diff --git a/src/librustc_mir/transform/nrvo.rs b/src/librustc_mir/transform/nrvo.rs index d249eaa2e43e6..941ffa94aa857 100644 --- a/src/librustc_mir/transform/nrvo.rs +++ b/src/librustc_mir/transform/nrvo.rs @@ -44,6 +44,18 @@ impl<'tcx> MirPass<'tcx> for RenameReturnPlace { } }; + // Sometimes, the return place is assigned a local of a different but coercable type, for + // example `&T` instead of `&mut T`. Overwriting the `LocalInfo` for the return place would + // result in it having an incorrect type. Although this doesn't seem to cause a problem in + // codegen, bail out anyways since it happens so rarely. + let ret_ty = body.local_decls[mir::RETURN_PLACE].ty; + let assigned_ty = body.local_decls[returned_local].ty; + if ret_ty != assigned_ty { + debug!("`{:?}` was eligible for NRVO but for type mismatch", src.def_id()); + debug!("typeof(_0) != typeof({:?}); {:?} != {:?}", returned_local, ret_ty, assigned_ty); + return; + } + debug!( "`{:?}` was eligible for NRVO, making {:?} the return place", src.def_id(), @@ -60,7 +72,6 @@ impl<'tcx> MirPass<'tcx> for RenameReturnPlace { // Overwrite the debuginfo of `_0` with that of the renamed local. let (renamed_decl, ret_decl) = body.local_decls.pick2_mut(returned_local, mir::RETURN_PLACE); - debug_assert_eq!(ret_decl.ty, renamed_decl.ty); ret_decl.clone_from(renamed_decl); // The return place is always mutable.