Re: Proposed major change to combine

[Torbjorn Granlund <tege at swox dot com>]

kenner@vlsi1.ultra.nyu.edu (Richard Kenner) writes:

  I'd like to propose getting rid of the mechanisms where it tries to
  substitute things inside RTL and instead always make new RTL.  This costs
  most memory, but is less of an issue with GC.
  
  Aside from making the code cleaner, the major advantage of this is that then
  all the simplification code in combine.c can be moved into simplify-rtx.c and
  all the other passes will benefit from it.
  
  Any comments/objections?
  
Sounds good to me.

I think it would also be good to make combine use rtx_cost for
determining which rewrites to perform.  By requiring each change to
decrease the rtx_cost, we could do things recursively without risk of
non-termination.

The would open to allow define_split that generate more insns than
they "consume".

-- 
Torbjörn