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[PATCH] Line map table allocation


Here's a line-map patch to make the new_linemap logic simpler. On the modules branch I need to allocate blocks of linemaps, and found the current allocation scheme a little confusing to adjust. This'll make that subsequent change simpler.

While there, I set the default allocator (xmalloc) in the init routine, rather than check it for each allocation. I doubt the loss of a devirtualization possibility is significant (we're doing allocation wrong if it is).

booted & tested on x86_64-linux

ok?

nathan
--
Nathan Sidwell
2018-08-06  Nathan Sidwell  <nathan@acm.org>

	* line-map.c: (linemap_init): Set default allocator here.
	(new_linemap): Rather than here.  Refactor allocation logic.

Index: line-map.c
===================================================================
--- line-map.c	(revision 263332)
+++ line-map.c	(working copy)
@@ -346,6 +346,8 @@ linemap_init (struct line_maps *set,
 #else
   new (set) line_maps();
 #endif
+  /* Set default allocator.  */
+  set->reallocator = (line_map_realloc) xrealloc;
   set->highest_location = RESERVED_LOCATION_COUNT - 1;
   set->highest_line = RESERVED_LOCATION_COUNT - 1;
   set->location_adhoc_data_map.htab =
@@ -376,81 +378,58 @@ linemap_check_files_exited (struct line_
 static struct line_map *
 new_linemap (struct line_maps *set,  source_location start_location)
 {
-  struct line_map *result;
-  bool macro_map_p = start_location >= LINE_MAP_MAX_LOCATION;
+  bool macro_p = start_location >= LINE_MAP_MAX_LOCATION;
+  unsigned alloc = LINEMAPS_ALLOCATED (set, macro_p);
+  unsigned used = LINEMAPS_USED (set, macro_p);
 
-  if (LINEMAPS_USED (set, macro_map_p) == LINEMAPS_ALLOCATED (set, macro_map_p))
+  if (used == alloc)
     {
-      /* We ran out of allocated line maps. Let's allocate more.  */
-      size_t alloc_size;
-
-      /* Cast away extern "C" from the type of xrealloc.  */
-      line_map_realloc reallocator = (set->reallocator
-				      ? set->reallocator
-				      : (line_map_realloc) xrealloc);
-      line_map_round_alloc_size_func round_alloc_size =
-	set->round_alloc_size;
-
-      size_t map_size = (macro_map_p
-			 ? sizeof (line_map_macro)
-			 : sizeof (line_map_ordinary));
+      /* We need more space!  */
+      if (!alloc)
+	alloc = 128;
+      alloc *= 2;
+
+      size_t map_size;
+      void *buffer;
+      if (macro_p)
+	{
+	  map_size = sizeof (line_map_macro);
+	  buffer = set->info_macro.maps;
+	}
+      else
+	{
+	  map_size = sizeof (line_map_ordinary);
+	  buffer = set->info_ordinary.maps;
+	}
 
       /* We are going to execute some dance to try to reduce the
 	 overhead of the memory allocator, in case we are using the
 	 ggc-page.c one.
 	 
 	 The actual size of memory we are going to get back from the
-	 allocator is the smallest power of 2 that is greater than the
-	 size we requested.  So let's consider that size then.  */
-
-      alloc_size =
-	(2 * LINEMAPS_ALLOCATED (set, macro_map_p) +  256)
-	* map_size;
-
-      /* Get the actual size of memory that is going to be allocated
-	 by the allocator.  */
-      alloc_size = round_alloc_size (alloc_size);
+	 allocator may well be larger than what we ask for.  Use this
+	 hook to find what that size is.  */
+      size_t alloc_size = set->round_alloc_size (alloc * map_size);
 
       /* Now alloc_size contains the exact memory size we would get if
 	 we have asked for the initial alloc_size amount of memory.
 	 Let's get back to the number of macro map that amounts
 	 to.  */
-      LINEMAPS_ALLOCATED (set, macro_map_p) =
-	alloc_size / map_size;
-
-      /* And now let's really do the re-allocation.  */
-      if (macro_map_p)
-	{
-	  set->info_macro.maps
-	    = (line_map_macro *) (*reallocator) (set->info_macro.maps,
-						 (LINEMAPS_ALLOCATED (set, macro_map_p)
-						  * map_size));
-	  result = &set->info_macro.maps[LINEMAPS_USED (set, macro_map_p)];
-	}
-      else
-	{
-	  set->info_ordinary.maps =
-	    (line_map_ordinary *) (*reallocator) (set->info_ordinary.maps,
-						  (LINEMAPS_ALLOCATED (set, macro_map_p)
-						   * map_size));
-	  result = &set->info_ordinary.maps[LINEMAPS_USED (set, macro_map_p)];
-	}
-      memset (result, 0,
-	      ((LINEMAPS_ALLOCATED (set, macro_map_p)
-		- LINEMAPS_USED (set, macro_map_p))
-	       * map_size));
-    }
-  else
-    {
-      if (macro_map_p)
-	result = &set->info_macro.maps[LINEMAPS_USED (set, macro_map_p)];
+      unsigned num_maps = alloc_size / map_size;
+      buffer = set->reallocator (buffer, num_maps * map_size);
+      memset ((char *)buffer + used * map_size, 0, (num_maps - used) * map_size);
+      if (macro_p)
+	set->info_macro.maps = (line_map_macro *)buffer;
       else
-	result = &set->info_ordinary.maps[LINEMAPS_USED (set, macro_map_p)];
+	set->info_ordinary.maps = (line_map_ordinary *)buffer;
+      LINEMAPS_ALLOCATED (set, macro_p) = num_maps;
     }
 
-  result->start_location = start_location;
+  line_map *result = (macro_p ? (line_map *)&set->info_macro.maps[used]
+		      : (line_map *)&set->info_ordinary.maps[used]);
+  LINEMAPS_USED (set, macro_p)++;
 
-  LINEMAPS_USED (set, macro_map_p)++;
+  result->start_location = start_location;
 
   return result;
 }

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