CPROP and spec2000 slowdown in mid february

[Richard Kenner]

    In my previous experiments this turned out to be neccesary, since
    certain backends require insns to be in non-canonical form. This may
    be considered as bug in the backend tought.

Yes, they are.

    The function recurses by calling simplify_gen_* familly of
    fuctions. When it reach something that don't have such function, it
    just stops recursing and doing substitutions.  This does include the
    MEM, SUBREG, SIGN_EXTEND and some other RTX constructs we would
    probably want to handle.

Oh, that's just a matter of adding that code.  What's there is most
definitely meant to be preliminary!

    OK. I believed that you wanted to replace current way of doing
    substituations on RTX stream by generating new RTX with modified
    content, as current simplify_* functions does.

Yes, but that's only a very minor change in the way substitution is
done.  Given how quickly we can nnow allocate an rtx, I think the
performance difference will be negligable and made up for by removing
the code that deals with the subst table.