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.

libcpp/include/line-map.h

@@ -757,6 +757,7 @@ struct GTY(()) location_adhoc_data {
   location_t locus;
   source_range src_range;
   void * GTY((skip)) data;
+  unsigned discriminator;
 };
 
 struct htab;
@@ -1034,12 +1035,14 @@ LINEMAPS_LAST_ALLOCATED_MACRO_MAP (const line_maps *set)
 }
 
 extern location_t get_combined_adhoc_loc (line_maps *, location_t,
-					  source_range, void *);
+					  source_range, void *, unsigned);
 extern void *get_data_from_adhoc_loc (const line_maps *, location_t);
+extern unsigned get_discriminator_from_adhoc_loc (const line_maps *, location_t);
 extern location_t get_location_from_adhoc_loc (const line_maps *,
 					       location_t);
 
 extern source_range get_range_from_loc (line_maps *set, location_t loc);
+extern unsigned get_discriminator_from_loc (line_maps *set, location_t loc);
 
 /* Get whether location LOC is a "pure" location, or
    whether it is an ad-hoc location, or embeds range information.  */
@@ -1058,9 +1061,10 @@ inline location_t
 COMBINE_LOCATION_DATA (class line_maps *set,
 		       location_t loc,
 		       source_range src_range,
-		       void *block)
+		       void *block,
+		       unsigned discriminator)
 {
-  return get_combined_adhoc_loc (set, loc, src_range, block);
+  return get_combined_adhoc_loc (set, loc, src_range, block, discriminator);
 }
 
 extern void rebuild_location_adhoc_htab (class line_maps *);