Warn about virtual table mismatches

[Jan Hubicka <hubicka at ucw dot cz>]

Hi,
this patch implements warning when we merge two virtual tables that do not
match.  It compares the size and also go into fields.  I had to implement my
own comparsion code, since the vtables may subtly differ - in RTTI and also I
need to do so during DECL merging (since we will forget about the decl then)

Here is an example of real ODR violation in bugzilla it finds.
../../dist/include/mozilla/a11y/DocAccessible.h:40:0: warning: type ïstruct DocAccessibleï violates one definition rule [enabled by default]
 class DocAccessible : public HyperTextAccessibleWrap,
 ^
/aux/hubicka/firefox/accessible/src/generic/DocAccessible.h:40:0: note: a type with the same name but different virtual table is defined in another translation unit
 class DocAccessible : public HyperTextAccessibleWrap,
 ^
/aux/hubicka/firefox/accessible/src/generic/DocAccessible.cpp:1232:0: note: the first different method is ïHandleAccEventï
 DocAccessible::HandleAccEvent(AccEvent* aEvent)
 ^
/aux/hubicka/firefox/accessible/src/atk/AccessibleWrap.cpp:956:0: note: a conflicting method is ïHandleAccEventï
 AccessibleWrap::HandleAccEvent(AccEvent* aEvent)
 ^

The patch is not terribly pretty, but does the job.  I will wait for few
days for comments/suggestins and then plan to commit it.

	PR lto/59468
	* lto/lto-symtab.c (lto_symtab_prevailing_decl): Check
	virtual tables for ODR violations.
	* ipa-devirt.c (compare_virtual_tables): New function.
	* ipa-utils.h (compare_virtual_tables): Declare.
Index: lto/lto-symtab.c
===================================================================
--- lto/lto-symtab.c	(revision 207702)
+++ lto/lto-symtab.c	(working copy)
@@ -679,5 +679,13 @@ lto_symtab_prevailing_decl (tree decl)
   if (!ret)
     return decl;
 
+  /* Check and report ODR violations on virtual tables.  */
+  if (decl != ret->decl && DECL_VIRTUAL_P (decl))
+    {
+      compare_virtual_tables (ret->decl, decl);
+      /* We are done with checking and DECL will die after merigng.  */
+      DECL_VIRTUAL_P (decl) = 0;
+    }
+
   return ret->decl;
 }
Index: ipa-devirt.c
===================================================================
--- ipa-devirt.c	(revision 207702)
+++ ipa-devirt.c	(working copy)
@@ -1675,6 +1673,101 @@ update_type_inheritance_graph (void)
 }
 
 
+/* Compare two virtual tables, PREVAILING and VTABLE and output ODR
+   violation warings.  */
+
+void
+compare_virtual_tables (tree prevailing, tree vtable)
+{
+  tree init1 = DECL_INITIAL (prevailing), init2 = DECL_INITIAL (vtable);
+  if (init1 == init2)
+    return;
+  if (init2 == error_mark_node)
+    return;
+  /* Be sure to keep virtual table contents even for external
+     vtables when they are available.  */
+  if (init1 == error_mark_node || !init1)
+    {
+      DECL_INITIAL (prevailing) = DECL_INITIAL (vtable);
+      return;
+    }
+  if (!init2 && DECL_EXTERNAL (vtable))
+    return;
+  if (DECL_VIRTUAL_P (prevailing) && init1 && init2
+      && CONSTRUCTOR_NELTS (init1) == CONSTRUCTOR_NELTS (init2))
+    {
+      unsigned i;
+      tree field1, field2;
+      tree val1, val2;
+      bool matched = true;
+
+      FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (init1),
+				 i, field1, val1)
+	{
+	  gcc_assert (!field1);
+	  field2 = CONSTRUCTOR_ELT (init2, i)->index;
+	  val2 = CONSTRUCTOR_ELT (init2, i)->value;
+	  gcc_assert (!field2);
+	  if (val2 == val1)
+	    continue;
+	  STRIP_NOPS (val1);
+	  STRIP_NOPS (val2);
+	  /* Unwind
+	      val <addr_expr type <pointer_type>
+	       readonly constant
+	       arg 0 <mem_ref type <pointer_type __vtbl_ptr_type>
+		   readonly
+		   arg 0 <addr_expr type <pointer_type>
+		       arg 0 <var_decl _ZTCSd0_Si>> arg 1 <integer_cst 24>>> */
+
+	  while ((TREE_CODE (val1) == MEM_REF
+	          && TREE_CODE (val2) == MEM_REF
+		  && (TREE_OPERAND (val1, 1)
+		      == TREE_OPERAND (val2, 1)))
+		 || (TREE_CODE (val1) == ADDR_EXPR
+		     && TREE_CODE (val2) == ADDR_EXPR))
+	    {
+	      val1 = TREE_OPERAND (val1, 0);
+	      val2 = TREE_OPERAND (val2, 0);
+	    }
+	  if (val1 == val2)
+	    continue;
+	  if (TREE_CODE (val2) == ADDR_EXPR)
+	    {
+	      tree tmp = val1;
+	      val1 = val2;
+	      val2 = tmp;
+            }
+	  /* Allow combining RTTI and non-RTTI is OK.  */
+	  if (TREE_CODE (val1) == ADDR_EXPR
+	      && TREE_CODE (TREE_OPERAND (val1, 0)) == VAR_DECL
+	      && !DECL_VIRTUAL_P (TREE_OPERAND (val1, 0))
+	      && TREE_CODE (val2) == NOP_EXPR
+	      && integer_zerop (TREE_OPERAND (val2, 0)))
+	    continue;
+	  if (TREE_CODE (val1) == NOP_EXPR
+	      && TREE_CODE (val2) == NOP_EXPR
+	      && integer_zerop (TREE_OPERAND (val1, 0))
+	      && integer_zerop (TREE_OPERAND (val2, 0)))
+	    continue;
+	  if (DECL_P (val1) && DECL_P (val2)
+	      && DECL_ASSEMBLER_NAME (val1) == DECL_ASSEMBLER_NAME (val2))
+	    continue;
+	  matched = false;
+	  break;
+	}
+      if (matched)
+	return;
+    }
+  odr_violation_reported = true;
+  if (warning_at (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (vtable))), 0,
+		     "type %qD violates one definition rule  ",
+		     DECL_CONTEXT (vtable)))
+    inform (DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (prevailing))),
+	    "a type with the same name but different virtual table is "
+	    "defined in another translation unit");
+}
+
 /* Return true if N looks like likely target of a polymorphic call.
    Rule out cxa_pure_virtual, noreturns, function declared cold and
    other obvious cases.  */
Index: ipa-utils.h
===================================================================
--- ipa-utils.h	(revision 207702)
+++ ipa-utils.h	(working copy)
@@ -92,6 +92,7 @@ bool get_polymorphic_call_info_from_inva
 					       tree, tree, HOST_WIDE_INT);
 tree vtable_pointer_value_to_binfo (tree t);
 bool vtable_pointer_value_to_vtable (tree, tree *, unsigned HOST_WIDE_INT *);
+void compare_virtual_tables (tree, tree);
 
 /* Return vector containing possible targets of polymorphic call E.
    If FINALP is non-NULL, store true if the list is complette.