[C++ patch] Reduce vtable alignment

[Jan Hubicka]

Hi,
compiling:

struct A
{
  virtual void foo(void) {};
  virtual void foo2(void) {};
  virtual void foo3(void) {};
  virtual void foo4(void) {};
  virtual void foo5(void) {};
} a;

give 32 byte alignment to the virtual table on i386, because we bump up
alignments of arrays to size of vector operations.  This is wasteful, since
virutal tables are never really accessed this way.

I am testing the following patch, OK if it passes?
The patch also removes apparently 20 years old hack for SPARC.

Honza
        * class.c (build_vtable): Force alignment of virtual tables
        to be pointer size only to save space.
Index: class.c
===================================================================
--- class.c     (revision 210521)
+++ class.c     (working copy)
@@ -768,11 +768,8 @@ build_vtable (tree class_type, tree name
   TREE_READONLY (decl) = 1;
   DECL_VIRTUAL_P (decl) = 1;
   DECL_ALIGN (decl) = TARGET_VTABLE_ENTRY_ALIGN;
+  DECL_USER_ALIGN (decl) = true;
   DECL_VTABLE_OR_VTT_P (decl) = 1;
-  /* At one time the vtable info was grabbed 2 words at a time.  This
-     fails on sparc unless you have 8-byte alignment.  (tiemann) */
-  DECL_ALIGN (decl) = MAX (TYPE_ALIGN (double_type_node),
-                          DECL_ALIGN (decl));
   set_linkage_according_to_type (class_type, decl);
   /* The vtable has not been defined -- yet.  */
   DECL_EXTERNAL (decl) = 1;