[Bug target/30801] [4.3 Regression] performance regression on uint64_t operations

[rask at gcc dot gnu dot org]

------- Comment #3 from rask at gcc dot gnu dot org  2007-10-25 18:58 -------
I see a substantial improvent when testing on the compile farm hardware:

processor       : 3
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 65
model name      : Dual-Core AMD Opteron(tm) Processor 2212
stepping        : 3
cpu MHz         : 2000.240
cache size      : 1024 KB
...

$ gcc --version | head -n 1
gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
$ gcc -O3 ~/pr30801.c && time ./a.out
064069fbc13963b920219c3e939225e38e38e38e3956d81c71c71c71c0ba0f00

real    0m0.555s
user    0m0.552s
sys     0m0.004s

$ (cd ~/build/gcc-x86_64-unknown-linux-gnu/gcc && ./xgcc --version | head -n 1)
xgcc (GCC) 4.3.0 20071022 (experimental)
$ (cd ~/build/gcc-x86_64-unknown-linux-gnu/gcc && ./xgcc -B./ -O3 ~/pr30801.c
&& time ./a.out)
064069fbc13963b920219c3e939225e38e38e38e3956d81c71c71c71c0ba0f00

real    0m0.455s
user    0m0.452s
sys     0m0.004s

Note that your -march=pentium4 option is rejected without -m32:
$ gcc -march=pentium4 -O3 ~/pr30801.c && time ./a.out
/home/rask/pr30801.c:1: error: CPU you selected does not support x86-64
instruction set
/home/rask/pr30801.c:1: error: CPU you selected does not support x86-64
instruction set

$ gcc -O3 ~/pr30801.c -m32 -march=pentium4 && time ./a.out
064069fbc13963b920219c3e939225e38e38e38e3956d81c71c71c71c0ba0f00

real    0m2.234s
user    0m2.232s
sys     0m0.004s

$ (cd ~/build/gcc-x86_64-unknown-linux-gnu/gcc && ./xgcc -B./ -O3 ~/pr30801.c
-m32 -march=pentium4 && time ./a.out)
064069fbc13963b920219c3e939225e38e38e38e3956d81c71c71c71c0ba0f00

real    0m1.488s
user    0m1.484s
sys     0m0.004s

So GCC 4.3 is 22 % faster with just the default -m64 + no -march and an
impressive 50 % faster with -m32 -march=pentium4.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30801