------- Comment #5 from rguenth at gcc dot gnu dot org 2006-10-24 13:28 -------
With more registers (x86_64) the stack moves are gone, but: (!)
[EMAIL PROTECTED]:/abuild/rguenther/trunk-g/gcc> ./xgcc -B. -O2 -o t t.c
-mfpmath=387
[EMAIL PROTECTED]:/abuild/rguenther/trunk-g/gcc> /usr/bin/time ./t
Start?
Stop!
Result = 0.000000, 0.000000, 1.000000
5.31user 0.00system 0:05.32elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+135minor)pagefaults 0swaps
[EMAIL PROTECTED]:/abuild/rguenther/trunk-g/gcc> ./xgcc -B. -O2 -o t t.c
[EMAIL PROTECTED]:/abuild/rguenther/trunk-g/gcc> /usr/bin/time ./t
Start?
Stop!
Result = 0.000000, 0.000000, 1.000000
9.96user 0.05system 0:10.06elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+135minor)pagefaults 0swaps
that is almost twice as fast with 387 math than with SSE math on x86_64!
The inner loop is
.L7:
movaps %xmm3, %xmm6
movaps %xmm1, %xmm5
movaps %xmm0, %xmm4
.L2:
movaps %xmm2, %xmm3
mulss %xmm6, %xmm2
movaps %xmm7, %xmm0
addl $1, %eax
mulss %xmm4, %xmm3
movaps %xmm7, %xmm1
mulss %xmm5, %xmm0
cmpl $1000000000, %eax
mulss %xmm6, %xmm1
movaps %xmm4, %xmm7
subss %xmm0, %xmm3
movaps %xmm8, %xmm0
mulss %xmm4, %xmm0
subss %xmm0, %xmm1
movaps %xmm8, %xmm0
movaps %xmm6, %xmm8
mulss %xmm5, %xmm0
subss %xmm2, %xmm0
movaps %xmm5, %xmm2
jne .L7
vs.
.L7:
fxch %st(3)
fxch %st(2)
.L2:
fld %st(2)
addl $1, %eax
cmpl $1000000000, %eax
fmul %st(1), %st
flds 76(%rsp)
fmul %st(5), %st
fsubrp %st, %st(1)
flds 76(%rsp)
fmul %st(3), %st
flds 72(%rsp)
fmul %st(3), %st
fsubrp %st, %st(1)
flds 72(%rsp)
fmul %st(6), %st
fxch %st(5)
fmul %st(4), %st
fsubrp %st, %st(5)
fxch %st(2)
fstps 76(%rsp)
fxch %st(2)
fstps 72(%rsp)
jne .L7
(testing done on AMD Athlon fam 15 model 35 stepping 2)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19780
