vtables patch 2/3: fold vtable refs that use COMPONENT_REFs

[Bernd Schmidt]

This is another preliminary piece. It teaches some folding code that
vtable references could contain COMPONENT_REFs and how to deal with that.

Bootstrapped and tested on x86_64-linux, both with and without the final
vtables patch. Ok?


Bernd


commit d1b84c0bbdb1816b7173dca29486bc88124e4641
Author: Bernd Schmidt <ber...@codesourcery.com>
Date:   Tue Apr 23 15:17:34 2013 +0200

    Allow virtual table refs to be COMPONENT_REFs
    
    This is a preparation patch for changing the C++ vtable layout.  It makes
    gimple-fold aware of how to fold a vtable reference that is a COMPONENT_REF.
    
          * gimple-fold.c (gimple_get_virt_method_for_binfo): Allow
          COMPONENT_REFs.

diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
index b9211a9..e2364bf 100644
--- a/gcc/gimple-fold.c
+++ b/gcc/gimple-fold.c
@@ -3118,16 +3118,25 @@ gimple_get_virt_method_for_binfo (HOST_WIDE_INT token, tree known_binfo)
   if (TREE_CODE (v) != ADDR_EXPR)
     return NULL_TREE;
   v = TREE_OPERAND (v, 0);
+  tree v_outer = v;
+  if (TREE_CODE (v_outer) == COMPONENT_REF)
+    {
+      tree field = TREE_OPERAND (v_outer, 1);
+      offset += tree_low_cst (DECL_FIELD_OFFSET (field), 1) * BITS_PER_UNIT;
+      offset += tree_low_cst (DECL_FIELD_BIT_OFFSET (field), 1);
+      v_outer = TREE_OPERAND (v_outer, 0);
+    }
 
-  if (TREE_CODE (v) != VAR_DECL
-      || !DECL_VIRTUAL_P (v)
-      || !DECL_INITIAL (v)
-      || DECL_INITIAL (v) == error_mark_node)
+  if (TREE_CODE (v_outer) != VAR_DECL
+      || !DECL_VIRTUAL_P (v_outer)
+      || !DECL_INITIAL (v_outer)
+      || DECL_INITIAL (v_outer) == error_mark_node)
     return NULL_TREE;
   gcc_checking_assert (TREE_CODE (TREE_TYPE (v)) == ARRAY_TYPE);
   size = tree_low_cst (TYPE_SIZE (TREE_TYPE (TREE_TYPE (v))), 1);
   offset += token * size;
-  fn = fold_ctor_reference (TREE_TYPE (TREE_TYPE (v)), DECL_INITIAL (v),
+  fn = fold_ctor_reference (TREE_TYPE (TREE_TYPE (v)),
+			    DECL_INITIAL (v_outer),
 			    offset, size, vtable);
   if (!fn || integer_zerop (fn))
     return NULL_TREE;