[PATCH 0/50] Faster for_each_rtx-like iterators

[Richard Sandiford <rdsandiford at googlemail dot com>]

In May I posted an RFC about a worklist-based replacement for for_each_rtx:
https://gcc.gnu.org/ml/gcc-patches/2014-05/msg00435.html (see there for
rationale).

This series is the first part of the process.  It adds the new iterators
and converts all for_each_rtx users in generic code.  If these patches
are OK, the remaining changes would be:

(1) do the same for config/
(2) get rid of for_each_rtx
(3) (optionally) convert recursive format walkers to use the new
    iterators too, if that makes things better

I have local patches for some of (3) but they're a lower priority than
(1) or (2).

I think the only changes I made since last time are to address the
feedback from the RFC.

Bootstrapped & regression-tested on x86_64-linux-gnu.  Also tested by
making sure there were no assembly differences for gcc.dg, g++.dg and
gcc.c-torture for:

  x86_64-linux-gnu
  i686-linux-gnu
  sh64-linux-gnu
  powerpc64-linux-gnu
  mips64-linux-gnu
  hppa64-hp-hpux11.23
  aarch64-linux-gnueabi
  arm-linux-gnueabi

which includes auto-inc/dec targets and a user of bt-load.c (sh64-elf).

Many of the patches are pretty mechanical conversions to FOR_EACH_SUBRTX.
I've only added a covering note if there's something unusual going on.