SSA usage question

[Richard Kenner]

    Implicit references cannot be put into SSA form, and thus cannot
    be put through the tree optimizer at all.  QED.

Since SSA talks about *assignments* and the implicit references are all
*uses* I don't understand your "proof" above.  Can you say more?

    That's what rtl did.  I don't see that we're really doing anything
    different.  Yes, we could do *better* if we figured out *some other*
    representation that preserved information longer, but I really don't
    believe we'll do significantly worse in the mean time.

No, the RTL structure kept the aliasing and alignment information intact.  We
knew which fields two references were to and if they were to different
fields, we knew they couldn't alias.  With your proposal, we lose that.  We
may be able to preserve some of this information, but it'll be much harder if
we collapse it all away.