Regression due to tree loop opt / expand weirdness

[Paolo Bonzini]

> could you please explain in more detail what you mean by "wrong"?  It
> preserves semantics of the program (unless there is some weird property
> of pointers I am not aware of).

I'll try to answer since your timezone is more similar to mine than to 
Richard's.

Since expr.c seemed to dislike doing operations on pointers in modes 
different from Pmode, many people said in the other thread that your 
optimization is not respecting some invariant that the expander expects.

Paolo