prefetch question

[Thomas Witzel]

Hello all again,

I now have a question regarding the prefetch command generation for x86_64.
The option -fprefetch-loop-arrays generates prefetch commands for
non-vectorized code,
but not for vectorized one. Is that the intended functionality ? Is
there a way to get prefetching also
for the vectorized routines ?
Thanks, Thomas

Example: (compiled with g++-4.5.0)
g++ -O3 -fcx-fortran-rules -fprefetch-loop-arrays -mtune=core2
-march=core2 -mssse3 -S -c ../test_loop.cpp

The code for a complex multiplication loop done this way:

void f(std::complex<float> *a, std::complex<float> *b, std::complex<float> *r)
{
        for(std::size_t s=0; s<N; s++)
                r[s] = a[s]*b[s];
}

Is generated two-fold, one vectorized (.L3) and one not (L5):

.LFB1292:
	leaq	32(%rdi), %rcx
	leaq	32(%rdx), %rax
	cmpq	%rcx, %rdx
	seta	%r8b
	cmpq	%rdi, %rax
	setb	%cl
	orb	%r8b, %cl
	jne	.L9
.L2:
	movq	%rdx, %rax
	xorl	%edx, %edx
	.p2align 4,,10
	.p2align 3
.L5:
	movss	(%rdi), %xmm4
	movss	4(%rdi), %xmm3
	movss	(%rsi), %xmm2
	movss	4(%rsi), %xmm0
	prefetcht0	80(%rdi)
	movaps	%xmm4, %xmm1
	movaps	%xmm3, %xmm5
	mulss	%xmm2, %xmm1
	mulss	%xmm0, %xmm5
	mulss	%xmm3, %xmm2
	subss	%xmm5, %xmm1
	mulss	%xmm4, %xmm0
	movss	%xmm1, (%rax)
	addss	%xmm2, %xmm0
	incq	%rdx
	movss	%xmm0, 4(%rax)
	addq	$8, %rdi
	addq	$8, %rsi
	addq	$8, %rax
	cmpq	$2097152, %rdx
	jne	.L5
	rep
	ret
.L9:
	leaq	32(%rsi), %rcx
	cmpq	%rcx, %rdx
	seta	%cl
	cmpq	%rax, %rsi
	seta	%al
	orb	%al, %cl
	je	.L2
	movq	%rdx, %rax
	xorps	%xmm3, %xmm3
	leaq	16777216(%rdi), %rdx
	.p2align 4,,10
	.p2align 3
.L3:
	movaps	%xmm3, %xmm2
	movaps	%xmm3, %xmm1
	movlps	(%rdi), %xmm2
	movlps	16(%rdi), %xmm1
	movhps	8(%rdi), %xmm2
	movhps	24(%rdi), %xmm1
	movaps	%xmm2, %xmm0
	movaps	%xmm2, %xmm5
	shufps	$136, %xmm1, %xmm0
	shufps	$221, %xmm1, %xmm5
	movaps	%xmm3, %xmm2
	movaps	%xmm3, %xmm1
	movlps	(%rsi), %xmm2
	movlps	16(%rsi), %xmm1
	movhps	8(%rsi), %xmm2
	movhps	24(%rsi), %xmm1
	movaps	%xmm2, %xmm4
	movaps	%xmm5, %xmm6
	shufps	$221, %xmm1, %xmm2
	shufps	$136, %xmm1, %xmm4
	mulps	%xmm2, %xmm6
	movaps	%xmm0, %xmm1
	addq	$32, %rdi
	mulps	%xmm4, %xmm1
	mulps	%xmm2, %xmm0
	subps	%xmm6, %xmm1
	mulps	%xmm5, %xmm4
	movaps	%xmm1, %xmm2
	addps	%xmm4, %xmm0
	addq	$32, %rsi
	unpcklps	%xmm0, %xmm2
	unpckhps	%xmm0, %xmm1
	movlps	%xmm2, (%rax)
	movhps	%xmm2, 8(%rax)
	movlps	%xmm1, 16(%rax)
	movhps	%xmm1, 24(%rax)
	addq	$32, %rax
	cmpq	%rdx, %rdi
	jne	.L3
	rep
	ret