Add instruction level discriminator support.

This is the first in a series of patches to enable discriminator support
in AutoFDO.

This patch switches to tracking discriminators per statement/instruction
instead of per basic block. Tracking per basic block was problematic since
not all statements in a basic block needed a discriminator and, also, later
optimizations could move statements between basic blocks making correlation
during AutoFDO compilation unreliable. Tracking per statement also allows
us to assign different discriminators to multiple function calls in the same
basic block. A subsequent patch will add that support.

The idea of this patch is based on commit 4c311d95cf6d9519c3c20f641cc77af7df491fdf
by Dehao Chen in vendors/google/heads/gcc-4_8 but uses a slightly different
approach. In Dehao's work special (normally unused) location ids and side tables
were used to keep track of locations with discriminators. Things have changed
since then and I don't think we have unused location ids anymore. Instead,
I made discriminators a part of ad-hoc locations.

The difference from Dehao's work also includes support for discriminator
reading/writing in lto streaming and in modules.

Tested on x86_64-pc-linux-gnu.

gcc/ChangeLog:

	* basic-block.h: Remove discriminator from basic blocks.
	* cfghooks.cc (split_block_1): Remove discriminator from basic blocks.
	* final.cc (final_start_function_1): Switch from per-bb to per statement
	discriminator.
	(final_scan_insn_1): Don't keep track of basic block discriminators.
	(compute_discriminator): Switch from basic block discriminators to
	instruction discriminators.
	(insn_discriminator): New function to return instruction discriminator.
	(notice_source_line): Use insn_discriminator.
	* gimple-pretty-print.cc (dump_gimple_bb_header): Remove dumping of
	basic block discriminators.
	* gimple-streamer-in.cc (input_bb): Remove reading of basic block
	discriminators.
	* gimple-streamer-out.cc (output_bb): Remove writing of basic block
	discriminators.
	* input.cc (make_location): Pass 0 discriminator to COMBINE_LOCATION_DATA.
	(location_with_discriminator): New function to combine locus with
	a discriminator.
	(has_discriminator): New function to check if a location has a discriminator.
	(get_discriminator_from_loc): New function to get the discriminator
	from a location.
	* input.h: Declarations of new functions.
	* lto-streamer-in.cc (cmp_loc): Use discriminators in location comparison.
	(apply_location_cache): Keep track of current discriminator.
	(input_location_and_block): Read discriminator from stream.
	* lto-streamer-out.cc (clear_line_info): Set current discriminator to
	UINT_MAX.
	(lto_output_location_1): Write discriminator to stream.
	* lto-streamer.h: Add discriminator to cached_location.
	Add current_discr to lto_location_cache.
	Add current_discr to output_block.
	* print-rtl.cc (print_rtx_operand_code_i): Print discriminator.
	* rtl.h: Add extern declaration of insn_discriminator.
	* tree-cfg.cc (assign_discriminator): New function to assign a unique
	discriminator value to all statements in a basic block that have the given
	line number.
	(assign_discriminators): Assign discriminators to statement locations.
	* tree-pretty-print.cc (dump_location): Dump discriminators.
	* tree.cc (set_block): Preserve discriminator when setting block.
	(set_source_range): Preserve discriminator when setting source range.

gcc/cp/ChangeLog:
	* module.cc (write_location): Write discriminator.
	(read_location): Read discriminator.

libcpp/ChangeLog:

	* include/line-map.h: Add discriminator to location_adhoc_data.
	(get_combined_adhoc_loc): Add discriminator parameter.
	(get_discriminator_from_adhoc_loc): Add external declaration.
	(get_discriminator_from_loc): Add external declaration.
	(COMBINE_LOCATION_DATA): Add discriminator parameter.
	* lex.cc (get_location_for_byte_range_in_cur_line) Pass 0 discriminator
	in a call to COMBINE_LOCATION_DATA.
	(warn_about_normalization): Pass 0 discriminator in a call to
	COMBINE_LOCATION_DATA.
	(_cpp_lex_direct): Pass 0 discriminator in a call to
	COMBINE_LOCATION_DATA.
	* line-map.cc (location_adhoc_data_hash): Use discriminator compute
	location_adhoc_data hash.
	(location_adhoc_data_eq): Use discriminator when comparing
	location_adhoc_data.
	(can_be_stored_compactly_p): Check discriminator to determine
	compact storage.
	(get_combined_adhoc_loc): Add discriminator parameter.
	(get_discriminator_from_adhoc_loc): New function to get the discriminator
	from an ad-hoc location.
	(get_discriminator_from_loc): New function to get the discriminator
	from a location.

gcc/testsuite/ChangeLog:

	* c-c++-common/ubsan/pr85213.c: Pass -gno-statement-frontiers.

18 files changed, 145 insertions, 42 deletions

diff --git a/gcc/basic-block.h b/gcc/basic-block.h
index c9d1fc9..1eae03d 100644
--- a/gcc/basic-block.h
+++ b/gcc/basic-block.h
@@ -148,11 +148,6 @@ struct GTY((chain_next ("%h.next_bb"), chain_prev ("%h.prev_bb"))) basic_block_d
 
   /* Expected number of executions: calculated in profile.cc.  */
   profile_count count;
-
-  /* The discriminator for this block.  The discriminator distinguishes
-     among several basic blocks that share a common locus, allowing for
-     more accurate sample-based profiling.  */
-  int discriminator;
 };
 
 /* This ensures that struct gimple_bb_info is smaller than
diff --git a/gcc/cfghooks.cc b/gcc/cfghooks.cc
index c6ac953..29ded57 100644
--- a/gcc/cfghooks.cc
+++ b/gcc/cfghooks.cc
@@ -541,7 +541,6 @@ split_block_1 (basic_block bb, void *i)
     return NULL;
 
   new_bb->count = bb->count;
-  new_bb->discriminator = bb->discriminator;
 
   if (dom_info_available_p (CDI_DOMINATORS))
     {
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 7496df5..d965017 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -15777,6 +15777,8 @@ module_state::write_location (bytes_out &sec, location_t loc)
 	range.m_start = UNKNOWN_LOCATION;
       write_location (sec, range.m_start);
       write_location (sec, range.m_finish);
+      unsigned discriminator = get_discriminator_from_adhoc_loc (line_table, loc);
+      sec.u (discriminator);
     }
   else if (loc >= LINEMAPS_MACRO_LOWEST_LOCATION (line_table))
     {
@@ -15902,8 +15904,9 @@ module_state::read_location (bytes_in &sec) const
 	if (range.m_start == UNKNOWN_LOCATION)
 	  range.m_start = locus;
 	range.m_finish = read_location (sec);
+	unsigned discriminator = sec.u ();
 	if (locus != loc && range.m_start != loc && range.m_finish != loc)
-	  locus = get_combined_adhoc_loc (line_table, locus, range, NULL);
+	  locus = get_combined_adhoc_loc (line_table, locus, range, NULL, discriminator);
       }
       break;
 
diff --git a/gcc/final.cc b/gcc/final.cc
index c0bfdf6..eea5722 100644
--- a/gcc/final.cc
+++ b/gcc/final.cc
@@ -118,18 +118,10 @@ static int last_columnnum;
 /* Discriminator written to assembly.  */
 static int last_discriminator;
 
-/* Discriminator to be written to assembly for current instruction.
+/* Compute discriminator to be written to assembly for current instruction.
    Note: actual usage depends on loc_discriminator_kind setting.  */
-static int discriminator;
 static inline int compute_discriminator (location_t loc);
 
-/* Discriminator identifying current basic block among others sharing
-   the same locus.  */
-static int bb_discriminator;
-
-/* Basic block discriminator for previous instruction.  */
-static int last_bb_discriminator;
-
 /* Highest line number in current block.  */
 static int high_block_linenum;
 
@@ -1688,8 +1680,7 @@ final_start_function_1 (rtx_insn **firstp, FILE *file, int *seen,
   last_filename = LOCATION_FILE (prologue_location);
   last_linenum = LOCATION_LINE (prologue_location);
   last_columnnum = LOCATION_COLUMN (prologue_location);
-  last_discriminator = discriminator = 0;
-  last_bb_discriminator = bb_discriminator = 0;
+  last_discriminator = 0;
   force_source_line = false;
 
   high_block_linenum = high_function_linenum = last_linenum;
@@ -2234,7 +2225,6 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
 	  if (targetm.asm_out.unwind_emit)
 	    targetm.asm_out.unwind_emit (asm_out_file, insn);
 
-	  bb_discriminator = NOTE_BASIC_BLOCK (insn)->discriminator;
 	  break;
 
 	case NOTE_INSN_EH_REGION_BEG:
@@ -2939,7 +2929,7 @@ compute_discriminator (location_t loc)
   int discriminator;
 
   if (!decl_to_instance_map)
-    discriminator = bb_discriminator;
+    discriminator = get_discriminator_from_loc (loc);
   else
     {
       tree block = LOCATION_BLOCK (loc);
@@ -2963,6 +2953,13 @@ compute_discriminator (location_t loc)
   return discriminator;
 }
 
+/* Return discriminator of the statement that produced this insn.  */
+int
+insn_discriminator (const rtx_insn *insn)
+{
+  return compute_discriminator (INSN_LOCATION (insn));
+}
+
 /* Return whether a source line note needs to be emitted before INSN.
    Sets IS_STMT to TRUE if the line should be marked as a possible
    breakpoint location.  */
@@ -2972,6 +2969,7 @@ notice_source_line (rtx_insn *insn, bool *is_stmt)
 {
   const char *filename;
   int linenum, columnnum;
+  int discriminator;
 
   if (NOTE_MARKER_P (insn))
     {
@@ -3001,7 +2999,7 @@ notice_source_line (rtx_insn *insn, bool *is_stmt)
       filename = xloc.file;
       linenum = xloc.line;
       columnnum = xloc.column;
-      discriminator = compute_discriminator (INSN_LOCATION (insn));
+      discriminator = insn_discriminator (insn);
     }
   else
     {
diff --git a/gcc/gimple-pretty-print.cc b/gcc/gimple-pretty-print.cc
index f18baec..a87e2ae 100644
--- a/gcc/gimple-pretty-print.cc
+++ b/gcc/gimple-pretty-print.cc
@@ -2875,8 +2875,6 @@ dump_gimple_bb_header (FILE *outf, basic_block bb, int indent,
 			 indent, "", get_lineno (gsi_stmt (gsi)));
 		break;
 	      }
-	  if (bb->discriminator)
-	    fprintf (outf, ", discriminator %i", bb->discriminator);
 	  fputc ('\n', outf);
 	}
     }
diff --git a/gcc/gimple-streamer-in.cc b/gcc/gimple-streamer-in.cc
index e7f3256..ea8891e 100644
--- a/gcc/gimple-streamer-in.cc
+++ b/gcc/gimple-streamer-in.cc
@@ -267,7 +267,6 @@ input_bb (class lto_input_block *ib, enum LTO_tags tag,
     bb->count
       = bb->count.apply_scale (count_materialization_scale, REG_BR_PROB_BASE);
   bb->flags = streamer_read_hwi (ib);
-  bb->discriminator = streamer_read_hwi (ib);
 
   /* LTO_bb1 has statements.  LTO_bb0 does not.  */
   if (tag == LTO_bb0)
diff --git a/gcc/gimple-streamer-out.cc b/gcc/gimple-streamer-out.cc
index 3336525..4583254 100644
--- a/gcc/gimple-streamer-out.cc
+++ b/gcc/gimple-streamer-out.cc
@@ -208,7 +208,6 @@ output_bb (struct output_block *ob, basic_block bb, struct function *fn)
   streamer_write_uhwi (ob, bb->index);
   bb->count.stream_out (ob);
   streamer_write_hwi (ob, bb->flags);
-  streamer_write_hwi (ob, bb->discriminator);
 
   if (!gsi_end_p (bsi) || phi_nodes (bb))
     {
diff --git a/gcc/input.cc b/gcc/input.cc
index 060ca16..a28abfa 100644
--- a/gcc/input.cc
+++ b/gcc/input.cc
@@ -1082,7 +1082,8 @@ make_location (location_t caret, location_t start, location_t finish)
   location_t combined_loc = COMBINE_LOCATION_DATA (line_table,
 						   pure_loc,
 						   src_range,
-						   NULL);
+						   NULL,
+						   0);
   return combined_loc;
 }
 
@@ -1092,7 +1093,7 @@ location_t
 make_location (location_t caret, source_range src_range)
 {
   location_t pure_loc = get_pure_location (caret);
-  return COMBINE_LOCATION_DATA (line_table, pure_loc, src_range, NULL);
+  return COMBINE_LOCATION_DATA (line_table, pure_loc, src_range, NULL, 0);
 }
 
 /* An expanded_location stores the column in byte units.  This function
@@ -1766,6 +1767,37 @@ get_location_within_string (cpp_reader *pfile,
   return NULL;
 }
 
+/* Associate the DISCRIMINATOR with LOCUS, and return a new locus. */
+
+location_t
+location_with_discriminator (location_t locus, int discriminator)
+{
+  tree block = LOCATION_BLOCK (locus);
+  source_range src_range = get_range_from_loc (line_table, locus);
+  locus = get_pure_location (locus);
+
+  if (locus == UNKNOWN_LOCATION)
+    return locus;
+
+  return COMBINE_LOCATION_DATA (line_table, locus, src_range, block, discriminator);
+}
+
+/* Return TRUE if LOCUS represents a location with a discriminator.  */
+
+bool
+has_discriminator (location_t locus)
+{
+  return get_discriminator_from_loc (locus) != 0;
+}
+
+/* Return the discriminator for LOCUS.  */
+
+int
+get_discriminator_from_loc (location_t locus)
+{
+  return get_discriminator_from_loc (line_table, locus);
+}
+
 #if CHECKING_P
 
 namespace selftest {
diff --git a/gcc/input.h b/gcc/input.h
index f1ae3ae..11c571d 100644
--- a/gcc/input.h
+++ b/gcc/input.h
@@ -165,6 +165,10 @@ extern location_t expansion_point_location (location_t);
 
 extern location_t input_location;
 
+extern location_t location_with_discriminator (location_t, int);
+extern bool has_discriminator (location_t);
+extern int get_discriminator_from_loc (location_t);
+
 #define LOCATION_FILE(LOC) ((expand_location (LOC)).file)
 #define LOCATION_LINE(LOC) ((expand_location (LOC)).line)
 #define LOCATION_COLUMN(LOC)((expand_location (LOC)).column)
diff --git a/gcc/lto-streamer-in.cc b/gcc/lto-streamer-in.cc
index a7dad70..fa89634 100644
--- a/gcc/lto-streamer-in.cc
+++ b/gcc/lto-streamer-in.cc
@@ -409,6 +409,8 @@ lto_location_cache::cmp_loc (const void *pa, const void *pb)
     return a->line - b->line;
   if (a->col != b->col)
     return a->col - b->col;
+  if (a->discr != b->discr)
+    return a->discr - b->discr;
   if ((a->block == NULL_TREE) != (b->block == NULL_TREE))
     return a->block ? 1 : -1;
   if (a->block)
@@ -460,6 +462,8 @@ lto_location_cache::apply_location_cache ()
 	  current_loc = linemap_position_for_column (line_table, loc.col);
 	  if (loc.block)
 	    current_loc = set_block (current_loc, loc.block);
+	  if (loc.discr)
+	    current_loc = location_with_discriminator (current_loc, loc.discr);
 	}
       else if (current_block != loc.block)
 	{
@@ -467,12 +471,17 @@ lto_location_cache::apply_location_cache ()
 	    current_loc = set_block (current_loc, loc.block);
 	  else
 	    current_loc = LOCATION_LOCUS (current_loc);
+	  if (loc.discr)
+	    current_loc = location_with_discriminator (current_loc, loc.discr);
 	}
+      else if (current_discr != loc.discr)
+	current_loc = location_with_discriminator (current_loc, loc.discr);
       *loc.loc = current_loc;
       current_line = loc.line;
       prev_file = current_file = loc.file;
       current_col = loc.col;
       current_block = loc.block;
+      current_discr = loc.discr;
     }
   loc_cache.truncate (0);
   accepted_length = 0;
@@ -512,6 +521,7 @@ lto_location_cache::input_location_and_block (location_t *loc,
   static int stream_col;
   static bool stream_sysp;
   static tree stream_block;
+  static unsigned stream_discr;
   static const char *stream_relative_path_prefix;
 
   gcc_assert (current_cache == this);
@@ -538,6 +548,7 @@ lto_location_cache::input_location_and_block (location_t *loc,
   *loc = RESERVED_LOCATION_COUNT;
   bool line_change = bp_unpack_value (bp, 1);
   bool column_change = bp_unpack_value (bp, 1);
+  bool discr_change = bp_unpack_value (bp, 1);
 
   if (file_change)
     {
@@ -563,6 +574,9 @@ lto_location_cache::input_location_and_block (location_t *loc,
   if (column_change)
     stream_col = bp_unpack_var_len_unsigned (bp);
 
+  if (discr_change)
+    stream_discr = bp_unpack_var_len_unsigned (bp);
+
   tree block = NULL_TREE;
   if (ib)
     {
@@ -578,7 +592,8 @@ lto_location_cache::input_location_and_block (location_t *loc,
   if (current_file == stream_file
       && current_line == stream_line
       && current_col == stream_col
-      && current_sysp == stream_sysp)
+      && current_sysp == stream_sysp
+      && current_discr == stream_discr)
     {
       if (current_block == block)
 	*loc = current_loc;
@@ -590,7 +605,7 @@ lto_location_cache::input_location_and_block (location_t *loc,
     }
 
   struct cached_location entry
-    = {stream_file, loc, stream_line, stream_col, stream_sysp, block};
+    = {stream_file, loc, stream_line, stream_col, stream_sysp, block, stream_discr};
   loc_cache.safe_push (entry);
 }
 
diff --git a/gcc/lto-streamer-out.cc b/gcc/lto-streamer-out.cc
index 1bc3f55..2e7af03 100644
--- a/gcc/lto-streamer-out.cc
+++ b/gcc/lto-streamer-out.cc
@@ -67,6 +67,7 @@ clear_line_info (struct output_block *ob)
      so that the first location with block in a function etc.
      always streams a change_block bit and the first block.  */
   ob->current_block = void_node;
+  ob->current_discr = UINT_MAX;
 }
 
 
@@ -194,6 +195,7 @@ lto_output_location_1 (struct output_block *ob, struct bitpack_d *bp,
   if (loc >= RESERVED_LOCATION_COUNT)
     {
       expanded_location xloc = expand_location (loc);
+      unsigned discr = get_discriminator_from_loc (orig_loc);
 
       if (ob->reset_locus)
 	{
@@ -216,6 +218,7 @@ lto_output_location_1 (struct output_block *ob, struct bitpack_d *bp,
 
       bp_pack_value (bp, ob->current_line != xloc.line, 1);
       bp_pack_value (bp, ob->current_col != xloc.column, 1);
+      bp_pack_value (bp, ob->current_discr != discr, 1);
 
       if (ob->current_file != xloc.file)
 	{
@@ -242,6 +245,10 @@ lto_output_location_1 (struct output_block *ob, struct bitpack_d *bp,
       if (ob->current_col != xloc.column)
 	bp_pack_var_len_unsigned (bp, xloc.column);
       ob->current_col = xloc.column;
+
+      if (ob->current_discr != discr)
+	bp_pack_var_len_unsigned (bp, discr);
+      ob->current_discr = discr;
     }
   else
     bp_pack_int_in_range (bp, 0, RESERVED_LOCATION_COUNT + 1, loc);
diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
index 597e9e4..2e3abd9 100644
--- a/gcc/lto-streamer.h
+++ b/gcc/lto-streamer.h
@@ -311,6 +311,7 @@ private:
     int line, col;
     bool sysp;
     tree block;
+    unsigned discr;
   };
 
   /* The location cache.  */
@@ -333,6 +334,7 @@ private:
   bool current_sysp;
   location_t current_loc;
   tree current_block;
+  unsigned current_discr;
 };
 
 /* Structure used as buffer for reading an LTO file.  */
@@ -723,6 +725,7 @@ struct output_block
   bool reset_locus;
   bool emit_pwd;
   tree current_block;
+  unsigned current_discr;
 
   /* Cache of nodes written in this section.  */
   struct streamer_tree_cache_d *writer_cache;
diff --git a/gcc/print-rtl.cc b/gcc/print-rtl.cc
index 60c8454..e115f98 100644
--- a/gcc/print-rtl.cc
+++ b/gcc/print-rtl.cc
@@ -453,6 +453,10 @@ rtx_writer::print_rtx_operand_code_i (const_rtx in_rtx, int idx)
 	  expanded_location xloc = insn_location (in_insn);
 	  fprintf (m_outfile, " \"%s\":%i:%i", xloc.file, xloc.line,
 		   xloc.column);
+	  int discriminator = insn_discriminator (in_insn);
+	    if (discriminator)
+	      fprintf (m_outfile, " discrim %d", discriminator);
+
 	}
 #endif
     }
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 645c009..7a8c470 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -3369,6 +3369,7 @@ extern int insn_line (const rtx_insn *);
 extern const char * insn_file (const rtx_insn *);
 extern tree insn_scope (const rtx_insn *);
 extern expanded_location insn_location (const rtx_insn *);
+extern int insn_discriminator (const rtx_insn *);
 extern location_t prologue_location, epilogue_location;
 
 /* In jump.cc */
diff --git a/gcc/testsuite/c-c++-common/ubsan/pr85213.c b/gcc/testsuite/c-c++-common/ubsan/pr85213.c
index 8a6be81..e903e97 100644
--- a/gcc/testsuite/c-c++-common/ubsan/pr85213.c
+++ b/gcc/testsuite/c-c++-common/ubsan/pr85213.c
@@ -1,6 +1,11 @@
 /* PR sanitizer/85213 */
 /* { dg-do compile } */
-/* { dg-options "-O1 -fsanitize=undefined -fcompare-debug" } */
+/* Pass -gno-statement-frontiers to work around
+   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100733 :
+   without it the IR coming from the front end may be different with and without
+   debug information turned on. That may cause e.g., different discriminator values
+   and -fcompare-debug failures. */
+/* { dg-options "-O1 -fsanitize=undefined -fcompare-debug -gno-statement-frontiers" } */
 
 int
 foo (int x)
diff --git a/gcc/tree-cfg.cc b/gcc/tree-cfg.cc
index 53be0c2..ade66c5 100644
--- a/gcc/tree-cfg.cc
+++ b/gcc/tree-cfg.cc
@@ -1166,7 +1166,33 @@ same_line_p (location_t locus1, expanded_location *from, location_t locus2)
           && filename_cmp (from->file, to.file) == 0);
 }
 
-/* Assign discriminators to each basic block.  */
+/* Assign a unique discriminator value to all statements in block bb that
+   have the same line number as locus. */
+
+static void
+assign_discriminator (location_t locus, basic_block bb)
+{
+  gimple_stmt_iterator gsi;
+  int discriminator;
+
+  if (locus == UNKNOWN_LOCATION)
+    return;
+
+  expanded_location locus_e = expand_location (locus);
+
+  discriminator = next_discriminator_for_locus (locus_e.line);
+
+  for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+    {
+      gimple *stmt = gsi_stmt (gsi);
+      location_t stmt_locus = gimple_location (stmt);
+      if (same_line_p (locus, &locus_e, stmt_locus))
+	gimple_set_location (stmt,
+	    location_with_discriminator (stmt_locus, discriminator));
+    }
+}
+
+/* Assign discriminators to statement locations.  */
 
 static void
 assign_discriminators (void)
@@ -1189,17 +1215,22 @@ assign_discriminators (void)
 	{
 	  gimple *first = first_non_label_stmt (e->dest);
 	  gimple *last = last_stmt (e->dest);
-	  if ((first && same_line_p (locus, &locus_e,
+
+	  gimple *stmt_on_same_line = NULL;
+	  if (first && same_line_p (locus, &locus_e,
 				     gimple_location (first)))
-	      || (last && same_line_p (locus, &locus_e,
-				       gimple_location (last))))
+	    stmt_on_same_line = first;
+	  else if (last && same_line_p (locus, &locus_e,
+					gimple_location (last)))
+	    stmt_on_same_line = last;
+
+	  if (stmt_on_same_line)
 	    {
-	      if (e->dest->discriminator != 0 && bb->discriminator == 0)
-		bb->discriminator
-		  = next_discriminator_for_locus (locus_e.line);
+	      if (has_discriminator (gimple_location (stmt_on_same_line))
+		  && !has_discriminator (locus))
+		assign_discriminator (locus, bb);
 	      else
-		e->dest->discriminator
-		  = next_discriminator_for_locus (locus_e.line);
+		assign_discriminator (locus, e->dest);
 	    }
 	}
     }
diff --git a/gcc/tree-pretty-print.cc b/gcc/tree-pretty-print.cc
index 33b12c7..e7a8c94 100644
--- a/gcc/tree-pretty-print.cc
+++ b/gcc/tree-pretty-print.cc
@@ -1455,6 +1455,7 @@ void
 dump_location (pretty_printer *pp, location_t loc)
 {
   expanded_location xloc = expand_location (loc);
+  int discriminator = get_discriminator_from_loc (loc);
 
   pp_left_bracket (pp);
   if (xloc.file)
@@ -1465,6 +1466,11 @@ dump_location (pretty_printer *pp, location_t loc)
   pp_decimal_int (pp, xloc.line);
   pp_colon (pp);
   pp_decimal_int (pp, xloc.column);
+  if (discriminator)
+  {
+    pp_string (pp, " discrim ");
+    pp_decimal_int (pp, discriminator);
+  }
   pp_string (pp, "] ");
 }
 
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 756c14f..f8d24b5 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -14253,7 +14253,8 @@ set_block (location_t loc, tree block)
 {
   location_t pure_loc = get_pure_location (loc);
   source_range src_range = get_range_from_loc (line_table, loc);
-  return COMBINE_LOCATION_DATA (line_table, pure_loc, src_range, block);
+  unsigned discriminator = get_discriminator_from_loc (line_table, loc);
+  return COMBINE_LOCATION_DATA (line_table, pure_loc, src_range, block, discriminator);
 }
 
 location_t
@@ -14271,11 +14272,14 @@ set_source_range (tree expr, source_range src_range)
   if (!EXPR_P (expr))
     return UNKNOWN_LOCATION;
 
-  location_t pure_loc = get_pure_location (EXPR_LOCATION (expr));
+  location_t expr_location = EXPR_LOCATION (expr);
+  location_t pure_loc = get_pure_location (expr_location);
+  unsigned discriminator = get_discriminator_from_loc (expr_location);
   location_t adhoc = COMBINE_LOCATION_DATA (line_table,
 					    pure_loc,
 					    src_range,
-					    NULL);
+					    NULL,
+					    discriminator);
   SET_EXPR_LOCATION (expr, adhoc);
   return adhoc;
 }