For

---
double a[1024];
float b[1024];
int c[1024];

void dependence_distance_4_mixed_0 (void)
{
  int i;
  for (i = 0; i < 1020; ++i)
    a[i + 4] = a[i] + a[i + 4] + c[i];
}
---

with -O3 -ffast-math -mavx, vect256 branch generates:

.L2:
	vmovapd	a(%rax,%rax), %ymm0
	vcvtdq2pd	c(%rax), %ymm1
	vaddpd	a+32(%rax,%rax), %ymm0, %ymm0
	vaddpd	%ymm1, %ymm0, %ymm0
	vmovapd	%ymm0, a+32(%rax,%rax)
	addq	$16, %rax
	cmpq	$4080, %rax
	jne	.L2

Trunk at revision 165455 generates

.L2:
	vmovapd	16(%rax), %xmm2
	vaddpd	-16(%rax), %xmm2, %xmm2
	vmovdqa	(%rdx), %xmm0
	addq	$16, %rdx
	vpshufd	$238, %xmm0, %xmm1
	vcvtdq2pd	%xmm0, %xmm0
	vcvtdq2pd	%xmm1, %xmm1
	vaddpd	%xmm1, %xmm2, %xmm1
	vmovapd	(%rax), %xmm2
	vaddpd	-32(%rax), %xmm2, %xmm2
	vmovapd	%xmm1, 16(%rax)
	vaddpd	%xmm0, %xmm2, %xmm0
	vmovapd	%xmm0, (%rax)
	addq	$32, %rax
	cmpq	%rax, %rcx
	jne	.L2