Auto merge of #74238 - RalfJung:offset_from, r=oli-obk

stabilize ptr_offset_from

This stabilizes ptr::offset_from, and closes https://github.com/rust-lang/rust/issues/41079. It also removes the deprecated `wrapping_offset_from`. This function was deprecated 19 days ago and was never stable; given an FCP of 10 days and some waiting time until FCP starts, that leaves at least a month between deprecation and removal which I think is fine for a nightly-only API.

Regarding the open questions in https://github.com/rust-lang/rust/issues/41079:
* Should offset_from abort instead of panic on ZSTs? -- As far as I know, there is no precedent for such aborts. We could, however, declare this UB. Given that the size is always known statically and the check thus rather cheap, UB seems excessive.
* Should there be more methods like this with different restrictions (to allow nuw/nsw, perhaps) or that return usize (like how isize-taking offset is more conveniently done with usize-taking add these days)? -- No reason to block stabilization on that, we can always add such methods later.

Also nominating the lang team because this exposes an intrinsic.

The stabilized method is best described [by its doc-comment](https://github.com/RalfJung/rust/blob/56d4b2d69abb93e4f0ca79471deca7aaaaeca214/src/libcore/ptr/const_ptr.rs#L227). The documentation forgot to mention the requirement that both pointers must "have the same provenance", aka "be derived from pointers to the same allocation", which I am adding in this PR. This is a precondition that [Miri already implements](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=a3b9d0a07a01321f5202cd99e9613480) and that, should LLVM ever obtain a `psub` operation to subtract pointers, will likely be required for that operation (following the semantics in [this paper](https://people.mpi-sws.org/~jung/twinsem/twinsem.pdf)).

5 files changed, 10 insertions, 15 deletions

diff --git a/src/test/ui/consts/offset.rs b/src/test/ui/consts/offset.rs
index f64242d568e..a491f1c92d3 100644
--- a/src/test/ui/consts/offset.rs
+++ b/src/test/ui/consts/offset.rs
@@ -1,7 +1,6 @@
 // run-pass
 #![feature(const_ptr_offset)]
 #![feature(const_ptr_offset_from)]
-#![feature(ptr_offset_from)]
 use std::ptr;
 
 #[repr(C)]
diff --git a/src/test/ui/consts/offset_from.rs b/src/test/ui/consts/offset_from.rs
index 8c1b2784262..8d501e0d953 100644
--- a/src/test/ui/consts/offset_from.rs
+++ b/src/test/ui/consts/offset_from.rs
@@ -2,7 +2,6 @@
 
 #![feature(const_raw_ptr_deref)]
 #![feature(const_ptr_offset_from)]
-#![feature(ptr_offset_from)]
 
 struct Struct {
     field: (),
diff --git a/src/test/ui/consts/offset_from_ub.rs b/src/test/ui/consts/offset_from_ub.rs
index a7902f20467..b73191d56a6 100644
--- a/src/test/ui/consts/offset_from_ub.rs
+++ b/src/test/ui/consts/offset_from_ub.rs
@@ -1,6 +1,5 @@
 #![feature(const_raw_ptr_deref)]
 #![feature(const_ptr_offset_from)]
-#![feature(ptr_offset_from)]
 
 #[repr(C)]
 struct Struct {
diff --git a/src/test/ui/consts/offset_from_ub.stderr b/src/test/ui/consts/offset_from_ub.stderr
index bd57e68e137..a89dcefd839 100644
--- a/src/test/ui/consts/offset_from_ub.stderr
+++ b/src/test/ui/consts/offset_from_ub.stderr
@@ -6,9 +6,9 @@ LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    |
    |                    ptr_offset_from cannot compute offset of pointers into different allocations.
    |                    inside `std::ptr::const_ptr::<impl *const Struct>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
-   |                    inside `DIFFERENT_ALLOC` at $DIR/offset_from_ub.rs:17:27
+   |                    inside `DIFFERENT_ALLOC` at $DIR/offset_from_ub.rs:16:27
    | 
-  ::: $DIR/offset_from_ub.rs:11:1
+  ::: $DIR/offset_from_ub.rs:10:1
    |
 LL | / pub const DIFFERENT_ALLOC: usize = {
 LL | |
@@ -29,9 +29,9 @@ LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    |
    |                    unable to turn bytes into a pointer
    |                    inside `std::ptr::const_ptr::<impl *const u8>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
-   |                    inside `NOT_PTR` at $DIR/offset_from_ub.rs:23:14
+   |                    inside `NOT_PTR` at $DIR/offset_from_ub.rs:22:14
    | 
-  ::: $DIR/offset_from_ub.rs:21:1
+  ::: $DIR/offset_from_ub.rs:20:1
    |
 LL | / pub const NOT_PTR: usize = {
 LL | |
@@ -47,9 +47,9 @@ LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    |
    |                    exact_div: 1_isize cannot be divided by 2_isize without remainder
    |                    inside `std::ptr::const_ptr::<impl *const u16>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
-   |                    inside `NOT_MULTIPLE_OF_SIZE` at $DIR/offset_from_ub.rs:31:14
+   |                    inside `NOT_MULTIPLE_OF_SIZE` at $DIR/offset_from_ub.rs:30:14
    | 
-  ::: $DIR/offset_from_ub.rs:26:1
+  ::: $DIR/offset_from_ub.rs:25:1
    |
 LL | / pub const NOT_MULTIPLE_OF_SIZE: isize = {
 LL | |
@@ -68,9 +68,9 @@ LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    |
    |                    inbounds test failed: 0x0 is not a valid pointer
    |                    inside `std::ptr::const_ptr::<impl *const u8>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
-   |                    inside `OFFSET_FROM_NULL` at $DIR/offset_from_ub.rs:37:14
+   |                    inside `OFFSET_FROM_NULL` at $DIR/offset_from_ub.rs:36:14
    | 
-  ::: $DIR/offset_from_ub.rs:34:1
+  ::: $DIR/offset_from_ub.rs:33:1
    |
 LL | / pub const OFFSET_FROM_NULL: isize = {
 LL | |
@@ -87,9 +87,9 @@ LL |           unsafe { intrinsics::ptr_offset_from(self, origin) }
    |                    |
    |                    unable to turn bytes into a pointer
    |                    inside `std::ptr::const_ptr::<impl *const u8>::offset_from` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
-   |                    inside `DIFFERENT_INT` at $DIR/offset_from_ub.rs:44:14
+   |                    inside `DIFFERENT_INT` at $DIR/offset_from_ub.rs:43:14
    | 
-  ::: $DIR/offset_from_ub.rs:40:1
+  ::: $DIR/offset_from_ub.rs:39:1
    |
 LL | / pub const DIFFERENT_INT: isize = { // offset_from with two different integers: like DIFFERENT_ALLOC
 LL | |
diff --git a/src/test/ui/offset_from.rs b/src/test/ui/offset_from.rs
index cbbb2adf15f..aa59c119706 100644
--- a/src/test/ui/offset_from.rs
+++ b/src/test/ui/offset_from.rs
@@ -1,7 +1,5 @@
 // run-pass
 
-#![feature(ptr_offset_from)]
-
 fn main() {
     let mut a = [0; 5];
     let ptr1: *mut i32 = &mut a[1];