define i32 @xor4_popcount(i32 %x) {
  %m = and i32 %x, 15
  %p = tail call i32 @llvm.ctpop.i32(i32 %m)
  %r = and i32 %p, 1
  ret i32 %r
}

declare i32 @llvm.ctpop.i32(i32)

--------------------------------------------------------------------
% llc -o - pop.ll              
	xorl	%eax, %eax
	testb	$15, %dil
	setnp	%al

% llc -o - pop.ll -mattr=popcnt
	andl	$15, %edi
	popcntl	%edi, %eax
	andl	$1, %eax

--------------------------------------------------------------------

Debug spew shows that we convert to a parity node either way, but then convert back to ctpop for a target that supports that instruction.

Test and set likely has better latency/throughput than popcnt + 2 mask instructions on all recent x86 CPUs.