Hi Richard,

> I think it should have the same rank as op or op + 1 which is the current
> behavior.  Sth else doesn't work correctly here I think, like inserting the
> multiplication not near the definition of op.
>
> Well, the whole "clever insertion" logic is simply flawed.

What I meant to say was that the simple logic we have now wouldn’t
work. "clever logic" is knowing where exactly where it is needed and
inserting there.  I think thats what  you are suggesting below in a
simple to implement way.

> I'd say that ideally we would delay inserting the multiplication to
> rewrite_expr_tree time.  For example by adding a ops->stmt_to_insert
> member.
>

Here is an implementation based on above. Bootstrap on x86-linux-gnu
is OK. regression testing is ongoing.

Thanks,
Kugan

gcc/ChangeLog:

2016-05-20  Kugan Vivekanandarajah  <kugan.vivekanandarajah@linaro.org>

    * tree-ssa-reassoc.c (struct operand_entry): Add field stmt_to_insert.
    (add_to_ops_vec): Add stmt_to_insert.
    (add_repeat_to_ops_vec): Init stmt_to_insert.
    (transform_add_to_multiply): Remove mult_stmt insertion and add it
to ops vector.
    (get_ops): Init stmt_to_insert.
    (maybe_optimize_range_tests): Likewise.
    (rewrite_expr_tree): Insert  stmt_to_insert before use stmt.
    (rewrite_expr_tree_parallel): Likewise.