re PR c++/22488 (C++ frontend generates RECORD_TYPEs with overlapping FIELD_DECLs)

2005-10-06  Daniel Berlin  <dberlin@dberlin.org>

	Fix PR tree-optimization/22488
	* tree-ssa-structalias.c (check_for_overlaps): New function.
	(create_variable_info_for): Use it.

From-SVN: r105052

gcc/ChangeLog

+2005-10-06  Daniel Berlin  <dberlin@dberlin.org>
+	
+	Fix PR tree-optimization/22488
+	* tree-ssa-structalias.c (check_for_overlaps): New function.
+	(create_variable_info_for): Use it.
+
 2005-10-06  Richard Henderson  <rth@redhat.com>
 
 	PR debug/24070

gcc/testsuite/g++.dg/tree-ssa/pr22488.C

+// PR tree-optimization/22488
+// This testcase is really a C++ FE bug in represnting virtual inheritance
+// It gives the appearance to the middle end that the fields exist twice
+// which resulted in a very confused structure analyzer
+// { dg-do compile }
+// { dg-options "-O" }
+struct X
+{
+    int i0, i1;
+      char c;
+};
+
+struct A
+{
+    int i;
+      char c0, c1;
+
+        virtual ~A();
+};
+
+struct B : virtual A {};
+
+struct C : B
+{
+    X x;
+
+      void bar(X y) { x = y; }
+};
+
+void foo()
+{
+    C().bar(X());
+}

gcc/tree-ssa-structalias.c

@@ -3020,6 +3020,26 @@ make_constraint_to_anything (varinfo_t vi)
   process_constraint (new_constraint (lhs, rhs));
 }
 
+
+/* Return true if FIELDSTACK contains fields that overlap. 
+   FIELDSTACK is assumed to be sorted by offset.  */
+
+static bool
+check_for_overlaps (VEC (fieldoff_s,heap) *fieldstack)
+{
+  fieldoff_s *fo = NULL;
+  unsigned int i;
+  unsigned int lastoffset = ~0;
+
+  for (i = 0; VEC_iterate (fieldoff_s, fieldstack, i, fo); i++)
+    {
+      if (fo->offset == lastoffset)
+	return true;
+      lastoffset = fo->offset;
+    }
+  return false;
+}
+
 /* Create a varinfo structure for NAME and DECL, and add it to VARMAP.
    This will also create any varinfo structures necessary for fields
    of DECL.  */
@@ -3104,8 +3124,16 @@ create_variable_info_for (tree decl, const char *name)
 	 which will make notokay = true.  In that case, we are going to return
 	 without creating varinfos for the fields anyway, so sorting them is a
 	 waste to boot.  */
-      if (!notokay)	
-	sort_fieldstack (fieldstack);
+      if (!notokay)
+	{	
+	  sort_fieldstack (fieldstack);
+	  /* Due to some C++ FE issues, like PR 22488, we might end up
+	     what appear to be overlapping fields even though they,
+	     in reality, do not overlap.  Until the C++ FE is fixed,
+	     we will simply disable field-sensitivity for these cases.  */
+	  notokay = check_for_overlaps (fieldstack);
+	}
+      
       
       if (VEC_length (fieldoff_s, fieldstack) != 0)
 	fo = VEC_index (fieldoff_s, fieldstack, 0);