Rollup merge of #53329 - frewsxcv:frewsxcv-ptr-add-sub, r=RalfJung

Replace usages of ptr::offset with ptr::{add,sub}.

Rust provides these helper methods – so let's use them!

src/test/run-pass/method-mut-self-modifies-mut-slice-lvalue.rs

@@ -27,7 +27,7 @@ impl<'a> MyWriter for &'a mut [u8] {
         let write_len = buf.len();
         unsafe {
             *self = slice::from_raw_parts_mut(
-                self.as_mut_ptr().offset(write_len as isize),
+                self.as_mut_ptr().add(write_len),
                 self.len() - write_len
             );
         }

src/test/run-pass/realloc-16687.rs

@@ -37,8 +37,8 @@ unsafe fn test_triangle() -> bool {
         for i in 0..COUNT / 2 {
             let (p0, p1, size) = (ascend[2*i], ascend[2*i+1], idx_to_size(i));
             for j in 0..size {
-                assert_eq!(*p0.offset(j as isize), i as u8);
-                assert_eq!(*p1.offset(j as isize), i as u8);
+                assert_eq!(*p0.add(j), i as u8);
+                assert_eq!(*p1.add(j), i as u8);
             }
         }
     }
@@ -100,8 +100,8 @@ unsafe fn test_triangle() -> bool {
     for i in 0..COUNT / 2 {
         let (p0, p1, size) = (ascend[2*i], ascend[2*i+1], idx_to_size(i));
         for j in 0..size {
-            *p0.offset(j as isize) = i as u8;
-            *p1.offset(j as isize) = i as u8;
+            *p0.add(j) = i as u8;
+            *p1.add(j) = i as u8;
         }
     }
 

src/test/run-pass/running-with-no-runtime.rs

@@ -36,7 +36,7 @@ fn start(argc: isize, argv: *const *const u8) -> isize {
 
     let args = unsafe {
         (0..argc as usize).map(|i| {
-            let ptr = *argv.offset(i as isize) as *const _;
+            let ptr = *argv.add(i) as *const _;
             CStr::from_ptr(ptr).to_bytes().to_vec()
         }).collect::<Vec<_>>()
     };