Put FnAbiError behind reference to shrink result

The `FnAbi` is just a pointer, so the error type should not be bigger.

compiler/rustc_middle/src/query/erase.rs

@@ -71,8 +71,8 @@ impl<T> EraseType for Result<&'_ T, traits::CodegenObligationError> {
     type Result = [u8; size_of::<Result<&'static (), traits::CodegenObligationError>>()];
 }
 
-impl<T> EraseType for Result<&'_ T, ty::layout::FnAbiError<'_>> {
-    type Result = [u8; size_of::<Result<&'static (), ty::layout::FnAbiError<'static>>>()];
+impl<T> EraseType for Result<&'_ T, &'_ ty::layout::FnAbiError<'_>> {
+    type Result = [u8; size_of::<Result<&'static (), &'static ty::layout::FnAbiError<'static>>>()];
 }
 
 impl<T> EraseType for Result<(&'_ T, rustc_middle::thir::ExprId), rustc_errors::ErrorGuaranteed> {

compiler/rustc_middle/src/query/mod.rs

@@ -1394,7 +1394,7 @@ rustc_queries! {
     /// instead, where the instance is an `InstanceDef::Virtual`.
     query fn_abi_of_fn_ptr(
         key: ty::ParamEnvAnd<'tcx, (ty::PolyFnSig<'tcx>, &'tcx ty::List<Ty<'tcx>>)>
-    ) -> Result<&'tcx abi::call::FnAbi<'tcx, Ty<'tcx>>, ty::layout::FnAbiError<'tcx>> {
+    ) -> Result<&'tcx abi::call::FnAbi<'tcx, Ty<'tcx>>, &'tcx ty::layout::FnAbiError<'tcx>> {
         desc { "computing call ABI of `{}` function pointers", key.value.0 }
     }
 
@@ -1405,7 +1405,7 @@ rustc_queries! {
     /// to an `InstanceDef::Virtual` instance (of `<dyn Trait as Trait>::fn`).
     query fn_abi_of_instance(
         key: ty::ParamEnvAnd<'tcx, (ty::Instance<'tcx>, &'tcx ty::List<Ty<'tcx>>)>
-    ) -> Result<&'tcx abi::call::FnAbi<'tcx, Ty<'tcx>>, ty::layout::FnAbiError<'tcx>> {
+    ) -> Result<&'tcx abi::call::FnAbi<'tcx, Ty<'tcx>>, &'tcx ty::layout::FnAbiError<'tcx>> {
         desc { "computing call ABI of `{}`", key.value.0 }
     }
 

compiler/rustc_middle/src/ty/layout.rs

@@ -1260,18 +1260,6 @@ pub enum FnAbiError<'tcx> {
     AdjustForForeignAbi(call::AdjustForForeignAbiError),
 }
 
-impl<'tcx> From<LayoutError<'tcx>> for FnAbiError<'tcx> {
-    fn from(err: LayoutError<'tcx>) -> Self {
-        Self::Layout(err)
-    }
-}
-
-impl From<call::AdjustForForeignAbiError> for FnAbiError<'_> {
-    fn from(err: call::AdjustForForeignAbiError) -> Self {
-        Self::AdjustForForeignAbi(err)
-    }
-}
-
 impl<'a, 'b> IntoDiagnostic<'a, !> for FnAbiError<'b> {
     fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, !> {
         match self {
@@ -1331,7 +1319,7 @@ pub trait FnAbiOf<'tcx>: FnAbiOfHelpers<'tcx> {
         let tcx = self.tcx().at(span);
 
         MaybeResult::from(tcx.fn_abi_of_fn_ptr(self.param_env().and((sig, extra_args))).map_err(
-            |err| self.handle_fn_abi_err(err, span, FnAbiRequest::OfFnPtr { sig, extra_args }),
+            |err| self.handle_fn_abi_err(*err, span, FnAbiRequest::OfFnPtr { sig, extra_args }),
         ))
     }
 
@@ -1358,7 +1346,11 @@ pub trait FnAbiOf<'tcx>: FnAbiOfHelpers<'tcx> {
                 // However, we don't do this early in order to avoid calling
                 // `def_span` unconditionally (which may have a perf penalty).
                 let span = if !span.is_dummy() { span } else { tcx.def_span(instance.def_id()) };
-                self.handle_fn_abi_err(err, span, FnAbiRequest::OfInstance { instance, extra_args })
+                self.handle_fn_abi_err(
+                    *err,
+                    span,
+                    FnAbiRequest::OfInstance { instance, extra_args },
+                )
             }),
         )
     }

compiler/rustc_ty_utils/src/abi.rs

@@ -202,7 +202,7 @@ fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi) -> Conv {
 fn fn_abi_of_fn_ptr<'tcx>(
     tcx: TyCtxt<'tcx>,
     query: ty::ParamEnvAnd<'tcx, (ty::PolyFnSig<'tcx>, &'tcx ty::List<Ty<'tcx>>)>,
-) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, FnAbiError<'tcx>> {
+) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, &'tcx FnAbiError<'tcx>> {
     let (param_env, (sig, extra_args)) = query.into_parts();
 
     let cx = LayoutCx { tcx, param_env };
@@ -212,7 +212,7 @@ fn fn_abi_of_fn_ptr<'tcx>(
 fn fn_abi_of_instance<'tcx>(
     tcx: TyCtxt<'tcx>,
     query: ty::ParamEnvAnd<'tcx, (ty::Instance<'tcx>, &'tcx ty::List<Ty<'tcx>>)>,
-) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, FnAbiError<'tcx>> {
+) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, &'tcx FnAbiError<'tcx>> {
     let (param_env, (instance, extra_args)) = query.into_parts();
 
     let sig = fn_sig_for_fn_abi(tcx, instance, param_env);
@@ -331,7 +331,7 @@ fn fn_abi_new_uncached<'tcx>(
     fn_def_id: Option<DefId>,
     // FIXME(eddyb) replace this with something typed, like an `enum`.
     force_thin_self_ptr: bool,
-) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, FnAbiError<'tcx>> {
+) -> Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, &'tcx FnAbiError<'tcx>> {
     let sig = cx.tcx.normalize_erasing_late_bound_regions(cx.param_env, sig);
 
     let conv = conv_from_spec_abi(cx.tcx(), sig.abi);
@@ -376,7 +376,7 @@ fn fn_abi_new_uncached<'tcx>(
     let is_drop_in_place =
         fn_def_id.is_some() && fn_def_id == cx.tcx.lang_items().drop_in_place_fn();
 
-    let arg_of = |ty: Ty<'tcx>, arg_idx: Option<usize>| -> Result<_, FnAbiError<'tcx>> {
+    let arg_of = |ty: Ty<'tcx>, arg_idx: Option<usize>| -> Result<_, &'tcx FnAbiError<'tcx>> {
         let span = tracing::debug_span!("arg_of");
         let _entered = span.enter();
         let is_return = arg_idx.is_none();
@@ -386,7 +386,8 @@ fn fn_abi_new_uncached<'tcx>(
             _ => bug!("argument to drop_in_place is not a raw ptr: {:?}", ty),
         });
 
-        let layout = cx.layout_of(ty).map_err(|err| *err)?;
+        let layout =
+            cx.layout_of(ty).map_err(|err| &*cx.tcx.arena.alloc(FnAbiError::Layout(*err)))?;
         let layout = if force_thin_self_ptr && arg_idx == Some(0) {
             // Don't pass the vtable, it's not an argument of the virtual fn.
             // Instead, pass just the data pointer, but give it the type `*const/mut dyn Trait`
@@ -454,7 +455,7 @@ fn fn_abi_adjust_for_abi<'tcx>(
     fn_abi: &mut FnAbi<'tcx, Ty<'tcx>>,
     abi: SpecAbi,
     fn_def_id: Option<DefId>,
-) -> Result<(), FnAbiError<'tcx>> {
+) -> Result<(), &'tcx FnAbiError<'tcx>> {
     if abi == SpecAbi::Unadjusted {
         return Ok(());
     }
@@ -548,7 +549,9 @@ fn fn_abi_adjust_for_abi<'tcx>(
             fixup(arg, Some(arg_idx));
         }
     } else {
-        fn_abi.adjust_for_foreign_abi(cx, abi)?;
+        fn_abi
+            .adjust_for_foreign_abi(cx, abi)
+            .map_err(|err| &*cx.tcx.arena.alloc(FnAbiError::AdjustForForeignAbi(err)))?;
     }
 
     Ok(())