[APX EGPR] Add 16 new integer general purpose registers

[APX EGPR] Add 16 new integer general purpose registers

Extend GENERAL_REGS with extra r16-r31 registers like REX registers,
named as REX2 registers. They will only be enabled under
TARGET_APX_EGPR.

gcc/ChangeLog:

	* config/i386/i386-protos.h (x86_extended_rex2reg_mentioned_p):
	New function prototype.
	* config/i386/i386.cc (regclass_map): Add mapping for 16 new
	general registers.
	(debugger64_register_map): Likewise.
	(ix86_conditional_register_usage): Clear REX2 register when APX
	disabled.
	(ix86_code_end): Add handling for REX2 reg.
	(print_reg): Likewise.
	(ix86_output_jmp_thunk_or_indirect): Likewise.
	(ix86_output_indirect_branch_via_reg): Likewise.
	(ix86_attr_length_vex_default): Likewise.
	(ix86_emit_save_regs): Adjust to allow saving r31.
	(ix86_register_priority): Set REX2 reg priority same as REX.
	(x86_extended_reg_mentioned_p): Add check for REX2 regs.
	(x86_extended_rex2reg_mentioned_p): New function.
	* config/i386/i386.h (CALL_USED_REGISTERS): Add new extended
	registers.
	(REG_ALLOC_ORDER): Likewise.
	(FIRST_REX2_INT_REG): Define.
	(LAST_REX2_INT_REG): Ditto.
	(GENERAL_REGS): Add 16 new registers.
	(INT_SSE_REGS): Likewise.
	(FLOAT_INT_REGS): Likewise.
	(FLOAT_INT_SSE_REGS): Likewise.
	(INT_MASK_REGS): Likewise.
	(ALL_REGS):Likewise.
	(REX2_INT_REG_P): Define.
	(REX2_INT_REGNO_P): Ditto.
	(GENERAL_REGNO_P): Add REX2_INT_REGNO_P.
	(REGNO_OK_FOR_INDEX_P): Ditto.
	(REG_OK_FOR_INDEX_NONSTRICT_P): Add new extended registers.
	* config/i386/i386.md: Add 16 new integer general
	registers.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/apx-egprs-names.c: New test.
	* gcc.target/i386/apx-spill_to_egprs-1.c: Likewise.
	* gcc.target/i386/apx-interrupt-1.c: Likewise.

Co-authored-by: Hongyu Wang <hongyu.wang@intel.com>
Co-authored-by: Hongtao Liu <hongtao.liu@intel.com>