split checksum into cfg checksum and line checksum

From-SVN: r173147

13 files changed, 264 insertions, 82 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 794c496..fdbc4f1 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,29 @@
+2011-04-28  David Li  <davidxl@google.com>
+
+	* tree.c (crc32_string): Use crc32_byte.
+	(crc32_byte): New function.
+	* tree.h (crc32_byte): New function.
+	* gcov.c (read_graph_file): Handle new cfg_cksum.
+	(read_count_file): Ditto.
+	* profile.c (instrument_values): Ditto.
+	(get_exec_counts): Ditto.
+	(read_profile_edge_counts): Ditto.
+	(compute_branch_probabilities): Ditto.
+	(compute_value_histograms): Ditto.
+	(branch_prob): Ditto.
+	(end_branch_prob): Ditto.
+	* coverage.c (read_counts_file): Ditto.
+	(get_coverage_counts): Ditto.
+	(tree_coverage_counter_addr): Ditto.
+	(coverage_checksum_string): Ditto.
+	(coverage_begin_output): Ditto.
+	(coverage_end_function): Ditto.
+	(build_fn_info_type): Ditto.
+	(build_fn_info_value): Ditto.
+	* libgcov.c (gcov_exit): Ditto.
+	* gcov-dump.c (tag_function): Ditto.
+	(compute_checksum): Remove.
+
 2011-04-29  Alan Modra  <amodra@gmail.com>
 
 	* config/rs6000/rs6000.c (rs6000_delegitimize_address): Handle
diff --git a/gcc/coverage.c b/gcc/coverage.c
index 58b7c69..1efd714 100644
--- a/gcc/coverage.c
+++ b/gcc/coverage.c
@@ -51,13 +51,15 @@ along with GCC; see the file COPYING3.  If not see
 #include "intl.h"
 #include "filenames.h"
 
+#include "gcov-io.h"
 #include "gcov-io.c"
 
 struct function_list
 {
   struct function_list *next;	 /* next function */
   unsigned ident;		 /* function ident */
-  unsigned checksum;	         /* function checksum */
+  unsigned lineno_checksum;	 /* function lineno checksum */
+  unsigned cfg_checksum;	 /* function cfg checksum */
   unsigned n_ctrs[GCOV_COUNTERS];/* number of counters.  */
 };
 
@@ -69,7 +71,8 @@ typedef struct counts_entry
   unsigned ctr;
 
   /* Store  */
-  unsigned checksum;
+  unsigned lineno_checksum;
+  unsigned cfg_checksum;
   gcov_type *counts;
   struct gcov_ctr_summary summary;
 
@@ -114,8 +117,6 @@ static hashval_t htab_counts_entry_hash (const void *);
 static int htab_counts_entry_eq (const void *, const void *);
 static void htab_counts_entry_del (void *);
 static void read_counts_file (void);
-static unsigned compute_checksum (void);
-static unsigned coverage_checksum_string (unsigned, const char *);
 static tree build_fn_info_type (unsigned);
 static tree build_fn_info_value (const struct function_list *, tree);
 static tree build_ctr_info_type (void);
@@ -171,11 +172,12 @@ static void
 read_counts_file (void)
 {
   gcov_unsigned_t fn_ident = 0;
-  gcov_unsigned_t checksum = -1;
   counts_entry_t *summaried = NULL;
   unsigned seen_summary = 0;
   gcov_unsigned_t tag;
   int is_error = 0;
+  unsigned lineno_checksum = 0;
+  unsigned cfg_checksum = 0;
 
   if (!gcov_open (da_file_name, 1))
     return;
@@ -215,7 +217,8 @@ read_counts_file (void)
       if (tag == GCOV_TAG_FUNCTION)
 	{
 	  fn_ident = gcov_read_unsigned ();
-	  checksum = gcov_read_unsigned ();
+	  lineno_checksum = gcov_read_unsigned ();
+	  cfg_checksum = gcov_read_unsigned ();
 	  if (seen_summary)
 	    {
 	      /* We have already seen a summary, this means that this
@@ -265,24 +268,26 @@ read_counts_file (void)
 	  if (!entry)
 	    {
 	      *slot = entry = XCNEW (counts_entry_t);
-	      entry->ident = elt.ident;
+	      entry->ident = fn_ident;
 	      entry->ctr = elt.ctr;
-	      entry->checksum = checksum;
+	      entry->lineno_checksum = lineno_checksum;
+	      entry->cfg_checksum = cfg_checksum;
 	      entry->summary.num = n_counts;
 	      entry->counts = XCNEWVEC (gcov_type, n_counts);
 	    }
-	  else if (entry->checksum != checksum)
+	  else if (entry->lineno_checksum != lineno_checksum
+		   || entry->cfg_checksum != cfg_checksum)
 	    {
-	      error ("coverage mismatch for function %u while reading execution counters",
-		     fn_ident);
-	      error ("checksum is %x instead of %x", entry->checksum, checksum);
+	      error ("Profile data for function %u is corrupted", fn_ident);
+	      error ("checksum is (%x,%x) instead of (%x,%x)",
+		     entry->lineno_checksum, entry->cfg_checksum,
+		     lineno_checksum, cfg_checksum);
 	      htab_delete (counts_hash);
 	      break;
 	    }
 	  else if (entry->summary.num != n_counts)
 	    {
-	      error ("coverage mismatch for function %u while reading execution counters",
-		     fn_ident);
+	      error ("Profile data for function %u is corrupted", fn_ident);
 	      error ("number of counters is %d instead of %d", entry->summary.num, n_counts);
 	      htab_delete (counts_hash);
 	      break;
@@ -324,10 +329,10 @@ read_counts_file (void)
 
 gcov_type *
 get_coverage_counts (unsigned counter, unsigned expected,
+                     unsigned cfg_checksum, unsigned lineno_checksum,
 		     const struct gcov_ctr_summary **summary)
 {
   counts_entry_t *entry, elt;
-  gcov_unsigned_t checksum = -1;
 
   /* No hash table, no counts.  */
   if (!counts_hash)
@@ -352,26 +357,21 @@ get_coverage_counts (unsigned counter, unsigned expected,
       return NULL;
     }
 
-  checksum = compute_checksum ();
-  if (entry->checksum != checksum
+  if (entry->cfg_checksum != cfg_checksum
       || entry->summary.num != expected)
     {
       static int warned = 0;
       bool warning_printed = false;
       tree id = DECL_ASSEMBLER_NAME (current_function_decl);
 
-      warning_printed = 
-	warning_at (input_location, OPT_Wcoverage_mismatch, 
-		    "coverage mismatch for function "
-		    "%qE while reading counter %qs", id, ctr_names[counter]);
+      warning_printed =
+	warning_at (input_location, OPT_Wcoverage_mismatch,
+		    "The control flow of function %qE does not match "
+		    "its profile data (counter %qs)", id, ctr_names[counter]);
       if (warning_printed)
 	{
-	  if (entry->checksum != checksum)
-	    inform (input_location, "checksum is %x instead of %x",
-		    entry->checksum, checksum);
-	  else
-	    inform (input_location, "number of counters is %d instead of %d",
-		    entry->summary.num, expected);
+	 inform (input_location, "Use -Wno-error=coverage-mismatch to tolerate "
+	 	 "the mismatch but performance may drop if the function is hot");
 	  
 	  if (!seen_error ()
 	      && !warned++)
@@ -388,6 +388,12 @@ get_coverage_counts (unsigned counter, unsigned expected,
 
       return NULL;
     }
+    else if (entry->lineno_checksum != lineno_checksum)
+      {
+        warning (0, "Source location for function %qE have changed,"
+                 " the profile data may be out of date",
+                 DECL_ASSEMBLER_NAME (current_function_decl));
+      }
 
   if (summary)
     *summary = &entry->summary;
@@ -467,6 +473,7 @@ tree_coverage_counter_addr (unsigned counter, unsigned no)
 				       NULL, NULL));
 }
 
+
 /* Generate a checksum for a string.  CHKSUM is the current
    checksum.  */
 
@@ -529,8 +536,8 @@ coverage_checksum_string (unsigned chksum, const char *string)
 
 /* Compute checksum for the current function.  We generate a CRC32.  */
 
-static unsigned
-compute_checksum (void)
+unsigned
+coverage_compute_lineno_checksum (void)
 {
   expanded_location xloc
     = expand_location (DECL_SOURCE_LOCATION (current_function_decl));
@@ -542,6 +549,36 @@ compute_checksum (void)
 
   return chksum;
 }
+
+/* Compute cfg checksum for the current function.
+   The checksum is calculated carefully so that
+   source code changes that doesn't affect the control flow graph
+   won't change the checksum.
+   This is to make the profile data useable across source code change.
+   The downside of this is that the compiler may use potentially
+   wrong profile data - that the source code change has non-trivial impact
+   on the validity of profile data (e.g. the reversed condition)
+   but the compiler won't detect the change and use the wrong profile data.  */
+
+unsigned
+coverage_compute_cfg_checksum (void)
+{
+  basic_block bb;
+  unsigned chksum = n_basic_blocks;
+
+  FOR_EACH_BB (bb)
+    {
+      edge e;
+      edge_iterator ei;
+      chksum = crc32_byte (chksum, bb->index);
+      FOR_EACH_EDGE (e, ei, bb->succs)
+        {
+          chksum = crc32_byte (chksum, e->dest->index);
+        }
+    }
+
+  return chksum;
+}
 
 /* Begin output to the graph file for the current function.
    Opens the output file, if not already done. Writes the
@@ -549,7 +586,7 @@ compute_checksum (void)
    should be output.  */
 
 int
-coverage_begin_output (void)
+coverage_begin_output (unsigned lineno_checksum, unsigned cfg_checksum)
 {
   /* We don't need to output .gcno file unless we're under -ftest-coverage
      (e.g. -fprofile-arcs/generate/use don't need .gcno to work). */
@@ -575,12 +612,14 @@ coverage_begin_output (void)
 	  bbg_file_opened = 1;
 	}
 
+
       /* Announce function */
       offset = gcov_write_tag (GCOV_TAG_FUNCTION);
       gcov_write_unsigned (current_function_funcdef_no + 1);
-      gcov_write_unsigned (compute_checksum ());
+      gcov_write_unsigned (lineno_checksum);
+      gcov_write_unsigned (cfg_checksum);
       gcov_write_string (IDENTIFIER_POINTER
-			 (DECL_ASSEMBLER_NAME (current_function_decl)));
+                         (DECL_ASSEMBLER_NAME (current_function_decl)));
       gcov_write_string (xloc.file);
       gcov_write_unsigned (xloc.line);
       gcov_write_length (offset);
@@ -594,7 +633,7 @@ coverage_begin_output (void)
    error has occurred.  Save function coverage counts.  */
 
 void
-coverage_end_function (void)
+coverage_end_function (unsigned lineno_checksum, unsigned cfg_checksum)
 {
   unsigned i;
 
@@ -613,9 +652,11 @@ coverage_end_function (void)
       *functions_tail = item;
       functions_tail = &item->next;
 
+
       item->next = 0;
       item->ident = current_function_funcdef_no + 1;
-      item->checksum = compute_checksum ();
+      item->lineno_checksum = lineno_checksum;
+      item->cfg_checksum = cfg_checksum;
       for (i = 0; i != GCOV_COUNTERS; i++)
 	{
 	  item->n_ctrs[i] = fn_n_ctrs[i];
@@ -640,13 +681,18 @@ build_fn_info_type (unsigned int counters)
   /* ident */
   fields = build_decl (BUILTINS_LOCATION,
 		       FIELD_DECL, NULL_TREE, get_gcov_unsigned_t ());
-
-  /* checksum */
+  /* lineno_checksum */
   field = build_decl (BUILTINS_LOCATION,
 		      FIELD_DECL, NULL_TREE, get_gcov_unsigned_t ());
   DECL_CHAIN (field) = fields;
   fields = field;
 
+  /* cfg checksum */
+  field = build_decl (BUILTINS_LOCATION,
+                      FIELD_DECL, NULL_TREE, get_gcov_unsigned_t ());
+  DECL_CHAIN (field) = fields;
+  fields = field;
+
   array_type = build_int_cst (NULL_TREE, counters - 1);
   array_type = build_index_type (array_type);
   array_type = build_array_type (get_gcov_unsigned_t (), array_type);
@@ -680,10 +726,16 @@ build_fn_info_value (const struct function_list *function, tree type)
 					  function->ident));
   fields = DECL_CHAIN (fields);
 
-  /* checksum */
+  /* lineno_checksum */
+  CONSTRUCTOR_APPEND_ELT (v1, fields,
+			  build_int_cstu (get_gcov_unsigned_t (),
+					  function->lineno_checksum));
+  fields = DECL_CHAIN (fields);
+
+  /* cfg_checksum */
   CONSTRUCTOR_APPEND_ELT (v1, fields,
 			  build_int_cstu (get_gcov_unsigned_t (),
-					  function->checksum));
+					  function->cfg_checksum));
   fields = DECL_CHAIN (fields);
 
   /* counters */
diff --git a/gcc/coverage.h b/gcc/coverage.h
index cabf3c7..6935c2d 100644
--- a/gcc/coverage.h
+++ b/gcc/coverage.h
@@ -28,11 +28,17 @@ extern void coverage_finish (void);
 
 /* Complete the coverage information for the current function. Once
    per function.  */
-extern void coverage_end_function (void);
+extern void coverage_end_function (unsigned, unsigned);
 
 /* Start outputting coverage information for the current
    function. Repeatable per function.  */
-extern int coverage_begin_output (void);
+extern int coverage_begin_output (unsigned, unsigned);
+
+/* Compute the control flow checksum for the current function.  */
+extern unsigned coverage_compute_cfg_checksum (void);
+
+/* Compute the line number checksum for the current function.  */
+extern unsigned coverage_compute_lineno_checksum (void);
 
 /* Allocate some counters. Repeatable per function.  */
 extern int coverage_counter_alloc (unsigned /*counter*/, unsigned/*num*/);
@@ -44,6 +50,8 @@ extern tree tree_coverage_counter_addr (unsigned /*counter*/, unsigned/*num*/);
 /* Get all the counters for the current function.  */
 extern gcov_type *get_coverage_counts (unsigned /*counter*/,
 				       unsigned /*expected*/,
+				       unsigned /*cfg_checksum*/,
+				       unsigned /*lineno_checksum*/,
 				       const struct gcov_ctr_summary **);
 
 extern tree get_gcov_type (void);
diff --git a/gcc/gcov-dump.c b/gcc/gcov-dump.c
index 3706f9e..e9c3843 100644
--- a/gcc/gcov-dump.c
+++ b/gcc/gcov-dump.c
@@ -267,7 +267,8 @@ tag_function (const char *filename ATTRIBUTE_UNUSED,
   unsigned long pos = gcov_position ();
 
   printf (" ident=%u", gcov_read_unsigned ());
-  printf (", checksum=0x%08x", gcov_read_unsigned ());
+  printf (", lineno_checksum=0x%08x", gcov_read_unsigned ());
+  printf (", cfg_checksum_checksum=0x%08x", gcov_read_unsigned ());
 
   if (gcov_position () - pos < length)
     {
diff --git a/gcc/gcov-io.h b/gcc/gcov-io.h
index ffc62ca..4f5013e 100644
--- a/gcc/gcov-io.h
+++ b/gcc/gcov-io.h
@@ -103,7 +103,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    	note: unit function-graph*
 	unit: header int32:checksum string:source
 	function-graph: announce_function basic_blocks {arcs | lines}*
-	announce_function: header int32:ident int32:checksum
+	announce_function: header int32:ident
+		int32:lineno_checksum int32:cfg_checksum
 		string:name string:source int32:lineno
 	basic_block: header int32:flags*
 	arcs: header int32:block_no arc*
@@ -132,7 +133,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
         data: {unit function-data* summary:object summary:program*}*
 	unit: header int32:checksum
         function-data:	announce_function arc_counts
-	announce_function: header int32:ident int32:checksum
+	announce_function: header int32:ident
+		int32:lineno_checksum int32:cfg_checksum
 	arc_counts: header int64:count*
 	summary: int32:checksum {count-summary}GCOV_COUNTERS
 	count-summary:	int32:num int32:runs int64:sum
@@ -294,7 +296,7 @@ typedef HOST_WIDEST_INT gcov_type;
    file marker -- it is not required to be present.  */
 
 #define GCOV_TAG_FUNCTION	 ((gcov_unsigned_t)0x01000000)
-#define GCOV_TAG_FUNCTION_LENGTH (2)
+#define GCOV_TAG_FUNCTION_LENGTH (3)
 #define GCOV_TAG_BLOCKS		 ((gcov_unsigned_t)0x01410000)
 #define GCOV_TAG_BLOCKS_LENGTH(NUM) (NUM)
 #define GCOV_TAG_BLOCKS_NUM(LENGTH) (LENGTH)
@@ -412,10 +414,12 @@ struct gcov_summary
    idiom. The number of counters is determined from the counter_mask
    in gcov_info.  We hold an array of function info, so have to
    explicitly calculate the correct array stride.  */
+
 struct gcov_fn_info
 {
   gcov_unsigned_t ident;	/* unique ident of function */
-  gcov_unsigned_t checksum;	/* function checksum */
+  gcov_unsigned_t lineno_checksum;	/* function lineo_checksum */
+  gcov_unsigned_t cfg_checksum;	/* function cfg checksum */
   unsigned n_ctrs[0];		/* instrumented counters */
 };
 
diff --git a/gcc/gcov.c b/gcc/gcov.c
index bb27913..27ae036 100644
--- a/gcc/gcov.c
+++ b/gcc/gcov.c
@@ -54,6 +54,13 @@ along with Gcov; see the file COPYING3.  If not see
    some places we make use of the knowledge of how profile.c works to
    select particular algorithms here.  */
 
+/* The code validates that the profile information read in corresponds
+   to the code currently being compiled.  Rather than checking for
+   identical files, the code below computes a checksum on the CFG
+   (based on the order of basic blocks and the arcs in the CFG).  If
+   the CFG checksum in the gcda file match the CFG checksum for the
+   code currently being compiled, the profile data will be used.  */
+
 /* This is the size of the buffer used to read in source file lines.  */
 
 #define STRING_SIZE 200
@@ -161,7 +168,8 @@ typedef struct function_info
   /* Name of function.  */
   char *name;
   unsigned ident;
-  unsigned checksum;
+  unsigned lineno_checksum;
+  unsigned cfg_checksum;
 
   /* Array of basic blocks.  */
   block_t *blocks;
@@ -807,12 +815,14 @@ read_graph_file (void)
       if (tag == GCOV_TAG_FUNCTION)
 	{
 	  char *function_name;
-	  unsigned ident, checksum, lineno;
+	  unsigned ident, lineno;
+	  unsigned lineno_checksum, cfg_checksum;
 	  source_t *src;
 	  function_t *probe, *prev;
 
 	  ident = gcov_read_unsigned ();
-	  checksum = gcov_read_unsigned ();
+	  lineno_checksum = gcov_read_unsigned ();
+	  cfg_checksum = gcov_read_unsigned ();
 	  function_name = xstrdup (gcov_read_string ());
 	  src = find_source (gcov_read_string ());
 	  lineno = gcov_read_unsigned ();
@@ -820,7 +830,8 @@ read_graph_file (void)
 	  fn = XCNEW (function_t);
 	  fn->name = function_name;
 	  fn->ident = ident;
-	  fn->checksum = checksum;
+	  fn->lineno_checksum = lineno_checksum;
+	  fn->cfg_checksum = cfg_checksum;
 	  fn->src = src;
 	  fn->line = lineno;
 
@@ -1107,7 +1118,8 @@ read_count_file (void)
 
 	  if (!fn)
 	    ;
-	  else if (gcov_read_unsigned () != fn->checksum)
+	  else if (gcov_read_unsigned () != fn->lineno_checksum
+		   || gcov_read_unsigned () != fn->cfg_checksum)
 	    {
 	    mismatch:;
 	      fnotice (stderr, "%s:profile mismatch for '%s'\n",
diff --git a/gcc/libgcov.c b/gcc/libgcov.c
index 6f32e85..7d1f6d0 100644
--- a/gcc/libgcov.c
+++ b/gcc/libgcov.c
@@ -372,9 +372,10 @@ gcov_exit (void)
 
 	      /* Check function.  */
 	      if (tag != GCOV_TAG_FUNCTION
-		  || length != GCOV_TAG_FUNCTION_LENGTH
+	          || length != GCOV_TAG_FUNCTION_LENGTH
 		  || gcov_read_unsigned () != fi_ptr->ident
-		  || gcov_read_unsigned () != fi_ptr->checksum)
+		  || gcov_read_unsigned () != fi_ptr->lineno_checksum
+		  || gcov_read_unsigned () != fi_ptr->cfg_checksum)
 		{
 		read_mismatch:;
 		  fprintf (stderr, "profiling:%s:Merge mismatch for %s\n",
@@ -517,7 +518,8 @@ gcov_exit (void)
 	  /* Announce function.  */
 	  gcov_write_tag_length (GCOV_TAG_FUNCTION, GCOV_TAG_FUNCTION_LENGTH);
 	  gcov_write_unsigned (fi_ptr->ident);
-	  gcov_write_unsigned (fi_ptr->checksum);
+	  gcov_write_unsigned (fi_ptr->lineno_checksum);
+	  gcov_write_unsigned (fi_ptr->cfg_checksum);
 
 	  c_ix = 0;
 	  for (t_ix = 0; t_ix < GCOV_COUNTERS; t_ix++)
diff --git a/gcc/profile.c b/gcc/profile.c
index e40bfec..e85702e 100644
--- a/gcc/profile.c
+++ b/gcc/profile.c
@@ -102,13 +102,6 @@ static int total_num_branches;
 
 /* Forward declarations.  */
 static void find_spanning_tree (struct edge_list *);
-static unsigned instrument_edges (struct edge_list *);
-static void instrument_values (histogram_values);
-static void compute_branch_probabilities (void);
-static void compute_value_histograms (histogram_values);
-static gcov_type * get_exec_counts (void);
-static basic_block find_group (basic_block);
-static void union_groups (basic_block, basic_block);
 
 /* Add edge instrumentation code to the entire insn chain.
 
@@ -233,10 +226,12 @@ instrument_values (histogram_values values)
 }
 
 
-/* Computes hybrid profile for all matching entries in da_file.  */
+/* Computes hybrid profile for all matching entries in da_file.  
+   
+   CFG_CHECKSUM is the precomputed checksum for the CFG.  */
 
 static gcov_type *
-get_exec_counts (void)
+get_exec_counts (unsigned cfg_checksum, unsigned lineno_checksum)
 {
   unsigned num_edges = 0;
   basic_block bb;
@@ -253,7 +248,8 @@ get_exec_counts (void)
 	  num_edges++;
     }
 
-  counts = get_coverage_counts (GCOV_COUNTER_ARCS, num_edges, &profile_info);
+  counts = get_coverage_counts (GCOV_COUNTER_ARCS, num_edges, cfg_checksum,
+				lineno_checksum, &profile_info);
   if (!counts)
     return NULL;
 
@@ -442,10 +438,12 @@ read_profile_edge_counts (gcov_type *exec_counts)
 }
 
 /* Compute the branch probabilities for the various branches.
-   Annotate them accordingly.  */
+   Annotate them accordingly.  
+
+   CFG_CHECKSUM is the precomputed checksum for the CFG.  */
 
 static void
-compute_branch_probabilities (void)
+compute_branch_probabilities (unsigned cfg_checksum, unsigned lineno_checksum)
 {
   basic_block bb;
   int i;
@@ -454,7 +452,7 @@ compute_branch_probabilities (void)
   int passes;
   int hist_br_prob[20];
   int num_branches;
-  gcov_type *exec_counts = get_exec_counts ();
+  gcov_type *exec_counts = get_exec_counts (cfg_checksum, lineno_checksum);
   int inconsistent = 0;
 
   /* Very simple sanity checks so we catch bugs in our profiling code.  */
@@ -772,10 +770,13 @@ compute_branch_probabilities (void)
 }
 
 /* Load value histograms values whose description is stored in VALUES array
-   from .gcda file.  */
+   from .gcda file.  
+
+   CFG_CHECKSUM is the precomputed checksum for the CFG.  */
 
 static void
-compute_value_histograms (histogram_values values)
+compute_value_histograms (histogram_values values, unsigned cfg_checksum,
+                          unsigned lineno_checksum)
 {
   unsigned i, j, t, any;
   unsigned n_histogram_counters[GCOV_N_VALUE_COUNTERS];
@@ -803,7 +804,8 @@ compute_value_histograms (histogram_values values)
 
       histogram_counts[t] =
 	get_coverage_counts (COUNTER_FOR_HIST_TYPE (t),
-			     n_histogram_counters[t], NULL);
+			     n_histogram_counters[t], cfg_checksum,
+			     lineno_checksum, NULL);
       if (histogram_counts[t])
 	any = 1;
       act_count[t] = histogram_counts[t];
@@ -905,6 +907,7 @@ branch_prob (void)
   unsigned num_instrumented;
   struct edge_list *el;
   histogram_values values = NULL;
+  unsigned cfg_checksum, lineno_checksum;
 
   total_num_times_called++;
 
@@ -1058,11 +1061,19 @@ branch_prob (void)
   if (dump_file)
     fprintf (dump_file, "%d ignored edges\n", ignored_edges);
 
+
+  /* Compute two different checksums. Note that we want to compute
+     the checksum in only once place, since it depends on the shape
+     of the control flow which can change during 
+     various transformations.  */
+  cfg_checksum = coverage_compute_cfg_checksum ();
+  lineno_checksum = coverage_compute_lineno_checksum ();
+
   /* Write the data from which gcov can reconstruct the basic block
      graph.  */
 
   /* Basic block flags */
-  if (coverage_begin_output ())
+  if (coverage_begin_output (lineno_checksum, cfg_checksum))
     {
       gcov_position_t offset;
 
@@ -1079,7 +1090,7 @@ branch_prob (void)
   EXIT_BLOCK_PTR->index = last_basic_block;
 
   /* Arcs */
-  if (coverage_begin_output ())
+  if (coverage_begin_output (lineno_checksum, cfg_checksum))
     {
       gcov_position_t offset;
 
@@ -1120,7 +1131,7 @@ branch_prob (void)
     }
 
   /* Line numbers.  */
-  if (coverage_begin_output ())
+  if (coverage_begin_output (lineno_checksum, cfg_checksum))
     {
       /* Initialize the output.  */
       output_location (NULL, 0, NULL, NULL);
@@ -1175,9 +1186,9 @@ branch_prob (void)
 
   if (flag_branch_probabilities)
     {
-      compute_branch_probabilities ();
+      compute_branch_probabilities (cfg_checksum, lineno_checksum);
       if (flag_profile_values)
-	compute_value_histograms (values);
+	compute_value_histograms (values, cfg_checksum, lineno_checksum);
     }
 
   remove_fake_edges ();
@@ -1205,7 +1216,7 @@ branch_prob (void)
 
   VEC_free (histogram_value, heap, values);
   free_edge_list (el);
-  coverage_end_function ();
+  coverage_end_function (lineno_checksum, cfg_checksum);
 }
 
 /* Union find algorithm implementation for the basic blocks using
@@ -1372,4 +1383,3 @@ end_branch_prob (void)
 	}
     }
 }
-
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index cc8797f..16666ce 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2011-04-28  Xinliang David Li  <davidxl@google.com>
+
+	* testsuite/gcc.dg/tree-prof/prof-robust-1.c: New test.
+	* testsuite/g++.dg/prof-robust-1.C: New test.
+
 2011-04-28  Ira Rosen  <ira.rosen@linaro.org>
 
 	PR tree-optimization/48765
diff --git a/gcc/testsuite/g++.dg/prof-robust-1.C b/gcc/testsuite/g++.dg/prof-robust-1.C
new file mode 100644
index 0000000..a5d8cb3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/prof-robust-1.C
@@ -0,0 +1,24 @@
+/* { dg-options "-O2 -fno-weak" } */
+
+#include <stdio.h>
+
+namespace {
+  namespace {
+    
+    class MyClass {
+    public:
+      void foo() const;
+      ~MyClass() { foo(); }
+    };
+    
+    void MyClass::foo() const { printf("Goodbye World\n"); }
+    
+  }
+  
+  static MyClass variable;
+  
+}
+
+int main() {
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/tree-prof/prof-robust-1.c b/gcc/testsuite/gcc.dg/tree-prof/prof-robust-1.c
new file mode 100644
index 0000000..316cfc7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/prof-robust-1.c
@@ -0,0 +1,25 @@
+/* { dg-options "-O2 -w" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifdef _PROFILE_USE
+int foo(int x) {
+  return 3 * x;
+}
+#else
+int foo(int x) {
+  return 3 * x;
+}
+#endif
+
+int x = 1000;
+
+int main(int argc, char *argv[]) {
+  int i;
+  int sum = 0;
+  for (i = 0; i < x; i++)
+    sum += i;
+  printf("%d\n", sum);
+  return 0;
+}
diff --git a/gcc/tree.c b/gcc/tree.c
index b175221..ba90df8 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -8510,14 +8510,12 @@ dump_tree_statistics (void)
 
 #define FILE_FUNCTION_FORMAT "_GLOBAL__%s_%s"
 
-/* Generate a crc32 of a string.  */
+/* Generate a crc32 of a byte.  */
 
 unsigned
-crc32_string (unsigned chksum, const char *string)
+crc32_byte (unsigned chksum, char byte)
 {
-  do
-    {
-      unsigned value = *string << 24;
+  unsigned value = (unsigned) byte << 24;
       unsigned ix;
 
       for (ix = 8; ix--; value <<= 1)
@@ -8528,6 +8526,18 @@ crc32_string (unsigned chksum, const char *string)
  	  chksum <<= 1;
  	  chksum ^= feedback;
   	}
+  return chksum;
+}
+
+
+/* Generate a crc32 of a string.  */
+
+unsigned
+crc32_string (unsigned chksum, const char *string)
+{
+  do
+    {
+      chksum = crc32_byte (chksum, *string);
     }
   while (*string++);
   return chksum;
@@ -8551,8 +8561,10 @@ clean_symbol_name (char *p)
       *p = '_';
 }
 
-/* Generate a name for a special-purpose function function.
+/* Generate a name for a special-purpose function.
    The generated name may need to be unique across the whole link.
+   Changes to this function may also require corresponding changes to
+   xstrdup_mask_random.
    TYPE is some string to identify the purpose of this function to the
    linker or collect2; it must start with an uppercase letter,
    one of:
diff --git a/gcc/tree.h b/gcc/tree.h
index 8baaf7b..c20206fe 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5001,6 +5001,7 @@ inlined_function_outer_scope_p (const_tree block)
 
 /* In tree.c */
 extern unsigned crc32_string (unsigned, const char *);
+extern unsigned crc32_byte (unsigned, char);
 extern void clean_symbol_name (char *);
 extern tree get_file_function_name (const char *);
 extern tree get_callee_fndecl (const_tree);