re PR tree-optimization/59287 (points-to analysis confused by union accesses)

2013-11-26  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/59287
	* tree-ssa-structalias.c (get_constraint_for_component_ref):
	Remove no longer necessary special-casing of union accesses.

	* gcc.dg/tree-ssa/alias-29.c: New testcase.

From-SVN: r205380

gcc/ChangeLog

 2013-11-26  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/59287
+	* tree-ssa-structalias.c (get_constraint_for_component_ref):
+	Remove no longer necessary special-casing of union accesses.
+
+2013-11-26  Richard Biener  <rguenther@suse.de>
+
 	* pretty-print.c (output_buffer::~output_buffer): Really
 	free the obstacks.
 

gcc/testsuite/ChangeLog

+2013-11-26  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/59287
+	* gcc.dg/tree-ssa/alias-29.c: New testcase.
+
 2013-11-25  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/54485

gcc/testsuite/gcc.dg/tree-ssa/alias-29.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+union X {
+    int i;
+    void *p;
+};
+void bar (int);
+
+int * __attribute__((noinline,noclone))
+baz (int *p) { return p; }
+
+void foo (union X *x)
+{
+  struct Y { int i; } ystruct = {};
+  ystruct.i = * baz (&ystruct.i);
+  bar (x->i);
+}
+
+/* DSE and then DCE should be able to remove all uses of ystruct.
+   Formerly the union access for the parameter to bar let 'anything'
+   escape which made the call to bar possibly use ystruct and thus
+   prevent the store to ystruct.i from being eliminated.  The call to
+   baz makes sure that ystruct has its address taken.  */
+
+/* { dg-final { scan-tree-dump-not "ystruct" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */

gcc/tree-ssa-structalias.c

@@ -3163,29 +3163,6 @@ get_constraint_for_component_ref (tree t, vec<ce_s> *results,
       return;
     }
 
-  /* Handle type-punning through unions.  If we are extracting a pointer
-     from a union via a possibly type-punning access that pointer
-     points to anything, similar to a conversion of an integer to
-     a pointer.  */
-  if (!lhs_p)
-    {
-      tree u;
-      for (u = t;
-	   TREE_CODE (u) == COMPONENT_REF || TREE_CODE (u) == ARRAY_REF;
-	   u = TREE_OPERAND (u, 0))
-	if (TREE_CODE (u) == COMPONENT_REF
-	    && TREE_CODE (TREE_TYPE (TREE_OPERAND (u, 0))) == UNION_TYPE)
-	  {
-	    struct constraint_expr temp;
-
-	    temp.offset = 0;
-	    temp.var = anything_id;
-	    temp.type = ADDRESSOF;
-	    results->safe_push (temp);
-	    return;
-	  }
-    }
-
   t = get_ref_base_and_extent (t, &bitpos, &bitsize, &bitmaxsize);
 
   /* Pretend to take the address of the base, we'll take care of