I already checked in the patch that uses 'rax'
The extra r11 doesn't make it *more* leaky though, how can it? 
Plus if conservatism were an issue, then anywhere we align by 'and %rsp, -32' which is more than just this one place, we would zero the possibly-1-word-above, but that's a lot of noise in the code.

The right thing is what stas said: just make the math come out right by aligning, then subtracting what you need to make it end up aligned.