Loop optimizer issues

[Richard Kenner]

    libcalls are a disgusting hack and I can't see any way I'd consider
    tree-ssa a success if libcalls survive in the long term.

I don't understand the relationship between tree-ssa and libcalls.
The only way you can eliminate libcalls without losing optimization is
to *guarantee* that any possible optimization that could be done with
them can be done at a higher level.  Why would you want to do that?

I can easily envision some machine where some addressing calculation
requires a libcall and in such a machine they will always survive to the 
RTL level.