spirv: lower get_union_tag

1 files changed, 17 insertions, 0 deletions

diff --git a/src/codegen/spirv.zig b/src/codegen/spirv.zig
index d1def8a02e..1793e9fe18 100644
--- a/src/codegen/spirv.zig
+++ b/src/codegen/spirv.zig
@@ -1735,6 +1735,7 @@ pub const DeclGen = struct {
             .slice_elem_val => try self.airSliceElemVal(inst),
             .ptr_elem_ptr   => try self.airPtrElemPtr(inst),
 
+            .get_union_tag => try self.airGetUnionTag(inst),
             .struct_field_val => try self.airStructFieldVal(inst),
 
             .struct_field_ptr_index_0 => try self.airStructFieldPtrIndex(inst, 0),
@@ -2320,6 +2321,22 @@ pub const DeclGen = struct {
         return result_id;
     }
 
+    fn airGetUnionTag(self: *DeclGen, inst: Air.Inst.Index) !?IdRef {
+        const ty_op = self.air.instructions.items(.data)[inst].ty_op;
+        const un_ty = self.air.typeOf(ty_op.operand);
+
+        const target = self.module.getTarget();
+        const layout = un_ty.unionGetLayout(target);
+        if (layout.tag_size == 0) return null;
+
+        const union_handle = try self.resolve(ty_op.operand);
+        if (layout.payload_size == 0) return union_handle;
+
+        const tag_ty = un_ty.unionTagTypeSafety().?;
+        const tag_index = @boolToInt(layout.tag_align < layout.payload_align);
+        return try self.extractField(tag_ty, union_handle, tag_index);
+    }
+
     fn airStructFieldVal(self: *DeclGen, inst: Air.Inst.Index) !?IdRef {
         if (self.liveness.isUnused(inst)) return null;