[Bug tree-optimization/81611] [8 Regression] gcc un-learned loop / post-increment optimization

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81611

--- Comment #24 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
Author: aoliva
Date: Wed Feb 28 05:25:34 2018
New Revision: 258053

URL: https://gcc.gnu.org/viewcvs?rev=258053&root=gcc&view=rev
Log:
[PR81611] turn inc-and-use-of-dead-orig into auto-inc

When the addressing modes available on the machine don't allow offsets
in addresses, odds are that post-increments will be represented in
trees and RTL as:

  y <= x + 1
  ... *(x) ...
  x <= y

so deal with it by turning such RTL as:

  (set y (plus x n))
  ... (mem x) ...

without intervening uses of y into

  (set y x)
  ... (mem (post_add y n)) ...

so as to create auto-inc addresses that we'd otherwise miss.


for  gcc/ChangeLog

        PR rtl-optimization/81611
        * auto-inc-dec.c (attempt_change): Move dead note from
        mem_insn if it's the next use of regno
        (find_address): Take address use of reg holding
        non-incremented value.  Add parm to limit search to the named
        reg only.
        (merge_in_block): Attempt to use a mem insn that is the next
        use of the original regno.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/auto-inc-dec.c