compile: double test() {}

into:

_test:
	fldz
	ret

instead of:

_test:
	subl	$12, %esp
	#IMPLICIT_DEF %xmm0
	movsd	%xmm0, (%esp)
	fldl	(%esp)
	addl	$12, %esp
	ret

llvm-svn: 48213