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Bail out if new return place has different type than old

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This commit is contained in:
Dylan MacKenzie 2020-05-20 22:44:57 -07:00
parent 856cd6609f
commit f509862057
1 changed files with 12 additions and 1 deletions
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13
src/librustc_mir/transform/nrvo.rs
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@ -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.