[Bug rtl-optimization/56590] New: Replace auto-inc-dec pass with generic address mode selection pass

["olegendo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56590

             Bug #: 56590
           Summary: Replace auto-inc-dec pass with generic address mode
                    selection pass
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: olegendo@gcc.gnu.org
            Target: sh*-*-*


At least on SH there are several address mode selection issues which I'd like
to group in this PR.

PR 54065
[SH] Prefer @(R0,Rn) addressing for floating-point load/store

PR 53911
[SH] Improve displacement addressing

PR 50749
Auto-inc-dec does not find subsequent contiguous mem accesses

PR 39423
[4.6/4.7/4.8 Regression] [SH] performance regression: lost mov @(disp,Rn)

PR 52049
SH Target: Inefficient constant address access

Based on my observations so far, I think the right thing to do is to replace
the current auto-inc-dec pass with a pass that optimizes address mode selection
in a more generic way, instead of just trying to find auto inc/dec
opportunities.

The basic idea is to look at all memory accesses in a function (or basic block
as a start) that share a base address and then try to select the cheapest
addressing modes for each memory access.  The current address cost target hook
can be used to determine the costs of a memory access with a particular
address.

I have already started working on such a replacement pass a while ago and would
like to first do a trial with the SH target.  Other targets might then also
pick it up if it seems beneficial to do so.