didn't preserve b6 and r11 anymore.  Unfortunately, preserving them costs
	a few cycles (~5 cycles in the cached case).  The uncached case is hopefully
	mostly unaffected because the number of cache-lines touched is the same
	(without preserving b6 and r11, the entry-patch _almost_ got away with
	touching a single 128-byte cacheline, but not quite, because r8 also
	had to be initialized).