C++: Correct the size of construction vtables

[Daniel Jacobowitz <drow at false dot org>]

The attached testcase fails on arm-none-eabi.  I believe it will fail
on MIPS and PowerPC targets too, because those also turn on
-fsection-anchors.

build_ctor_vtbl_group first builds a decl with the wrong type, then
uses it to construct various other things and determine the proper
type, then sets the proper type.  At some point in this process
DECL_SIZE gets set and it is never recalculated.  So when
-fsection-anchors goes to lay out the anchored block, it thinks
this vtable is only the size of a single pointer.  Access to
everything else in the block is off by the delta.

Without -fsection-anchors I don't know if anything cares about the
size of this DECL.  It seems not, since it's been wrong for a
long time.

Bootstrapped and regression tested on x86_64-pc-linux-gnu (C, C++, and
Java since this is a front end change).  Also verified that it
fixes the testcase on ARM.  OK to commit?

-- 
Daniel Jacobowitz
CodeSourcery

2007-11-07  Daniel Jacobowitz  <dan@codesourcery.com>

	* class.c (build_ctor_vtbl_group): Lay out the new type and decl.

2007-11-07  Daniel Jacobowitz  <dan@codesourcery.com>

	* g++.dg/opt/anchor1.C: New.

Index: gcc/testsuite/g++.dg/opt/anchor1.C
===================================================================
--- gcc/testsuite/g++.dg/opt/anchor1.C	(revision 0)
+++ gcc/testsuite/g++.dg/opt/anchor1.C	(revision 0)
@@ -0,0 +1,59 @@
+// { dg-do run }
+// { dg-options "-O2" }
+
+// The size of the construction vtable for YFont in YCoreFont was not
+// updated to reflect its actual size.  On targets with section anchor
+// support, the vtable for YCoreFont was laid out immediately after
+// that, but the compiler thought it was about 40 bytes closer to the
+// anchor than it actually was.
+
+extern "C" void abort (void);
+
+class refcounted {
+public:
+    int __refcount;
+
+public:
+    refcounted(): __refcount(0) {};
+    virtual ~refcounted() {}
+};
+
+class YFont : public virtual refcounted {
+public:
+    virtual ~YFont() {}
+
+    virtual int ascent() const = 0;
+};
+
+struct XFontStruct {
+};
+
+class YCoreFont : public YFont {
+public:
+    YCoreFont(char const * name);
+    virtual ~YCoreFont();
+
+    virtual int ascent() const { return 2; }
+
+private:
+    XFontStruct * fFont;
+};
+
+YCoreFont::YCoreFont(char const * name) {
+}
+
+YCoreFont::~YCoreFont() {
+}
+
+int foo(YCoreFont *ycf)
+{
+  ycf->ascent ();
+}
+
+int main()
+{
+  YCoreFont ycf("");
+  if (foo(&ycf) != 2)
+    abort ();
+  return 0;
+}
Index: gcc/cp/class.c
===================================================================
--- gcc/cp/class.c	(revision 129944)
+++ gcc/cp/class.c	(working copy)
@@ -7006,7 +7006,10 @@ build_ctor_vtbl_group (tree binfo, tree 
   /* Figure out the type of the construction vtable.  */
   type = build_index_type (size_int (list_length (inits) - 1));
   type = build_cplus_array_type (vtable_entry_type, type);
+  layout_type (type);
   TREE_TYPE (vtbl) = type;
+  DECL_SIZE (vtbl) = DECL_SIZE_UNIT (vtbl) = NULL_TREE;
+  layout_decl (vtbl, 0);
 
   /* Initialize the construction vtable.  */
   CLASSTYPE_VTABLES (t) = chainon (CLASSTYPE_VTABLES (t), vtbl);