allow mplace_to_imm_ptr to return different types of pointers

compiler/rustc_const_eval/src/const_eval/type_info.rs

@@ -261,7 +261,7 @@ fn write_field(
                         None => Cow::Owned(idx.to_string()), // For tuples
                     };
                     let name_place = self.allocate_str_dedup(&name)?;
-                    let ptr = self.mplace_to_imm_ptr(&name_place)?;
+                    let ptr = self.mplace_to_imm_ptr(&name_place, None)?;
                     self.write_immediate(*ptr, &field_place)?
                 }
                 sym::ty => {
@@ -444,7 +444,7 @@ pub(crate) fn write_fn_ptr_type_info(
                     other_abi => {
                         let (variant, variant_place) = self.downcast(&field_place, sym::Named)?;
                         let str_place = self.allocate_str_dedup(other_abi.as_str())?;
-                        let str_ref = self.mplace_to_imm_ptr(&str_place)?;
+                        let str_ref = self.mplace_to_imm_ptr(&str_place, None)?;
                         let payload = self.project_field(&variant_place, FieldIdx::ZERO)?;
                         self.write_immediate(*str_ref, &payload)?;
                         self.write_discriminant(variant, &field_place)?;

compiler/rustc_const_eval/src/const_eval/type_info/adt.rs

@@ -165,7 +165,7 @@ fn write_enum_variant(
             match field_def.name {
                 sym::name => {
                     let name_place = self.allocate_str_dedup(variant_def.name.as_str())?;
-                    let ptr = self.mplace_to_imm_ptr(&name_place)?;
+                    let ptr = self.mplace_to_imm_ptr(&name_place, None)?;
                     self.write_immediate(*ptr, &field_place)?
                 }
                 sym::fields => {

compiler/rustc_const_eval/src/interpret/call.rs

@@ -898,7 +898,7 @@ pub(super) fn init_drop_in_place_call(
         };
         let fn_abi = self.fn_abi_of_instance_no_deduced_attrs(instance, ty::List::empty())?;
 
-        let arg = self.mplace_to_imm_ptr(&place)?;
+        let arg = self.mplace_to_imm_ptr(&place, None)?;
         let ret = MPlaceTy::fake_alloc_zst(self.layout_of(self.tcx.types.unit)?);
 
         self.init_fn_call(

compiler/rustc_const_eval/src/interpret/place.rs

@@ -439,14 +439,24 @@ pub fn imm_ptr_to_mplace(
     }
 
     /// Turn a mplace into a (thin or wide) mutable raw pointer, pointing to the same space.
+    ///
     /// `align` information is lost!
     /// This is the inverse of `imm_ptr_to_mplace`.
+    ///
+    /// If `ptr_ty` is provided, the resulting pointer will be of that type. Otherwise, it defaults to `*mut _`.
+    /// `ptr_ty` must be a type with builtin deref which derefs to the type of `mplace` (`mplace.layout.ty`).
     pub fn mplace_to_imm_ptr(
         &self,
         mplace: &MPlaceTy<'tcx, M::Provenance>,
+        ptr_ty: Option<Ty<'tcx>>,
     ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
         let imm = mplace.mplace.to_ref(self);
-        let layout = self.layout_of(Ty::new_mut_ptr(self.tcx.tcx, mplace.layout.ty))?;
+
+        let ptr_ty = ptr_ty
+            .inspect(|t| assert_eq!(t.builtin_deref(true), Some(mplace.layout.ty)))
+            .unwrap_or_else(|| Ty::new_mut_ptr(self.tcx.tcx, mplace.layout.ty));
+
+        let layout = self.layout_of(ptr_ty)?;
         interp_ok(ImmTy::from_immediate(imm, layout))
     }
 

src/tools/miri/src/shims/panic.rs

@@ -20,7 +20,7 @@ fn start_panic(&mut self, msg: &str, unwind: mir::UnwindAction) -> InterpResult<
         this.call_function(
             panic,
             ExternAbi::Rust,
-            &[this.mplace_to_imm_ptr(&msg)?],
+            &[this.mplace_to_imm_ptr(&msg, None)?],
             None,
             ReturnContinuation::Goto { ret: None, unwind },
         )
@@ -39,7 +39,7 @@ fn start_panic_nounwind(&mut self, msg: &str) -> InterpResult<'tcx> {
         this.call_function(
             panic,
             ExternAbi::Rust,
-            &[this.mplace_to_imm_ptr(&msg)?],
+            &[this.mplace_to_imm_ptr(&msg, None)?],
             None,
             ReturnContinuation::Goto { ret: None, unwind: mir::UnwindAction::Unreachable },
         )