Use cmeq, cmge, cmgt (zero) when one of the operands is Vector64/128<T>.Zero

[echesakov]

For example,

The code as in #33749 (comment) BitArray:.ctor

dup     v17.16b, wzr
cmeq    v16.16b, v16.16b, v17.16b

should be optimized down to

cmeq    v16.16b, v16.16b, #0

This applies to all the intrinsics that are mapped to cmeq, cmge, cmgt, cmle, cmlt, fcmeq, fcmge, fcmgt, fcmle and fcmlt instructions

category:cq
theme:hardware-intrinsics
skill-level:intermediate
cost:small

[Gnbrkm41]

runtime/src/libraries/System.Collections/src/System/Collections/BitArray.cs

Lines 183 to 195 in c74407f

	// JIT does not support code hoisting for SIMD yet
	// However comparison against zero can be replaced to cmeq against zero (vceqzq_s8)
	// See dotnet/runtime#33972 for details
	Vector128<byte> zero = Vector128<byte>.Zero;
	fixed (bool* ptr = values)
	{
	for (; (i + Vector128ByteCount * 2u) <= (uint)values.Length; i += Vector128ByteCount * 2u)
	{
	// Same logic as SSE2 path, however we lack MoveMask (equivalent) instruction
	// As a workaround, mask out the relevant bit after comparison
	// and combine by ORing all of them together (In this case, adding all of them does the same thing)
	Vector128<byte> lowerVector = AdvSimd.LoadVector128((byte*)ptr + i);
	Vector128<byte> lowerIsFalse = AdvSimd.CompareEqual(lowerVector, zero);