Miri: make size/align_of_val work for dangling raw ptrs

Author: RalfJung

compiler/rustc_mir/src/interpret/intrinsics.rs

@@ -141,9 +141,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             sym::min_align_of_val | sym::size_of_val => {
-                let place = self.deref_operand(args[0])?;
+                // Avoid `deref_operand` -- this is not a deref, the ptr does not have to be
+                // dereferencable!
+                let place = self.ref_to_mplace(self.read_immediate(args[0])?)?;
                 let (size, align) = self
-                    .size_and_align_of(place.meta, place.layout)?
+                    .size_and_align_of_mplace(place)?
                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 
                 let result = match intrinsic_name {

compiler/rustc_mir/src/interpret/validity.rs

@@ -391,7 +391,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
         }
         // Make sure this is dereferenceable and all.
         let size_and_align = try_validation!(
-            self.ecx.size_and_align_of(place.meta, place.layout),
+            self.ecx.size_and_align_of_mplace(place),
             self.path,
             err_ub!(InvalidMeta(msg)) => { "invalid {} metadata: {}", kind, msg },
         );