Rollup merge of #100822 - WaffleLapkin:no_offset_question_mark, r=scottmcm

Replace most uses of `pointer::offset` with `add` and `sub`

As PR title says, it replaces `pointer::offset` in compiler and standard library with `pointer::add` and `pointer::sub`. This generally makes code cleaner, easier to grasp and removes (or, well, hides) integer casts.

This is generally trivially correct, `.offset(-constant)` is just `.sub(constant)`, `.offset(usized as isize)` is just `.add(usized)`, etc. However in some cases we need to be careful with signs of things.

r? ````@scottmcm````

_split off from #100746_

4 files changed, 8 insertions, 8 deletions

diff --git a/library/alloc/src/vec/in_place_collect.rs b/library/alloc/src/vec/in_place_collect.rs
index 55dcb84ad16..b211421b202 100644
--- a/library/alloc/src/vec/in_place_collect.rs
+++ b/library/alloc/src/vec/in_place_collect.rs
@@ -267,7 +267,7 @@ where
             // one slot in the underlying storage will have been freed up and we can immediately
             // write back the result.
             unsafe {
-                let dst = dst_buf.offset(i as isize);
+                let dst = dst_buf.add(i);
                 debug_assert!(dst as *const _ <= end, "InPlaceIterable contract violation");
                 ptr::write(dst, self.__iterator_get_unchecked(i));
                 // Since this executes user code which can panic we have to bump the pointer
diff --git a/library/alloc/src/vec/into_iter.rs b/library/alloc/src/vec/into_iter.rs
index 1b483e3fc77..e02ad391a59 100644
--- a/library/alloc/src/vec/into_iter.rs
+++ b/library/alloc/src/vec/into_iter.rs
@@ -160,7 +160,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
             Some(unsafe { mem::zeroed() })
         } else {
             let old = self.ptr;
-            self.ptr = unsafe { self.ptr.offset(1) };
+            self.ptr = unsafe { self.ptr.add(1) };
 
             Some(unsafe { ptr::read(old) })
         }
@@ -272,7 +272,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
             // Make up a value of this ZST.
             Some(unsafe { mem::zeroed() })
         } else {
-            self.end = unsafe { self.end.offset(-1) };
+            self.end = unsafe { self.end.sub(1) };
 
             Some(unsafe { ptr::read(self.end) })
         }
@@ -288,7 +288,7 @@ impl<T, A: Allocator> DoubleEndedIterator for IntoIter<T, A> {
             }
         } else {
             // SAFETY: same as for advance_by()
-            self.end = unsafe { self.end.offset(step_size.wrapping_neg() as isize) };
+            self.end = unsafe { self.end.sub(step_size) };
         }
         let to_drop = ptr::slice_from_raw_parts_mut(self.end as *mut T, step_size);
         // SAFETY: same as for advance_by()
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index fe4dcafe14c..cea943602f7 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -1393,7 +1393,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 if index < len {
                     // Shift everything over to make space. (Duplicating the
                     // `index`th element into two consecutive places.)
-                    ptr::copy(p, p.offset(1), len - index);
+                    ptr::copy(p, p.add(1), len - index);
                 } else if index == len {
                     // No elements need shifting.
                 } else {
@@ -1455,7 +1455,7 @@ impl<T, A: Allocator> Vec<T, A> {
                 ret = ptr::read(ptr);
 
                 // Shift everything down to fill in that spot.
-                ptr::copy(ptr.offset(1), ptr, len - index - 1);
+                ptr::copy(ptr.add(1), ptr, len - index - 1);
             }
             self.set_len(len - 1);
             ret
@@ -2408,7 +2408,7 @@ impl<T, A: Allocator> Vec<T, A> {
             // Write all elements except the last one
             for _ in 1..n {
                 ptr::write(ptr, value.next());
-                ptr = ptr.offset(1);
+                ptr = ptr.add(1);
                 // Increment the length in every step in case next() panics
                 local_len.increment_len(1);
             }
diff --git a/library/alloc/src/vec/spec_extend.rs b/library/alloc/src/vec/spec_extend.rs
index 506ee0ecfa2..1ea9c827afd 100644
--- a/library/alloc/src/vec/spec_extend.rs
+++ b/library/alloc/src/vec/spec_extend.rs
@@ -39,7 +39,7 @@ where
                 let mut local_len = SetLenOnDrop::new(&mut self.len);
                 iterator.for_each(move |element| {
                     ptr::write(ptr, element);
-                    ptr = ptr.offset(1);
+                    ptr = ptr.add(1);
                     // Since the loop executes user code which can panic we have to bump the pointer
                     // after each step.
                     // NB can't overflow since we would have had to alloc the address space