with my rustc patch that's almost ready for review

to_errno.asm

.section __TEXT,__text,regular,pure_instructions
	.build_version macos, 11, 0
	.globl	_to_errno
	.p2align	2
_to_errno:
Lfunc_begin0:
	.cfi_startproc
		// /Volumes/Q/repos/rust/library/core/src/slice/mod.rs : 2113
		if mid <= self.len() {
	sub x8, x1, #28
	cmn x8, #28
	b.hi LBB0_2
		// /Volumes/Q/repos/rust/library/core/src/slice/cmp.rs : 91
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldp x8, x9, [x0]
	ldr x10, [x0, #16]
	ldur x11, [x0, #19]
	mov x12, #29295
	movk x12, #11879, lsl #16
	movk x12, #29286, lsl #32
	movk x12, #25957, lsl #48
	cmp x8, x12
	mov x8, #25956
	movk x8, #27507, lsl #16
	movk x8, #28532, lsl #32
	movk x8, #11888, lsl #48
	ccmp x9, x8, #0, eq
	mov x8, #16964
	movk x8, #29557, lsl #16
	movk x8, #17710, lsl #32
	movk x8, #29298, lsl #48
	ccmp x10, x8, #0, eq
	mov x8, #11891
	movk x8, #29253, lsl #16
	movk x8, #28530, lsl #32
	movk x8, #11890, lsl #48
	ccmp x11, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 6
		if pfx != STANDARD_BASE {
	b.eq LBB0_4
LBB0_2:
	mov w8, #0
LBB0_3:
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	mov x0, x8
	ret
LBB0_4:
	mov w8, #0
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 10
		b"NoMemory" => NonZero::new(1),
	cmp x1, #40
	b.le LBB0_10
	cmp x1, #43
	b.gt LBB0_17
	cmp x1, #41
	b.eq LBB0_36
	cmp x1, #42
	b.eq LBB0_29
	cmp x1, #43
	b.ne LBB0_3
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldur x9, [x0, #34]
	mov x10, #28245
	movk x10, #28267, lsl #16
	movk x10, #30575, lsl #32
	movk x10, #20590, lsl #48
	cmp x8, x10
	mov x8, #29264
	movk x8, #28783, lsl #16
	movk x8, #29285, lsl #32
	movk x8, #31092, lsl #48
	b LBB0_39
LBB0_10:
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 10
		b"NoMemory" => NonZero::new(1),
	cmp x1, #36
	b.le LBB0_21
	cmp x1, #37
	b.eq LBB0_33
	cmp x1, #38
	b.eq LBB0_27
	cmp x1, #40
	b.ne LBB0_3
	mov w8, #26990
	movk w8, #25701, lsl #16
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x9, [x0, #27]
	ldur w10, [x0, #35]
	mov x11, #25409
	movk x11, #25955, lsl #16
	movk x11, #29555, lsl #32
	movk x11, #25924, lsl #48
	cmp x9, x11
	ccmp w10, w8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 13
		b"AccessDenied" | b"AuthFailed" | b"InteractiveAuthorizationRequired" => {
	b.eq LBB0_28
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x9, [x0, #27]
	ldur w10, [x0, #35]
	add x8, x8, #2820
	mov x11, #28494
	movk x11, #21364, lsl #16
	movk x11, #28789, lsl #32
	movk x11, #28528, lsl #48
	cmp x9, x11
	ccmp x10, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 19
		b"NotSupported" => NonZero::new(228),
	b.eq LBB0_43
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldur w9, [x0, #35]
	mov x10, #25665
	movk x10, #29284, lsl #16
	movk x10, #29541, lsl #32
	movk x10, #18803, lsl #48
	cmp x8, x10
	mov w8, #21870
	movk w8, #25971, lsl #16
	b LBB0_34
LBB0_17:
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 10
		b"NoMemory" => NonZero::new(1),
	cmp x1, #44
	b.eq LBB0_38
	cmp x1, #48
	b.eq LBB0_32
	cmp x1, #60
	b.ne LBB0_3
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldur x9, [x0, #35]
	ldur x10, [x0, #43]
	ldur x11, [x0, #51]
	mov x12, #28233
	movk x12, #25972, lsl #16
	movk x12, #24946, lsl #32
	movk x12, #29795, lsl #48
	cmp x8, x12
	mov x8, #30313
	movk x8, #16741, lsl #16
	movk x8, #29813, lsl #32
	movk x8, #28520, lsl #48
	ccmp x9, x8, #0, eq
	mov x8, #26994
	movk x8, #24954, lsl #16
	movk x8, #26996, lsl #32
	movk x8, #28271, lsl #48
	ccmp x10, x8, #0, eq
	mov x8, #25938
	movk x8, #30065, lsl #16
	movk x8, #29289, lsl #32
	movk x8, #25701, lsl #48
	ccmp x11, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 13
		b"AccessDenied" | b"AuthFailed" | b"InteractiveAuthorizationRequired" => {
	b.ne LBB0_2
	b LBB0_28
LBB0_21:
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 10
		b"NoMemory" => NonZero::new(1),
	cmp x1, #35
	b.eq LBB0_25
	cmp x1, #36
	b.ne LBB0_3
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	mov x9, #28494
	movk x9, #25933, lsl #16
	movk x9, #28525, lsl #32
	movk x9, #31090, lsl #48
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 10
		b"NoMemory" => NonZero::new(1),
	cmp x8, x9
	b.eq LBB0_42
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	mov x9, #26964
	movk x9, #25965, lsl #16
	movk x9, #20324, lsl #32
	movk x9, #29813, lsl #48
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 17
		b"Timeout" | b"TimedOut" => NonZero::new(420),
	cmp x8, x9
	b.ne LBB0_2
	b LBB0_41
LBB0_25:
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur w8, [x0, #27]
	ldur w9, [x0, #30]
	mov w10, #26964
	movk w10, #25965, lsl #16
	cmp w8, w10
	mov w8, #28517
	movk w8, #29813, lsl #16
	ccmp w9, w8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 17
		b"Timeout" | b"TimedOut" => NonZero::new(420),
	b.eq LBB0_41
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur w8, [x0, #27]
	ldur w9, [x0, #30]
	mov w10, #20297
	movk w10, #29253, lsl #16
	cmp w8, w10
	mov w8, #29298
	movk w8, #29295, lsl #16
	b LBB0_34
LBB0_27:
	ldur x8, [x0, #27]
	ldurh w9, [x0, #35]
	mov x10, #30017
	movk x10, #26740, lsl #16
	movk x10, #24902, lsl #32
	movk x10, #27753, lsl #48
	cmp x8, x10
	mov w8, #25701
	ccmp w9, w8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 13
		b"AccessDenied" | b"AuthFailed" | b"InteractiveAuthorizationRequired" => {
	b.ne LBB0_2
LBB0_28:
	mov w0, #1245
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	ret
LBB0_29:
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldur x9, [x0, #33]
	mov x10, #25939
	movk x10, #30322, lsl #16
	movk x10, #25449, lsl #32
	movk x10, #21861, lsl #48
	cmp x8, x10
	mov x8, #21861
	movk x8, #27502, lsl #16
	movk x8, #28526, lsl #32
	movk x8, #28279, lsl #48
	ccmp x9, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 11
		b"ServiceUnknown" | b"UnknownObject" | b"UnknownInterface" | b"UnknownMethod"
	b.eq LBB0_40
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldur x9, [x0, #33]
	mov x10, #24910
	movk x10, #25965, lsl #16
	movk x10, #24904, lsl #32
	movk x10, #20083, lsl #48
	cmp x8, x10
	mov x8, #20083
	movk x8, #20335, lsl #16
	movk x8, #28279, lsl #32
	movk x8, #29285, lsl #48
	ccmp x9, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 12
		| b"UnknownProperty" | b"NameHasNoOwner" => NonZero::new(18),
	b.eq LBB0_40
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	mov x9, #26956
	movk x9, #26989, lsl #16
	movk x9, #29556, lsl #32
	movk x9, #30789, lsl #48
	eor x8, x8, x9
	ldur x9, [x0, #33]
	mov x10, #30789
	movk x10, #25955, lsl #16
	movk x10, #25701, lsl #32
	movk x10, #25701, lsl #48
	eor x9, x9, x10
	orr x8, x8, x9
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 16
		b"LimitsExceeded" => NonZero::new(9),
	cmp x8, #0
	mov w8, #9
	csel w0, wzr, w8, ne
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	ret
LBB0_32:
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	mov x9, #28245
	movk x9, #30825, lsl #16
	movk x9, #29264, lsl #32
	movk x9, #25455, lsl #48
	eor x8, x8, x9
	ldur x9, [x0, #35]
	mov x10, #29541
	movk x10, #18803, lsl #16
	movk x10, #21860, lsl #32
	movk x10, #27502, lsl #48
	eor x9, x9, x10
	ldur w10, [x0, #43]
	mov w11, #28526
	movk w11, #28279, lsl #16
	eor x10, x10, x11
	orr x8, x8, x9
	orr x8, x8, x10
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 18
		b"UnixProcessIdUnknown" => NonZero::new(69),
	cmp x8, #0
	mov w8, #69
	csel w0, wzr, w8, ne
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	ret
LBB0_33:
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldrb w9, [x0, #35]
	mov x10, #28494
	movk x10, #25934, lsl #16
	movk x10, #30580, lsl #32
	movk x10, #29295, lsl #48
	cmp x8, x10
	mov w8, #107
LBB0_34:
	ccmp w9, w8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 20
		b"IOError" | b"NoNetwork" | b"AddressInUse" => NonZero::new(100500),
	b.ne LBB0_2
	mov w0, #34964
	movk w0, #1, lsl #16
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	ret
LBB0_36:
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldr x9, [x0, #32]
	mov x10, #28245
	movk x10, #28267, lsl #16
	movk x10, #30575, lsl #32
	movk x10, #20334, lsl #48
	cmp x8, x10
	mov x8, #28279
	movk x8, #25167, lsl #16
	movk x8, #25962, lsl #32
	movk x8, #29795, lsl #48
	ccmp x9, x8, #0, eq
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 11
		b"ServiceUnknown" | b"UnknownObject" | b"UnknownInterface" | b"UnknownMethod"
	b.eq LBB0_40
		// /Volumes/Q/repos/rust/library/core/src/cmp/pattern.rs : 71
		compare_bytes(self.as_ptr() as *const u8, other.as_ptr() as *const u8, size) == 0
	ldur x8, [x0, #27]
	ldr x9, [x0, #32]
	mov x10, #28245
	movk x10, #28267, lsl #16
	movk x10, #30575, lsl #32
	movk x10, #19822, lsl #48
	cmp x8, x10
	mov x8, #28279
	movk x8, #25933, lsl #16
	movk x8, #26740, lsl #32
	movk x8, #25711, lsl #48
	b LBB0_39
LBB0_38:
	ldur x8, [x0, #27]
	ldur x9, [x0, #35]
	mov x10, #28245
	movk x10, #28267, lsl #16
	movk x10, #30575, lsl #32
	movk x10, #18798, lsl #48
	cmp x8, x10
	mov x8, #29806
	movk x8, #29285, lsl #16
	movk x8, #24934, lsl #32
	movk x8, #25955, lsl #48
LBB0_39:
	ccmp x9, x8, #0, eq
	b.ne LBB0_2
LBB0_40:
	mov w0, #18
		// /Volumes/Q/repos/bytestr-match/src/lib.rs : 23
		}
	ret
LBB0_41:
	mov w0, #420
	ret
LBB0_42:
	mov w0, #1
	ret
LBB0_43:
	mov w0, #228
	ret