On Wed, Aug 10, 2016 at 08:51:32AM +1000, kugan wrote:
> I see it now. The problem is we are just looking at (-1) being in the ops
> list for passing changed to rewrite_expr_tree in the case of multiplication
> by negate. If we have combined (-1), as in the testcase, we will not have
> the (-1) and will pass changed=false to rewrite_expr_tree.
>
> We should set changed based on what happens in try_special_add_to_ops.
> Attached patch does this. Bootstrap and regression testing are ongoing. Is
> this OK for trunk if there is no regression.
I think the bug is elsewhere. In particular in
undistribute_ops_list/zero_one_operation/decrement_power.
All those look problematic in this regard, they change RHS of statements
to something that holds a different value, while keeping the LHS.
So, generally you should instead just add a new stmt next to the old one,
and adjust data structures (replace the old SSA_NAME in some ->op with
the new one). decrement_power might be a problem here, dunno if all the
builtins are const in all cases that DSE would kill the old one,
Richard, any preferences for that? reset flow sensitive info + reset debug
stmt uses, or something different? Though, replacing the LHS with a new
anonymous SSA_NAME might be needed too, in case it is before SSA_NAME of a
user var that doesn't yet have any debug stmts.
Jakub
