re PR tree-optimization/77745 (Inconsistent application of aliasing rules)

2016-09-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/77745
	* tree-ssa-pre.c (eliminate_dom_walker::before_dom_children):
	When removing redundant stores make sure to check compatibility
	of the TBAA state for downstream accesses.
	* tree-ssa-sccvn.c (visit_reference_op_store): Likewise for when
	value-numbering virtual operands for store matches.

	* g++.dg/torture/pr77745.C: New testcase.

From-SVN: r240534

gcc/ChangeLog

+2016-09-27  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/77745
+	* tree-ssa-pre.c (eliminate_dom_walker::before_dom_children):
+	When removing redundant stores make sure to check compatibility
+	of the TBAA state for downstream accesses.
+	* tree-ssa-sccvn.c (visit_reference_op_store): Likewise for when
+	value-numbering virtual operands for store matches.
+
 2016-09-27  Oleg Endo  <olegendo@gcc.gnu.org>
 
 	PR target/51244

gcc/testsuite/ChangeLog

 2016-09-27  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/77745
+	* g++.dg/torture/pr77745.C: New testcase.
+
+2016-09-27  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/77478
 	* gcc.dg/torture/pr77478.c: New testcase.
 

gcc/testsuite/g++.dg/torture/pr77745.C

+// { dg-do run }
+
+inline void* operator new(__SIZE_TYPE__, void* __p) noexcept { return __p; }
+
+long foo(char *c1, char *c2)
+{
+  long *p1 = new (c1) long;
+  *p1 = 100;
+  long long *p2 = new (c2) long long;
+  *p2 = 200;
+  long *p3 = new (c2) long;
+  *p3 = 200;
+  return *p1;
+}
+int main()
+{
+  union {
+      char c;
+      long l;
+      long long ll;
+  } c;
+  if (foo(&c.c, &c.c) != 200)
+    __builtin_abort();
+}

gcc/tree-ssa-pre.c

@@ -4431,26 +4431,34 @@ eliminate_dom_walker::before_dom_children (basic_block b)
 	  && !is_gimple_reg (gimple_assign_lhs (stmt))
 	  && (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME
 	      || is_gimple_min_invariant (gimple_assign_rhs1 (stmt))))
-        {
-          tree val;
+	{
+	  tree val;
 	  tree rhs = gimple_assign_rhs1 (stmt);
-          val = vn_reference_lookup (gimple_assign_lhs (stmt),
-                                     gimple_vuse (stmt), VN_WALK, NULL, false);
-          if (TREE_CODE (rhs) == SSA_NAME)
-            rhs = VN_INFO (rhs)->valnum;
-          if (val
-              && operand_equal_p (val, rhs, 0))
-            {
-              if (dump_file && (dump_flags & TDF_DETAILS))
-                {
-                  fprintf (dump_file, "Deleted redundant store ");
-                  print_gimple_stmt (dump_file, stmt, 0, 0);
-                }
+	  vn_reference_t vnresult;
+	  val = vn_reference_lookup (lhs, gimple_vuse (stmt), VN_WALKREWRITE,
+				     &vnresult, false);
+	  if (TREE_CODE (rhs) == SSA_NAME)
+	    rhs = VN_INFO (rhs)->valnum;
+	  if (val
+	      && operand_equal_p (val, rhs, 0))
+	    {
+	      /* We can only remove the later store if the former aliases
+		 at least all accesses the later one does.  */
+	      alias_set_type set = get_alias_set (lhs);
+	      if (vnresult->set == set
+		  || alias_set_subset_of (set, vnresult->set))
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    {
+		      fprintf (dump_file, "Deleted redundant store ");
+		      print_gimple_stmt (dump_file, stmt, 0, 0);
+		    }
 
-              /* Queue stmt for removal.  */
-              el_to_remove.safe_push (stmt);
-	      continue;
-            }
+		  /* Queue stmt for removal.  */
+		  el_to_remove.safe_push (stmt);
+		  continue;
+		}
+	    }
 	}
 
       /* If this is a control statement value numbering left edges

gcc/tree-ssa-sccvn.c

@@ -3599,13 +3599,21 @@ visit_reference_op_store (tree lhs, tree op, gimple *stmt)
      Otherwise, the vdefs for the store are used when inserting into
      the table, since the store generates a new memory state.  */
 
-  result = vn_reference_lookup (lhs, vuse, VN_NOWALK, NULL, false);
-
+  result = vn_reference_lookup (lhs, vuse, VN_NOWALK, &vnresult, false);
   if (result)
     {
       if (TREE_CODE (result) == SSA_NAME)
 	result = SSA_VAL (result);
       resultsame = expressions_equal_p (result, op);
+      if (resultsame)
+	{
+	  /* If the TBAA state isn't compatible for downstream reads
+	     we cannot value-number the VDEFs the same.  */
+	  alias_set_type set = get_alias_set (lhs);
+	  if (vnresult->set != set
+	      && ! alias_set_subset_of (set, vnresult->set))
+	    resultsame = false;
+	}
     }
 
   if ((!result || !resultsame)