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From: "astrange at ithinksw dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/40992]  New: [4.2/4.3/4.4/4.5 Regression] cunroll ignoring asm size
Date: Fri, 07 Aug 2009 04:25:00 -0000	[thread overview]
Message-ID: <bug-40992-10175@http.gcc.gnu.org/bugzilla/> (raw)

The attached file is a loop over the same function implemented in C and inline
asm. 

When compiled with:
gcc -O3 -fno-pic -fomit-frame-pointer -fdump-tree-cunroll-details -S
cabac_unroll.i
cunroll thinks they're different sizes:

size: 55-4, last_iteration: 55-4
  Loop size: 55
  Estimated size after unrolling: 442

size: 8-4, last_iteration: 8-4
  Loop size: 8
  Estimated size after unrolling: 34

and expands the asm loop all 13 times.

This is reduced from ffmpeg decode_cabac_residual, where it apparently causes
significant decoding slowdown.

Besides that, cunroll seems to be hurting ffmpeg in general on x86-32
(http://multimedia.cx/eggs/last-performance-smackdown-for-awhile/), maybe we'll
turn it down some.


-- 
           Summary: [4.2/4.3/4.4/4.5 Regression] cunroll ignoring asm size
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: astrange at ithinksw dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40992


             reply	other threads:[~2009-08-07  4:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-08-07  4:25 astrange at ithinksw dot com [this message]
2009-08-07  4:25 ` [Bug tree-optimization/40992] " astrange at ithinksw dot com
2009-08-07 12:07 ` rguenth at gcc dot gnu dot org
2009-08-08 16:44 ` astrange at ithinksw dot com
2009-08-16 21:40 ` [Bug tree-optimization/40992] [4.3/4.4/4.5 " rguenth at gcc dot gnu dot org
2009-08-16 21:42 ` rguenth at gcc dot gnu dot org
2009-10-05  0:40 ` pinskia at gcc dot gnu dot org
2009-10-05  0:56 ` pinskia at gcc dot gnu dot org
2009-10-05  0:57 ` pinskia at gcc dot gnu dot org
2009-10-05 17:47 ` [Bug tree-optimization/40992] [4.3/4.4 " pinskia at gcc dot gnu dot org
2009-10-05 17:47 ` pinskia at gcc dot gnu dot org
2010-05-22 18:33 ` rguenth at gcc dot gnu dot org

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