Rework the legitimize_address_displacement hook

Rework the legitimize_address_displacement hook

This patch:

- tweaks the handling of legitimize_address_displacement
  so that it gets called before rather than after the address has
  been expanded.  This means that we're no longer at the mercy
  of LRA being able to interpret the expanded instructions.

- passes the original offset to legitimize_address_displacement.

- adds SVE support to the AArch64 implementation of
  legitimize_address_displacement.

2018-01-13  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* target.def (legitimize_address_displacement): Take the original
	offset as a poly_int.
	* targhooks.h (default_legitimize_address_displacement): Update
	accordingly.
	* targhooks.c (default_legitimize_address_displacement): Likewise.
	* doc/tm.texi: Regenerate.
	* lra-constraints.c (base_plus_disp_to_reg): Take the displacement
	as an argument, moving assert of ad->disp == ad->disp_term to...
	(process_address_1): ...here.  Update calls to base_plus_disp_to_reg.
	Try calling targetm.legitimize_address_displacement before expanding
	the address rather than afterwards, and adjust for the new interface.
	* config/aarch64/aarch64.c (aarch64_legitimize_address_displacement):
	Match the new hook interface.  Handle SVE addresses.
	* config/sh/sh.c (sh_legitimize_address_displacement): Make the
	new hook interface.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r256637