[commit/dwarf2] Allocate attributes inside the DIE

[Daniel Jacobowitz <drow at false dot org>]

Another performance-neutral update.  There's no need to allocate these
two items separately, since there's a 1:1 correspondence and we know
their fixed sizes at allocation time.  So I removed the indirection
and combined the allocations, shrinking struct die_info further
(though at least at the moment, the space savings do not matter;
they're inside the alignment constant of the obstack on a 64-bit
host).

Tested on x86_64-linux, committed.

-- 
Daniel Jacobowitz
CodeSourcery

2008-08-20  Daniel Jacobowitz  <dan@codesourcery.com>

	* dwarf2read.c (struct attribute): Move earlier.
	(struct die_info): Change attrs to a trailing array.
	(dwarf_alloc_die): Take the number of attributes.  Allocate space
	for them.
	(read_full_die): Update call to dwarf_alloc_die.  Do not manually
	allocate attributes.

---
 gdb/dwarf2read.c |   52 ++++++++++++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 24 deletions(-)

Index: src/gdb/dwarf2read.c
===================================================================
--- src.orig/gdb/dwarf2read.c	2008-08-10 11:10:07.000000000 -0400
+++ src/gdb/dwarf2read.c	2008-08-10 11:15:27.000000000 -0400
@@ -521,6 +521,22 @@ struct attr_abbrev
     enum dwarf_form form;
   };
 
+/* Attributes have a name and a value */
+struct attribute
+  {
+    enum dwarf_attribute name;
+    enum dwarf_form form;
+    union
+      {
+	char *str;
+	struct dwarf_block *blk;
+	unsigned long unsnd;
+	long int snd;
+	CORE_ADDR addr;
+      }
+    u;
+  };
+
 /* This data structure holds a complete die structure. */
 struct die_info
   {
@@ -528,7 +544,6 @@ struct die_info
     unsigned int abbrev;	/* Abbrev number */
     unsigned int offset;	/* Offset in .debug_info section */
     unsigned int num_attrs;	/* Number of attributes */
-    struct attribute *attrs;	/* An array of attributes */
 
     /* The dies in a compilation unit form an n-ary tree.  PARENT
        points to this die's parent; CHILD points to the first child of
@@ -538,22 +553,11 @@ struct die_info
     struct die_info *child;	/* Its first child, if any.  */
     struct die_info *sibling;	/* Its next sibling, if any.  */
     struct die_info *parent;	/* Its parent, if any.  */
-  };
 
-/* Attributes have a name and a value */
-struct attribute
-  {
-    enum dwarf_attribute name;
-    enum dwarf_form form;
-    union
-      {
-	char *str;
-	struct dwarf_block *blk;
-	unsigned long unsnd;
-	long int snd;
-	CORE_ADDR addr;
-      }
-    u;
+    /* An array of attributes, with NUM_ATTRS elements.  There may be
+       zero, but it's not common and zero-sized arrays are not
+       sufficiently portable C.  */
+    struct attribute attrs[1];
   };
 
 struct function_range
@@ -997,7 +1001,7 @@ static struct dwarf_block *dwarf_alloc_b
 
 static struct abbrev_info *dwarf_alloc_abbrev (struct dwarf2_cu *);
 
-static struct die_info *dwarf_alloc_die (struct dwarf2_cu *);
+static struct die_info *dwarf_alloc_die (struct dwarf2_cu *, int);
 
 static void initialize_cu_func_list (struct dwarf2_cu *);
 
@@ -6060,15 +6064,12 @@ read_full_die (struct die_info **diep, b
 	     abbrev_number,
 	     bfd_get_filename (abfd));
     }
-  die = dwarf_alloc_die (cu);
+  die = dwarf_alloc_die (cu, abbrev->num_attrs);
   die->offset = offset;
   die->tag = abbrev->tag;
   die->abbrev = abbrev_number;
 
   die->num_attrs = abbrev->num_attrs;
-  die->attrs = (struct attribute *)
-    obstack_alloc (&cu->comp_unit_obstack,
-		   die->num_attrs * sizeof (struct attribute));
 
   for (i = 0; i < abbrev->num_attrs; ++i)
     {
@@ -9448,12 +9449,15 @@ dwarf_alloc_abbrev (struct dwarf2_cu *cu
 }
 
 static struct die_info *
-dwarf_alloc_die (struct dwarf2_cu *cu)
+dwarf_alloc_die (struct dwarf2_cu *cu, int num_attrs)
 {
   struct die_info *die;
+  size_t size = sizeof (struct die_info);
+
+  if (num_attrs > 1)
+    size += (num_attrs - 1) * sizeof (struct attribute);
 
-  die = (struct die_info *)
-    obstack_alloc (&cu->comp_unit_obstack, sizeof (struct die_info));
+  die = (struct die_info *) obstack_alloc (&cu->comp_unit_obstack, size);
   memset (die, 0, sizeof (struct die_info));
   return (die);
 }