Box CastTarget within PassMode.

Because `PassMode::Cast` is by far the largest variant, but is
relatively rare.

This requires making `PassMode` not impl `Copy`, and `Clone` is no
longer necessary. This causes lots of sigil adjusting, but nothing very
notable.

Author: nnethercote

src/abi.rs

@@ -133,7 +133,7 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             match self.ret.mode {
                 PassMode::Ignore => cx.type_void(),
                 PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_gcc_type(cx),
-                PassMode::Cast(cast) => cast.gcc_type(cx),
+                PassMode::Cast(ref cast) => cast.gcc_type(cx),
                 PassMode::Indirect { .. } => {
                     argument_tys.push(cx.type_ptr_to(self.ret.memory_ty(cx)));
                     cx.type_void()
@@ -157,7 +157,7 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 PassMode::Indirect { extra_attrs: Some(_), .. } => {
                     unimplemented!();
                 }
-                PassMode::Cast(cast) => cast.gcc_type(cx),
+                PassMode::Cast(ref cast) => cast.gcc_type(cx),
                 PassMode::Indirect { extra_attrs: None, on_stack: true, .. } => {
                     on_stack_param_indices.insert(argument_tys.len());
                     arg.memory_ty(cx)

src/intrinsic/mod.rs

@@ -130,7 +130,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                 sym::volatile_load | sym::unaligned_volatile_load => {
                     let tp_ty = substs.type_at(0);
                     let mut ptr = args[0].immediate();
-                    if let PassMode::Cast(ty) = fn_abi.ret.mode {
+                    if let PassMode::Cast(ty) = &fn_abi.ret.mode {
                         ptr = self.pointercast(ptr, self.type_ptr_to(ty.gcc_type(self)));
                     }
                     let load = self.volatile_load(ptr.get_type(), ptr);
@@ -320,7 +320,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
             };
 
         if !fn_abi.ret.is_ignore() {
-            if let PassMode::Cast(ty) = fn_abi.ret.mode {
+            if let PassMode::Cast(ty) = &fn_abi.ret.mode {
                 let ptr_llty = self.type_ptr_to(ty.gcc_type(self));
                 let ptr = self.pointercast(result.llval, ptr_llty);
                 self.store(llval, ptr, result.align);
@@ -416,7 +416,7 @@ impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
         else if self.is_unsized_indirect() {
             bug!("unsized `ArgAbi` must be handled through `store_fn_arg`");
         }
-        else if let PassMode::Cast(cast) = self.mode {
+        else if let PassMode::Cast(ref cast) = self.mode {
             // FIXME(eddyb): Figure out when the simpler Store is safe, clang
             // uses it for i16 -> {i8, i8}, but not for i24 -> {i8, i8, i8}.
             let can_store_through_cast_ptr = false;