poly_int: extract_bit_field bitrange

poly_int: extract_bit_field bitrange

Similar to the previous store_bit_field patch, but for extractions
rather than insertions.  The patch splits out the extraction-as-subreg
handling into a new function (extract_bit_field_as_subreg), both for
ease of writing and because a later patch will add another caller.

The simplify_gen_subreg overload is temporary; it goes away
in a later patch.

2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* rtl.h (simplify_gen_subreg): Add a temporary overload that
	accepts poly_uint64 offsets.
	* expmed.h (extract_bit_field): Take bitsize and bitnum as
	poly_uint64s rather than unsigned HOST_WIDE_INTs.
	* expmed.c (lowpart_bit_field_p): Likewise.
	(extract_bit_field_as_subreg): New function, split out from...
	(extract_bit_field_1): ...here.  Take bitsize and bitnum as
	poly_uint64s rather than unsigned HOST_WIDE_INTs.  For vector
	extractions, check that BITSIZE matches the size of the extracted
	value and that BITNUM is an exact multiple of that size.
	If all else fails, try forcing the value into memory if
	BITNUM is variable, and adjusting the address so that the
	offset is constant.  Split the part that can only handle constant
	bitsize and bitnum out into...
	(extract_integral_bit_field): ...this new function.
	(extract_bit_field): Take bitsize and bitnum as poly_uint64s
	rather than unsigned HOST_WIDE_INTs.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@255878 138bc75d-0d04-0410-961f-82ee72b054a4