Optimize SliceIndex::get impl for RangeInclusive

The check for `self.end() == usize::MAX` can be combined with the
`self.end() + 1 > slice.len()` check into `self.end() >= slice.len()`,
since `self.end() < slice.len()` implies both
`self.end() <= slice.len()` and `self.end() < usize::MAX`.

Author: Kmeakin

library/core/src/slice/index.rs

@@ -658,7 +658,6 @@ unsafe impl<T> const SliceIndex<[T]> for ops::RangeFull {
 }
 
 /// The methods `index` and `index_mut` panic if:
-/// - the end of the range is `usize::MAX` or
 /// - the start of the range is greater than the end of the range or
 /// - the end of the range is out of bounds.
 #[stable(feature = "inclusive_range", since = "1.26.0")]
@@ -668,12 +667,12 @@ unsafe impl<T> const SliceIndex<[T]> for ops::RangeInclusive<usize> {
 
     #[inline]
     fn get(self, slice: &[T]) -> Option<&[T]> {
-        if *self.end() == usize::MAX { None } else { self.into_slice_range().get(slice) }
+        if *self.end() >= slice.len() { None } else { self.into_slice_range().get(slice) }
     }
 
     #[inline]
     fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
-        if *self.end() == usize::MAX { None } else { self.into_slice_range().get_mut(slice) }
+        if *self.end() >= slice.len() { None } else { self.into_slice_range().get_mut(slice) }
     }
 
     #[inline]
@@ -697,7 +696,7 @@ unsafe impl<T> const SliceIndex<[T]> for ops::RangeInclusive<usize> {
             start = if exhausted { end } else { start };
             if let Some(new_len) = usize::checked_sub(end, start) {
                 // SAFETY: `self` is checked to be valid and in bounds above.
-                unsafe { return &*get_offset_len_noubcheck(slice, start, new_len) }
+                unsafe { return &*get_offset_len_noubcheck(slice, start, new_len) };
             }
         }
         slice_index_fail(start, end, slice.len())
@@ -712,7 +711,7 @@ unsafe impl<T> const SliceIndex<[T]> for ops::RangeInclusive<usize> {
             start = if exhausted { end } else { start };
             if let Some(new_len) = usize::checked_sub(end, start) {
                 // SAFETY: `self` is checked to be valid and in bounds above.
-                unsafe { return &mut *get_offset_len_mut_noubcheck(slice, start, new_len) }
+                unsafe { return &mut *get_offset_len_mut_noubcheck(slice, start, new_len) };
             }
         }
         slice_index_fail(start, end, slice.len())

tests/codegen-llvm/slice-range-indexing.rs

@@ -58,9 +58,9 @@ tests!(RangeTo<usize>, get_range_to, index_range_to);
 // CHECK: ret
 tests!(RangeFrom<usize>, get_range_from, index_range_from);
 
-// 3 comparisons required: (range.end != usize::MAX) && (range.end < slice.len()) && (range.start <= range.end + 1)
+// 2 comparisons required: (range.end < slice.len()) && (range.start <= range.end + 1)
 // CHECK-LABEL: @get_range_inclusive
-// CHECK-COUNT-3: %{{.+}} = icmp
+// CHECK-COUNT-2: %{{.+}} = icmp
 // CHECK-NOT: %{{.+}} = icmp
 // CHECK: ret
 
@@ -71,9 +71,9 @@ tests!(RangeFrom<usize>, get_range_from, index_range_from);
 // CHECK: ret
 tests!(RangeInclusive<usize>, get_range_inclusive, index_range_inclusive);
 
-// 2 comparisons required: (range.end != usize::MAX) && (range.end < slice.len())
+// 1 comparison required: (range.end < slice.len())
 // CHECK-LABEL: @get_range_to_inclusive
-// CHECK-COUNT-2: %{{.+}} = icmp
+// CHECK-COUNT-1: %{{.+}} = icmp
 // CHECK-NOT: %{{.+}} = icmp
 // CHECK: ret