsigned_t __gcov_sample_counter = 0;
 
@@ -659,16 +667,16 @@ gcov_clear (void)
 void
 __gcov_init (struct gcov_info *info)
 {
-  if (!gcov_sampling_rate_initialized)
+  if (!gcov_sampling_period_initialized)
     {
-      const char* env_value_str = getenv ("GCOV_SAMPLING_RATE");
+      const char* env_value_str = getenv ("GCOV_SAMPLING_PERIOD");
       if (env_value_str)
         {
           int env_value_int = atoi(env_value_str);
           if (env_value_int >= 1)
-            __gcov_sampling_rate = env_value_int;
+            __gcov_sampling_period = env_value_int;
         }
-      gcov_sampling_rate_initialized = 1;
+      gcov_sampling_period_initialized = 1;
     }
 
   if (!info->version || !info->n_functions)
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 187470)
+++ gcc/doc/invoke.texi	(working copy)
@@ -8335,12 +8335,12 @@ the profile feedback data files. See @option{-fpro
 @opindex -fprofile-generate-sampling
 
 Enable sampling for instrumented binaries.  Instead of recording every event,
-record only every N-th event, where N (the sampling rate) can be set either
+record only every N-th event, where N (the sampling period) can be set either
 at compile time using
-@option{--param profile-generate-sampling-rate=@var{value}}, or
-at execution start time through environment variable @samp{GCOV_SAMPLING_RATE}.
+@option{--param profile-generate-sampling-period=@var{value}}, or at
+execution start time through environment variable @samp{GCOV_SAMPLING_PERIOD}.
 
-At this time sampling applies only to branch counters.  A sampling rate of 100
+At this time sampling applies only to branch counters.  A sampling period of 100
 decreases instrumentated binary slowdown from up to 20x for heavily threaded
 applications down to around 2x.  @option{-fprofile-correction} is always
 needed with sampling.
Index: gcc/tree-profile.c
===================================================================
--- gcc/tree-profile.c	(revision 187470)
+++ gcc/tree-profile.c	(working copy)
@@ -165,9 +165,12 @@ static struct pointer_set_t *instrumentation_to_be
 /* extern __thread gcov_unsigned_t __gcov_sample_counter  */
 static tree gcov_sample_counter_decl = NULL_TREE;
 
-/* extern gcov_unsigned_t __gcov_sampling_rate  */
-static tree gcov_sampling_rate_decl = NULL_TREE;
+/* extern gcov_unsigned_t __gcov_sampling_period  */
+static tree gcov_sampling_period_decl = NULL_TREE;
 
+/* extern gcov_unsigned_t __gcov_has_sampling  */
+static tree gcov_has_sampling_decl = NULL_TREE;
+
 /* forward declaration.  */
 void gimple_init_instrumentation_sampling (void);
 
@@ -200,7 +203,7 @@ insert_if_then (gimple stmt_start, gimple stmt_end
    Into:
 
    __gcov_sample_counter++;
-   if (__gcov_sample_counter >= __gcov_sampling_rate)
+   if (__gcov_sample_counter >= __gcov_sampling_period)
      {
        __gcov_sample_counter = 0;
        ORIGINAL CODE
@@ -214,7 +217,7 @@ add_sampling_wrapper (gimple stmt_start, gimple st
 {
   tree zero, one, tmp_var, tmp1, tmp2, tmp3;
   gimple stmt_inc_counter1, stmt_inc_counter2, stmt_inc_counter3;
-  gimple stmt_reset_counter, stmt_assign_rate, stmt_if;
+  gimple stmt_reset_counter, stmt_assign_period, stmt_if;
   gimple_stmt_iterator gsi;
 
   tmp_var = create_tmp_reg (get_gcov_unsigned_t (), "PROF_sample");
@@ -230,7 +233,7 @@ add_sampling_wrapper (gimple stmt_start, gimple st
   zero = build_int_cst (get_gcov_unsigned_t (), 0);
   stmt_reset_counter = gimple_build_assign (gcov_sample_counter_decl, zero);
   tmp3 = make_ssa_name (tmp_var, NULL);
-  stmt_assign_rate = gimple_build_assign (tmp3, gcov_sampling_rate_decl);
+  stmt_assign_period = gimple_build_assign (tmp3, gcov_sampling_period_decl);
   stmt_if = gimple_build_cond (GE_EXPR, tmp2, tmp3, NULL_TREE, NULL_TREE);
 
   /* Insert them for now in the original basic block.  */
@@ -238,7 +241,7 @@ add_sampling_wrapper (gimple stmt_start, gimple st
   gsi_insert_before (&gsi, stmt_inc_counter1, GSI_SAME_STMT);
   gsi_insert_before (&gsi, stmt_inc_counter2, GSI_SAME_STMT);
   gsi_insert_before (&gsi, stmt_inc_counter3, GSI_SAME_STMT);
-  gsi_insert_before (&gsi, stmt_assign_rate, GSI_SAME_STMT);
+  gsi_insert_before (&gsi, stmt_assign_period, GSI_SAME_STMT);
   gsi_insert_before (&gsi, stmt_reset_counter, GSI_SAME_STMT);
 
   /* Insert IF block.  */
@@ -293,27 +296,49 @@ add_sampling_to_edge_counters (void)
 void
 gimple_init_instrumentation_sampling (void)
 {
-  if (!gcov_sampling_rate_decl)
+  if (!gcov_sampling_period_decl)
     {
-      /* Define __gcov_sampling_rate regardless of -fprofile-generate-sampling.
-         Otherwise the extern reference to it from libgcov becomes unmatched.
+      /* Define __gcov_sampling_period regardless of
+         -fprofile-generate-sampling. Otherwise the extern reference to
+         it from libgcov becomes unmatched.
       */
-      gcov_sampling_rate_decl = build_decl (
+      gcov_sampling_period_decl = build_decl (
           UNKNOWN_LOCATION,
           VAR_DECL,
-          get_identifier ("__gcov_sampling_rate"),
+          get_identifier ("__gcov_sampling_period"),
           get_gcov_unsigned_t ());
-      TREE_PUBLIC (gcov_sampling_rate_decl) = 1;
-      DECL_ARTIFICIAL (gcov_sampling_rate_decl) = 1;
-      DECL_COMDAT_GROUP (gcov_sampling_rate_decl)
-          = DECL_ASSEMBLER_NAME (gcov_sampling_rate_decl);
-      TREE_STATIC (gcov_sampling_rate_decl) = 1;
-      DECL_INITIAL (gcov_sampling_rate_decl) = build_int_cst (
+      TREE_PUBLIC (gcov_sampling_period_decl) = 1;
+      DECL_ARTIFICIAL (gcov_sampling_period_decl) = 1;
+      DECL_COMDAT_GROUP (gcov_sampling_period_decl)
+          = DECL_ASSEMBLER_NAME (gcov_sampling_period_decl);
+      TREE_STATIC (gcov_sampling_period_decl) = 1;
+      DECL_INITIAL (gcov_sampling_period_decl) = build_int_cst (
           get_gcov_unsigned_t (),
-          PARAM_VALUE (PARAM_PROFILE_GENERATE_SAMPLING_RATE));
-      varpool_finalize_decl (gcov_sampling_rate_decl);
+          PARAM_VALUE (PARAM_PROFILE_GENERATE_SAMPLING_PERIOD));
+      varpool_finalize_decl (gcov_sampling_period_decl);
     }
 
+  if (!gcov_has_sampling_decl)
+    {
+      /* Initialize __gcov_has_sampling to 1 if -fprofile-generate-sampling
+         specified, 0 otherwise. Used by libgcov to determine whether
+         a request to set the sampling period makes sense.  */
+      gcov_has_sampling_decl = build_decl (
+          UNKNOWN_LOCATION,
+          VAR_DECL,
+          get_identifier ("__gcov_has_sampling"),
+          get_gcov_unsigned_t ());
+      TREE_PUBLIC (gcov_has_sampling_decl) = 1;
+      DECL_ARTIFICIAL (gcov_has_sampling_decl) = 1;
+      DECL_COMDAT_GROUP (gcov_has_sampling_decl)
+          = DECL_ASSEMBLER_NAME (gcov_has_sampling_decl);
+      TREE_STATIC (gcov_has_sampling_decl) = 1;
+      DECL_INITIAL (gcov_has_sampling_decl) = build_int_cst (
+          get_gcov_unsigned_t (),
+          flag_profile_generate_sampling ? 1 : 0);
+      varpool_finalize_decl (gcov_has_sampling_decl);
+    }
+
   if (flag_profile_generate_sampling && !instrumentation_to_be_sampled)
     {
       instrumentation_to_be_sampled = pointer_set_create ();
Index: gcc/params.def
===================================================================
--- gcc/params.def	(revision 187470)
+++ gcc/params.def	(working copy)
@@ -919,8 +919,8 @@ DEFPARAM (PARAM_MAX_LIPO_MEMORY,
 	  "don't import aux files if memory consumption exceeds this value",
 	  2400000, 0, 0)
 
-DEFPARAM (PARAM_PROFILE_GENERATE_SAMPLING_RATE,
-         "profile-generate-sampling-rate",
+DEFPARAM (PARAM_PROFILE_GENERATE_SAMPLING_PERIOD,
+         "profile-generate-sampling-period",
          "sampling rate with -fprofile-generate-sampling",
          100, 0, 2000000000)
 

--
This patch is available for review at http://codereview.appspot.com/6210058


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