lto: Cache location_ts including BLOCKs in GIMPLE streaming [PR94311]

As mentioned in the PR, when compiling valgrind even on fairly small
testcase where in one larger function the location keeps oscillating
between a small line number and 8000-ish line number in the same file
we very quickly run out of all possible location_t numbers and because of
that emit non-sensical line numbers in .debug_line.
There are ways how to decrease speed of depleting location_t numbers
in libcpp, but the main reason of this is that we use
stream_input_location_now for streaming in location_t for gimple_location
and phi arg locations.  libcpp strongly prefers that the locations
it is given are sorted by the different files and by line numbers in
ascending order, otherwise it depletes quickly no matter what and is much
more costly (many extra file changes etc.).
The reason for not caching those were the BLOCKs that were streamed
immediately after the location and encoded into the locations (and for PHIs
we failed to stream the BLOCKs altogether).
This patch enhances the location cache to handle also BLOCKs (but not for
everything, only for the spots we care about the BLOCKs) and also optimizes
the size of the LTO stream by emitting a single bit into a pack whether the
BLOCK changed from last case and only streaming the BLOCK tree if it
changed.

2020-09-03  Jakub Jelinek  <jakub@redhat.com>

	PR lto/94311
	* gimple.h (gimple_location_ptr, gimple_phi_arg_location_ptr): New
	functions.
	* streamer-hooks.h (struct streamer_hooks): Add
	output_location_and_block callback.  Fix up formatting for
	output_location.
	(stream_output_location_and_block): Define.
	* lto-streamer.h (class lto_location_cache): Fix comment typo.  Add
	current_block member.
	(lto_location_cache::input_location_and_block): New method.
	(lto_location_cache::lto_location_cache): Initialize current_block.
	(lto_location_cache::cached_location): Add block member.
	(struct output_block): Add current_block member.
	(lto_output_location): Formatting fix.
	(lto_output_location_and_block): Declare.
	* lto-streamer.c (lto_streamer_hooks_init): Initialize
	streamer_hooks.output_location_and_block.
	* lto-streamer-in.c (lto_location_cache::cmp_loc): Also compare
	block members.
	(lto_location_cache::apply_location_cache): Handle blocks.
	(lto_location_cache::accept_location_cache,
	lto_location_cache::revert_location_cache): Fix up function comments.
	(lto_location_cache::input_location_and_block): New method.
	(lto_location_cache::input_location): Implement using
	input_location_and_block.
	(input_function): Invoke apply_location_cache after streaming in all
	bbs.
	* lto-streamer-out.c (clear_line_info): Set current_block.
	(lto_output_location_1): New function, moved from lto_output_location,
	added block handling.
	(lto_output_location): Implement using lto_output_location_1.
	(lto_output_location_and_block): New function.
	* gimple-streamer-in.c (input_phi): Use input_location_and_block
	to input and cache both location and block.
	(input_gimple_stmt): Likewise.
	* gimple-streamer-out.c (output_phi): Use
	stream_output_location_and_block.
	(output_gimple_stmt): Likewise.

8 files changed, 200 insertions, 69 deletions

diff --git a/gcc/gimple-streamer-in.c b/gcc/gimple-streamer-in.c
index 87dd962e610..3bd4a86b156 100644
--- a/gcc/gimple-streamer-in.c
+++ b/gcc/gimple-streamer-in.c
@@ -57,11 +57,7 @@ input_phi (class lto_input_block *ib, basic_block bb, class data_in *data_in,
       tree def = stream_read_tree (ib, data_in);
       int src_index = streamer_read_uhwi (ib);
       bitpack_d bp = streamer_read_bitpack (ib);
-      /* Do not cache a location - we do not have API to get pointer to the
-	 location in PHI statement and we may trigger reallocation.  */
-      location_t arg_loc = stream_input_location_now (&bp, data_in);
       basic_block sbb = BASIC_BLOCK_FOR_FN (fn, src_index);
-
       edge e = NULL;
       int j;
 
@@ -72,7 +68,11 @@ input_phi (class lto_input_block *ib, basic_block bb, class data_in *data_in,
 	    break;
 	  }
 
-      add_phi_arg (result, def, e, arg_loc);
+      add_phi_arg (result, def, e, UNKNOWN_LOCATION);
+      /* Read location and lexical block information.  */
+      location_t *arg_locp = gimple_phi_arg_location_ptr (result, e->dest_idx);
+      data_in->location_cache.input_location_and_block (arg_locp, &bp, ib,
+							data_in);
     }
 
   return result;
@@ -106,12 +106,9 @@ input_gimple_stmt (class lto_input_block *ib, class data_in *data_in,
   has_hist = bp_unpack_value (&bp, 1);
   stmt->subcode = bp_unpack_var_len_unsigned (&bp);
 
-  /* Read location information.  Caching here makes no sense until streamer
-     cache can handle the following gimple_set_block.  */
-  gimple_set_location (stmt, stream_input_location_now (&bp, data_in));
-
-  /* Read lexical block reference.  */
-  gimple_set_block (stmt, stream_read_tree (ib, data_in));
+  /* Read location and lexical block information.  */
+  data_in->location_cache.input_location_and_block (gimple_location_ptr (stmt),
+						    &bp, ib, data_in);
 
   /* Read in all the operands.  */
   switch (code)
diff --git a/gcc/gimple-streamer-out.c b/gcc/gimple-streamer-out.c
index 232453713dc..2e55c5f3d1e 100644
--- a/gcc/gimple-streamer-out.c
+++ b/gcc/gimple-streamer-out.c
@@ -48,8 +48,8 @@ output_phi (struct output_block *ob, gphi *phi)
       stream_write_tree (ob, gimple_phi_arg_def (phi, i), true);
       streamer_write_uhwi (ob, gimple_phi_arg_edge (phi, i)->src->index);
       bitpack_d bp = bitpack_create (ob->main_stream);
-      stream_output_location (ob, &bp, gimple_phi_arg_location (phi, i));
-      streamer_write_bitpack (&bp);
+      location_t loc = gimple_phi_arg_location (phi, i);
+      stream_output_location_and_block (ob, &bp, loc);
     }
 }
 
@@ -84,12 +84,8 @@ output_gimple_stmt (struct output_block *ob, struct function *fn, gimple *stmt)
   bp_pack_value (&bp, hist != NULL, 1);
   bp_pack_var_len_unsigned (&bp, stmt->subcode);
 
-  /* Emit location information for the statement.  */
-  stream_output_location (ob, &bp, LOCATION_LOCUS (gimple_location (stmt)));
-  streamer_write_bitpack (&bp);
-
-  /* Emit the lexical block holding STMT.  */
-  stream_write_tree (ob, gimple_block (stmt), true);
+  /* Emit location information for the statement, including gimple_block.  */
+  stream_output_location_and_block (ob, &bp, gimple_location (stmt));
 
   /* Emit the operands.  */
   switch (gimple_code (stmt))
diff --git a/gcc/gimple.h b/gcc/gimple.h
index 6f7c7ff6a5f..6cc7e66059d 100644
--- a/gcc/gimple.h
+++ b/gcc/gimple.h
@@ -1879,6 +1879,14 @@ gimple_set_location (gimple *g, location_t location)
   g->location = location;
 }
 
+/* Return address of the location information for statement G.  */
+
+static inline location_t *
+gimple_location_ptr (gimple *g)
+{
+  return &g->location;
+}
+
 
 /* Return true if G contains location information.  */
 
@@ -4581,6 +4589,14 @@ gimple_phi_arg_set_location (gphi *phi, size_t i, location_t loc)
   gimple_phi_arg (phi, i)->locus = loc;
 }
 
+/* Return address of source location of gimple argument I of phi node PHI.  */
+
+static inline location_t *
+gimple_phi_arg_location_ptr (gphi *phi, size_t i)
+{
+  return &gimple_phi_arg (phi, i)->locus;
+}
+
 /* Return TRUE if argument I of phi node PHI has a location record.  */
 
 static inline bool
diff --git a/gcc/lto-streamer-in.c b/gcc/lto-streamer-in.c
index e02d69cc196..478125aed19 100644
--- a/gcc/lto-streamer-in.c
+++ b/gcc/lto-streamer-in.c
@@ -156,7 +156,18 @@ lto_location_cache::cmp_loc (const void *pa, const void *pb)
     return a->sysp ? 1 : -1;
   if (a->line != b->line)
     return a->line - b->line;
-  return a->col - b->col;
+  if (a->col != b->col)
+    return a->col - b->col;
+  if ((a->block == NULL_TREE) != (b->block == NULL_TREE))
+    return a->block ? 1 : -1;
+  if (a->block)
+    {
+      if (BLOCK_NUMBER (a->block) < BLOCK_NUMBER (b->block))
+	return -1;
+      if (BLOCK_NUMBER (a->block) > BLOCK_NUMBER (b->block))
+	return 1;
+    }
+  return 0;
 }
 
 /* Apply all changes in location cache.  Add locations into linemap and patch
@@ -191,22 +202,33 @@ lto_location_cache::apply_location_cache ()
 	  linemap_line_start (line_table, loc.line, max + 1);
 	}
       gcc_assert (*loc.loc == BUILTINS_LOCATION + 1);
-      if (current_file == loc.file && current_line == loc.line
-	  && current_col == loc.col)
-	*loc.loc = current_loc;
-      else
-        current_loc = *loc.loc = linemap_position_for_column (line_table,
-							      loc.col);
+      if (current_file != loc.file
+	  || current_line != loc.line
+	  || current_col != loc.col)
+	{
+	  current_loc = linemap_position_for_column (line_table, loc.col);
+	  if (loc.block)
+	    current_loc = set_block (current_loc, loc.block);
+	}
+      else if (current_block != loc.block)
+	{
+	  if (loc.block)
+	    current_loc = set_block (current_loc, loc.block);
+	  else
+	    current_loc = LOCATION_LOCUS (current_loc);
+	}
+      *loc.loc = current_loc;
       current_line = loc.line;
       prev_file = current_file = loc.file;
       current_col = loc.col;
+      current_block = loc.block;
     }
   loc_cache.truncate (0);
   accepted_length = 0;
   return true;
 }
 
-/* Tree merging did not suceed; mark all changes in the cache as accepted.  */
+/* Tree merging did not succeed; mark all changes in the cache as accepted.  */
 
 void
 lto_location_cache::accept_location_cache ()
@@ -215,7 +237,7 @@ lto_location_cache::accept_location_cache ()
   accepted_length = loc_cache.length ();
 }
 
-/* Tree merging did suceed; throw away recent changes.  */
+/* Tree merging did succeed; throw away recent changes.  */
 
 void
 lto_location_cache::revert_location_cache ()
@@ -223,33 +245,46 @@ lto_location_cache::revert_location_cache ()
   loc_cache.truncate (accepted_length);
 }
 
-/* Read a location bitpack from input block IB and either update *LOC directly
-   or add it to the location cache.
+/* Read a location bitpack from bit pack BP and either update *LOC directly
+   or add it to the location cache.  If IB is non-NULL, stream in a block
+   afterwards.
    It is neccesary to call apply_location_cache to get *LOC updated.  */
 
 void
-lto_location_cache::input_location (location_t *loc, struct bitpack_d *bp,
-				    class data_in *data_in)
+lto_location_cache::input_location_and_block (location_t *loc,
+					      struct bitpack_d *bp,
+					      class lto_input_block *ib,
+					      class data_in *data_in)
 {
   static const char *stream_file;
   static int stream_line;
   static int stream_col;
   static bool stream_sysp;
-  bool file_change, line_change, column_change;
+  static tree stream_block;
 
   gcc_assert (current_cache == this);
 
   *loc = bp_unpack_int_in_range (bp, "location", 0, RESERVED_LOCATION_COUNT);
 
   if (*loc < RESERVED_LOCATION_COUNT)
-    return;
+    {
+      if (ib)
+	{
+	  bool block_change = bp_unpack_value (bp, 1);
+	  if (block_change)
+	    stream_block = stream_read_tree (ib, data_in);
+	  if (stream_block)
+	    *loc = set_block (*loc, stream_block);
+	}
+      return;
+    }
 
   /* Keep value RESERVED_LOCATION_COUNT in *loc as linemap lookups will
      ICE on it.  */
 
-  file_change = bp_unpack_value (bp, 1);
-  line_change = bp_unpack_value (bp, 1);
-  column_change = bp_unpack_value (bp, 1);
+  bool file_change = bp_unpack_value (bp, 1);
+  bool line_change = bp_unpack_value (bp, 1);
+  bool column_change = bp_unpack_value (bp, 1);
 
   if (file_change)
     {
@@ -263,21 +298,48 @@ lto_location_cache::input_location (location_t *loc, struct bitpack_d *bp,
   if (column_change)
     stream_col = bp_unpack_var_len_unsigned (bp);
 
-  /* This optimization saves location cache operations druing gimple
+  tree block = NULL_TREE;
+  if (ib)
+    {
+      bool block_change = bp_unpack_value (bp, 1);
+      if (block_change)
+	stream_block = stream_read_tree (ib, data_in);
+      block = stream_block;
+    }
+
+  /* This optimization saves location cache operations during gimple
      streaming.  */
      
-  if (current_file == stream_file && current_line == stream_line
-      && current_col == stream_col && current_sysp == stream_sysp)
+  if (current_file == stream_file
+      && current_line == stream_line
+      && current_col == stream_col
+      && current_sysp == stream_sysp)
     {
-      *loc = current_loc;
+      if (current_block == block)
+	*loc = current_loc;
+      else if (block)
+	*loc = set_block (current_loc, block);
+      else
+	*loc = LOCATION_LOCUS (current_loc);
       return;
     }
 
   struct cached_location entry
-    = {stream_file, loc, stream_line, stream_col, stream_sysp};
+    = {stream_file, loc, stream_line, stream_col, stream_sysp, block};
   loc_cache.safe_push (entry);
 }
 
+/* Read a location bitpack from bit pack BP and either update *LOC directly
+   or add it to the location cache.
+   It is neccesary to call apply_location_cache to get *LOC updated.  */
+
+void
+lto_location_cache::input_location (location_t *loc, struct bitpack_d *bp,
+				    class data_in *data_in)
+{
+  return input_location_and_block (loc, bp, NULL, data_in);
+}
+
 /* Read a location bitpack from input block IB and either update *LOC directly
    or add it to the location cache.
    It is neccesary to call apply_location_cache to get *LOC updated.  */
@@ -1101,6 +1163,9 @@ input_function (tree fn_decl, class data_in *data_in,
       tag = streamer_read_record_start (ib);
     }
 
+  /* Finalize gimple_location/gimple_block of stmts and phis.  */
+  data_in->location_cache.apply_location_cache ();
+
   /* Fix up the call statements that are mentioned in the callgraph
      edges.  */
   set_gimple_stmt_max_uid (cfun, 0);
diff --git a/gcc/lto-streamer-out.c b/gcc/lto-streamer-out.c
index ec28928b56a..914d5eb70b0 100644
--- a/gcc/lto-streamer-out.c
+++ b/gcc/lto-streamer-out.c
@@ -60,6 +60,10 @@ clear_line_info (struct output_block *ob)
   ob->current_line = 0;
   ob->current_col = 0;
   ob->current_sysp = false;
+  /* Initialize to something that will never appear as block,
+     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;
 }
 
 
@@ -178,40 +182,72 @@ tree_is_indexable (tree t)
    After outputting bitpack, lto_output_location_data has
    to be done to output actual data.  */
 
-void
-lto_output_location (struct output_block *ob, struct bitpack_d *bp,
-		     location_t loc)
+static void
+lto_output_location_1 (struct output_block *ob, struct bitpack_d *bp,
+		       location_t orig_loc, bool block_p)
 {
-  expanded_location xloc;
+  location_t loc = LOCATION_LOCUS (orig_loc);
 
-  loc = LOCATION_LOCUS (loc);
   bp_pack_int_in_range (bp, 0, RESERVED_LOCATION_COUNT,
 		        loc < RESERVED_LOCATION_COUNT
 			? loc : RESERVED_LOCATION_COUNT);
-  if (loc < RESERVED_LOCATION_COUNT)
-    return;
+  if (loc >= RESERVED_LOCATION_COUNT)
+    {
+      expanded_location xloc = expand_location (loc);
 
-  xloc = expand_location (loc);
+      bp_pack_value (bp, ob->current_file != xloc.file, 1);
+      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_file != xloc.file, 1);
-  bp_pack_value (bp, ob->current_line != xloc.line, 1);
-  bp_pack_value (bp, ob->current_col != xloc.column, 1);
+      if (ob->current_file != xloc.file)
+	{
+	  bp_pack_string (ob, bp, remap_debug_filename (xloc.file), true);
+	  bp_pack_value (bp, xloc.sysp, 1);
+	}
+      ob->current_file = xloc.file;
+      ob->current_sysp = xloc.sysp;
+
+      if (ob->current_line != xloc.line)
+	bp_pack_var_len_unsigned (bp, xloc.line);
+      ob->current_line = xloc.line;
+
+      if (ob->current_col != xloc.column)
+	bp_pack_var_len_unsigned (bp, xloc.column);
+      ob->current_col = xloc.column;
+    }
 
-  if (ob->current_file != xloc.file)
+  if (block_p)
     {
-      bp_pack_string (ob, bp, remap_debug_filename (xloc.file), true);
-      bp_pack_value (bp, xloc.sysp, 1);
+      tree block = LOCATION_BLOCK (orig_loc);
+      bp_pack_value (bp, ob->current_block != block, 1);
+      streamer_write_bitpack (bp);
+      if (ob->current_block != block)
+	lto_output_tree (ob, block, true, true);
+      ob->current_block = block;
     }
-  ob->current_file = xloc.file;
-  ob->current_sysp = xloc.sysp;
+}
+
+/* Output info about new location into bitpack BP.
+   After outputting bitpack, lto_output_location_data has
+   to be done to output actual data.  */
 
-  if (ob->current_line != xloc.line)
-    bp_pack_var_len_unsigned (bp, xloc.line);
-  ob->current_line = xloc.line;
+void
+lto_output_location (struct output_block *ob, struct bitpack_d *bp,
+		     location_t loc)
+{
+  lto_output_location_1 (ob, bp, loc, false);
+}
+
+/* Output info about new location into bitpack BP.
+   After outputting bitpack, lto_output_location_data has
+   to be done to output actual data.  Like lto_output_location, but
+   additionally output LOCATION_BLOCK info too and write the BP bitpack.  */
 
-  if (ob->current_col != xloc.column)
-    bp_pack_var_len_unsigned (bp, xloc.column);
-  ob->current_col = xloc.column;
+void
+lto_output_location_and_block (struct output_block *ob, struct bitpack_d *bp,
+			       location_t loc)
+{
+  lto_output_location_1 (ob, bp, loc, true);
 }
 
 
diff --git a/gcc/lto-streamer.c b/gcc/lto-streamer.c
index 7d0fd3924c0..9d12d47d909 100644
--- a/gcc/lto-streamer.c
+++ b/gcc/lto-streamer.c
@@ -272,4 +272,5 @@ lto_streamer_hooks_init (void)
   streamer_hooks.read_tree = lto_input_tree;
   streamer_hooks.input_location = lto_input_location;
   streamer_hooks.output_location = lto_output_location;
+  streamer_hooks.output_location_and_block = lto_output_location_and_block;
 }
diff --git a/gcc/lto-streamer.h b/gcc/lto-streamer.h
index 0129f00cc1a..938298459eb 100644
--- a/gcc/lto-streamer.h
+++ b/gcc/lto-streamer.h
@@ -262,7 +262,7 @@ typedef void (lto_free_section_data_f) (struct lto_file_decl_data *,
 
 /* The location cache holds expanded locations for streamed in trees.
    This is done to reduce memory usage of libcpp linemap that strongly prefers
-   locations to be inserted in the soruce order.  */
+   locations to be inserted in the source order.  */
 
 class lto_location_cache
 {
@@ -276,9 +276,13 @@ public:
   void revert_location_cache ();
   void input_location (location_t *loc, struct bitpack_d *bp,
 		       class data_in *data_in);
+  void input_location_and_block (location_t *loc, struct bitpack_d *bp,
+				 class lto_input_block *ib,
+				 class data_in *data_in);
   lto_location_cache ()
      : loc_cache (), accepted_length (0), current_file (NULL), current_line (0),
-       current_col (0), current_sysp (false), current_loc (UNKNOWN_LOCATION)
+       current_col (0), current_sysp (false), current_loc (UNKNOWN_LOCATION),
+       current_block (NULL_TREE)
   {
     gcc_assert (!current_cache);
     current_cache = this;
@@ -304,6 +308,7 @@ private:
     location_t *loc;
     int line, col;
     bool sysp;
+    tree block;
   };
 
   /* The location cache.  */
@@ -325,6 +330,7 @@ private:
   int current_col;
   bool current_sysp;
   location_t current_loc;
+  tree current_block;
 };
 
 /* Structure used as buffer for reading an LTO file.  */
@@ -711,6 +717,7 @@ struct output_block
   int current_line;
   int current_col;
   bool current_sysp;
+  tree current_block;
 
   /* Cache of nodes written in this section.  */
   struct streamer_tree_cache_d *writer_cache;
@@ -881,7 +888,10 @@ void lto_output_decl_state_streams (struct output_block *,
 void lto_output_decl_state_refs (struct output_block *,
 			         struct lto_output_stream *,
 			         struct lto_out_decl_state *);
-void lto_output_location (struct output_block *, struct bitpack_d *, location_t);
+void lto_output_location (struct output_block *, struct bitpack_d *,
+			  location_t);
+void lto_output_location_and_block (struct output_block *, struct bitpack_d *,
+				    location_t);
 void lto_output_init_mode_table (void);
 void lto_prepare_function_for_streaming (cgraph_node *);
 
diff --git a/gcc/streamer-hooks.h b/gcc/streamer-hooks.h
index 734f9ca04ac..4085bf4ba3d 100644
--- a/gcc/streamer-hooks.h
+++ b/gcc/streamer-hooks.h
@@ -54,8 +54,15 @@ struct streamer_hooks {
   /* [REQ] Called by every streaming routine that needs to read a location.  */
   void (*input_location) (location_t *, struct bitpack_d *, class data_in *);
 
-  /* [REQ] Called by every streaming routine that needs to write a location.  */
-  void (*output_location) (struct output_block *, struct bitpack_d *, location_t);
+  /* [REQ] Called by every streaming routine that needs to write a
+     location.  */
+  void (*output_location) (struct output_block *, struct bitpack_d *,
+			   location_t);
+
+  /* [REQ] Called by every streaming routine that needs to write a
+     location, both LOCATION_LOCUS and LOCATION_BLOCK.  */
+  void (*output_location_and_block) (struct output_block *, struct bitpack_d *,
+				     location_t);
 };
 
 #define stream_write_tree(OB, EXPR, REF_P) \
@@ -73,6 +80,9 @@ struct streamer_hooks {
 #define stream_output_location(OB, BP, LOC) \
     streamer_hooks.output_location (OB, BP, LOC)
 
+#define stream_output_location_and_block(OB, BP, LOC) \
+    streamer_hooks.output_location_and_block (OB, BP, LOC)
+
 /* Streamer hooks.  */
 extern struct streamer_hooks streamer_hooks;