Language-independent functions-as-trees representation

[Mark Mitchell]

> Why?  We don't currently share expressions in RTL; why would we want to do
> so in SIMPLE?

Maybe this will make more sense after my other comment below.

Besides that, it makes things like rtx_equal_p simple/faster to implement,
and could save tons of memory.

> Sorry, I don't follow.  Most computations care very much about where they
> are in the control flow; if I move computations about arbitrarily, their
> values will tend to change.  The value of "x + y" is different before and
> after I increment x.  It's the job of CSE to recognize when we can share
> values between multiple instances of an expression.

I was implicitly (sorry!) in SSA form.

-- 
Mark Mitchell                mark@codesourcery.com
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