Auto merge of #117525 - GKFX:remove_option_payload_ptr, r=petrochenkov

Remove option_payload_ptr; redundant to offset_of

The `option_payload_ptr` intrinsic is no longer required as `offset_of` supports traversing enums (#114208). This PR removes it in order to dogfood offset_of (as suggested at #106655 (comment)). However, it will not build until those changes reach beta (which I think is within the next 8 days?) so I've opened it as a draft.

Author: bors

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -225,25 +225,6 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                 ],
                 Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
             ),
-            sym::option_payload_ptr => {
-                let option_def_id = tcx.require_lang_item(hir::LangItem::Option, None);
-                let p0 = param(0);
-                (
-                    1,
-                    vec![Ty::new_ptr(
-                        tcx,
-                        ty::TypeAndMut {
-                            ty: Ty::new_adt(
-                                tcx,
-                                tcx.adt_def(option_def_id),
-                                tcx.mk_args_from_iter([ty::GenericArg::from(p0)].into_iter()),
-                            ),
-                            mutbl: hir::Mutability::Not,
-                        },
-                    )],
-                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: p0, mutbl: hir::Mutability::Not }),
-                )
-            }
             sym::ptr_mask => (
                 1,
                 vec![

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -4,7 +4,6 @@ use crate::MirPass;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::sym;
-use rustc_target::abi::{FieldIdx, VariantIdx};
 
 pub struct LowerIntrinsics;
 
@@ -251,37 +250,6 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                         });
                         terminator.kind = TerminatorKind::Goto { target };
                     }
-                    sym::option_payload_ptr => {
-                        if let (Some(target), Some(arg)) = (*target, args[0].place()) {
-                            let ty::RawPtr(ty::TypeAndMut { ty: dest_ty, .. }) =
-                                destination.ty(local_decls, tcx).ty.kind()
-                            else {
-                                bug!();
-                            };
-
-                            block.statements.push(Statement {
-                                source_info: terminator.source_info,
-                                kind: StatementKind::Assign(Box::new((
-                                    *destination,
-                                    Rvalue::AddressOf(
-                                        Mutability::Not,
-                                        arg.project_deeper(
-                                            &[
-                                                PlaceElem::Deref,
-                                                PlaceElem::Downcast(
-                                                    Some(sym::Some),
-                                                    VariantIdx::from_u32(1),
-                                                ),
-                                                PlaceElem::Field(FieldIdx::from_u32(0), *dest_ty),
-                                            ],
-                                            tcx,
-                                        ),
-                                    ),
-                                ))),
-                            });
-                            terminator.kind = TerminatorKind::Goto { target };
-                        }
-                    }
                     sym::transmute | sym::transmute_unchecked => {
                         let dst_ty = destination.ty(local_decls, tcx).ty;
                         let Ok([arg]) = <[_; 1]>::try_from(std::mem::take(args)) else {

compiler/rustc_span/src/symbol.rs

@@ -1164,7 +1164,6 @@ symbols! {
         optin_builtin_traits,
         option,
         option_env,
-        option_payload_ptr,
         options,
         or,
         or_patterns,

library/core/src/intrinsics.rs

@@ -2487,12 +2487,6 @@ extern "rust-intrinsic" {
     where
         G: FnOnce<ARG, Output = RET>,
         F: FnOnce<ARG, Output = RET>;
-
-    /// This method creates a pointer to any `Some` value. If the argument is
-    /// `None`, an invalid within-bounds pointer (that is still acceptable for
-    /// constructing an empty slice) is returned.
-    #[rustc_nounwind]
-    pub fn option_payload_ptr<T>(arg: *const Option<T>) -> *const T;
 }
 
 // Some functions are defined here because they accidentally got made

library/core/src/iter/adapters/filter_map.rs

@@ -97,9 +97,11 @@ where
             // SAFETY: Loop conditions ensure the index is in bounds.
 
             unsafe {
-                let opt_payload_at = core::intrinsics::option_payload_ptr(&val);
+                let opt_payload_at: *const MaybeUninit<B> = (&val as *const Option<B>)
+                    .byte_add(core::mem::offset_of!(Option<B>, Some.0))
+                    .cast();
                 let dst = guard.array.as_mut_ptr().add(idx);
-                crate::ptr::copy_nonoverlapping(opt_payload_at.cast(), dst, 1);
+                crate::ptr::copy_nonoverlapping(opt_payload_at, dst, 1);
                 crate::mem::forget(val);
             };
 

library/core/src/lib.rs

@@ -178,6 +178,8 @@
 #![feature(is_ascii_octdigit)]
 #![feature(isqrt)]
 #![feature(maybe_uninit_uninit_array)]
+#![feature(offset_of)]
+#![feature(offset_of_enum)]
 #![feature(ptr_alignment_type)]
 #![feature(ptr_metadata)]
 #![feature(set_ptr_value)]

library/core/src/option.rs

@@ -780,7 +780,7 @@ impl<T> Option<T> {
         // `None` case it's just padding).
         unsafe {
             slice::from_raw_parts(
-                crate::intrinsics::option_payload_ptr(crate::ptr::from_ref(self)),
+                (self as *const Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
                 usize::from(self.is_some()),
             )
         }
@@ -836,8 +836,7 @@ impl<T> Option<T> {
         // the `None` case it's just padding).
         unsafe {
             slice::from_raw_parts_mut(
-                crate::intrinsics::option_payload_ptr(crate::ptr::from_mut(self).cast_const())
-                    .cast_mut(),
+                (self as *mut Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(),
                 usize::from(self.is_some()),
             )
         }

library/core/tests/option.rs

@@ -568,3 +568,11 @@ fn zip_unzip_roundtrip() {
     let a = z.unzip();
     assert_eq!(a, (x, y));
 }
+
+#[test]
+fn as_slice() {
+    assert_eq!(Some(42).as_slice(), &[42]);
+    assert_eq!(Some(43).as_mut_slice(), &[43]);
+    assert_eq!(None::<i32>.as_slice(), &[]);
+    assert_eq!(None::<i32>.as_mut_slice(), &[]);
+}

tests/mir-opt/lower_intrinsics.option_payload.LowerIntrinsics.panic-abort.diff

@@ -222,18 +222,6 @@ pub fn write_via_move_string(r: &mut String, v: String) {
 
 pub enum Never {}
 
-// EMIT_MIR lower_intrinsics.option_payload.LowerIntrinsics.diff
-pub fn option_payload(o: &Option<usize>, p: &Option<String>) {
-    // CHECK-LABEL: fn option_payload(
-    // CHECK: {{_.*}} = &raw const (((*{{_.*}}) as Some).0: usize);
-    // CHECK: {{_.*}} = &raw const (((*{{_.*}}) as Some).0: std::string::String);
-
-    unsafe {
-        let _x = core::intrinsics::option_payload_ptr(o);
-        let _y = core::intrinsics::option_payload_ptr(p);
-    }
-}
-
 // EMIT_MIR lower_intrinsics.ptr_offset.LowerIntrinsics.diff
 pub unsafe fn ptr_offset(p: *const i32, d: isize) -> *const i32 {
     // CHECK-LABEL: fn ptr_offset(