Re: Proposed major change to combine

[Jeffrey A Law <law at redhat dot com>]

  In message <10103081452.AA03138@vlsi1.ultra.nyu.edu>you write:
  > 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.
Hopefully some of the simplification code could then be shared.  It's
really kind of silly to have two completely different sets of routines to
simplify hunks of RTL in roughly the same way.

It's also conceptually cleaner, and given the state of our compiler, I'm
willing to give up some memory usage to get a compiler that we can understand.

If the memory usage really is an issue after measurement, then we can
probably look at running the collector after we've finished processing
a basic block or extended basic block or after we've created N new hunks
of RTL.


jeff