give Pointer::into_parts a more scary name and offer a safer alternative

Author: RalfJung

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -133,7 +133,7 @@ pub(crate) fn codegen_const_value<'tcx>(
                 }
             }
             Scalar::Ptr(ptr, _size) => {
-                let (prov, offset) = ptr.into_parts(); // we know the `offset` is relative
+                let (prov, offset) = ptr.prov_and_relative_offset();
                 let alloc_id = prov.alloc_id();
                 let base_addr = match fx.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {

compiler/rustc_codegen_gcc/src/common.rs

@@ -261,7 +261,7 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                 }
             }
             Scalar::Ptr(ptr, _size) => {
-                let (prov, offset) = ptr.into_parts(); // we know the `offset` is relative
+                let (prov, offset) = ptr.prov_and_relative_offset();
                 let alloc_id = prov.alloc_id();
                 let base_addr = match self.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {

compiler/rustc_codegen_llvm/src/common.rs

@@ -268,7 +268,7 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                 }
             }
             Scalar::Ptr(ptr, _size) => {
-                let (prov, offset) = ptr.into_parts();
+                let (prov, offset) = ptr.prov_and_relative_offset();
                 let global_alloc = self.tcx.global_alloc(prov.alloc_id());
                 let base_addr = match global_alloc {
                     GlobalAlloc::Memory(alloc) => {

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -209,9 +209,9 @@ pub(super) fn op_to_const<'tcx>(
 
     match immediate {
         Left(ref mplace) => {
-            // We know `offset` is relative to the allocation, so we can use `into_parts`.
-            let (prov, offset) = mplace.ptr().into_parts();
-            let alloc_id = prov.expect("cannot have `fake` place for non-ZST type").alloc_id();
+            let (prov, offset) =
+                mplace.ptr().into_pointer_or_addr().unwrap().prov_and_relative_offset();
+            let alloc_id = prov.alloc_id();
             ConstValue::Indirect { alloc_id, offset }
         }
         // see comment on `let force_as_immediate` above
@@ -232,9 +232,10 @@ pub(super) fn op_to_const<'tcx>(
                     imm.layout.ty,
                 );
                 let msg = "`op_to_const` on an immediate scalar pair must only be used on slice references to the beginning of an actual allocation";
-                // We know `offset` is relative to the allocation, so we can use `into_parts`.
-                let (prov, offset) = a.to_pointer(ecx).expect(msg).into_parts();
-                let alloc_id = prov.expect(msg).alloc_id();
+                let ptr = a.to_pointer(ecx).expect(msg);
+                let (prov, offset) =
+                    ptr.into_pointer_or_addr().expect(msg).prov_and_relative_offset();
+                let alloc_id = prov.alloc_id();
                 let data = ecx.tcx.global_alloc(alloc_id).unwrap_memory();
                 assert!(offset == abi::Size::ZERO, "{}", msg);
                 let meta = b.to_target_usize(ecx).expect(msg);

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -756,8 +756,7 @@ pub macro compile_time_machine(<$tcx: lifetime>) {
         ptr: Pointer<CtfeProvenance>,
         _size: i64,
     ) -> Option<(AllocId, Size, Self::ProvenanceExtra)> {
-        // We know `offset` is relative to the allocation, so we can use `into_parts`.
-        let (prov, offset) = ptr.into_parts();
+        let (prov, offset) = ptr.prov_and_relative_offset();
         Some((prov.alloc_id(), offset, prov.immutable()))
     }
 

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -1596,7 +1596,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 Some((alloc_id, offset, extra)) => Ok((alloc_id, offset, extra)),
                 None => {
                     assert!(M::Provenance::OFFSET_IS_ADDR);
-                    let (_, addr) = ptr.into_parts();
+                    // Offset is absolute, as we just asserted.
+                    let (_, addr) = ptr.into_raw_parts();
                     Err(addr.bytes())
                 }
             },

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -868,7 +868,9 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
     fn add_data_range(&mut self, ptr: Pointer<Option<M::Provenance>>, size: Size) {
         if let Some(data_bytes) = self.data_bytes.as_mut() {
             // We only have to store the offset, the rest is the same for all pointers here.
-            let (_prov, offset) = ptr.into_parts();
+            // The logic is agnostic to wether the offset is relative or absolute as long as
+            // it is consistent.
+            let (_prov, offset) = ptr.into_raw_parts();
             // Add this.
             data_bytes.add_range(offset, size);
         };
@@ -894,7 +896,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
             .as_mplace_or_imm()
             .expect_left("place must be in memory")
             .ptr();
-        let (_prov, offset) = ptr.into_parts();
+        let (_prov, offset) = ptr.into_raw_parts();
         offset
     }
 
@@ -903,7 +905,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
         // Our value must be in memory, otherwise we would not have set up `data_bytes`.
         let mplace = self.ecx.force_allocation(place)?;
         // Determine starting offset and size.
-        let (_prov, start_offset) = mplace.ptr().into_parts();
+        let (_prov, start_offset) = mplace.ptr().into_raw_parts();
         let (size, _align) = self
             .ecx
             .size_and_align_of_val(&mplace)?

compiler/rustc_middle/src/mir/consts.rs

@@ -168,8 +168,9 @@ impl<'tcx> ConstValue<'tcx> {
                     return Some(&[]);
                 }
                 // Non-empty slice, must have memory. We know this is a relative pointer.
-                let (inner_prov, offset) = ptr.into_parts();
-                let data = tcx.global_alloc(inner_prov?.alloc_id()).unwrap_memory();
+                let (inner_prov, offset) =
+                    ptr.into_pointer_or_addr().ok()?.prov_and_relative_offset();
+                let data = tcx.global_alloc(inner_prov.alloc_id()).unwrap_memory();
                 (data, offset.bytes(), offset.bytes() + len)
             }
         };

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -526,7 +526,7 @@ impl Allocation {
             let ptr_bytes = &mut bytes[idx..idx + ptr_size];
             let bits = read_target_uint(endian, ptr_bytes).unwrap();
             let (ptr_prov, ptr_offset) =
-                adjust_ptr(Pointer::new(alloc_id, Size::from_bytes(bits)))?.into_parts();
+                adjust_ptr(Pointer::new(alloc_id, Size::from_bytes(bits)))?.into_raw_parts();
             write_target_uint(endian, ptr_bytes, ptr_offset.bytes().into()).unwrap();
             new_provenance.push((offset, ptr_prov));
         }
@@ -769,7 +769,7 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         // as-is into memory. This also double-checks that `val.size()` matches `range.size`.
         let (bytes, provenance) = match val.to_bits_or_ptr_internal(range.size)? {
             Right(ptr) => {
-                let (provenance, offset) = ptr.into_parts();
+                let (provenance, offset) = ptr.into_raw_parts();
                 (u128::from(offset.bytes()), Some(provenance))
             }
             Left(data) => (data, None),

compiler/rustc_middle/src/mir/interpret/pointer.rs

@@ -288,7 +288,7 @@ impl From<CtfeProvenance> for Pointer {
 impl<Prov> From<Pointer<Prov>> for Pointer<Option<Prov>> {
     #[inline(always)]
     fn from(ptr: Pointer<Prov>) -> Self {
-        let (prov, offset) = ptr.into_parts();
+        let (prov, offset) = ptr.into_raw_parts();
         Pointer::new(Some(prov), offset)
     }
 }
@@ -314,9 +314,7 @@ impl<Prov> Pointer<Option<Prov>> {
         assert!(Prov::OFFSET_IS_ADDR);
         self.offset
     }
-}
 
-impl<Prov> Pointer<Option<Prov>> {
     /// Creates a pointer to the given address, with invalid provenance (i.e., cannot be used for
     /// any memory access).
     #[inline(always)]
@@ -336,11 +334,11 @@ impl<Prov> Pointer<Prov> {
         Pointer { provenance, offset }
     }
 
-    /// Obtain the constituents of this pointer. Not that the meaning of the offset depends on the type `Prov`!
-    /// This function must only be used in the implementation of `Machine::ptr_get_alloc`,
-    /// and when a `Pointer` is taken apart to be stored efficiently in an `Allocation`.
+    /// Obtain the constituents of this pointer. Note that the meaning of the offset depends on the
+    /// type `Prov`! This is a low-level function that should only be used when absolutely
+    /// necessary. Prefer `prov_and_relative_offset` if possible.
     #[inline(always)]
-    pub fn into_parts(self) -> (Prov, Size) {
+    pub fn into_raw_parts(self) -> (Prov, Size) {
         (self.provenance, self.offset)
     }
 
@@ -361,3 +359,12 @@ impl<Prov> Pointer<Prov> {
         self.wrapping_offset(Size::from_bytes(i as u64), cx)
     }
 }
+
+impl Pointer<CtfeProvenance> {
+    /// Return the provenance and relative offset stored in this pointer. Safer alternative to
+    /// `into_raw_parts` since the type ensures that the offset is indeed relative.
+    #[inline(always)]
+    pub fn prov_and_relative_offset(self) -> (CtfeProvenance, Size) {
+        (self.provenance, self.offset)
+    }
+}