use .get().unwrap() in [T]::get_unchecked

Author: bend-n

library/core/src/slice/mod.rs

@@ -662,7 +662,7 @@ impl<T> [T] {
         // SAFETY: the caller must uphold most of the safety requirements for `get_unchecked`;
         // the slice is dereferenceable because `self` is a safe reference.
         // The returned pointer is safe because impls of `SliceIndex` have to guarantee that it is.
-        unsafe { &*index.get_unchecked(self) }
+        unsafe { &*index.get(self).unwrap_unchecked() }
     }
 
     /// Returns a mutable reference to an element or subslice, without doing

tests/codegen/issues/issue-116878.rs

@@ -0,0 +1,13 @@
+// no-system-llvm
+// compile-flags: -O
+// ignore-debug: the debug assertions get in the way
+#![crate_type = "lib"]
+
+/// Make sure no bounds checks are emitted after a `get_unchecked`.
+// CHECK-LABEL: @unchecked_slice_no_bounds_check
+#[no_mangle]
+pub unsafe fn unchecked_slice_no_bounds_check(s: &[u8]) -> u8 {
+    let a = *s.get_unchecked(1);
+    // CHECK-NOT: panic_bounds_check
+    a + s[0]
+}