Vectorize basic_string::find_first_of

[AlexGuteniev]

Resolves #4497

Benchmark	main	this
bm<AlgType::str_member, char>/2/3	5.52 ns	5.84 ns
bm<AlgType::str_member, char>/7/4	12.7 ns	12.7 ns
bm<AlgType::str_member, char>/9/3	13.1 ns	11.4 ns
bm<AlgType::str_member, char>/22/5	16.9 ns	11.9 ns
bm<AlgType::str_member, char>/58/2	30.9 ns	13.1 ns
bm<AlgType::str_member, char>/102/4	44.8 ns	15.6 ns
bm<AlgType::str_member, char>/325/1	101 ns	36.0 ns
bm<AlgType::str_member, char>/1011/11	269 ns	100 ns
bm<AlgType::str_member, char>/1502/23	400 ns	316 ns
bm<AlgType::str_member, char>/3056/7	763 ns	286 ns
bm<AlgType::str_member, wchar_t>/2/3	6.11 ns	14.2 ns
bm<AlgType::str_member, wchar_t>/7/4	12.2 ns	16.2 ns
bm<AlgType::str_member, wchar_t>/9/3	12.6 ns	14.6 ns
bm<AlgType::str_member, wchar_t>/22/5	17.3 ns	15.7 ns
bm<AlgType::str_member, wchar_t>/58/2	36.1 ns	20.0 ns
bm<AlgType::str_member, wchar_t>/102/4	55.7 ns	27.2 ns
bm<AlgType::str_member, wchar_t>/325/1	137 ns	66.9 ns
bm<AlgType::str_member, wchar_t>/1011/11	392 ns	400 ns
bm<AlgType::str_member, wchar_t>/1502/23	576 ns	587 ns
bm<AlgType::str_member, wchar_t>/3056/7	1142 ns	574 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/2/3	7.12 ns	15.9 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/7/4	24.3 ns	27.2 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/9/3	26.3 ns	14.6 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/22/5	63.3 ns	15.7 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/58/2	61.3 ns	19.5 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/102/4	134 ns	26.9 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/325/1	141 ns	66.2 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/1011/11	2953 ns	429 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/1502/23	9272 ns	908 ns
bm<AlgType::str_member, wchar_t, L'\x03B1'>/3056/7	5572 ns	560 ns

[AlexGuteniev]

My experiment on having _Use_bitmap to always true or always false

Benchmark	never bitmap	always bitmap
bm<AlgType::str_member, char>/22/5	11.3 ns	17.5 ns
bm<AlgType::str_member, char>/58/2	12.6 ns	41.2 ns
bm<AlgType::str_member, char>/102/4	15.4 ns	54.8 ns
bm<AlgType::str_member, char>/325/1	35.7 ns	132 ns
bm<AlgType::str_member, char>/1011/11	96.8 ns	355 ns
bm<AlgType::str_member, char>/1502/23	320 ns	607 ns
bm<AlgType::str_member, char>/3056/7	282 ns	1026 ns
bm<AlgType::str_member, wchar_t>/22/5	12.5 ns	17.8 ns
bm<AlgType::str_member, wchar_t>/58/2	16.9 ns	31.5 ns
bm<AlgType::str_member, wchar_t>/102/4	23.4 ns	54.6 ns
bm<AlgType::str_member, wchar_t>/325/1	63.0 ns	134 ns
bm<AlgType::str_member, wchar_t>/1011/11	406 ns	376 ns
bm<AlgType::str_member, wchar_t>/1502/23	870 ns	553 ns
bm<AlgType::str_member, wchar_t>/3056/7	514 ns	1100 ns
bm<AlgType::str_member, char32_t>/22/5	10.7 ns	21.3 ns
bm<AlgType::str_member, char32_t>/58/2	9.36 ns	43.0 ns
bm<AlgType::str_member, char32_t>/102/4	16.7 ns	58.9 ns
bm<AlgType::str_member, char32_t>/325/1	18.8 ns	134 ns
bm<AlgType::str_member, char32_t>/1011/11	338 ns	385 ns
bm<AlgType::str_member, char32_t>/1502/23	1015 ns	639 ns
bm<AlgType::str_member, char32_t>/3056/7	541 ns	1109 ns

[frederick-vs-ja]

I had the assumption that _Special is the case where we definitely have one of the standard character types. But apparently char_traits can be specialized for custom character types, so _Special may be true for something not behaving as a character.

It seems that we should fix _Special for all _Traits_meow algorithms. Perhaps in another PR?
(Also, it's possibly better to make _Special not a template parameter, which would shorten mangled names.)

The strategy may be like this:

template <class>
constexpr bool _Is_std_char_traits_specialization = false;
template <class _CharT>
constexpr bool _Is_std_char_traits_specialization<char_traits<_CharT>> = _Is_EcharT<_CharT>;

[AlexGuteniev]

It seems that we should fix _Special for all _Traits_meow algorithms. Perhaps in another PR?

Yes, I think I can do this some time later (If you or someone else won't do it before me).
I'd prefer keeping the current PR draft, until it can be merged with main containing the changes of that PR.
This way basic_string won't become more broken for odd character types.

(Also, it's possibly better to make _Special not a template parameter, which would shorten mangled names.)

Good idea.

The strategy may be like this:

Also agree.

[AlexGuteniev]

I'm marking this PR as ready again.

Turns out that basic_string::find_meow_of rejects unicorns here:

STL/stl/inc/__msvc_string_view.hpp

Lines 678 to 680 in 91e4255

	static_assert(is_unsigned_v<_Elem>,
	"Standard char_traits is only provided for char, wchar_t, char16_t, and char32_t. See N4950 [char.traits]. "
	"Visual C++ accepts other unsigned integral types as an extension.");

Since it is compile-time error already, vectorization doesn't make this case any more broken.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

🧶 🐈‍⬛ 🎉