internal-fn: Add VCOND_MASK_LEN.

internal-fn: Add VCOND_MASK_LEN.

In order to prevent simplification of a COND_OP with degenerate mask
(CONSTM1_RTX) into just an OP in the presence of length masking this
patch introduces a length-masked analog to VEC_COND_EXPR:
IFN_VCOND_MASK_LEN.

It also adds new match patterns that allow the combination of
unconditional unary, binary and ternay operations with the
VCOND_MASK_LEN into a conditional operation if the target supports it.

gcc/ChangeLog:

	PR tree-optimization/111760

	* config/riscv/autovec.md (vcond_mask_len_<mode><vm>): Add
	expander.
	* config/riscv/riscv-protos.h (enum insn_type): Add.
	* config/riscv/riscv-v.cc (needs_fp_rounding): Add !pred_mov.
	* doc/md.texi: Add vcond_mask_len.
	* gimple-match-exports.cc (maybe_resimplify_conditional_op):
	Create VCOND_MASK_LEN when length masking.
	* gimple-match.h (gimple_match_op::gimple_match_op): Always
	initialize len and bias.
	* internal-fn.cc (vec_cond_mask_len_direct): Add.
	(direct_vec_cond_mask_len_optab_supported_p): Add.
	(internal_fn_len_index): Add VCOND_MASK_LEN.
	(internal_fn_mask_index): Ditto.
	* internal-fn.def (VCOND_MASK_LEN): New internal function.
	* match.pd: Combine unconditional unary, binary and ternary
	operations into the respective COND_LEN operations.
	* optabs.def (OPTAB_D): Add vcond_mask_len optab.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/vect-cond-arith-2.c: No vect cost model for
	riscv_v.