re PR tree-optimization/73434 (Wrong code with casting, branches and aliasing)

2016-08-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/73434
	* tree-ssa-sccvn.c (vn_reference_maybe_forwprop_address): Preserve
	TBAA info on the base when forwarding a non-invariant address.

	* gcc.dg/torture/pr73434.c: New testcase.

From-SVN: r239471

gcc/ChangeLog

+2016-08-15  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/73434
+	* tree-ssa-sccvn.c (vn_reference_maybe_forwprop_address): Preserve
+	TBAA info on the base when forwarding a non-invariant address.
+
 2016-08-15  Jakub Jelinek  <jakub@redhat.com>
 
 	* dwarf2out.c (struct checksum_attributes): Add

gcc/testsuite/ChangeLog

+2016-08-15  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/73434
+	* gcc.dg/torture/pr73434.c: New testcase.
+
 2016-08-15  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/72824

gcc/testsuite/gcc.dg/torture/pr73434.c

+/* { dg-do run } */
+
+typedef struct { unsigned char x; } A;
+typedef struct { unsigned char x; } B;
+
+int idx = 0;
+
+A objs[1] = {{0}};
+
+int main()
+{
+  B *b = (B*)&objs[idx];
+  b->x++;
+  if (b->x)
+    b->x = 0;
+  if (b->x)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-ssa-sccvn.c

@@ -1225,6 +1225,18 @@ vn_reference_maybe_forwprop_address (vec<vn_reference_op_s> *ops,
 	{
 	  auto_vec<vn_reference_op_s, 32> tem;
 	  copy_reference_ops_from_ref (TREE_OPERAND (addr, 0), &tem);
+	  /* Make sure to preserve TBAA info.  The only objects not
+	     wrapped in MEM_REFs that can have their address taken are
+	     STRING_CSTs.  */
+	  if (tem.length () >= 2
+	      && tem[tem.length () - 2].opcode == MEM_REF)
+	    {
+	      vn_reference_op_t new_mem_op = &tem[tem.length () - 2];
+	      new_mem_op->op0 = fold_convert (TREE_TYPE (mem_op->op0),
+					      new_mem_op->op0);
+	    }
+	  else
+	    gcc_assert (tem.last ().opcode == STRING_CST);
 	  ops->pop ();
 	  ops->pop ();
 	  ops->safe_splice (tem);