>
> Err.  I think the way you implement that in reassoc is ad-hoc and not
> related to reassoc at all.
>
> In fact what reassoc is missing is to handle
>
>   -y * z * (-w) * x -> y * x * w * x
>
> thus optimize negates as if they were additional * -1 entries in a
> multiplication chain.  And
> then optimize a single remaining * -1 in the result chain to a negate.
>
> Then match.pd handles x + (-y) -> x - y (independent of -frounding-math btw).
>
> So no, this isn't ok as-is, IMHO you want to expand the multiplication ops chain
> pulling in the * -1 ops (if single-use, of course).
>

I agree. Here is the updated patch along what you suggested. Does this 
look better ?

Thanks,
Kugan