Use Option's discriminant as its size hint
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336e89bd15
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@ -770,6 +770,13 @@ pub const fn as_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>> {
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}
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}
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#[inline]
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const fn len(&self) -> usize {
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// Using the intrinsic avoids emitting a branch to get the 0 or 1.
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let discriminant: isize = crate::intrinsics::discriminant_value(self);
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discriminant as usize
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}
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/// Returns a slice of the contained value, if any. If this is `None`, an
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/// empty slice is returned. This can be useful to have a single type of
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/// iterator over an `Option` or slice.
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@ -812,7 +819,7 @@ pub const fn as_slice(&self) -> &[T] {
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unsafe {
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slice::from_raw_parts(
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(self as *const Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
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self.is_some() as usize,
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self.len(),
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)
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}
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}
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@ -869,7 +876,7 @@ pub const fn as_mut_slice(&mut self) -> &mut [T] {
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unsafe {
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slice::from_raw_parts_mut(
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(self as *mut Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
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self.is_some() as usize,
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self.len(),
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)
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}
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}
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@ -2242,10 +2249,8 @@ fn next(&mut self) -> Option<A> {
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#[inline]
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fn size_hint(&self) -> (usize, Option<usize>) {
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match self.opt {
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Some(_) => (1, Some(1)),
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None => (0, Some(0)),
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}
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let len = self.len();
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(len, Some(len))
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}
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}
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@ -2256,7 +2261,12 @@ fn next_back(&mut self) -> Option<A> {
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}
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}
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impl<A> ExactSizeIterator for Item<A> {}
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impl<A> ExactSizeIterator for Item<A> {
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#[inline]
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fn len(&self) -> usize {
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self.opt.len()
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}
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}
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impl<A> FusedIterator for Item<A> {}
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unsafe impl<A> TrustedLen for Item<A> {}
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@ -14,6 +14,14 @@ pub fn u64_opt_as_slice(o: &Option<u64>) -> &[u64] {
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// CHECK-NOT: br
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[LEN:.+]] = load i64,{{.+}} !range ![[META_U64:.+]], !noundef
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// CHECK-NOT: select
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// CHECK-NOT: br
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %{{.+}}, 0
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// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
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// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
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o.as_slice()
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}
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@ -25,10 +33,35 @@ pub fn nonzero_u64_opt_as_slice(o: &Option<NonZero<u64>>) -> &[NonZero<u64>] {
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[NZ:.+]] = icmp ne i64 %{{.+}}, 0
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// CHECK-NEXT: zext i1 %[[NZ]] to i64
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// CHECK-NEXT: %[[LEN:.+]] = zext i1 %[[NZ]] to i64
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// CHECK-NOT: select
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// CHECK-NOT: br
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %o, 0
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// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
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// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
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o.as_slice()
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}
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// CHECK-LABEL: @u8_opt_as_slice
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#[no_mangle]
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pub fn u8_opt_as_slice(o: &Option<u8>) -> &[u8] {
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// CHECK-NOT: select
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// CHECK-NOT: br
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[TAG:.+]] = load i8,{{.+}} !range ![[META_U8:.+]], !noundef
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// CHECK: %[[LEN:.+]] = zext{{.*}} i8 %[[TAG]] to i64
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// CHECK-NOT: select
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// CHECK-NOT: br
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// CHECK-NOT: switch
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// CHECK-NOT: icmp
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// CHECK: %[[T0:.+]] = insertvalue { ptr, i64 } poison, ptr %{{.+}}, 0
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// CHECK-NEXT: %[[T1:.+]] = insertvalue { ptr, i64 } %[[T0]], i64 %[[LEN]], 1
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// CHECK-NEXT: ret { ptr, i64 } %[[T1]]
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o.as_slice()
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}
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// CHECK: ![[META_U64]] = !{i64 0, i64 2}
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// CHECK: ![[META_U8]] = !{i8 0, i8 2}
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