Patchwork [google,gcc-4_7] coverage callback instrumentation (issue9630043)

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Submitter Rong Xu
Date May 21, 2013, 10:28 p.m.
Message ID <20130521222829.1C77B44403@xur2.mtv.corp.google.com>
Download mbox | patch
Permalink /patch/245428/
State New
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Comments

Rong Xu - May 21, 2013, 10:28 p.m.
This patch is to be used with customized coverage reduction.

The functionalities are under two parameter options:
--param=COVERAGE-CALLBACK={0|1}
when enabled with 1, it injects a callback function for
each arc counter. Default off.
--param=COVERAGE-CALLONCE={0|1}
when enabled with 1, it stops incrementing the arc counter
when they flip to 1. Default off. Even with an extra condition
check, this is drastically faster than the normal coverage test
for highly threaded applications.

It also fixes a bug in profile sampling where some counters
(like those after the call stmt) are not sampled.

It disables the may-uninit check if the warning will not be
emitted.

Tested with bootstrap, regressions test and google internal
benchmarks.

Thanks,

-Rong

2013-05-21  Rong Xu  <xur@google.com>

	* gcc/tree-ssa-uninit.c (gate_warn_uninitialized): Disable if
        may-uninit warning will not emitted.
	* gcc/params.def : (PARAM_COVERAGE_CALLBACK) New.
        (PARAM_COVERAGE_CALLONCE): NEW.
	* gcc/profile.c (branch_prob): Not increment edge counter after
        first update.
	(tree_init_instrumentation_sampling): Ditto.
        (COVERAGE_CALLBACK_FUNC_NAME): New.
        (COVERAGE_INSERT_CALL): New.
	(insert_if_then): Update branch probability.
	(add_sampling_wrapper): Ditto.
	(add_callback_wrapper): New.
	(add_sampling_to_edge_counters): Make predicate insertion
        complete.
	(gimple_gen_edge_profiler): Add coverage callback function.
	(gimple_gen_ic_profiler): Fix trailing space.
	(gimple_gen_ic_func_topn_profiler): Ditto.
	(gimple_gen_dc_profiler): Ditto.
	* libgcc/libgcov.c (__coverage_callback): Add an empty callback
        function.


--
This patch is available for review at http://codereview.appspot.com/9630043
Xinliang David Li - May 22, 2013, 4:07 p.m.
Looks ok to me in general.
1) the parameter name is not ideal -- it is not callonce.
2) it might be better to extend the callonce parameter into
-ftest-coverage option such as -ftest-coverage=exec_once?
3) need documentation in invoke.texi
4) watch out for long lines.

cc Teresa.

David

On Tue, May 21, 2013 at 3:28 PM, Rong Xu <xur@google.com> wrote:
> This patch is to be used with customized coverage reduction.
>
> The functionalities are under two parameter options:
> --param=COVERAGE-CALLBACK={0|1}
> when enabled with 1, it injects a callback function for
> each arc counter. Default off.
> --param=COVERAGE-CALLONCE={0|1}
> when enabled with 1, it stops incrementing the arc counter
> when they flip to 1. Default off. Even with an extra condition
> check, this is drastically faster than the normal coverage test
> for highly threaded applications.
>
> It also fixes a bug in profile sampling where some counters
> (like those after the call stmt) are not sampled.
>
> It disables the may-uninit check if the warning will not be
> emitted.
>
> Tested with bootstrap, regressions test and google internal
> benchmarks.
>
> Thanks,
>
> -Rong
>
> 2013-05-21  Rong Xu  <xur@google.com>
>
>         * gcc/tree-ssa-uninit.c (gate_warn_uninitialized): Disable if
>         may-uninit warning will not emitted.
>         * gcc/params.def : (PARAM_COVERAGE_CALLBACK) New.
>         (PARAM_COVERAGE_CALLONCE): NEW.
>         * gcc/profile.c (branch_prob): Not increment edge counter after
>         first update.
>         (tree_init_instrumentation_sampling): Ditto.
>         (COVERAGE_CALLBACK_FUNC_NAME): New.
>         (COVERAGE_INSERT_CALL): New.
>         (insert_if_then): Update branch probability.
>         (add_sampling_wrapper): Ditto.
>         (add_callback_wrapper): New.
>         (add_sampling_to_edge_counters): Make predicate insertion
>         complete.
>         (gimple_gen_edge_profiler): Add coverage callback function.
>         (gimple_gen_ic_profiler): Fix trailing space.
>         (gimple_gen_ic_func_topn_profiler): Ditto.
>         (gimple_gen_dc_profiler): Ditto.
>         * libgcc/libgcov.c (__coverage_callback): Add an empty callback
>         function.
>
> Index: libgcc/libgcov.c
> ===================================================================
> --- libgcc/libgcov.c    (revision 198952)
> +++ libgcc/libgcov.c    (working copy)
> @@ -135,6 +135,14 @@ extern int gcov_dump_complete ATTRIBUTE_HIDDEN;
>     these symbols will always need to be resolved.  */
>  void (*__gcov_dummy_ref1)() = &__gcov_reset;
>  void (*__gcov_dummy_ref2)() = &__gcov_dump;
> +
> +__attribute__((weak)) void
> +__coverage_callback (gcov_type funcdef_no __attribute__ ((unused)),
> +                     int edge_no __attribute__ ((unused)))
> +{
> +   /* nothing */
> +}
> +
>  #endif /* __GCOV_KERNEL__ */
>
>  /* Utility function for outputing errors.  */
> Index: gcc/profile.c
> ===================================================================
> --- gcc/profile.c       (revision 198952)
> +++ gcc/profile.c       (working copy)
> @@ -69,6 +69,7 @@ along with GCC; see the file COPYING3.  If not see
>  #include "timevar.h"
>  #include "cfgloop.h"
>  #include "tree-pass.h"
> +#include "params.h"
>
>  #include "profile.h"
>
> @@ -1480,7 +1481,8 @@ branch_prob (void)
>        /* Commit changes done by instrumentation.  */
>        gsi_commit_edge_inserts ();
>
> -      if (flag_profile_generate_sampling)
> +      if (flag_profile_generate_sampling
> +          || PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
>          add_sampling_to_edge_counters ();
>      }
>
> Index: gcc/params.def
> ===================================================================
> --- gcc/params.def      (revision 198952)
> +++ gcc/params.def      (working copy)
> @@ -1060,6 +1060,16 @@ DEFPARAM (PARAM_PROFILE_GENERATE_SAMPLING_PERIOD,
>           "sampling rate with -fprofile-generate-sampling",
>           100, 0, 2000000000)
>
> +DEFPARAM (PARAM_COVERAGE_CALLBACK,
> +         "coverage-callback",
> +         "callback a user-define function when for arc counter increments.",
> +         0, 0, 1)
> +
> +DEFPARAM (PARAM_COVERAGE_CALLONCE,
> +         "coverage-callonce",
> +         "Stop increment coverage counts once they become 1.",
> +         0, 0, 1)
> +
>  /* Used for debugging purpose. Tell the compiler to find
>     the gcda file in the current directory.  */
>  DEFPARAM (PARAM_GCOV_DEBUG,
> Index: gcc/tree-profile.c
> ===================================================================
> --- gcc/tree-profile.c  (revision 198952)
> +++ gcc/tree-profile.c  (working copy)
> @@ -54,6 +54,15 @@ along with GCC; see the file COPYING3.  If not see
>  #include "target.h"
>  #include "output.h"
>
> +/* Default name for coverage callback function.  */
> +#define COVERAGE_CALLBACK_FUNC_NAME "__coverage_callback"
> +
> +/* If we insert a callback to edge instrumentation code. Avoid this
> +   for the callback function itself.  */
> +#define COVERAGE_INSERT_CALL   ((PARAM_VALUE (PARAM_COVERAGE_CALLBACK) == 1) \
> +                                 && strcmp (get_name (current_function_decl), \
> +                                        COVERAGE_CALLBACK_FUNC_NAME))
> +
>  /* Number of statements inserted for each edge counter increment.  */
>  #define EDGE_COUNTER_STMT_COUNT 3
>
> @@ -202,14 +211,16 @@ static tree GTY(()) gcov_lipo_merge_modu_edges = N
>  static tree GTY(()) gcov_lipo_strict_inclusion = NULL_TREE;
>
>  /* Insert STMT_IF around given sequence of consecutive statements in the
> -   same basic block starting with STMT_START, ending with STMT_END.  */
> +   same basic block starting with STMT_START, ending with STMT_END.
> +   PROB is the probability of the taken branch.  */
>
>  static void
> -insert_if_then (gimple stmt_start, gimple stmt_end, gimple stmt_if)
> +insert_if_then (gimple stmt_start, gimple stmt_end, gimple stmt_if, int prob)
>  {
>    gimple_stmt_iterator gsi;
>    basic_block bb_original, bb_before_if, bb_after_if;
> -  edge e_if_taken, e_then_join;
> +  edge e_if_taken, e_then_join, e_else;
> +  int orig_frequency;
>
>    gsi = gsi_for_stmt (stmt_start);
>    gsi_insert_before (&gsi, stmt_if, GSI_SAME_STMT);
> @@ -220,7 +231,11 @@ static void
>    e_then_join = split_block (e_if_taken->dest, stmt_end);
>    bb_before_if = e_if_taken->src;
>    bb_after_if = e_then_join->dest;
> -  make_edge (bb_before_if, bb_after_if, EDGE_FALSE_VALUE);
> +  e_else = make_edge (bb_before_if, bb_after_if, EDGE_FALSE_VALUE);
> +  orig_frequency = bb_original->frequency;
> +  e_if_taken->probability = prob;
> +  e_else->probability = REG_BR_PROB_BASE - prob;
> +  e_if_taken->dest->frequency = orig_frequency * (prob / REG_BR_PROB_BASE);
>  }
>
>  /* Transform:
> @@ -274,9 +289,34 @@ add_sampling_wrapper (gimple stmt_start, gimple st
>    gsi_insert_before (&gsi, stmt_reset_counter, GSI_SAME_STMT);
>
>    /* Insert IF block.  */
> -  insert_if_then (stmt_reset_counter, stmt_end, stmt_if);
> +  /* Sampling rate can be changed runtime: hard to guess the branch prob,
> +     so make it 1.  */
> +  insert_if_then (stmt_reset_counter, stmt_end, stmt_if, REG_BR_PROB_BASE);
>  }
>
> +static void
> +add_callonce_wrapper (gimple stmt_start, gimple stmt_end)
> +{
> +  tree zero, tmp_var, tmp1;
> +  gimple stmt_if, stmt_assign;
> +  gimple_stmt_iterator gsi;
> +
> +  /* Create all the new statements needed.  */
> +  tmp_var = create_tmp_reg (get_gcov_type (), "PROF_temp");
> +  tmp1 = make_ssa_name (tmp_var, NULL);
> +  stmt_assign = gimple_build_assign (tmp1, gimple_assign_lhs (stmt_end));
> +
> +  zero = build_int_cst (get_gcov_type (), 0);
> +  stmt_if = gimple_build_cond (EQ_EXPR, tmp1, zero, NULL_TREE, NULL_TREE);
> +  find_referenced_vars_in (stmt_if);
> +
> +  gsi = gsi_for_stmt (stmt_start);
> +  gsi_insert_before (&gsi, stmt_assign, GSI_SAME_STMT);
> +
> +  /* Insert IF block.  */
> +  insert_if_then (stmt_start, stmt_end, stmt_if, 1);
> +}
> +
>  /* Return whether STMT is the beginning of an instrumentation block to be
>     applied sampling.  */
>
> @@ -295,22 +335,34 @@ add_sampling_to_edge_counters (void)
>    basic_block bb;
>
>    FOR_EACH_BB_REVERSE (bb)
> -    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
> +    for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); gsi_prev (&gsi))
>        {
> -        gimple stmt = gsi_stmt (gsi);
> -        if (is_instrumentation_to_be_sampled (stmt))
> +        gimple stmt_end = gsi_stmt (gsi);
> +        if (is_instrumentation_to_be_sampled (stmt_end))
>            {
> -            gimple stmt_end;
> +            gimple stmt_beg;
>              int i;
> +            int edge_counter_stmt_count = EDGE_COUNTER_STMT_COUNT;
> +
>              /* The code for edge counter increment has EDGE_COUNTER_STMT_COUNT
>                 gimple statements. Advance that many statements to find the
> -               last statement.  */
> -            for (i = 0; i < EDGE_COUNTER_STMT_COUNT - 1; i++)
> -              gsi_next (&gsi);
> -            stmt_end = gsi_stmt (gsi);
> -            gcc_assert (stmt_end);
> -            add_sampling_wrapper (stmt, stmt_end);
> -            break;
> +               beginning statement.  */
> +            if (COVERAGE_INSERT_CALL)
> +              edge_counter_stmt_count++;
> +
> +            for (i = 0; i < edge_counter_stmt_count - 1; i++)
> +              gsi_prev (&gsi);
> +            stmt_beg = gsi_stmt (gsi);
> +            gcc_assert (stmt_beg);
> +
> +
> +            if (flag_profile_generate_sampling)
> +              add_sampling_wrapper (stmt_beg, stmt_end);
> +            if (PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
> +              add_callonce_wrapper (stmt_beg, stmt_end);
> +
> +            /* reset the iterator and continue.  */
> +            gsi = gsi_last (bb_seq (bb));
>            }
>        }
>  }
> @@ -508,6 +560,9 @@ tree_init_instrumentation_sampling (void)
>          DECL_TLS_MODEL (gcov_sample_counter_decl) =
>              decl_default_tls_model (gcov_sample_counter_decl);
>      }
> +  if (PARAM_VALUE (PARAM_COVERAGE_CALLONCE)
> +      && instrumentation_to_be_sampled == 0)
> +    instrumentation_to_be_sampled = pointer_set_create ();
>  }
>
>  void
> @@ -675,6 +730,30 @@ gimple_gen_edge_profiler (int edgeno, edge e)
>      ref = tree_coverage_counter_ref (GCOV_COUNTER_ARCS, edgeno);
>
>    one = build_int_cst (gcov_type_node, 1);
> +
> +  /* insert a callback stmt stmt */
> +  if (COVERAGE_INSERT_CALL)
> +    {
> +      gimple call;
> +      tree tree_edgeno = build_int_cst (gcov_type_node, edgeno);
> +      tree tree_uid = build_int_cst (gcov_type_node, current_function_funcdef_no);
> +      tree callback_fn_type
> +              = build_function_type_list (void_type_node,
> +                                          gcov_type_node,
> +                                          integer_type_node,
> +                                          NULL_TREE);
> +      tree tree_callback_fn = build_fn_decl (COVERAGE_CALLBACK_FUNC_NAME,
> +                                             callback_fn_type);
> +      TREE_NOTHROW (tree_callback_fn) = 1;
> +      DECL_ATTRIBUTES (tree_callback_fn)
> +        = tree_cons (get_identifier ("leaf"), NULL,
> +                     DECL_ATTRIBUTES (tree_callback_fn));
> +
> +      call = gimple_build_call (tree_callback_fn, 2, tree_uid, tree_edgeno);
> +      find_referenced_vars_in (call);
> +      gsi_insert_on_edge(e, call);
> +    }
> +
>    if (PROFILE_GEN_EDGE_ATOMIC)
>      {
>        /* __atomic_fetch_add (&counter, 1, MEMMODEL_RELAXED); */
> @@ -695,13 +774,14 @@ gimple_gen_edge_profiler (int edgeno, edge e)
>        gimple_assign_set_lhs (stmt2, make_ssa_name (gcov_type_tmp_var, stmt2));
>        stmt3 = gimple_build_assign (unshare_expr (ref), gimple_assign_lhs (stmt2));
>
> -      if (flag_profile_generate_sampling)
> -        pointer_set_insert (instrumentation_to_be_sampled, stmt1);
> -
>        gsi_insert_on_edge (e, stmt1);
>        gsi_insert_on_edge (e, stmt2);
>      }
>    gsi_insert_on_edge (e, stmt3);
> +
> +  if (flag_profile_generate_sampling
> +      || PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
> +    pointer_set_insert (instrumentation_to_be_sampled, stmt3);
>  }
>
>  /* Emits code to get VALUE to instrument at GSI, and returns the
> @@ -802,7 +882,7 @@ gimple_gen_ic_profiler (histogram_value value, uns
>    gimple stmt;
>    gimple_stmt_iterator gsi;
>    tree ref_ptr;
> -
> +
>    stmt = value->hvalue.stmt;
>    gsi = gsi_for_stmt (stmt);
>    ref_ptr = tree_coverage_counter_addr (tag, base);
> @@ -905,7 +985,7 @@ gimple_gen_ic_func_topn_profiler (void)
>    gcov_info = build_fold_addr_expr (gcov_info_decl);
>    cur_func_id = build_int_cst (get_gcov_unsigned_t (),
>                                FUNC_DECL_FUNC_ID (cfun));
> -  stmt1 = gimple_build_call (tree_indirect_call_topn_profiler_fn,
> +  stmt1 = gimple_build_call (tree_indirect_call_topn_profiler_fn,
>                              3, cur_func, gcov_info, cur_func_id);
>    gsi_insert_before (&gsi, stmt1, GSI_SAME_STMT);
>  }
> @@ -922,7 +1002,7 @@ gimple_gen_dc_profiler (unsigned base, gimple call
>    gimple stmt1, stmt2, stmt3;
>    gimple_stmt_iterator gsi = gsi_for_stmt (call_stmt);
>    tree tmp1, tmp2, tmp3, callee = gimple_call_fn (call_stmt);
> -
> +
>    /* Insert code:
>       __gcov_direct_call_counters = get_relevant_counter_ptr ();
>       __gcov_callee = (void *) callee;
> Index: gcc/tree-ssa-uninit.c
> ===================================================================
> --- gcc/tree-ssa-uninit.c       (revision 198952)
> +++ gcc/tree-ssa-uninit.c       (working copy)
> @@ -2033,7 +2033,7 @@ execute_late_warn_uninitialized (void)
>  static bool
>  gate_warn_uninitialized (void)
>  {
> -  return warn_uninitialized != 0;
> +  return (warn_uninitialized != 0 && warn_maybe_uninitialized != 0);
>  }
>
>  struct gimple_opt_pass pass_late_warn_uninitialized =
>
> --
> This patch is available for review at http://codereview.appspot.com/9630043

Patch

Index: libgcc/libgcov.c
===================================================================
--- libgcc/libgcov.c	(revision 198952)
+++ libgcc/libgcov.c	(working copy)
@@ -135,6 +135,14 @@  extern int gcov_dump_complete ATTRIBUTE_HIDDEN;
    these symbols will always need to be resolved.  */
 void (*__gcov_dummy_ref1)() = &__gcov_reset;
 void (*__gcov_dummy_ref2)() = &__gcov_dump;
+
+__attribute__((weak)) void
+__coverage_callback (gcov_type funcdef_no __attribute__ ((unused)),
+                     int edge_no __attribute__ ((unused)))
+{
+   /* nothing */
+}
+
 #endif /* __GCOV_KERNEL__ */
 
 /* Utility function for outputing errors.  */
Index: gcc/profile.c
===================================================================
--- gcc/profile.c	(revision 198952)
+++ gcc/profile.c	(working copy)
@@ -69,6 +69,7 @@  along with GCC; see the file COPYING3.  If not see
 #include "timevar.h"
 #include "cfgloop.h"
 #include "tree-pass.h"
+#include "params.h"
 
 #include "profile.h"
 
@@ -1480,7 +1481,8 @@  branch_prob (void)
       /* Commit changes done by instrumentation.  */
       gsi_commit_edge_inserts ();
 
-      if (flag_profile_generate_sampling)
+      if (flag_profile_generate_sampling
+          || PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
         add_sampling_to_edge_counters ();
     }
 
Index: gcc/params.def
===================================================================
--- gcc/params.def	(revision 198952)
+++ gcc/params.def	(working copy)
@@ -1060,6 +1060,16 @@  DEFPARAM (PARAM_PROFILE_GENERATE_SAMPLING_PERIOD,
          "sampling rate with -fprofile-generate-sampling",
          100, 0, 2000000000)
 
+DEFPARAM (PARAM_COVERAGE_CALLBACK,
+         "coverage-callback",
+         "callback a user-define function when for arc counter increments.",
+         0, 0, 1)
+
+DEFPARAM (PARAM_COVERAGE_CALLONCE,
+         "coverage-callonce",
+         "Stop increment coverage counts once they become 1.",
+         0, 0, 1)
+
 /* Used for debugging purpose. Tell the compiler to find
    the gcda file in the current directory.  */
 DEFPARAM (PARAM_GCOV_DEBUG,
Index: gcc/tree-profile.c
===================================================================
--- gcc/tree-profile.c	(revision 198952)
+++ gcc/tree-profile.c	(working copy)
@@ -54,6 +54,15 @@  along with GCC; see the file COPYING3.  If not see
 #include "target.h"
 #include "output.h"
 
+/* Default name for coverage callback function.  */
+#define COVERAGE_CALLBACK_FUNC_NAME "__coverage_callback"
+
+/* If we insert a callback to edge instrumentation code. Avoid this
+   for the callback function itself.  */
+#define COVERAGE_INSERT_CALL   ((PARAM_VALUE (PARAM_COVERAGE_CALLBACK) == 1) \
+                                 && strcmp (get_name (current_function_decl), \
+                                        COVERAGE_CALLBACK_FUNC_NAME))
+
 /* Number of statements inserted for each edge counter increment.  */
 #define EDGE_COUNTER_STMT_COUNT 3
 
@@ -202,14 +211,16 @@  static tree GTY(()) gcov_lipo_merge_modu_edges = N
 static tree GTY(()) gcov_lipo_strict_inclusion = NULL_TREE;
 
 /* Insert STMT_IF around given sequence of consecutive statements in the
-   same basic block starting with STMT_START, ending with STMT_END.  */
+   same basic block starting with STMT_START, ending with STMT_END.
+   PROB is the probability of the taken branch.  */
 
 static void
-insert_if_then (gimple stmt_start, gimple stmt_end, gimple stmt_if)
+insert_if_then (gimple stmt_start, gimple stmt_end, gimple stmt_if, int prob)
 {
   gimple_stmt_iterator gsi;
   basic_block bb_original, bb_before_if, bb_after_if;
-  edge e_if_taken, e_then_join;
+  edge e_if_taken, e_then_join, e_else;
+  int orig_frequency;
 
   gsi = gsi_for_stmt (stmt_start);
   gsi_insert_before (&gsi, stmt_if, GSI_SAME_STMT);
@@ -220,7 +231,11 @@  static void
   e_then_join = split_block (e_if_taken->dest, stmt_end);
   bb_before_if = e_if_taken->src;
   bb_after_if = e_then_join->dest;
-  make_edge (bb_before_if, bb_after_if, EDGE_FALSE_VALUE);
+  e_else = make_edge (bb_before_if, bb_after_if, EDGE_FALSE_VALUE);
+  orig_frequency = bb_original->frequency;
+  e_if_taken->probability = prob;
+  e_else->probability = REG_BR_PROB_BASE - prob;
+  e_if_taken->dest->frequency = orig_frequency * (prob / REG_BR_PROB_BASE);
 }
 
 /* Transform:
@@ -274,9 +289,34 @@  add_sampling_wrapper (gimple stmt_start, gimple st
   gsi_insert_before (&gsi, stmt_reset_counter, GSI_SAME_STMT);
 
   /* Insert IF block.  */
-  insert_if_then (stmt_reset_counter, stmt_end, stmt_if);
+  /* Sampling rate can be changed runtime: hard to guess the branch prob,
+     so make it 1.  */
+  insert_if_then (stmt_reset_counter, stmt_end, stmt_if, REG_BR_PROB_BASE);
 }
 
+static void
+add_callonce_wrapper (gimple stmt_start, gimple stmt_end)
+{
+  tree zero, tmp_var, tmp1;
+  gimple stmt_if, stmt_assign;
+  gimple_stmt_iterator gsi;
+
+  /* Create all the new statements needed.  */
+  tmp_var = create_tmp_reg (get_gcov_type (), "PROF_temp");
+  tmp1 = make_ssa_name (tmp_var, NULL);
+  stmt_assign = gimple_build_assign (tmp1, gimple_assign_lhs (stmt_end));
+
+  zero = build_int_cst (get_gcov_type (), 0);
+  stmt_if = gimple_build_cond (EQ_EXPR, tmp1, zero, NULL_TREE, NULL_TREE);
+  find_referenced_vars_in (stmt_if);
+
+  gsi = gsi_for_stmt (stmt_start);
+  gsi_insert_before (&gsi, stmt_assign, GSI_SAME_STMT);
+
+  /* Insert IF block.  */
+  insert_if_then (stmt_start, stmt_end, stmt_if, 1);
+}
+
 /* Return whether STMT is the beginning of an instrumentation block to be
    applied sampling.  */
 
@@ -295,22 +335,34 @@  add_sampling_to_edge_counters (void)
   basic_block bb;
 
   FOR_EACH_BB_REVERSE (bb)
-    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+    for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); gsi_prev (&gsi))
       {
-        gimple stmt = gsi_stmt (gsi);
-        if (is_instrumentation_to_be_sampled (stmt))
+        gimple stmt_end = gsi_stmt (gsi);
+        if (is_instrumentation_to_be_sampled (stmt_end))
           {
-            gimple stmt_end;
+            gimple stmt_beg;
             int i;
+            int edge_counter_stmt_count = EDGE_COUNTER_STMT_COUNT;
+
             /* The code for edge counter increment has EDGE_COUNTER_STMT_COUNT
                gimple statements. Advance that many statements to find the
-               last statement.  */
-            for (i = 0; i < EDGE_COUNTER_STMT_COUNT - 1; i++)
-              gsi_next (&gsi);
-            stmt_end = gsi_stmt (gsi);
-            gcc_assert (stmt_end);
-            add_sampling_wrapper (stmt, stmt_end);
-            break;
+               beginning statement.  */
+            if (COVERAGE_INSERT_CALL)
+              edge_counter_stmt_count++;
+
+            for (i = 0; i < edge_counter_stmt_count - 1; i++)
+              gsi_prev (&gsi);
+            stmt_beg = gsi_stmt (gsi);
+            gcc_assert (stmt_beg);
+
+
+            if (flag_profile_generate_sampling)
+              add_sampling_wrapper (stmt_beg, stmt_end);
+            if (PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
+              add_callonce_wrapper (stmt_beg, stmt_end);
+
+            /* reset the iterator and continue.  */
+            gsi = gsi_last (bb_seq (bb));
           }
       }
 }
@@ -508,6 +560,9 @@  tree_init_instrumentation_sampling (void)
         DECL_TLS_MODEL (gcov_sample_counter_decl) =
             decl_default_tls_model (gcov_sample_counter_decl);
     }
+  if (PARAM_VALUE (PARAM_COVERAGE_CALLONCE)
+      && instrumentation_to_be_sampled == 0)
+    instrumentation_to_be_sampled = pointer_set_create ();
 }
 
 void
@@ -675,6 +730,30 @@  gimple_gen_edge_profiler (int edgeno, edge e)
     ref = tree_coverage_counter_ref (GCOV_COUNTER_ARCS, edgeno);
 
   one = build_int_cst (gcov_type_node, 1);
+
+  /* insert a callback stmt stmt */
+  if (COVERAGE_INSERT_CALL)
+    {
+      gimple call;
+      tree tree_edgeno = build_int_cst (gcov_type_node, edgeno);
+      tree tree_uid = build_int_cst (gcov_type_node, current_function_funcdef_no);
+      tree callback_fn_type
+              = build_function_type_list (void_type_node,
+                                          gcov_type_node,
+                                          integer_type_node,
+                                          NULL_TREE);
+      tree tree_callback_fn = build_fn_decl (COVERAGE_CALLBACK_FUNC_NAME,
+                                             callback_fn_type);
+      TREE_NOTHROW (tree_callback_fn) = 1;
+      DECL_ATTRIBUTES (tree_callback_fn)
+        = tree_cons (get_identifier ("leaf"), NULL,
+                     DECL_ATTRIBUTES (tree_callback_fn));
+  
+      call = gimple_build_call (tree_callback_fn, 2, tree_uid, tree_edgeno);
+      find_referenced_vars_in (call);
+      gsi_insert_on_edge(e, call);
+    }
+
   if (PROFILE_GEN_EDGE_ATOMIC)
     {
       /* __atomic_fetch_add (&counter, 1, MEMMODEL_RELAXED); */
@@ -695,13 +774,14 @@  gimple_gen_edge_profiler (int edgeno, edge e)
       gimple_assign_set_lhs (stmt2, make_ssa_name (gcov_type_tmp_var, stmt2));
       stmt3 = gimple_build_assign (unshare_expr (ref), gimple_assign_lhs (stmt2));
 
-      if (flag_profile_generate_sampling)
-        pointer_set_insert (instrumentation_to_be_sampled, stmt1);
-
       gsi_insert_on_edge (e, stmt1);
       gsi_insert_on_edge (e, stmt2);
     }
   gsi_insert_on_edge (e, stmt3);
+
+  if (flag_profile_generate_sampling
+      || PARAM_VALUE (PARAM_COVERAGE_CALLONCE))
+    pointer_set_insert (instrumentation_to_be_sampled, stmt3);
 }
 
 /* Emits code to get VALUE to instrument at GSI, and returns the
@@ -802,7 +882,7 @@  gimple_gen_ic_profiler (histogram_value value, uns
   gimple stmt;
   gimple_stmt_iterator gsi;
   tree ref_ptr;
- 
+
   stmt = value->hvalue.stmt;
   gsi = gsi_for_stmt (stmt);
   ref_ptr = tree_coverage_counter_addr (tag, base);
@@ -905,7 +985,7 @@  gimple_gen_ic_func_topn_profiler (void)
   gcov_info = build_fold_addr_expr (gcov_info_decl);
   cur_func_id = build_int_cst (get_gcov_unsigned_t (),
 			       FUNC_DECL_FUNC_ID (cfun));
-  stmt1 = gimple_build_call (tree_indirect_call_topn_profiler_fn, 
+  stmt1 = gimple_build_call (tree_indirect_call_topn_profiler_fn,
 			     3, cur_func, gcov_info, cur_func_id);
   gsi_insert_before (&gsi, stmt1, GSI_SAME_STMT);
 }
@@ -922,7 +1002,7 @@  gimple_gen_dc_profiler (unsigned base, gimple call
   gimple stmt1, stmt2, stmt3;
   gimple_stmt_iterator gsi = gsi_for_stmt (call_stmt);
   tree tmp1, tmp2, tmp3, callee = gimple_call_fn (call_stmt);
- 
+
   /* Insert code:
      __gcov_direct_call_counters = get_relevant_counter_ptr ();
      __gcov_callee = (void *) callee;
Index: gcc/tree-ssa-uninit.c
===================================================================
--- gcc/tree-ssa-uninit.c	(revision 198952)
+++ gcc/tree-ssa-uninit.c	(working copy)
@@ -2033,7 +2033,7 @@  execute_late_warn_uninitialized (void)
 static bool
 gate_warn_uninitialized (void)
 {
-  return warn_uninitialized != 0;
+  return (warn_uninitialized != 0 && warn_maybe_uninitialized != 0);
 }
 
 struct gimple_opt_pass pass_late_warn_uninitialized =