Getting rid of GET_RTX_CLASS?

[Paolo Bonzini]

> >> I'd like to turn rtx classes from characters to enums.  Would this be
> >> feasible?  Interesting?  It may result in slight compile time speedups,
> >> also.
> 
> Compact switch tables, presumably.

Yes; lookup tables instead of binary searching.  I also hope to learn something 
while reading the code -- low priority things are good for beginners (like me).

I'd also like to introduce new predicates (like OBJECT_P I already have a patch 
for) that express conditions like

  GET_RTX_CLASS (x) == '2'
  || GET_RTX_CLASS (x) == '<'
  || GET_RTX_CLASS (x) == 'c'

that abound in cse and other places that may be put under a diet after tree-ssa 
is merged.  These could become GET_RTX_CLASS (x) >= BINARY && GET_RTX_CLASS (x) 
<= BINARY_COMMUTATIVE (cheaper) as long as this is found only once, in rtl.h.

I suspect that an inordinate amount of time is spent in rtl.h if my very simple 
OBJECT_P patch had a 1% gain on bootstrap time.

Paolo

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