diff options
| -rw-r--r-- | compiler/rustc_mir_transform/src/mentioned_items.rs | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/compiler/rustc_mir_transform/src/mentioned_items.rs b/compiler/rustc_mir_transform/src/mentioned_items.rs index 765269a7c80..57b6126dece 100644 --- a/compiler/rustc_mir_transform/src/mentioned_items.rs +++ b/compiler/rustc_mir_transform/src/mentioned_items.rs @@ -1,6 +1,6 @@ use rustc_middle::mir::visit::Visitor; use rustc_middle::mir::{self, Location, MentionedItem, MirPass}; -use rustc_middle::ty::{adjustment::PointerCoercion, TyCtxt}; +use rustc_middle::ty::{self, adjustment::PointerCoercion, TyCtxt}; use rustc_session::Session; use rustc_span::source_map::Spanned; @@ -76,14 +76,21 @@ impl<'tcx> Visitor<'tcx> for MentionedItemsVisitor<'_, 'tcx> { ) | mir::Rvalue::Cast(mir::CastKind::DynStar, ref operand, target_ty) => { // This isn't monomorphized yet so we can't tell what the actual types are -- just - // add everything. - self.mentioned_items.push(Spanned { - node: MentionedItem::UnsizeCast { - source_ty: operand.ty(self.body, self.tcx), - target_ty, - }, - span: span(), - }); + // add everything that may involve a vtable. + let source_ty = operand.ty(self.body, self.tcx); + let may_involve_vtable = match ( + source_ty.builtin_deref(true).map(|t| t.ty.kind()), + target_ty.builtin_deref(true).map(|t| t.ty.kind()), + ) { + (Some(ty::Array(..)), Some(ty::Str | ty::Slice(..))) => false, // &str/&[T] unsizing + _ => true, + }; + if may_involve_vtable { + self.mentioned_items.push(Spanned { + node: MentionedItem::UnsizeCast { source_ty, target_ty }, + span: span(), + }); + } } // Similarly, record closures that are turned into function pointers. mir::Rvalue::Cast( |