re PR middle-end/83215 (C++: struct with char-array assumed to alias with everything)

2018-11-20  Richard Biener  <rguenther@suse.de>

	PR middle-end/83215
	* alias.c (component_uses_parent_alias_set_from): Remove
	alias-set zero and TYPE_TYPELESS_STORAGE case both already
	handled in other ways.

	* g++.dg/tree-ssa/pr83215.C: New testcase.

From-SVN: r266305

gcc/ChangeLog

 2018-11-20  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/83215
+	* alias.c (component_uses_parent_alias_set_from): Remove
+	alias-set zero and TYPE_TYPELESS_STORAGE case both already
+	handled in other ways.
+
+2018-11-20  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88087
 	* tree-ssa-pre.c (create_expression_by_pieces): Re-materialize
 	call fntype.

gcc/alias.c

@@ -601,8 +601,7 @@ objects_must_conflict_p (tree t1, tree t2)
 /* Return the outermost parent of component present in the chain of
    component references handled by get_inner_reference in T with the
    following property:
-     - the component is non-addressable, or
-     - the parent has alias set zero,
+     - the component is non-addressable
    or NULL_TREE if no such parent exists.  In the former cases, the alias
    set of this parent is the alias set that must be used for T itself.  */
 
@@ -611,10 +610,6 @@ component_uses_parent_alias_set_from (const_tree t)
 {
   const_tree found = NULL_TREE;
 
-  if (AGGREGATE_TYPE_P (TREE_TYPE (t))
-      && TYPE_TYPELESS_STORAGE (TREE_TYPE (t)))
-    return const_cast <tree> (t);
-
   while (handled_component_p (t))
     {
       switch (TREE_CODE (t))
@@ -652,9 +647,6 @@ component_uses_parent_alias_set_from (const_tree t)
 	  gcc_unreachable ();
 	}
 
-      if (get_alias_set (TREE_TYPE (TREE_OPERAND (t, 0))) == 0)
-	found = t;
-
       t = TREE_OPERAND (t, 0);
     }
  

gcc/testsuite/ChangeLog

+2018-11-20  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/83215
+	* g++.dg/tree-ssa/pr83215.C: New testcase.
+
 2018-11-20  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gcc.c-torture/execute/20181120-1.c: New test.

gcc/testsuite/g++.dg/tree-ssa/pr83215.C

+// { dg-do compile }
+// { dg-options "-O2 -fdump-tree-fre1" }
+
+struct mytest
+{
+  float a;
+  char buf[256];
+};
+
+int foo(mytest *m, int *i)
+{
+  int tmp = *i;
+  m->a = 10.0f;
+  return tmp + *i;
+}
+
+// we should be able to CSE *i despite mytest having a cbar[] buffer
+// and thus being subject to TYPE_TYPELESS_STORAGE
+// { dg-final { scan-tree-dump-times "\\*i" 1 "fre1" } }