Rollup merge of rust-lang#100822 - WaffleLapkin:no_offset_question_ma…

…rk, 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_

compiler/rustc_arena/src/lib.rs

@@ -219,7 +219,7 @@ impl<T> TypedArena<T> {
             } else {
                 let ptr = self.ptr.get();
                 // Advance the pointer.
-                self.ptr.set(self.ptr.get().offset(1));
+                self.ptr.set(self.ptr.get().add(1));
                 // Write into uninitialized memory.
                 ptr::write(ptr, object);
                 &mut *ptr

compiler/rustc_codegen_cranelift/example/alloc_system.rs

@@ -94,7 +94,7 @@ mod platform {
     struct Header(*mut u8);
     const HEAP_ZERO_MEMORY: DWORD = 0x00000008;
     unsafe fn get_header<'a>(ptr: *mut u8) -> &'a mut Header {
-        &mut *(ptr as *mut Header).offset(-1)
+        &mut *(ptr as *mut Header).sub(1)
     }
     unsafe fn align_ptr(ptr: *mut u8, align: usize) -> *mut u8 {
         let aligned = ptr.add(align - (ptr as usize & (align - 1)));

compiler/rustc_codegen_gcc/example/alloc_system.rs

@@ -156,7 +156,7 @@ mod platform {
     struct Header(*mut u8);
     const HEAP_ZERO_MEMORY: DWORD = 0x00000008;
     unsafe fn get_header<'a>(ptr: *mut u8) -> &'a mut Header {
-        &mut *(ptr as *mut Header).offset(-1)
+        &mut *(ptr as *mut Header).sub(1)
     }
     unsafe fn align_ptr(ptr: *mut u8, align: usize) -> *mut u8 {
         let aligned = ptr.add(align - (ptr as usize & (align - 1)));

compiler/rustc_serialize/src/serialize.rs

@@ -273,7 +273,7 @@ impl<D: Decoder, T: Decodable<D>> Decodable<D> for Vec<T> {
         unsafe {
             let ptr: *mut T = vec.as_mut_ptr();
             for i in 0..len {
-                std::ptr::write(ptr.offset(i as isize), Decodable::decode(d));
+                std::ptr::write(ptr.add(i), Decodable::decode(d));
             }
             vec.set_len(len);
         }

library/alloc/src/alloc/tests.rs

@@ -15,7 +15,7 @@ fn allocate_zeroed() {
         let end = i.add(layout.size());
         while i < end {
             assert_eq!(*i, 0);
-            i = i.offset(1);
+            i = i.add(1);
         }
         Global.deallocate(ptr.as_non_null_ptr(), layout);
     }

library/alloc/src/collections/vec_deque/mod.rs

@@ -2447,8 +2447,8 @@ impl<T, A: Allocator> VecDeque<T, A> {
                     let mut right_offset = 0;
                     for i in left_edge..right_edge {
                         right_offset = (i - left_edge) % (cap - right_edge);
-                        let src: isize = (right_edge + right_offset) as isize;
-                        ptr::swap(buf.add(i), buf.offset(src));
+                        let src = right_edge + right_offset;
+                        ptr::swap(buf.add(i), buf.add(src));
                     }
                     let n_ops = right_edge - left_edge;
                     left_edge += n_ops;

library/alloc/src/slice.rs

@@ -1024,7 +1024,7 @@ where
             // Consume the greater side.
             // If equal, prefer the right run to maintain stability.
             unsafe {
-                let to_copy = if is_less(&*right.offset(-1), &*left.offset(-1)) {
+                let to_copy = if is_less(&*right.sub(1), &*left.sub(1)) {
                     decrement_and_get(left)
                 } else {
                     decrement_and_get(right)
@@ -1038,12 +1038,12 @@ where
 
     unsafe fn get_and_increment<T>(ptr: &mut *mut T) -> *mut T {
         let old = *ptr;
-        *ptr = unsafe { ptr.offset(1) };
+        *ptr = unsafe { ptr.add(1) };
         old
     }
 
     unsafe fn decrement_and_get<T>(ptr: &mut *mut T) -> *mut T {
-        *ptr = unsafe { ptr.offset(-1) };
+        *ptr = unsafe { ptr.sub(1) };
         *ptr
     }
 

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

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()

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);
             }

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

library/alloc/tests/str.rs

@@ -1010,11 +1010,11 @@ fn test_as_bytes_fail() {
 fn test_as_ptr() {
     let buf = "hello".as_ptr();
     unsafe {
-        assert_eq!(*buf.offset(0), b'h');
-        assert_eq!(*buf.offset(1), b'e');
-        assert_eq!(*buf.offset(2), b'l');
-        assert_eq!(*buf.offset(3), b'l');
-        assert_eq!(*buf.offset(4), b'o');
+        assert_eq!(*buf.add(0), b'h');
+        assert_eq!(*buf.add(1), b'e');
+        assert_eq!(*buf.add(2), b'l');
+        assert_eq!(*buf.add(3), b'l');
+        assert_eq!(*buf.add(4), b'o');
     }
 }
 

library/core/src/slice/mod.rs

@@ -2924,7 +2924,7 @@ impl<T> [T] {
                 let prev_ptr_write = ptr.add(next_write - 1);
                 if !same_bucket(&mut *ptr_read, &mut *prev_ptr_write) {
                     if next_read != next_write {
-                        let ptr_write = prev_ptr_write.offset(1);
+                        let ptr_write = prev_ptr_write.add(1);
                         mem::swap(&mut *ptr_read, &mut *ptr_write);
                     }
                     next_write += 1;

library/core/src/slice/sort.rs

@@ -326,8 +326,8 @@ where
                 unsafe {
                     // Branchless comparison.
                     *end_l = i as u8;
-                    end_l = end_l.offset(!is_less(&*elem, pivot) as isize);
-                    elem = elem.offset(1);
+                    end_l = end_l.add(!is_less(&*elem, pivot) as usize);
+                    elem = elem.add(1);
                 }
             }
         }
@@ -352,9 +352,9 @@ where
                 //        Plus, `block_r` was asserted to be less than `BLOCK` and `elem` will therefore at most be pointing to the beginning of the slice.
                 unsafe {
                     // Branchless comparison.
-                    elem = elem.offset(-1);
+                    elem = elem.sub(1);
                     *end_r = i as u8;
-                    end_r = end_r.offset(is_less(&*elem, pivot) as isize);
+                    end_r = end_r.add(is_less(&*elem, pivot) as usize);
                 }
             }
         }
@@ -365,12 +365,12 @@ where
         if count > 0 {
             macro_rules! left {
                 () => {
-                    l.offset(*start_l as isize)
+                    l.add(*start_l as usize)
                 };
             }
             macro_rules! right {
                 () => {
-                    r.offset(-(*start_r as isize) - 1)
+                    r.sub((*start_r as usize) + 1)
                 };
             }
 
@@ -398,16 +398,16 @@ where
                 ptr::copy_nonoverlapping(right!(), left!(), 1);
 
                 for _ in 1..count {
-                    start_l = start_l.offset(1);
+                    start_l = start_l.add(1);
                     ptr::copy_nonoverlapping(left!(), right!(), 1);
-                    start_r = start_r.offset(1);
+                    start_r = start_r.add(1);
                     ptr::copy_nonoverlapping(right!(), left!(), 1);
                 }
 
                 ptr::copy_nonoverlapping(&tmp, right!(), 1);
                 mem::forget(tmp);
-                start_l = start_l.offset(1);
-                start_r = start_r.offset(1);
+                start_l = start_l.add(1);
+                start_r = start_r.add(1);
             }
         }
 
@@ -420,15 +420,15 @@ where
             // safe. Otherwise, the debug assertions in the `is_done` case guarantee that
             // `width(l, r) == block_l + block_r`, namely, that the block sizes have been adjusted to account
             // for the smaller number of remaining elements.
-            l = unsafe { l.offset(block_l as isize) };
+            l = unsafe { l.add(block_l) };
         }
 
         if start_r == end_r {
             // All out-of-order elements in the right block were moved. Move to the previous block.
 
             // SAFETY: Same argument as [block-width-guarantee]. Either this is a full block `2*BLOCK`-wide,
             // or `block_r` has been adjusted for the last handful of elements.
-            r = unsafe { r.offset(-(block_r as isize)) };
+            r = unsafe { r.sub(block_r) };
         }
 
         if is_done {
@@ -457,9 +457,9 @@ where
             //  - `offsets_l` contains valid offsets into `v` collected during the partitioning of
             //    the last block, so the `l.offset` calls are valid.
             unsafe {
-                end_l = end_l.offset(-1);
-                ptr::swap(l.offset(*end_l as isize), r.offset(-1));
-                r = r.offset(-1);
+                end_l = end_l.sub(1);
+                ptr::swap(l.add(*end_l as usize), r.sub(1));
+                r = r.sub(1);
             }
         }
         width(v.as_mut_ptr(), r)
@@ -470,9 +470,9 @@ where
         while start_r < end_r {
             // SAFETY: See the reasoning in [remaining-elements-safety].
             unsafe {
-                end_r = end_r.offset(-1);
-                ptr::swap(l, r.offset(-(*end_r as isize) - 1));
-                l = l.offset(1);
+                end_r = end_r.sub(1);
+                ptr::swap(l, r.sub((*end_r as usize) + 1));
+                l = l.add(1);
             }
         }
         width(v.as_mut_ptr(), l)

library/core/src/str/validations.rs

@@ -216,12 +216,12 @@ pub(super) const fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
                     // SAFETY: since `align - index` and `ascii_block_size` are
                     // multiples of `usize_bytes`, `block = ptr.add(index)` is
                     // always aligned with a `usize` so it's safe to dereference
-                    // both `block` and `block.offset(1)`.
+                    // both `block` and `block.add(1)`.
                     unsafe {
                         let block = ptr.add(index) as *const usize;
                         // break if there is a nonascii byte
                         let zu = contains_nonascii(*block);
-                        let zv = contains_nonascii(*block.offset(1));
+                        let zv = contains_nonascii(*block.add(1));
                         if zu || zv {
                             break;
                         }

library/panic_abort/src/android.rs

@@ -42,7 +42,7 @@ pub(crate) unsafe fn android_set_abort_message(payload: *mut &mut dyn BoxMeUp) {
         return; // allocation failure
     }
     copy_nonoverlapping(msg.as_ptr(), buf as *mut u8, msg.len());
-    buf.offset(msg.len() as isize).write(0);
+    buf.add(msg.len()).write(0);
 
     let func = transmute::<usize, SetAbortMessageType>(func_addr);
     func(buf);

library/panic_unwind/src/dwarf/eh.rs

@@ -75,7 +75,7 @@ pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result
 
     let call_site_encoding = reader.read::<u8>();
     let call_site_table_length = reader.read_uleb128();
-    let action_table = reader.ptr.offset(call_site_table_length as isize);
+    let action_table = reader.ptr.add(call_site_table_length as usize);
     let ip = context.ip;
 
     if !USING_SJLJ_EXCEPTIONS {

library/std/src/os/unix/net/addr.rs

@@ -329,7 +329,7 @@ impl SocketAddr {
 
             crate::ptr::copy_nonoverlapping(
                 namespace.as_ptr(),
-                addr.sun_path.as_mut_ptr().offset(1) as *mut u8,
+                addr.sun_path.as_mut_ptr().add(1) as *mut u8,
                 namespace.len(),
             );
             let len = (sun_path_offset(&addr) + 1 + namespace.len()) as libc::socklen_t;

library/std/src/sys/sgx/abi/usercalls/tests.rs

@@ -17,12 +17,12 @@ fn test_copy_to_userspace_function() {
             dst.copy_from_enclave(&[0u8; 100]);
 
             // Copy src[0..size] to dst + offset
-            unsafe { copy_to_userspace(src.as_ptr(), dst.as_mut_ptr().offset(offset), size) };
+            unsafe { copy_to_userspace(src.as_ptr(), dst.as_mut_ptr().add(offset), size) };
 
             // Verify copy
             for byte in 0..size {
                 unsafe {
-                    assert_eq!(*dst.as_ptr().offset(offset + byte as isize), src[byte as usize]);
+                    assert_eq!(*dst.as_ptr().add(offset + byte), src[byte as usize]);
                 }
             }
         }

library/std/src/sys/windows/alloc.rs

@@ -168,7 +168,7 @@ unsafe fn allocate(layout: Layout, zeroed: bool) -> *mut u8 {
         // SAFETY: Because the size and alignment of a header is <= `MIN_ALIGN` and `aligned`
         // is aligned to at least `MIN_ALIGN` and has at least `MIN_ALIGN` bytes of padding before
         // it, it is safe to write a header directly before it.
-        unsafe { ptr::write((aligned as *mut Header).offset(-1), Header(ptr)) };
+        unsafe { ptr::write((aligned as *mut Header).sub(1), Header(ptr)) };
 
         // SAFETY: The returned pointer does not point to the to the start of an allocated block,
         // but there is a header readable directly before it containing the location of the start
@@ -213,7 +213,7 @@ unsafe impl GlobalAlloc for System {
 
                 // SAFETY: Because of the contract of `System`, `ptr` is guaranteed to be non-null
                 // and have a header readable directly before it.
-                unsafe { ptr::read((ptr as *mut Header).offset(-1)).0 }
+                unsafe { ptr::read((ptr as *mut Header).sub(1)).0 }
             }
         };
 

library/std/src/sys/windows/fs.rs

@@ -512,7 +512,7 @@ impl File {
                     ));
                 }
             };
-            let subst_ptr = path_buffer.offset(subst_off as isize);
+            let subst_ptr = path_buffer.add(subst_off.into());
             let mut subst = slice::from_raw_parts(subst_ptr, subst_len as usize);
             // Absolute paths start with an NT internal namespace prefix `\??\`
             // We should not let it leak through.
@@ -1345,10 +1345,10 @@ fn symlink_junction_inner(original: &Path, junction: &Path) -> io::Result<()> {
         let v = br"\??\";
         let v = v.iter().map(|x| *x as u16);
         for c in v.chain(original.as_os_str().encode_wide()) {
-            *buf.offset(i) = c;
+            *buf.add(i) = c;
             i += 1;
         }
-        *buf.offset(i) = 0;
+        *buf.add(i) = 0;
         i += 1;
         (*db).ReparseTag = c::IO_REPARSE_TAG_MOUNT_POINT;
         (*db).ReparseTargetMaximumLength = (i * 2) as c::WORD;

library/std/src/sys/windows/os.rs

@@ -99,11 +99,11 @@ impl Iterator for Env {
                 }
                 let p = self.cur as *const u16;
                 let mut len = 0;
-                while *p.offset(len) != 0 {
+                while *p.add(len) != 0 {
                     len += 1;
                 }
-                let s = slice::from_raw_parts(p, len as usize);
-                self.cur = self.cur.offset(len + 1);
+                let s = slice::from_raw_parts(p, len);
+                self.cur = self.cur.add(len + 1);
 
                 // Windows allows environment variables to start with an equals
                 // symbol (in any other position, this is the separator between