amdgcn: Align VGPR pairs

amdgcn: Align VGPR pairs

Aligning the registers is not needed by the architecture, but doing so
allows us to remove the requirement for bug-prone early-clobber
constraints from many split patterns (and avoid adding more in future).

2020-02-21  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* config/gcn/gcn.c (gcn_hard_regno_mode_ok): Align VGPR pairs.
	* config/gcn/gcn-valu.md (addv64di3): Remove early-clobber.
	(addv64di3_exec): Likewise.
	(subv64di3): Likewise.
	(subv64di3_exec): Likewise.
	(addv64di3_zext): Likewise.
	(addv64di3_zext_exec): Likewise.
	(addv64di3_zext_dup): Likewise.
	(addv64di3_zext_dup_exec): Likewise.
	(addv64di3_zext_dup2): Likewise.
	(addv64di3_zext_dup2_exec): Likewise.
	(addv64di3_sext_dup2): Likewise.
	(addv64di3_sext_dup2_exec): Likewise.
	(<expander>v64di3): Likewise.
	(<expander>v64di3_exec): Likewise.
	(*<reduc_op>_dpp_shr_v64di): Likewise.
	(*plus_carry_dpp_shr_v64di): Likewise.
	* config/gcn/gcn.md (adddi3): Likewise.
	(addptrdi3): Likewise.
	(<expander>di3): Likewise.