------- Comment #4 from jv244 at cam dot ac dot uk 2008-01-07 22:00 -------
timings have improved a lot with a recent gfortran, at least on an opteron, I
have now for ifort 3.7s for gfortran 4.5s (20% slower only) for the following
code:
SUBROUTINE collocate_core_2_2_0_0(jg,cmax)
IMPLICIT NONE
integer, INTENT(IN) :: jg,cmax
INTEGER, PARAMETER :: wp = SELECTED_REAL_KIND ( 14, 200 )
INTEGER, PARAMETER :: N=10,Nit=100000000
TYPE vec
real(wp) :: a(2)
END TYPE vec
TYPE(vec) :: dpy(1000)
TYPE(vec) :: pxy(1000)
TYPE(vec) :: s(02)
integer :: i,j
DO i=1,N
pxy(i)%a=0.0_wp
ENDDO
DO i=1,N
dpy(i)%a=0.0_wp
ENDDO
s(01)%a(1)=0.0_wp
s(01)%a(2)=0.0_wp
s(02)%a(1)=0.0_wp
s(02)%a(2)=0.0_wp
CALL USE(dpy,pxy,s)
! this is the hot loop
DO j=1,Nit
DO i=1,N
s(01)%a(:)=s(01)%a(:)+pxy(i)%a(:)*dpy(i)%a(1)
s(02)%a(:)=s(02)%a(:)+pxy(i)%a(:)*dpy(i)%a(2)
ENDDO
ENDDO
CALL USE(dpy,pxy,s)
END SUBROUTINE
SUBROUTINE USE(a,b,c)
INTEGER, PARAMETER :: wp = SELECTED_REAL_KIND ( 14, 200 )
REAL(kind=wp) :: a(*),b(*),c(*)
END SUBROUTINE USE
PROGRAM TEST
integer, parameter :: cmax=5
integer*8 :: t1,t2,tbest
real :: time1,time2
jg=0
CALL cpu_time(time1)
tbest=huge(tbest)
DO i=1,1
! t1=nanotime_ia32()
CALL collocate_core_2_2_0_0(0,cmax)
! t2=nanotime_ia32()
! if(t2-t1>0 .AND. t2-t1<tbest) tbest=t2-t1
ENDDO
CALL cpu_time(time2)
! write(6,*) tbest,time2-time1
write(6,*) time2-time1
END PROGRAM TEST
using
ifort -xW -O3 test.f90
gfortran -march=native -O3 -ffast-math test.f90
gfortran's inner loop asm looks like:
.L8:
movlpd (%rbp,%rax), %xmm0
movsd %xmm0, %xmm1
mulsd (%rbx,%rax), %xmm1
addsd %xmm1, %xmm2
movsd %xmm2, 32000(%rsp)
mulsd 8(%rbx,%rax), %xmm0
addsd %xmm0, %xmm5
movsd %xmm5, 32008(%rsp)
movlpd 8(%rbp,%rax), %xmm0
movsd %xmm0, %xmm1
mulsd (%rbx,%rax), %xmm1
addsd %xmm1, %xmm4
movsd %xmm4, 32016(%rsp)
mulsd 8(%rbx,%rax), %xmm0
addq $16, %rax
cmpq $160, %rax
addsd %xmm0, %xmm3
movsd %xmm3, 32024(%rsp)
jne .L8
while ifort's loop looks like:
..B3.7: # Preds ..B3.7 ..B3.6
movsd collocate_core_2_2_0_0_$DPY.0.0(%rdx), %xmm2 #31.41
movsd 8+collocate_core_2_2_0_0_$DPY.0.0(%rdx), %xmm3 #32.41
movaps collocate_core_2_2_0_0_$PXY.0.0(%rdx), %xmm4 #31.7
unpcklpd %xmm2, %xmm2 #31.41
mulpd %xmm4, %xmm2 #31.40
addpd %xmm2, %xmm1 #31.7
unpcklpd %xmm3, %xmm3 #32.41
mulpd %xmm3, %xmm4 #32.40
addpd %xmm4, %xmm0 #32.7
addq $16, %rdx #30.5
cmpq $160, %rdx #30.5
jl ..B3.7 # Prob 90% #30.5
so I guess ifort vectorizes where gfortran does not.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31079
