slicc: support for transitions with a wildcard next state

This patches adds support for transitions of the form:

transition(START, EVENTS, *) { ACTIONS }

This allows a machine to collapse states that differ only in the next state
transition to collapse into one, and can help shorten/simplfy some protocols
significantly.

When * is encountered as an end state of a transition, the next state is
determined by calling the machine-specific getNextState function. The next
state is determined before any actions of the transition execute, and
therefore the next state calculation cannot depend on any of the transition
actions.

1 files changed, 11 insertions, 2 deletions

diff --git a/src/mem/slicc/symbols/StateMachine.py b/src/mem/slicc/symbols/StateMachine.py
index 174d66e0f..8a4d7d9b5 100644
--- a/src/mem/slicc/symbols/StateMachine.py
+++ b/src/mem/slicc/symbols/StateMachine.py
@@ -1310,8 +1310,17 @@ ${ident}_Controller::doTransitionWorker(${ident}_Event event,
             case = self.symtab.codeFormatter()
             # Only set next_state if it changes
             if trans.state != trans.nextState:
-                ns_ident = trans.nextState.ident
-                case('next_state = ${ident}_State_${ns_ident};')
+                if trans.nextState.isWildcard():
+                    # When * is encountered as an end state of a transition,
+                    # the next state is determined by calling the
+                    # machine-specific getNextState function. The next state
+                    # is determined before any actions of the transition
+                    # execute, and therefore the next state calculation cannot
+                    # depend on any of the transitionactions.
+                    case('next_state = getNextState(addr);')
+                else:
+                    ns_ident = trans.nextState.ident
+                    case('next_state = ${ident}_State_${ns_ident};')
 
             actions = trans.actions
             request_types = trans.request_types