Currently expressions like
  void foo(Array2d &a, const double s) {
    a = s - a;
  }

lead to this inefficient code (only excerpt shown, comments added):
	movapd	.LC0, %xmm0          #.LC0 is a {-0.0, -0.0}
	xorpd	(%eax), %xmm0        # negate elements of a
	movddup	8(%esp), %xmm1       # load s
	addpd	%xmm1, %xmm0         # add s + (-a)
	movapd	%xmm0, (%eax)        # store result

This could be implemented more efficiently using the subpd instruction:
	movddup	8(%esp), %xmm0       # load s
	subpd	(eax), %xmm0         # subtract s - a
	movapd	%xmm0, (%eax)        # store result