raw slices do not have to comply to the size limit

Author: RalfJung

src/librustc_mir/interpret/validity.rs

@@ -3,7 +3,7 @@ use std::ops::RangeInclusive;
 
 use syntax_pos::symbol::{sym, Symbol};
 use rustc::hir;
-use rustc::ty::layout::{self, Size, TyLayout, LayoutOf, VariantIdx};
+use rustc::ty::layout::{self, TyLayout, LayoutOf, VariantIdx};
 use rustc::ty;
 use rustc_data_structures::fx::FxHashSet;
 
@@ -276,20 +276,11 @@ impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M
                 // FIXME: More checks for the vtable.
             }
             ty::Slice(..) | ty::Str => {
-                let len = try_validation!(meta.unwrap().to_usize(self.ecx),
+                let _len = try_validation!(meta.unwrap().to_usize(self.ecx),
                     "non-integer slice length in wide pointer", self.path);
-                // check max slice length
-                let elem_size = match tail.sty {
-                    ty::Str => Size::from_bytes(1),
-                    ty::Slice(ty) => self.ecx.layout_of(ty)?.size,
-                    _ => bug!("It cannot be another type"),
-                };
-                if elem_size.checked_mul(len, &*self.ecx.tcx).is_none() {
-                    throw_validation_failure!(
-                        "too large slice (longer than isize::MAX bytes)",
-                        self.path
-                    );
-                }
+                // We do not check that `len * elem_size <= isize::MAX`:
+                // that is only required for references, and there it falls out of the
+                // "dereferencable" check performed by Stacked Borrows.
             }
             ty::Foreign(..) => {
                 // Unsized, but not wide.