arm: Add support for MVE Tail-Predicated Low Overhead Loops

arm: Add support for MVE Tail-Predicated Low Overhead Loops

This patch adds support for MVE Tail-Predicated Low Overhead Loops by using the
doloop funcitonality added to support predicated vectorized hardware loops.

gcc/ChangeLog:

	* config/arm/arm-protos.h (arm_target_bb_ok_for_lob): Change
	declaration to pass basic_block.
	(arm_attempt_dlstp_transform): New declaration.
	* config/arm/arm.cc (TARGET_LOOP_UNROLL_ADJUST): Define targethook.
	(TARGET_PREDICT_DOLOOP_P): Likewise.
	(arm_target_bb_ok_for_lob): Adapt condition.
	(arm_mve_get_vctp_lanes): New function.
	(arm_dl_usage_type): New internal enum.
	(arm_get_required_vpr_reg): New function.
	(arm_get_required_vpr_reg_param): New function.
	(arm_get_required_vpr_reg_ret_val): New function.
	(arm_mve_get_loop_vctp): New function.
	(arm_mve_insn_predicated_by): New function.
	(arm_mve_across_lane_insn_p): New function.
	(arm_mve_load_store_insn_p): New function.
	(arm_mve_impl_pred_on_outputs_p): New function.
	(arm_mve_impl_pred_on_inputs_p): New function.
	(arm_last_vect_def_insn): New function.
	(arm_mve_impl_predicated_p): New function.
	(arm_mve_check_reg_origin_is_num_elems): New function.
	(arm_mve_dlstp_check_inc_counter): New function.
	(arm_mve_dlstp_check_dec_counter): New function.
	(arm_mve_loop_valid_for_dlstp): New function.
	(arm_predict_doloop_p): New function.
	(arm_loop_unroll_adjust): New function.
	(arm_emit_mve_unpredicated_insn_to_seq): New function.
	(arm_attempt_dlstp_transform): New function.
	* config/arm/arm.opt (mdlstp): New option.
	* config/arm/iterators.md (dlstp_elemsize, letp_num_lanes,
	letp_num_lanes_neg, letp_num_lanes_minus_1): New attributes.
	(DLSTP, LETP): New iterators.
	* config/arm/mve.md (predicated_doloop_end_internal<letp_num_lanes>,
	dlstp<dlstp_elemsize>_insn): New insn patterns.
	* config/arm/thumb2.md (doloop_end): Adapt to support tail-predicated
	loops.
	(doloop_begin): Likewise.
	* config/arm/types.md (mve_misc): New mve type to represent
	predicated_loop_end insn sequences.
	* config/arm/unspecs.md:
	(DLSTP8, DLSTP16, DLSTP32, DSLTP64,
	LETP8, LETP16, LETP32, LETP64): New unspecs for DLSTP and LETP.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/lob.h: Add new helpers.
	* gcc.target/arm/lob1.c: Use new helpers.
	* gcc.target/arm/lob6.c: Likewise.
	* gcc.target/arm/mve/dlstp-compile-asm-1.c: New test.
	* gcc.target/arm/mve/dlstp-compile-asm-2.c: New test.
	* gcc.target/arm/mve/dlstp-compile-asm-3.c: New test.
	* gcc.target/arm/mve/dlstp-int8x16.c: New test.
	* gcc.target/arm/mve/dlstp-int8x16-run.c: New test.
	* gcc.target/arm/mve/dlstp-int16x8.c: New test.
	* gcc.target/arm/mve/dlstp-int16x8-run.c: New test.
	* gcc.target/arm/mve/dlstp-int32x4.c: New test.
	* gcc.target/arm/mve/dlstp-int32x4-run.c: New test.
	* gcc.target/arm/mve/dlstp-int64x2.c: New test.
	* gcc.target/arm/mve/dlstp-int64x2-run.c: New test.
	* gcc.target/arm/mve/dlstp-invalid-asm.c: New test.

Co-authored-by: Stam Markianos-Wright <stam.markianos-wright@arm.com>