[Bug tree-optimization/57303] [4.7/4.8/4.9 Regression] struct miscompiled at -O1 and above

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57303

--- Comment #6 from Marc Glisse <glisse at gcc dot gnu.org> ---
I wonder if, in addition to fixing the sink pass, we should add an optimization
like the following (it passes bootstrap+testsuite, but I am not so sure where
it should go and what it should look like exactly).

--- gimple-fold.c    (revision 199093)
+++ gimple-fold.c    (working copy)
@@ -1174,20 +1174,27 @@ fold_stmt_1 (gimple_stmt_iterator *gsi,
     if ((commutative_tree_code (subcode)
          || commutative_ternary_tree_code (subcode))
         && tree_swap_operands_p (gimple_assign_rhs1 (stmt),
                      gimple_assign_rhs2 (stmt), false))
       {
         tree tem = gimple_assign_rhs1 (stmt);
         gimple_assign_set_rhs1 (stmt, gimple_assign_rhs2 (stmt));
         gimple_assign_set_rhs2 (stmt, tem);
         changed = true;
       }
+    /* Remove *p = *p.  */
+    if (!inplace && TREE_CODE_CLASS (subcode) == tcc_reference
+        && operand_equal_p (lhs, gimple_assign_rhs1 (stmt), 0))
+      {
+        gsi_remove (gsi, true);
+        return true;
+      }
     new_rhs = fold_gimple_assign (gsi);
     if (new_rhs
         && !useless_type_conversion_p (TREE_TYPE (lhs),
                        TREE_TYPE (new_rhs)))
       new_rhs = fold_convert (TREE_TYPE (lhs), new_rhs);
     if (new_rhs
         && (!inplace
         || get_gimple_rhs_num_ops (TREE_CODE (new_rhs)) < old_num_ops))
       {
         gimple_assign_set_rhs_from_tree (gsi, new_rhs);