[Bug target/27827] [4.0/4.1/4.2 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[hjl at lucon dot org]

------- Comment #27 from hjl at lucon dot org  2006-06-29 02:32 -------
Created an attachment (id=11777)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=11777&action=view)
An integer loop

I changed the loop from double to long long. The 64bit code generated by gcc
4.0
is 10% slower than gcc 3.4 on Nocona:

/usr/gcc-3.4/bin/gcc -m32 -fomit-frame-pointer -O -c mmbench.c
/usr/gcc-3.4/bin/gcc -m32 -fomit-frame-pointer -O -c gemm_atlas.c
/usr/gcc-3.4/bin/gcc -m32 -fomit-frame-pointer -O -o xmm_gcc mmbench.o
gemm_atlas.o
rm -f *.o
/usr/gcc-4.0/bin/gcc -m32 -fomit-frame-pointer -O -c mmbench.c
/usr/gcc-4.0/bin/gcc -m32 -fomit-frame-pointer -O -c gemm_atlas.c
/usr/gcc-4.0/bin/gcc -m32 -fomit-frame-pointer -O -o xmm_gc4 mmbench.o
gemm_atlas.o
rm -f *.o
echo "GCC 3.x     performance:"
GCC 3.x     performance:
./xmm_gcc
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       60    250       0.381      283.51

echo "GCC 4.x     performance:"
GCC 4.x     performance:
./xmm_gc4
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       60    250       0.389      277.68

gnu-16:pts/2[5]> make                                     ~/bugs/gcc/27827/loop
/usr/gcc-3.4/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -c mmbench.c
/usr/gcc-3.4/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -c gemm_atlas.c
/usr/gcc-3.4/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -o xmm_gcc mmbench.o
gemm_atlas.o
rm -f *.o
/usr/gcc-4.0/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -c mmbench.c
/usr/gcc-4.0/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -c gemm_atlas.c
/usr/gcc-4.0/bin/gcc -DREPS=1000 -fomit-frame-pointer -O -o xmm_gc4 mmbench.o
gemm_atlas.o
rm -f *.o
echo "GCC 3.x     performance:"
GCC 3.x     performance:
./xmm_gcc
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       60   1000       0.172     2512.01

echo "GCC 4.x     performance:"
GCC 4.x     performance:
./xmm_gc4
ALGORITHM     NB   REPS        TIME      MFLOPS
=========  =====  =====  ==========  ==========

atlasmm       60   1000       0.193     2238.68

So the problem may be also loop related.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827