Put `LayoutError` behind reference to shrink result

`LayoutError` is 24 bytes, which is bigger than the `Ok` types, so let's
shrink that.

4 files changed, 34 insertions, 19 deletions

diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index f1ae4942b7b..9b9daac2392 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -96,15 +96,17 @@ impl EraseType for Result<ty::GenericArg<'_>, traits::query::NoSolution> {
     type Result = [u8; size_of::<Result<ty::GenericArg<'static>, traits::query::NoSolution>>()];
 }
 
-impl EraseType for Result<bool, ty::layout::LayoutError<'_>> {
-    type Result = [u8; size_of::<Result<bool, ty::layout::LayoutError<'static>>>()];
+impl EraseType for Result<bool, &ty::layout::LayoutError<'_>> {
+    type Result = [u8; size_of::<Result<bool, &'static ty::layout::LayoutError<'static>>>()];
 }
 
-impl EraseType for Result<rustc_target::abi::TyAndLayout<'_, Ty<'_>>, ty::layout::LayoutError<'_>> {
+impl EraseType
+    for Result<rustc_target::abi::TyAndLayout<'_, Ty<'_>>, &ty::layout::LayoutError<'_>>
+{
     type Result = [u8; size_of::<
         Result<
             rustc_target::abi::TyAndLayout<'static, Ty<'static>>,
-            ty::layout::LayoutError<'static>,
+            &'static ty::layout::LayoutError<'static>,
         >,
     >()];
 }
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 15215552f52..48b8de2ab52 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1383,7 +1383,7 @@ rustc_queries! {
     /// executes in "reveal all" mode, and will normalize the input type.
     query layout_of(
         key: ty::ParamEnvAnd<'tcx, Ty<'tcx>>
-    ) -> Result<ty::layout::TyAndLayout<'tcx>, ty::layout::LayoutError<'tcx>> {
+    ) -> Result<ty::layout::TyAndLayout<'tcx>, &'tcx ty::layout::LayoutError<'tcx>> {
         depth_limit
         desc { "computing layout of `{}`", key.value }
     }
@@ -2164,7 +2164,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query check_validity_requirement(key: (ValidityRequirement, ty::ParamEnvAnd<'tcx, Ty<'tcx>>)) -> Result<bool, ty::layout::LayoutError<'tcx>> {
+    query check_validity_requirement(key: (ValidityRequirement, ty::ParamEnvAnd<'tcx, Ty<'tcx>>)) -> Result<bool, &'tcx ty::layout::LayoutError<'tcx>> {
         desc { "checking validity requirement for `{}`: {}", key.1.value, key.0 }
     }
 
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index c1d6856d33c..46d6e0c1531 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -310,7 +310,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
         ty: Ty<'tcx>,
         tcx: TyCtxt<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-    ) -> Result<SizeSkeleton<'tcx>, LayoutError<'tcx>> {
+    ) -> Result<SizeSkeleton<'tcx>, &'tcx LayoutError<'tcx>> {
         debug_assert!(!ty.has_non_region_infer());
 
         // First try computing a static layout.
@@ -353,13 +353,13 @@ impl<'tcx> SizeSkeleton<'tcx> {
                             let size = s
                                 .bytes()
                                 .checked_mul(c)
-                                .ok_or_else(|| LayoutError::SizeOverflow(ty))?;
+                                .ok_or_else(|| &*tcx.arena.alloc(LayoutError::SizeOverflow(ty)))?;
                             return Ok(SizeSkeleton::Known(Size::from_bytes(size)));
                         }
                         let len = tcx.expand_abstract_consts(len);
                         let prev = ty::Const::from_target_usize(tcx, s.bytes());
                         let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, prev) else {
-                            return Err(LayoutError::SizeOverflow(ty));
+                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
                         };
                         Ok(SizeSkeleton::Generic(gen_size))
                     }
@@ -367,7 +367,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
                     SizeSkeleton::Generic(g) => {
                         let len = tcx.expand_abstract_consts(len);
                         let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, g) else {
-                            return Err(LayoutError::SizeOverflow(ty));
+                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
                         };
                         Ok(SizeSkeleton::Generic(gen_size))
                     }
@@ -672,7 +672,7 @@ pub trait LayoutOf<'tcx>: LayoutOfHelpers<'tcx> {
 
         MaybeResult::from(
             tcx.layout_of(self.param_env().and(ty))
-                .map_err(|err| self.handle_layout_err(err, span, ty)),
+                .map_err(|err| self.handle_layout_err(*err, span, ty)),
         )
     }
 }
@@ -680,16 +680,21 @@ pub trait LayoutOf<'tcx>: LayoutOfHelpers<'tcx> {
 impl<'tcx, C: LayoutOfHelpers<'tcx>> LayoutOf<'tcx> for C {}
 
 impl<'tcx> LayoutOfHelpers<'tcx> for LayoutCx<'tcx, TyCtxt<'tcx>> {
-    type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
+    type LayoutOfResult = Result<TyAndLayout<'tcx>, &'tcx LayoutError<'tcx>>;
 
     #[inline]
-    fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
-        err
+    fn handle_layout_err(
+        &self,
+        err: LayoutError<'tcx>,
+        _: Span,
+        _: Ty<'tcx>,
+    ) -> &'tcx LayoutError<'tcx> {
+        self.tcx.arena.alloc(err)
     }
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for LayoutCx<'tcx, TyCtxtAt<'tcx>> {
-    type LayoutOfResult = Result<TyAndLayout<'tcx>, LayoutError<'tcx>>;
+    type LayoutOfResult = Result<TyAndLayout<'tcx>, &'tcx LayoutError<'tcx>>;
 
     #[inline]
     fn layout_tcx_at_span(&self) -> Span {
@@ -697,8 +702,13 @@ impl<'tcx> LayoutOfHelpers<'tcx> for LayoutCx<'tcx, TyCtxtAt<'tcx>> {
     }
 
     #[inline]
-    fn handle_layout_err(&self, err: LayoutError<'tcx>, _: Span, _: Ty<'tcx>) -> LayoutError<'tcx> {
-        err
+    fn handle_layout_err(
+        &self,
+        err: LayoutError<'tcx>,
+        _: Span,
+        _: Ty<'tcx>,
+    ) -> &'tcx LayoutError<'tcx> {
+        self.tcx.arena.alloc(err)
     }
 }
 
diff --git a/compiler/rustc_middle/src/values.rs b/compiler/rustc_middle/src/values.rs
index a00c77ccbcd..8758cd04d67 100644
--- a/compiler/rustc_middle/src/values.rs
+++ b/compiler/rustc_middle/src/values.rs
@@ -106,9 +106,12 @@ impl<'tcx> Value<TyCtxt<'tcx>, DepKind> for ty::EarlyBinder<ty::Binder<'_, ty::F
     }
 }
 
-impl<'tcx, T> Value<TyCtxt<'tcx>, DepKind> for Result<T, ty::layout::LayoutError<'_>> {
+impl<'tcx, T> Value<TyCtxt<'tcx>, DepKind> for Result<T, &'_ ty::layout::LayoutError<'_>> {
     fn from_cycle_error(_tcx: TyCtxt<'tcx>, _cycle: &[QueryInfo<DepKind>]) -> Self {
-        Err(ty::layout::LayoutError::Cycle)
+        // tcx.arena.alloc cannot be used because we are not allowed to use &'tcx LayoutError under
+        // min_specialization. Since this is an error path anyways, leaking doesn't matter (and really,
+        // tcx.arena.alloc is pretty much equal to leaking).
+        Err(Box::leak(Box::new(ty::layout::LayoutError::Cycle)))
     }
 }