runs instructions that read other instructions' outputs

crates/cpu/src/reg_alloc.rs

@@ -415,6 +415,16 @@ pub fn reg_alloc(config: &CpuConfig) {
                 .element()
                 .HdlNone(),
         );
+        connect(
+            unit_forwarding_info.unit_reg_frees[unit_index],
+            HdlOption::map(
+                ReadyValid::firing_data(unit_free_regs_tracker.free_in[0]),
+                |value| {
+                    #[hdl]
+                    UnitOutRegNum::<_> { value }
+                },
+            ),
+        );
         #[hdl]
         if let HdlSome(output) = unit_to_reg_alloc.output {
             #[hdl]