------- Comment #9 from dorit at gcc dot gnu dot org 2009-01-27 12:40 ------- (In reply to comment #4) > The testcase should be > subroutine to_product_of(self,a,b,a1,a2) > complex(kind=8) :: self (:) > complex(kind=8), intent(in) :: a(:,:) > complex(kind=8), intent(in) :: b(:) > integer a1,a2 > do i = 1,a1 > do j = 1,a2 > self(i) = self(i) + a(j,i)*b(j) > end do > end do > end subroutine > to be meaningful - otherwise we are accessing a in non-continuous ways in the > inner loop which would prevent vectorization.
this change from a(i,j) to a(j,i) is not required if we try to vectorize the outer-loop, where the stride is 1. It's also a better way to vectorize the reduction. A few limitations on the way though are: 1) somehow don't let gcc create guard code around the innermost loop to check that it executes more than zero iterations. This creates a complicated control flow structure within the outer-loop. For now you have to have constant number of iterations for the inner-loop because of that, or insert a statement like "if (a2<=0) return;" before the loop... 2) use -fno-tree-sink cause otherwise it moves the loop iv increment to the latch block and the vectorizer likes to have the latch block empty... (see also PR33113 for related reference). > With the versioning for stride == 1 I get then > .L13: > movupd 16(%rax), %xmm1 > movupd (%rax), %xmm3 > incl %ecx > movupd (%rdx), %xmm4 > addq $32, %rax > movapd %xmm3, %xmm0 > unpckhpd %xmm1, %xmm3 > unpcklpd %xmm1, %xmm0 > movupd 16(%rdx), %xmm1 > movapd %xmm4, %xmm2 > addq $32, %rdx > movapd %xmm3, %xmm9 > cmpl %ecx, %r8d > unpcklpd %xmm1, %xmm2 > unpckhpd %xmm1, %xmm4 > movapd %xmm4, %xmm1 > movapd %xmm2, %xmm4 > mulpd %xmm1, %xmm9 > mulpd %xmm0, %xmm4 > mulpd %xmm3, %xmm2 > mulpd %xmm1, %xmm0 > subpd %xmm9, %xmm4 > addpd %xmm2, %xmm0 > addpd %xmm4, %xmm6 > addpd %xmm0, %xmm5 > ja .L13 > haddpd %xmm5, %xmm5 > cmpl %r15d, %edi > movl -4(%rsp), %ecx > haddpd %xmm6, %xmm6 > addsd %xmm5, %xmm8 > addsd %xmm6, %xmm7 > jne .L12 > jmp .L14 > for the innermost loop, followed by a tail loop (peel for niters). This is > about 15% faster on AMD K10 than the non-vectorized loop (if you disable > the cost-model and make sure to have enough iterations in the inner loop > to pay back for the extra guarding conditions). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37021
