AArch64: div-by-255, ensure that arguments are registers. [PR107988]

AArch64: div-by-255, ensure that arguments are registers. [PR107988]

At -O0 (as opposed to e.g. volatile) we can get into the situation where the
in0 and result RTL arguments passed to the division function are memory
locations instead of registers.  I think we could reject these early on by
checking that the gimple values are GIMPLE registers, but I think it's better to
handle it.

As such I force them to registers and emit a move to the memory locations and
leave it up to reload to handle.  This fixes the ICE and still allows the
optimization in these cases,  which improves the code quality a lot.

gcc/ChangeLog:

	PR target/107988
	* config/aarch64/aarch64.cc
	(aarch64_vectorize_can_special_div_by_constant): Ensure input and output
	RTL are registers.

gcc/testsuite/ChangeLog:

	PR target/107988
	* gcc.target/aarch64/pr107988-1.c: New test.