Mark scalar layout unions so that backends that do not support partially initialized scalars can special case them.

Author: oli-obk

src/common.rs

@@ -21,7 +21,7 @@ pub(crate) fn pointer_ty(tcx: TyCtxt<'_>) -> types::Type {
 }
 
 pub(crate) fn scalar_to_clif_type(tcx: TyCtxt<'_>, scalar: Scalar) -> Type {
-    match scalar.value {
+    match scalar.primitive() {
         Primitive::Int(int, _sign) => match int {
             Integer::I8 => types::I8,
             Integer::I16 => types::I16,

src/discriminant.rs

@@ -105,7 +105,7 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
     // Decode the discriminant (specifically if it's niche-encoded).
     match *tag_encoding {
         TagEncoding::Direct => {
-            let signed = match tag_scalar.value {
+            let signed = match tag_scalar.primitive() {
                 Int(_, signed) => signed,
                 _ => false,
             };

src/value_and_place.rs

@@ -50,7 +50,7 @@ fn codegen_field<'tcx>(
 }
 
 fn scalar_pair_calculate_b_offset(tcx: TyCtxt<'_>, a_scalar: Scalar, b_scalar: Scalar) -> Offset32 {
-    let b_offset = a_scalar.value.size(&tcx).align_to(b_scalar.value.align(&tcx).abi);
+    let b_offset = a_scalar.size(&tcx).align_to(b_scalar.align(&tcx).abi);
     Offset32::new(b_offset.bytes().try_into().unwrap())
 }