[Bug rtl-optimization/67864] New: [6 Regression] CSiBE size regression

[Bug rtl-optimization/67864] New: [6 Regression] CSiBE size regression

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67864

            Bug ID: 67864
           Summary: [6 Regression] CSiBE size regression
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
                CC: segher at kernel dot crashing.org
  Target Milestone: ---

http://gcc.opensuse.org/CSiBE/ shows a big size regression between r228310
(good)
and r228359 (bad).  Flags used are -Os -fgnu89-inline, suspect is


+2015-10-01  Segher Boessenkool  <segher@kernel.crashing.org>
+
+       * bb-reorder.c (reorder_basic_blocks): Use the algorithm selected
+       with flag_reorder_blocks_algorithm.
+       * common.opt (freorder-blocks-algorithm=): New flag.
+       (reorder_blocks_algorithm): New enum.
+       * flag-types.h (reorder_blocks_algorithm): New enum.
+       * opts.c (default_options_table): Use -freorder-blocks at -O1 and up,
+       and -freorder-blocks-algorithm=stc at -O2 and up (not at -Os).

The size regression is from 3562398 bytes to 3617915 bytes.

[Bug rtl-optimization/67864] [6 Regression] CSiBE size regression

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67864

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |6.0

[Bug rtl-optimization/67864] [6 Regression] CSiBE size regression

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67864

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Sun Oct 11 09:03:09 2015
New Revision: 228692

URL: https://gcc.gnu.org/viewcvs?rev=228692&root=gcc&view=rev
Log:
bb-reorder: Improve the simple algorithm for -Os (PR67864)

As the PR points out, the "simple" reorder algorithm makes bigger code
than the STC algorithm did, for -Os, for x86.  I now tested it for many
different targets and it turns out to be worse everywhere.

This simple patch tunes "simple" a bit; this makes it better than STC
almost everywhere.  The only exceptions (for the targets where I have
results) are x86 and mn10300.  For those targets it may be best to switch
the default algorithm for -Os to STC.


2015-10-11  Segher Boessenkool  <segher@kernel.crashing.org>

        PR rtl-optimization/67864
        * gcc/bb-reorder (reorder_basic_blocks_simple): Prefer existing
        fallthrough edges for conditional jumps.  Don't sort candidate
        edges if not optimizing for speed.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/bb-reorder.c

[Bug rtl-optimization/67864] [6 Regression] CSiBE size regression

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67864

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
No difference for x86 (but that may have been expected)