match statements

compiler/llvm/llvm.odin

@@ -253,7 +253,7 @@ valid_value :: proc(
 	}
 	switch instructions[value_id].op {
 	case .Param, .Const, .String, .Aggregate, .None, .Optional_Some,
-	     .Load_Global, .Function_Address, .Address_Of, .Load, .Slice, .Length, .Slice_Ptr,
+	     .Load_Global, .Function_Address, .Address_Of, .Load, .Union_Tag, .Slice, .Length, .Slice_Ptr,
 	     .Extract, .Select, .Unwrap,
 	     .Optional_Is_Some, .Optional_Value, .Orelse,
 	     .Widen, .C_Coerce, .C_Vararg_Promote, .Retype, .Weaken_Pointer, .Weaken_Slice, .Decay_Array_Pointer,
@@ -979,6 +979,20 @@ emit_instruction_stream :: proc(
 				llvm_type(instruction.type, &emitter.module.types),
 				instruction.a,
 			)
+		case .Union_Tag:
+			// `instruction.a` is the address of a tagged union; the discriminant lives at
+			// offset 0, so load the tag enum (`instruction.type`) straight from it.
+			if !valid_instruction(instructions, instruction.a) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid union tag base")
+				continue
+			}
+			fmt.sbprintf(
+				&emitter.builder,
+				"  %%v%d = load %s, ptr %%v%d\n",
+				instruction_index,
+				llvm_type(instruction.type, &emitter.module.types),
+				instruction.a,
+			)
 		case .Store:
 			if !valid_address(instructions, instruction.a, instruction.type, &emitter.module.types) ||
 			   !valid_value(instructions, instruction.b, instruction.type, &emitter.module.types) {