diff options
Diffstat (limited to 'compiler/rustc_middle/src/ty/layout.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/layout.rs | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs index c41a8318ec5..4491965347b 100644 --- a/compiler/rustc_middle/src/ty/layout.rs +++ b/compiler/rustc_middle/src/ty/layout.rs @@ -3266,7 +3266,12 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> { // this attribute doesn't make it UB for the pointed-to data to be undef. attrs.set(ArgAttribute::NoUndef); - // `Box` pointer parameters never alias because ownership is transferred + // The aliasing rules for `Box<T>` are still not decided, but currently we emit + // `noalias` for it. This can be turned off using an unstable flag. + // See https://github.com/rust-lang/unsafe-code-guidelines/issues/326 + let noalias_for_box = + self.tcx().sess.opts.unstable_opts.box_noalias.unwrap_or(true); + // `&mut` pointer parameters never alias other parameters, // or mutable global data // @@ -3281,7 +3286,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> { // `-Zmutable-noalias` debugging option. let no_alias = match kind { PointerKind::Shared | PointerKind::UniqueBorrowed => false, - PointerKind::UniqueOwned => true, + PointerKind::UniqueOwned => noalias_for_box, PointerKind::Frozen => !is_return, }; if no_alias { |