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Date: Sat, 13 Aug 2005 18:03:00 -0000
From: "martin at mpa-garching dot mpg dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20050813180312.23378.martin@mpa-garching.mpg.de>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug pending/23378] New: code quality regression for complicated loop
X-Bugzilla-Reason: CC
X-SW-Source: 2005-08/txt/msg01510.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

A code quality regression was introduced into CVS between the timestamps
"-D 20050729 22:00:00 UT" and "-D 20050729 23:00:00 UT". It appears that
it iss caused by Jan Hubicka's patch from
http://gcc.gnu.org/ml/gcc-patches/2005-07/msg02021.html

If the attached testcase is compiled with the newer compiler, the runtime
of the generated executable is more than 50 per cent higher:

old compiler:

~/tmp/tmp2>g++ -O3 -march=pentium4 -mfpmath=sse testcase.cc
~/tmp/tmp2>time ./a.out
14.250u 0.020s 0:14.27 100.0%   0+0k 0+0io 205pf+0w


new compiler:

~/tmp/tmp2>g++ -O3 -march=pentium4 -mfpmath=sse testcase.cc
~/tmp/tmp2>time ./a.out
22.430u 0.030s 0:22.46 100.0%   0+0k 0+0io 205pf+0w


Both compilers have the same "g++ -v" output:

~/tmp/tmp2>g++ -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /scratch/gcc/configure --quiet
--prefix=/afs/mpa/data/martin/ugcc --enable-languages=c++
--enable-mapped-location --disable-checking
Thread model: posix
gcc version 4.1.0 20050729 (experimental)


The hot spot of the code is the strange "loop" in lines 134-139
of alm_map_tools_orig.cc.

-- 
           Summary: code quality regression for complicated loop
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: pending
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: martin at mpa-garching dot mpg dot de
                CC: gcc-bugs at gcc dot gnu dot org,martin at mpa-garching
                    dot mpg dot de
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23378