1 files changed, 7 insertions, 4 deletions
diff --git a/library/core/src/ops/index_range.rs b/library/core/src/ops/index_range.rs
index 64214eae377..dce3514a159 100644
--- a/library/core/src/ops/index_range.rs
+++ b/library/core/src/ops/index_range.rs
@@ -45,7 +45,8 @@ impl IndexRange {
     #[inline]
     pub const fn len(&self) -> usize {
         // SAFETY: By invariant, this cannot wrap
-        unsafe { self.end.unchecked_sub(self.start) }
+        // Using the intrinsic because a UB check here impedes LLVM optimization. (#131563)
+        unsafe { crate::intrinsics::unchecked_sub(self.end, self.start) }
     }
 
     /// # Safety
@@ -82,7 +83,8 @@ impl IndexRange {
         let mid = if n <= self.len() {
             // SAFETY: We just checked that this will be between start and end,
             // and thus the addition cannot overflow.
-            unsafe { self.start.unchecked_add(n) }
+            // Using the intrinsic avoids a superfluous UB check.
+            unsafe { crate::intrinsics::unchecked_add(self.start, n) }
         } else {
             self.end
         };
@@ -100,8 +102,9 @@ impl IndexRange {
     pub fn take_suffix(&mut self, n: usize) -> Self {
         let mid = if n <= self.len() {
             // SAFETY: We just checked that this will be between start and end,
-            // and thus the addition cannot overflow.
-            unsafe { self.end.unchecked_sub(n) }
+            // and thus the subtraction cannot overflow.
+            // Using the intrinsic avoids a superfluous UB check.
+            unsafe { crate::intrinsics::unchecked_sub(self.end, n) }
         } else {
             self.start
         };