SMALL_REGISTER_CLASSES

[David Edelsohn]

	GCC asm statements require explicit registers to be specified for
clobbers.  This can cause problems for ports where some of the registers
specified are in small register classes but the SMALL_REGISTER_CLASSES
macro is not defined for the port because the MD file itself does not need
to mention those registers explicitly.  Defining the macro is not an
acceptable option.

	The MD file can clobber a match_scratch of the single register
class but asm statements do not appear to be able to express the same
thing.  Geoff Keating and I were wondering if clobbering a specific
register in a class containing only that register should not automatically
be converted into a match_scratch of that register class?  Is there any
reason this is not done or cannot be done?  This or something similar
would seem to solve the problem and prevent the GCC spill error.

David