RISC-V: Add fault first load C/C++ support

gcc/ChangeLog:

	* config/riscv/riscv-builtins.cc (riscv_gimple_fold_builtin): New function.
	* config/riscv/riscv-protos.h (riscv_gimple_fold_builtin): Ditto.
	(gimple_fold_builtin):  Ditto.
	* config/riscv/riscv-vector-builtins-bases.cc (class read_vl): New class.
	(class vleff): Ditto.
	(BASE): Ditto.
	* config/riscv/riscv-vector-builtins-bases.h: Ditto.
	* config/riscv/riscv-vector-builtins-functions.def (read_vl): Ditto.
	(vleff): Ditto.
	* config/riscv/riscv-vector-builtins-shapes.cc (struct read_vl_def): Ditto.
	(struct fault_load_def): Ditto.
	(SHAPE): Ditto.
	* config/riscv/riscv-vector-builtins-shapes.h: Ditto.
	* config/riscv/riscv-vector-builtins.cc
	(rvv_arg_type_info::get_tree_type): Add size_ptr.
	(gimple_folder::gimple_folder): New class.
	(gimple_folder::fold): Ditto.
	(gimple_fold_builtin): New function.
	(get_read_vl_instance): Ditto.
	(get_read_vl_decl): Ditto.
	* config/riscv/riscv-vector-builtins.def (size_ptr): Add size_ptr.
	* config/riscv/riscv-vector-builtins.h (class gimple_folder): New class.
	(get_read_vl_instance): New function.
	(get_read_vl_decl):  Ditto.
	* config/riscv/riscv-vsetvl.cc (fault_first_load_p): Ditto.
	(read_vl_insn_p): Ditto.
	(available_occurrence_p): Ditto.
	(backward_propagate_worthwhile_p): Ditto.
	(gen_vsetvl_pat): Adapt for vleff support.
	(get_forward_read_vl_insn): New function.
	(get_backward_fault_first_load_insn): Ditto.
	(source_equal_p): Adapt for vleff support.
	(first_ratio_invalid_for_second_sew_p): Remove.
	(first_ratio_invalid_for_second_lmul_p): Ditto.
	(first_lmul_less_than_second_lmul_p): Ditto.
	(first_ratio_less_than_second_ratio_p): Ditto.
	(support_relaxed_compatible_p): New function.
	(vector_insn_info::operator>): Remove.
	(vector_insn_info::operator>=): Refine.
	(vector_insn_info::parse_insn): Adapt for vleff support.
	(vector_insn_info::compatible_p): Ditto.
	(vector_insn_info::update_fault_first_load_avl): New function.
	(pass_vsetvl::transfer_after): Adapt for vleff support.
	(pass_vsetvl::demand_fusion): Ditto.
	(pass_vsetvl::cleanup_insns): Ditto.
	* config/riscv/riscv-vsetvl.def (DEF_INCOMPATIBLE_COND): Remove
	redundant condtions.
	* config/riscv/riscv-vsetvl.h (struct demands_cond): New function.
	* config/riscv/riscv.cc (TARGET_GIMPLE_FOLD_BUILTIN): New target hook.
	* config/riscv/riscv.md: Adapt for vleff support.
	* config/riscv/t-riscv: Ditto.
	* config/riscv/vector-iterators.md: New iterator.
	* config/riscv/vector.md (read_vlsi): New pattern.
	(read_vldi_zero_extend): Ditto.
	(@pred_fault_load<mode>): Ditto.