Added codegen test for elidings bounds check when indexes are manually checked

Closes #55147

Author: alex

tests/codegen/slice-indexing.rs

@@ -60,3 +60,40 @@ pub unsafe fn str_get_unchecked_mut_by_range(x: &mut str, r: Range<usize>) -> &m
     // CHECK: sub nuw i64
     x.get_unchecked_mut(r)
 }
+
+// CHECK-LABEL: @slice_repeated_indexing(
+#[no_mangle]
+pub fn slice_repeated_indexing(dst: &mut [u8], offset: usize) {
+    let mut i = offset;
+    // CHECK: panic_bounds_check
+    dst[i] = 1;
+    i += 1;
+    // CHECK: panic_bounds_check
+    dst[i] = 2;
+    i += 1;
+    // CHECK: panic_bounds_check
+    dst[i] = 3;
+    i += 1;
+    // CHECK: panic_bounds_check
+    dst[i] = 4;
+}
+
+// CHECK-LABEL: @slice_repeated_indexing_coalesced(
+#[no_mangle]
+pub fn slice_repeated_indexing_coalesced(dst: &mut [u8], offset: usize) {
+    let mut i = offset;
+    if i.checked_add(4).unwrap() <= dst.len() {
+        // CHECK-NOT: panic_bounds_check
+        dst[i] = 1;
+        i += 1;
+        // CHECK-NOT: panic_bounds_check
+        dst[i] = 2;
+        i += 1;
+        // CHECK-NOT: panic_bounds_check
+        dst[i] = 3;
+        i += 1;
+        // CHECK-NOT: panic_bounds_check
+        dst[i] = 4;
+    }
+    // CHECK: ret
+}