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
